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THE LOWER-MIDDLE CAMBRIAN STANDARD OF WESTERN GONDWANA

Introduction, Field Guide, Abstracts, and Proceedings of the First Conference of the Lower Cambrian Stage Subdivision Working Group and I. G. C. P. Project 366 Ecological Aspects of the Cambrian Radiation

Edited by Gerd Geyer & Ed Landing

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1001' 366 C1IMBRIRN ECOLOGII

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Redlichiacean trilobites with preserved soft-parts from the Lower Cambrian Chengjiang fauna (South China) SHU DEGAN, GERD GEYER, CI-IEN LING

SHU DEGAN, GEYER, G., CHEN LING & ZHANG

XINGLlANG

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ZHANG XINGLIANG

1995. Rcdlichiaccan trilobites with preserved soft-parts from the Lower

Cambrian Chengjiang fauna (South China). - l3eringeria Special issue 2: 203-241,21 lex I-figs., 1 pI.; WUrzburg_ Abstract. New material of Eoredlichia intermedia and Ymmanocephalus yunnanensis with preserved soft-parts from the Chcngjiang fauna is described. Remarks on the dorsal exoskeletons of both species focus on such incompletely described features as the presence of faint ridges and lines, caecal features, articulating devices, and the morphology of the pygidia. Preserved soH-parts include the digestive

tract and contiguous caeca, antennae, and biramous appendages, the anatomy of which is discussed in detail. Discussions on functional morphology and mode of life summarize the tentative reconstruction of the recognizable structures and organs within the living organisms. The exopodites of both species suggest filtering and swimming abilities rather than their usc in respiration. They confirm an imbrication with the posterior parts of the exopodite 'combs' overlying the anterior blade of the exopodite of the posteriorly adjacent segment. The limbs of Eoredlichia intermedia reflect a primitive condition among the trilobites and can be grouped together with those known from Olenoides and Kootenia . • Lower Cambrian, trilobites, Redlichiidae, soft-parI anatomy, morphology, antennae, biramous appendages, functional morphology, mode oflife, systemalics, Yangtze Platform, Sowh China.

Zusammenfassung: Beschrieben wird neues Material von £oredlichia intermedia und Yunnanocepha/us yunnanensis mit erhaltellcn Weichteilen aus der Chengjiang-Fauna. Die Beschreibungen des dorsalen ExoskeletlS beider Arten konzentrieren sich auf bisher nicht detaillicn diskutierte Mcrkmalc wie schwache Rippen und Linien, Artikulationshilfen und die Morphologic des Pygidiums. Die erhaltenen Weichteile umfasscn den Vcrdauungstrakt und mit ihm verbundcne Caeca, Antennen und zwei!lstige Anhfinge. Deren Anatomic wird detailliert beschrieben. Erlfiuterungen zur Funktionsmorphologie und Lebensweise crlfiutcrn die Rekonstruktion der erkennbaren Strukturen und Organe am Icbendcn Organismus. Die Exopoditen bcidcr Arten dcutcn auf filtcrnde Tatigkciten und Aktiviutten im Rahmen schwimmcnder Fortbewegung hin und schcinen kcinc rcspiratorischen Ftl-higkeiten bcsesscn zu haben. Sic besitzcn cine inverse Imbrikation, bei der die hinteren Partien der Exopoditenk:tmme deutlich Oberlappend auf den vorderen Abschnitten der benachbarten Exopoditen liegen. Die Anhfinge von Eoredlichia intermedia spiegeln eine ursprOngliche Zustand inncrhalb dcr Trilobiten wider und kann zusammen mitjenen gruppiert werden, die von O/enoides und Kootenia bckannt sind. • Unterkambrium, Trilobiten, Redlichiidae, Weichtei!-Anatomie, Morph%gie, Antennen, zweiaslige Anhange, Funktionsmorph%gie, Lebenswe;se, Systematik, Yangtse-Tafel, Siid-China.

Addresses of the authors: SHU DEGAN, Ci-LEN LING & ZHANG XINGLIANG, Department of Geology, Northwest University, Xi'an, 710069, People's Republic of China; GERD GEYER, Institut rur Palaontologie, Bayerische Julius-Maximilians-Universit:tt, Pleichcrwall I, D-97070 WOrzburg, Germany.

Introduction After a century of trilobite research in China, energetic work over the last several decades has shown that Chinese trilobites are among the most important of their clade worldwide (ZHANG et aI., 1980; Lu & CHEN, 1989)_ However, studies on Chinese trilobites are almost exclusively confined to their taxonomy, and very few of these studies have dealt with soft-parts. Nevertheless, examination of dorsal exoskeleton cannot solve such fundamental problems as the systematic po-

sition, phylogenetic relationships and natural classification, and functional morphology_ Thus, investigations of rare fossils with preserved soft parts are urgently needed to provide unequivocal evidence for biological and systematic relationships (SHU et aI., 1992). This report features an approach to the reconstruction of early polymerid trilobite anatomy and is also an attempt to characterize the species in tenns of intraspecific variability.

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Earlier studies on soft-parts of trilobites Among the more than tenthousand trilobite species described in the past twohundred years, only some twenty species have been found with more-or-Iess well preserved soft-parts. These species come almost exclusively from Europe and North America and from strata of Middle Cambrian or younger age. The only exception would be a single specimen of O/enellus getzi from the Lower Cambrian Kinzers Formation of Pennsylvania, which shows preserved antennae (DUNBAR, 1925). This specimen, however, has been subsequently suggested not to represent a trilobite. Probably the most famous and completely known trilobite species with preserved soft-parts is the olenid Triarthrus eatoni (HALL) from the Ordovician of the New York State (e.g., BEECHER, 1893, 1894, 1895a; WALcon, 1894, 1918, 1921 ; RAYMOND, 1920; STRMER, 1939, 1951; CISNE, 1974, 1975, 1981; WI-IITTINGTON & ALMOND, 1987; WHITrINGTON, 1992). Study of Ceraurus p/euroxanthemus GREEN by STRMER (1939) led to the understanding of the biramous trilobite appendage. This study had a tremendous impact, but anatomical details in other studies on the corynexochoid trilobites O/enoides serratus (ROMIN-

GER) (WALCOlT, 1912, 1918, 1921 ; RAYMOND, 1920; WHlnINGTON, 1975, 1992) and Kootenia burgessensis WALcon (WALCOn, 1918; STRMER, 1939; WI-IITTINGTON, 1975), on Crypto!ithus tesse/atus GREEN and Crypto!ithus bellu/us (ULRICH) (BEECHER, 1895b; RA YMOND, 1920; WALCOn, 1921; STRMER, 1939; CAMPBELL, 1975), and other work on Triarthrus eatoni contributed even more to our general concept of the trilobite limb. This concept, however, blocked an understanding of notable differences in the anatomy of the appendages (BERGSTROM, 1969) and created a perception of quite uniformly constructed limbs. Occasional finds of soft-parts, especially appendages, are known from such species as the ptychoparioid E/rathina cordillerae (ROMINGER) (WALcon, 1918), the calymenid F/exyca/ymene senaria (CONRAD) (WALCOlT, 1881, 1918), a species of Asteropyge (BROIL!, 1930; BERGSTROM, 1973), a species of Phacops (SEILACI-IER, 1962; STORMER, 1970; BERGSTROM, 1973) and others. However, none of the information on those species has significantly modified the text-book version of the trilobite-limb.

Geological setting and stratigraphy All of the material in this study comes from the Chengjiang fossil Lagerstdlle, one of the oldest occurrences of abundant and well-preserved soft-bodied metazoans and the oldest Obrutions-Lagerstdlle known thus far. Within recent years, the Chengjiang fossil Lagerstdlle has become one of the most discussed and best studied fossil sites and is certainly the most prominent Lower Cambrian fossil locality. Because of the revival of studies on Burgess Shale and recent focus on the Cambrian explosion, it has attracted many scientists. This increased interest led to a number of articles on the general geological setting, depositional environment, taphonomy, and a number of detailed as well as preliminary reports on the taxonomy and anatomy of various organisms from the locality. The systematic and morphologic studies include investigations on the soft-bodied trilobite Naraoia (ZHANG & Hou, 1985; Hou et aI., 1991), but detailed investigations on the morphology and anatomy of softparts from the more typical trilobites with calcified exoskeletons are still lacking (CHEN & ERDTMANN, 1991). This report presents anatomical features of two of the five species of trilobites with calcified exo-

skeletons from the Chengjiang fauna. The rare Kuanyangia sp. (ZHANG 1987b) as well as Ma/ungia sp. from the uppermost Lagerstdlle-type layers and an unnamed eodiscid from the lowermost part of the fossil Lagerstdlle have not been found yet with preserved soft-parts. In 1981, one of the authors (S. D.) discovered a large number of shelled fossils, including trilobites and bradoriids, at the Maotianshan locality of Chengjiang, together with the appendages of bivalved arthropods, which were described subsequently (HUO et aI., 1983; HuO & SHU, 1985; SHU, 1990). The first specimens of calcareous-shelled trilobites with preserved soft parts were discovered in 1991 (SHU et aI., 1992) and were supplemented by additional finds in 1992 and 1993 (SHU et aI., 1993). The material studied for this article come from the three localities, termed Maotianshan, Dapodou, and Xiaolantian, respectively (Fig. 1). The recent articles listed above sufficiently outline the geological and ecological setting, and there is no need for a further discussion on those aspects. An outline of the geographical and geological setting, taphonomy, stratigraphy, and the biotic assemblages has

Rcdlichiacean trilobites from Chengjiang

been presented by CHEN & ERDTMANN (1991) and Hou et al. (1991).

Chengjiong

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Fig. 1. Skelch map showing Sinian·Lower Cambrian geology and location of Chengjiang fossil sites Maotianshan, Dapodoll, and Xiaolanlian, respectively. Insert shows location of the Chengjiang area on the Yangtze Platform.

The Chengjiang locality is located in eastern Yunnan, South China. The deposits that yield the exceptionally well preserved fossils belong to the lower to middle part of the Yu'anshan Member in the Qiong-

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zhusi Stage (CHEN & LINDSTROM, 1991) and are part of the Eoredlichia Zone. This zone yields the oldest trilobites known so far from the Yangtze Platform. The traditional interpretation of the general age and international correlation by Chinese authors suggests these trilobites to be the oldest trilobites known (ZHANG, 1987a). In addition, the area is interpreted to represent the origin for trilobite radiation on a global scale (Luo, 1981). Although a direct correlation with regions outside China is difficult, recent investigations based on more advanced knowledge indicate a substantial· doubt about the correctness of these correlations. LANDING (1994) and ZHURAVLEV (this volume) assumed an age for the Qiongzhusi Stage that suggests correlation into the Botomian Stage of the Siberian Platform. Recent studies of carbon isotopes (KIRSliVINK et aI., 1991) more-or-Iess corroborate these interpretations, and the Chengjiang fossil beds are certainly not older than Ihe upper Aldabanian Stage of the Siberian Platform. Hence, the trilobites are definitely not among the oldest known. Nevertheless, they still represent the oldest known trilobites with preserved soft-parts. Additional layers with well-preserved, soft-bodied metazoans are known at Chengjiang at the transition from the Qiongzhusi to the Canglangpu Stage, but have not yet yielded trilobites with preserved softparts.

Preservation and taphonomy The mechanisms of formation of the Chengjiang fossil Lagers/tille are incompletely understood. The deposits consist dominantly of more-or-Iess pure mudstones and silty mudstones interbedded with stratified sandstone blankets. A 0-1.0 m-thick, lenticular unit in the upper part of the Chengj iang quarry consists of hummocky cross-stratified sandstone (E. LANDING, field observations, 1992). This setting is interpreted as indicating phases of rapid deposition. Rapid burial of the organisms preserved them in life position with their dorsal exoskeletons more or less parallel to the bedding. Their ventral appendages, however, usually penetrate several planar laminae in varying directions (Fig. 8). As a result, the rocks containing shelled fossils with preserved soft-parts break along the dorsal surface of the exoskeleton, and preserved soft-parts are usually not readily visible. Early diagenetic alteration led to a replacement of chitinous parts by hematite and iron-rich clay minerals (lIN et aI., 1991). In arthropod appendages, two types of taphonomically significant preservation have been

observed. The first type is similar to that of the Burgess Shale (WHllTlNGTON, 1975), in which the limbs are displaced with respect to the dorsal exoskeleton of the individual (PI. I, figs. I, 5). This kind of preservation suggests that the individuals died before burial: The appendages are obviously dislocated in a way that indicates that the muscles that originally linked the limbs and exoskeleton decayed, or were, at least, disconnected from their attachment sites. Exopodites and endopodites, which were originally located approximately dorsally and ventrally to each other, are sometimes found to lie on the same bedding plane. More commonly, however, the branches of the appendages are found to be preserved in roughly dorsoventral positions, which suggests burial of living individuals. No notable displacement between the limbs can be detected in these cases (Fig. 8, PI. I, figs. 5, 9). The individuals appear to have been unable to escape rapid deposition. Penetration of the limbs through several minute layers beneath the specimens may indicate the final struggle of the organisms.

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ZHANG

Methods A breakthrough in the study of soft parts in Chengjiang specimens was achieved in 1993 by dissection of the fossils. Careful excavation of the specimens through the dorsal exoskeleton permits examination of remnant soft parts. According to the relations between soft-parts of a fossil and the specific character of burial, the dorsal exoskelton of a trilobite and underlying matrix are removed as small particles with knives, needles and vibrotools until the preserved soft-parts are excavated. Before a specimen is dissected, it is necessary to determine whether the specimen actually has preserved soft-parts. Two helpful criteria exist in this evaluation: First, it is self-evident that the only individuals that might have soft-parts are organisms that were intact during burial, and the dorsal exoskeleton should, thus, be complete. Individuals which represent exuviae or suffered advanced decay before burial cannot have useful internal anatomy. Secondly, specimens with preserved soft-parts are usually, at least in part, red-wine colored or reddish brown. The exoskeleton, as well as soft parts with cuticular surface, were usually stained by body fluids. This staining subsequently underwent a permineralization, which is now visible as a reddish

color. In contrast, specimens in which the shell has a color similar to that of the matrix rarely have preserved soft-parts. Despite the visibility of soft-parts even with the unaided eye, these details are often extremely faint and unclear in photographs and generally cannot be documented satisfactorily. It should also be noted that darkcolored rocks of the Chengjiang site (which has experienced little weathering) have specimens, which are extremely difficult to prepare for examination of softparts. In contrast, light-colored layers (which are chemically weathered to some extent) are relatively easy to prepare and to obtain satisfactory results. The subsequent account differs slightly between the two types of specimens due to the mode of preservation. Specimens which obviously were dead before burial commonly have more easily prepared limbs (e.g., with their exopodites nearly parallel to the dorsal surface). In contrast, individuals, which were buried alive usually have gill-branches in a subvertical, often imbricate position, which makes their preparation and study difficult. In these cases, the recognition of the type of limb branches may be extremely difficult.

Morphological descriptions Eoredlichia intermedia is one of the well known Lower Cambrian trilobites of the Yangtze Platform (and possibly South Australia). Earlier studies included detailed descriptions of the exoskeleton (LU, 1940; ZHANG [CHANG], 1962, 1987b). Hence, our remarks focus on additional morphological characters, which have not yet been documented in adequate detail, or on features that supplement published information. The terminology used herein is in accordance with that of modem text-books. Major differences against the Treatise (HARRINGTON in MOORE, 1959) include the use of endopodite (instead of telopodite) and exopodite (instead of pre-epipodite). The material used for this study is stored in the collections of the Geological Institute of the Northwest University, Xi'an, People's Republic of China (acronym NWUS), the Institut fur Palaontologie, Universitat WUrzburg, Germany (acronym PIWG), and the Museum Nationale d'Histoire Naturelle, Paris, France (acronym MNHN).

Family Pararedlichiidae HUPE 1953 The concepts of the families of the Superfamily Redlichiacea are controversial and far from satisfactorily established. In addition, constituent genera have been referred to different families, to subfamilies raised to families, and vice versa. The diagnoses of a number of families have been changed at various times, and the later significance of characters used in diagnoses differs throughout the superfamily. Finally, the systematic arrangement, and thus the definition of higher taxa, is almost exclusively phenetic rather than cladisticphylogenetic. As a consequence, the existing systematic arrangement cannot be seriously regarded as a mirror to the radiation of one of the earliest trilobite groups. This problem is directly related to the concept of the Family Pararedlichiidae and the genera Pararedlichia, Eoredlichichia, and Wutingaspis. Pararedlichia HUI'E 1953 is based on P. pulchella HUI'E 1953 from the Lower Cambrian of Morocco (Fig. 2A), which is only known with certainty from the

Redlichiacean lrilobitcs from Chengjiang

holotype, a probable topo- and stratotypic paratype, and two additional stratotypic cranidia. All material consists of not entirely complete cranidia, which are usually slightly distorted. The other two species assigned by HUPE (1953) to the genus Pararedlichia, P. sublransversa HUPE 1953 (Fig. 2C) and P. rochi HUPE 1953 (Fig. 28), are only known from single, incomplete, slightly distorted cranidia, which are topo- and probably stratotypic with the type material of P. pulchella. Although they appear to differ in a few characters, these differences may be explained by the differences in size and deformation. P. sublransversa and P. rochi are hence tentatively regarded as synonyms of P. pulchella. Pararedlichia ovelensis SOZUY in L1NAN & SOZUY 1978 from Asturias, northern Spain, is again known from imperfect material and awaits further study. The shape of the eye ridges, described as an important characteristic of the genus by SOZUY in LINAN & SOZUY, 1978, differs indeed from that in most other genera of the Pararedlichiinae (including Eoredlicha), but is much less distinct in the holotype of Pararedli-

207

chia pulchella. The lack of information on librigenal, thoracic and pygidial morphology of Pararedlichia suggests a need for a temporary restriction of the genus to the type and typotypic material. A detailed comparison, or even synonymization, with Eoredlichia (ZHANG, 1966, ZHANG & LIN, 1980, and LUo, 198 I, as subgenus of Eoredlichia; PILLOLA, 1991) lacks any support from key morphological characters. Tentative assignment of two cranidia of Eoredlichia planifrons from the Yangtze platform to "Eoredlichia pulchella" by PILLOLA (1991) is unacceptable for these reasons. Moreover, even the limited characters visible on the specimens figured by PILLOLA (1991: pI. 31, figs. 1-2) suggest a different species (e.g., width of occipital ring, length of palpebral lobes). Nevertheless, the distinction of Pararedlichia from other, morphologically similar genera remains problematic. Valuable characters include three pairs of simple, lateral glabellar furrows; eye ridges, which are obliquely backward directed and taper conspicuously

rig. 2. A. Pararedliehia pulehel/a HUPE 1953. MNHN R.50889. Holotype, eranidium, Tazemmourt, Anti-Atlas, sample horizon TAZ-FI; 3x. B. Pararedliehia roehi 1·luPE 1953. MNHN R.50893. Holotype, eranidium, Tazemmourt, Anti-Atlas, sample horizon TAZ-I'I; 3x. C. Pararedliehia sublransversa IIUPE 1953. MNHN R.50909. Holotype, cranidium, Tazemmourt, AntiAtlas, sample horizon TAZ-I'I; 3x. 0, r. WUlingaspis lingi KOBAYASHI 1944. PIWG 95X15. Meishueun section, Jinning County, Yunnan; Qiongzhusi Fonnation, Yu'anshan Member, sample horizon unknown. Cranidium, internal mold; 4.5x. D. Lateral view. F. Dorsal view. E. Eoredliehia? noiri (JAGO 1980). MNHN C446. Limousis, MIS. du Cabardcs, Montagne Noire, Alternanees grcso-calcaires. Holotype cranidium in the center; 2.5x.

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SIIU, GEYER. CHEN

forward along the frontal lobe of the glabella; absence of a parafrontal band; a narrow preglabellar field; absence of a plectrum; and obliquely forward directed anterior branches of the suture. These characters are regarded as inadequate to characterize a distinct genus, and the morphology of the thorax is needed to permit precise comparison with other genera. However, the lack of this evidence does not allow synonymitaion of Pararedlichia with any similar genus (as with Eoredlichia; see ZHANG, 1966, ZHANG et aI., 1980, LUo, 1981, and PILLOLA, 1991), and attempts at precise intercontinental correlations based on such synonymization at the genus-level, as suggested by PILLOLA (199\), are definitely without any value. In contrast, Eoredlichia is distinctly characterized by features of the thorax and pygidium. These feature include a conspicuous axial spine on the ninth thoracic segment; a moderately large pygidium with two recognizable axial rings; and a large terminal axial piece with a median furrow. As a consequence of the nomenclatorial odyssey (sketched below under WUlingaspis), the genus Eoredlichia was omitted in the Treatise (MOORE, 1959). Galloredlichia JAGO 1980 (in COURTESSOLE & JAGO, 1980) is a monotypic genus from the Montagne Noire, southern France, based on Galloredlichia noiri JAGO 1980 (Fig. 2E). The type material from the Lower Cambrian Orbiel Formation, preserved in relatively coarse sandstones, is slightly deformed, and the characters are again imperfectly known. However, topotypic partial thoraxes and pygidia assigned to this species give information for a precise comparison with other genera: Isolated thoracic tergites indicate an an extremely long and backward directed spine on one of the axial rings. The pygidium has two axial rings plus a terminal axial piece with a median furrow and has narrow pleural areas. These characters suggest the closest similarity with Eoredlichia, and a placement in that genus might be proposed. JAGO (1980) regards a "broad ridge immediately in front of the glabella" (JAGO, 1980: 15) as the distinction between Galloredlichia and Eoredlichia. The parafrontal band in Galloredlichia, however, makes the recognition of a plectrum impossible, as in most of the material of Eoredlichia. Archaeops HUI'E 1953 (type species Archaeops lui HUI'E 1953 [= Redlichia walcolli Lu 1941 non MANSUY 1912]) and Sallkiandops HUI'E 1953 (type species Redlichia walcolli MANSUY 1912 non Lu 1941) were recognized as junior synonyms of Eoredlichia by earlier authors (ZHANG & LIN, 1980). Archaeops lui is, in

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ZUANG

addition, recognized as an objective synonym of Eoredlichia inlermedia, the type species of the genus. The cranidium of Pachyredlichia ZHANG 1966 (type species P. shensiensis ZHANG 1966) has an extremely narrow or lacks a preglabellar field in adult individuals, but is similar to Eoredlichia cranidia ins most other characters. Pachyredlichia was first established as a subgenus of Eoredlichia, and PILLOLA (1991) went so far to synonymize tlie taxon with Eoredlichia. Nevertheless, complete thoraces and pygidia are unknown, and a precise diagnosis is impossible for the moment. WUlingaspis KOBAYASHI 1944 from the Lower Cambrian of the Yangtze Platform is distinguished from Eoredlichia by such minor differences as the lack of a distinct boss in front of the glabella (which is reduced or totally lost in late holaspids of Eoredlichia inlermedia, too; compare ZHANG & LIN, 1980), slightly shorter palpebral lobes and longer eye ridges, and more transversely directed anterior branches of the facial suture. The type species of WUlingaspis, W. lingi KOBAYASHI 1944 (Fig. 2D, 2F), as well as W. condilils and YlInnanocephallls yaopingensis, was early regarded as a junior synonym of Eoredlichia inlermedia (Lu 1940) (ZHANG, 1953), and Eoredlichia became, in tum, a junior synonym of Wulingaspis. However, a later study (ZHANG, 1962) concluded that the material used for the 1953 report did not represent W. lingi, and the species W. lingi and the genus Eoredlichia were revived as distinct taxa. HARRINGTON (in Treatise, 1959) placed Willingaspis under the Family Abadiellidae, while REI'INA (1966) tentatively assigned the genus to the Pararedlichiinae. In the same year, ZHANG (1966) introduced the new Subfamily Wutingaspinae for the genus, and suggested the absence of axial spines on the thoracic segments as diagnostic for the subfamily. However, such species as Eoredlichia? shalanensis ZHANG & LIN 1980 and Pachyredlichia shensiensis ZHANG 1966 show close similarities in several related characters in the two genera, and thus indicate a common ancestry. It, consequently, remains questionable whether a subfamily Wutingaspinae is valid: From the phyletic point of view, the Wutingaspinae should branch off from the Pararedlichiinae and reflect a common ancestry by apomorphic features, which are not obviously developed. From the morphological point of view, the absence of axial spines on the thoracic segments can barely be regarded as an apomorphic character: the occurrence of similar thoracic morphologies in different higher taxa indicates distinct functional habits rather than systematic significances

Redlichiacean lIilobites from Chengjiang

for suprageneric taxa. It is, in addition, impossible to characterize the Wutingaspinae because knowledge about the morphology of the thorax lacks from taxa of the Pararedlichiinae as well.

Eored/ichia ZHANG 1951 Type species: RedlicMa inlermedia Lu 1940.

Discussion: The genus Eored/ichia was first proposed by ZHANG in an oral presentation during the annual meeting of the Paleontological Society of China in Beijing in 1950. Abstracts of these presentations, although dated "December 1950", were published not before March 195\, and the genus was formally estabIished in that year (ZHANG, 195 I).

Eored/ichia inlermedia (Lu 1940) • 1940 Redlichia intermedia. - Lu, On lhe ontogeny and phylogeny of Redlichia intermedia, p. 333ff, 1'1. I, figs. 1-10. 1951 Eoredlichia intermedia (Lu). - ZHANG, Trilobites from the Shipai Shale, p. 10. 1953 Redlichia intermedia Lu. - Lv in Lv & DONG, Cambrian standard sections of Shandong, p. 186 [incl. footnote I, non footnote 2 as stated elsewhere]. 1953 Wutingaspis intermedia (Lu 1940). - lllANG, Some Lower Cambrian trilobites, p. 121, 128, 141 [partim]. 1953 Redlichia (Wutingaspis) intermedia Lu. - lHANG, Some Lower Cambrian trilobites, p. 142-143 [partim J. non 1953 Wutingaspis intermedia (Lu 1940). - ZHANG, Some Lower Cambrian trilobites, p. 142-143, 1'1. III, figs. 112 [= Eoredlichia yaoyingensis, Wutingaspis conditus, and Wutingaspis lingi, respectively]. 1962 Eoredlichia intermedia (Lu). - ZHANG, On lhe genus Earedlichia, p. 38-39, fig. on p. 37,1'1. I, fig. la-b. 1980 Eoredlichia intermedia (Lu). - lllANG & LIN in ZHANG et aI., Cambrian lIilobile faunas of Southwestern China, p. 72,92-94 [ontogeny], 151-152,421,1'1. 33, figs. 9-14, 1'1. 34, figs. 1-6, 1'1. 36, figs. 3-4, text-figs. 47.5,50.2,67. 1981 Eoredlichia intermedia (Lu). - Luo, Trilobites from the Chiungehussu formation, p. 335, 1'1. II, fig. 7, 1'1. III, figs. 5-7. 1982 Eoredlichia inlermedia (Lu). - Luo et aI., The SinianCambrian boundary in Eastern Yunnan, p. 45, fig. 10.1, 1'1. 28, fig. 8,9 [eranidium on fig. 8 identical with that figured by Luo, 1981 J. 1984 £oredlichia inlermedia (Lu). . HE et ai., Biotic characteristics of the Sinian-Cambrian boundary beds, p. 40, fig. 7-2, 1'1. II, fig. 16 [eranidium identical with that figured by Luo, 1981]. 1987 Eoredlichia intermedia (Lu). - ZHANG, Early Cambrian Chengjiang fauna, p. 229-230, 1'1. II, figs. 1-3. v 1992 Eoredlichia intermedia (Lu).. SIIU et aI., The Lower Cambrian KIN fauna, p. 35, 1'1. 2, figs. 3,4. v 1993 £oredlichia intermedia (Lu). - SIIU el aI., New important findings, p. 100-10 I, 102, text-fig. 2A.

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1994 £oredlichia inrermedia. - SUN, Early multicellular fos·

sils, Fig. 7A. See ZIIANG & UN (1980) for additional synonymy.

Studied material from Chengjiang. Locality Xiaolantian, sample horizon X,: NWUS 94-1001A, NWUS 94-1002, NWUS 94-1010, NWUS 94-1022A,B, NWUS 94-104IA,B; sample horizon X,: NWUS 94-1020. Locality Maotianshan, sample horizon M,: NWUS 91-1001A, NWUS 93-1002A,B, NWUS 93-100M,B; sample horizon M3 : NWUS 92-1023A,B. Locality Dapodou, sample horizon D,: NWUS 92-1013B, NWUS 92-1017, NWUS 921018A,B, NWUS 93-1001; sample horizon D3 : NWUS 92-1019.

I. Dorsal exoskeleton

Cephalon. The cephalon has been described in detail by earlier authors (LU, 1940; ZHANG, 1962; ZHANG & LIN, 1980), and most of the features need not to be repeated here. A common preservational effect is that the hypostome was pressed against the cranidium during compaction. As a result, the shape of the hypostome is imprinted at the anterior part of the glabella. At NWUS 94-1002A and other specimens, the dorsal processes on the backside of the maculae created fractures and are thus marked on the anterior part of the glabella. On the same specimen, the sagittally narrow preglabellar field is separated from the preocular fields by fractures that mimic a plectrum-like extension of the anterior border. This feature coincides with the outline of the rostral plate (underlying that part of the dorsal exoskeleton) as known from other redlichiid trilobites (compare FORTEY, 1990: Fig. 6). It should be noted that the lateral margin of the librigena is defined at the base of the genal spine by a slight change in curvature that creates a faint concave section. This part of the sclerite is usually cracked transverse to the spine, and this indicates considerable deformation. The change is curvature is hence a taphonomic artifact created by compaction of the sediment. The genal spine appears originally to have subtended an angle of about 10 to 15° to the rest of the librigena, which again had a more ventrally deflected position during the life of the animal. The ocular platform and the lateral border furrow as well as the fixigenae are occasionally densely covered with caecal features that depict the arrangement of underlying vessels (Figs. 40, 5, I I). From the exterior rim of the eye, radially arranged and densely spaced ridges turn towards the lateral and anterolateral border but are interwoven into a dense net, which becomes slightly less compact shortly before the net reaches the border furrow. At NWUS 92-1023A, there are two faint ridges, which commence close to the anterior end

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Fig. 4. Eoredlichia intermedia (Lu 1940). All specimens blackened and coated with magnesium oxide. A. NWUS 92-1023A; sample horizon M3. Pleural tips of tergites 2 to 8 at the left side of the thorax. Skeletal material fairly decalcified, serves for a bener preservation of the granules surface. However, cracks that result from differential compaction are more strongly developed. They indicate the boundaries of the ventral doublures at the ventral sides of the pleural tips. Note progressive backwardly directed pleural spines. Magnification 6x. B. Fairly complete dorsal carapace; left genal spine, palpebral lobes, and thoracic spine on ninth segment broken off. Axial ring of the ninth tergite clearly enlarged. Note the grooves on the glabella, which result from the imprint of the hypostome's dorsal processes during compaction. Magnification 3x. C. Detail of B. Posterior part and pleural of tergites I to 7 at the left side. Internal mold showing smooth surface with single veins at the pleural tips. Faint lines close to the posterior rim of the pleurae indicate position of the doublure below. Note relatively well developed fulcral processes and sockets, and large facets. Note particularly broad facet at the first tergite. Bulbous swellings close to the dorsal furrows apparently acted as stopping devices. Magnification 6x. D. NWUS 92-1023A; sample horizon M3 . Detail of \ibrigena showing dense net of caecal features on ocular platform. Note pair of faint ridges, which commence close to the anterior end of the eye. Magnification 6x. E. NWUS 94-1002A; sample horizon M2 . Pleural tips of tergites I to 8 at the right side of the thorax. Pleural tips partly with faint terrace ridges parallel to the external margins and with faint veins. Furrows (primarily in the posterior half) are a result of differential compaction and indicate position of the ventral doublure. The doublure and an underlying vessel is also indicated e10se to the posterior margins of the pleurae. Magnification 6x. F. Detail of B. Posterior thorax and pygidium. Note slight sagittal constrictions of the axial rings. Magnification 8x.

Redlichiacean trilobites from Chengjiang

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SHU, GEYER, CHEN & ZHANG

of the eye and turn obliquely forward and outward to fade at the border furrow. Similar ridges are recognizable in two other specimens (NWUS 94-1002A, Fig. 5). These ridges were designated as »facial lines« by ZHANG (1962: unnumbered text-fig.). According to analogous structures in other arthropods these ridges may have housed the visual nerves or nerves for yet unknown sensory organs. However, similar structures in Yunnanocepha/us yunnanensis emerge from the center of the eye ridges and are interpreted as a cover over nerves to (yet unidentified) sensory organs along the anterior border. A granular ornament probably covered most of the cephalon except for the furrows. Faint terrace ridges can be seen along the anterior and lateral cephalic border.

Fig. 5. Eoredlichia il/termedia (Lv 1940). NWUS 94-1002A; sample

horizon X2 " Ccphalon with slighly dislocated librigcnac and articulated anterior thorax. Dorsal processes on the backside of the hypostomal maculae created fractures on the anterior part of the

glabella. Caecal features on the ocular platform include a dense net

that depict the arrangement of underlying vessels. Note faint terrace ridges at the exterior margin of the lateral cephalic border. Specimen

blackened and coated with magnesium oxide. Magnification 3x.

Thorax. The thorax consists of 15 segments in adult individuals. The rhachis generally tapers progressively toward the posterior, but has its maximum width at the second thoracic tergite. The axial furrows, however, are faintly s-shaped so that the posteriormost axial rings decrease little in width, and the decrease is much more conspicuous at tergites 9 to 1 I. The axial rings of the anterior tergites lack median nodes or spines, whereas the axial ring of tergite 9 bears an extremely long and backward-directed spine. This spine extends well beyond the pygidium and may exceed the total length of the thorax (Figs. 3, 4B, 15A). Its base envelopes the total length of the slightly en-

larged ninth axial ring, and stretches laterally almost to the axial furrows. The adjacent tenth axial ring is slightly reduced in sagittal length to compensate the enlarged ninth axial ring (Fig. 4B). The following axial rings I I to 15 are generally sagittally narrower than the anterior ones and carry an inconspicuous median node and, occasionally, a moderately prominent median sagittal crest (which is inconspicuous on tergite 15) (Fig. 4F). The axial rings, particularly of tergites I to 8, are transversely tripartite in dorsal view with anterolateral nodes, which are comparatively well defined by shallow furrows. The much wider median section has a slightly backset anterior rim that allows a view to the relatively wide furrow anterior to it (Fig. 4B). A faint transverse depression close to the posterior margin of the median section of the axial ring shows the limits of the underlying doublure. The axial rings of tergites I and 2 are conspicuously curved in dorsal view; the anterior rim of the median section at the tergites 3, 7,8, 10, II, 14 and 15 are clearly bent backwards (Fig. 4B). The articulating half-ring is visible on a few specimens. It is generally quite narrow and is not markedly elevated above the furrow to the posterior (Fig. 7B). The pleurae extend into acute, slender, moderately long spines, which show a progressive change in curvature (Figs. 4A, 4C, 4F). These pleural spines are slightly backward directed at the first tergites but become more strongly backward directed from about segment 9 on. As the axial rings, the pleurae are conspicuously narrower from about segment 10 backwards and are generally more curved. Tergite J 5 has short and crooked pleurae that envelop the anterior part of the pygidium (Figs. 4F, 6, 7B). As a consequence, tergites 10 or II to 15 form a part of the dorsal exoskeleton that is slightly different in dorsal view from the anterior part of the thorax (Figs. 3, 6). It is obvious that this morphological distinction corresponds to functional units. The pleural furrows are faintly s-shaped at the anterior tergite, roughly straight at tergites 10 and II, and slightly to conspicuously bent at tergites 12 to 15 (Figs. 4F, 6). They reach a maximum width at, or slightly distal, to the point where the pleurae deflect towards the ventral. The distal end of the pleural furrow is formed by a small elliptical depression. Fulcral joints (sensu BERGSTROM, 1973) are comparatively weakly developed at the anterior tergites, but are progressively more conspicuous backwards. Fulcral processes are developed at about midlength on the anterior pleurae. Their position, however, moves progressively

Rcdlichiaccan trilobites from Chengjiang

towards the axial furrows on more posterior pleurae (Fig. 48). The fulcral processes fit into corresponding sockets, which are faintly marked. The fulcral joints mark the beginning of the ventral denection of the pleurae. The pleurae usually developed as slightly bulbous swellings in the posterior areas close to the axial furrows (Fig. 4C, 4F). Due to these swellings, the posterior margin at these places extends slightly backward. It certainly actea as a stopping device because it meets the relatively elevated anterior border of the neighbouring tergite and prevented a notable concave curvature of the thorax. Comparatively well developed nanges served for an additional marginal connection between the tergites. These nanges can be seen in NWUS 92-10138 where the ventral sides of pleurae are partly exposed (Fig. I I).

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clearly triangular and broadest (sagittally) at the axial furrows, a fulcral joint to the a~terior that is in a relatively proximal position, and a correspondingly long (transversely) and comparatively strongly denected facet (Figs. 4C, 5). Dorsal furrow processes are weakly developed and fit into small, corresponding sockets (Fig. 11). The surface of the pleurae is densely covered by tiny granules (Fig. 4A). This ornament is not recognizable on the axial rings, probably due to imperfect preservation. Faint furrows more-or-Iess parallel to the anterior and posterior margins of the pleurae indicate underlying doublures. A few vessels may be preserved at the anterior or posterior part of the pleural furrow and at the pleural spines, and are usually changing into a small median ridge that is located along the pleural spines (Figs. 4C, 4E). A few very faint and extremely short terrace ridges may be present at the pleural tips. Common features on the thorax of E. inlermedia are sagittal furrows at the base of the pleural spines (Figs. 4A, 4E). These are a taphonomic artifact and result from compaction of the sediments. In addition to small cracks that are occasionally visible, this interpretation is also suggested by the change in transverse denection of the pleurae that can be seen beyond these furrows.

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Distal to the fulcral joints are well developed facets that mark the area of overlap during enrollment (except for tergites 14 and 15 where facets are weakly developed or entirely absent). These facets appear to be faintly concave in dorsal view and extend anteriorly into a stoutly triangular and upwardly nexed tongue (Figs. 4C, 6). The first thoracic tergite has slightly shorter (transversely) pleurae, a pleural furrow that is

Pygidium. The pygidium of adult specimens is 1.5 times wider than long. The pygidial axis is convex and has about 70 percent of the maximum width of the pygidium. It consists of two axial rings, a terminal axial piece, and an articulating half-ring. The axis has a subcylindrical shape although the terminal axial piece is slightly narrower than the two anterior axial rings. The terminal axial piece is roughly semicircular, but bears a shallow and weakly defined median furrow and a pair of almost fused nodes at the anterolateral corners. Its posterior end slopes gently and is more-or-Iess fused with the posterior border. The furrows between the axial rings and the terminal axial piece fade over the mid of the rhachis (Figs. 4F, 78). The pleural fields have only 2 to 3 interpleural furrows, which are directed strongly backward; the posterior ones are extremely weak. The anterior border is slightly raised and curves backward after a very short, triangular transverse section and is marked distally by a small fulcral process that indicates the articulation with thoracic tergite 15. The distal end of the anterior border is marked by a small triangular tip. The lateral border is weakly defined and relatively shallow. It is crossed by shallow extensions of the anteriormost pleural rib, and this creates small spines on the lateral margin. The posterior border forms merely connuent

214

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Fig. 7. Eoredlichia intermedia (LV 1940). Qiongzhusi section, Qiongzhusi Fonnation, Yu'anshan Member, sample CH 2. Both specimens blackened and coated with magnesium oxide. A. PIWG 95Xl3a. Slightly distorted cranidium, internal mold; 3x. B. PIW 95X14. Posterior thorax with articulated pygidium; internal mold; broken edges of thoracic pleurae and axial rings penn it recognition of facets and articulating half rings; 3x. with the terminal axial piece, and is usually only defined by weak furrows at the posterolateral comers of the terminal piece. The shell surface of the pygidium is covered by tiny granules, but the posterior border is smooth (Fig. 78). 2. Appendages

Eored/ichia inlermedia had a simple, uniramous first pair of appendages, or antennae as in other trilobites. The post-antennal limbs of Eored/ichia inlermedia are a series of biramous appendages on the cephalon and the thorax, which are not entirely uniform in shape and decrease in size backwards as in other trilobites. Antennae. The pair of antennae of Eored/ichia inlermedia are preserved on only 5 of the studied specimens from the Chengjiang locality. Their lengths clearly exceed that of the cephal on. They emerge from beneath the cephalic shield at the anterior rim of the cephalic margin and are usually anterior to the anterolateral comers of the glabellar frontal lobe (PI. I, figs. I, 8). This position indicates the location during life. Postmortem deformation sometimes moved the antennae into more lateral positions. The course of the antenna beneath the cephalic shield is recognizable on two specimens. In these specimens, the proximal parts of the antenna run more-or-Iess parallel to each other from the origin to the cephalic rim, and this section is clearly conical. The attachment site has not been observed with certainty, but appears to be close to the midline at about the medial point of the hypostome (PI. I, fig. 5: ab) as in Agnoslus pisiformis (see MOLLER & WALOSSEK, 1987). A short and particularly mobile

section lies just below the cephalic margin. The distal parts of the flagella are usually more-or-Iess straight and diverge strongly. The distal sections are narrower and taper slightly but progressively in width toward the tips (PI. I, fig. I). Due to the generally poor preservation of the antennae, morphological details are difficult to recognize, and single segments are usually not distinguishable in the studied specimens. However, information from specimen NWUS 93-100 I suggests that the proximal segments have a roughly tubular shape with a crested external/lateral rim. The relatively straight distal flagella indicates a stiffness that reflects a considerable scI erotization. As a consequence, curvature at about the cephalic margin and movements of the antennae were only possible with segmentation into distinct units.

!'ig. 8. Eoredlichia intermedia (Lu 1940). NWUS 93-1002A (see also PI. I, fig. 5); sample horizon M2 . Detail of thorax. Dorsal carapace largely removed to show ventral appendages. Visible arc a number of exopodites, mostly in a steeply inclined position,

penetrating several planar laminae. Magnification 3.5x.

Rcdlichiaccan trilobites from Chcngjiang

In summary, the antennae consisted of subparallel, anteriorly directed, massive proximal sections and

215

more slender, diverging distal flagella. The distal flagellum appears to have been relatively stiff.

Fig. 9. Eoredlichia intermedia (LV 1940). A. NWUS 92-1018A; sample horizon O2, Detail showing series of exposed endopodites with their weakly developed joints and the long podomere 2. Magnification 3x. B. NWUS 9\-\00IA; sample horizon M2' Partial carapace dissected at left flank, showing series of exopodites of the thoracic segments 3 through 8. Magnification 3x.

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of thoracic segment. Anteriormost of the visible endopodites belongs to the posterior cephalic segment. Abbreviations: fr, fracture; s, suture; cl, thorn- or claw-like spine. Further explanations in the text. Biramous appendages. Eoredlichia inlermedia only had biramous appendages posterior to the antennae. These included three pairs of normal biramous cephalic limbs. However, the endopodites differ slightly from those from other known polymerid trilobites. Unfortunately, the quality of the proximal parts of the

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appendages is insufficient for detailed study, and details of the coxa cannot be presented. At NWUS 92-10 18A, three endopodites of cephalic limbs dissected from the right side of the cephalon show an increase in size from the first to the third of the exposed endopodites (Fig.9A, PI. I, fig. 2). The

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exfoliated and with adhering fragments of ventral appendages. Also visible arc caecal features, the large doublurc below the facet at the

first thoracic tcrgilc, and comparatively well developed nangcs close to the anterior margins of the pleurae. Note also dorsal furrow process corresponding socket visible at anterior and second thoracic tergilcs. Sec Fig. 12 for further explanations. Magnification 3.5x.

second, fairly well-preserved endopodite exemplifies the general morphology of the endopodites in Eoredlichia inlermedia. These 'leg branches' are composed of feebly defined podomeres with weakly developed joints that suggest relatively light sclerotization of the cuticle. Stronger compaction led to preservation of the endopodites as smooth, tapering bands. At NWUS 92-10 18A, the visible part of the endopodite consists of at least six podomeres (Fig. 10, PI. I, fig. 2). The coxa is not clearly identifiable in this specimen. Podomere 2 is an unusually long, clearly tapered tube, which includes almost half the total length of the endopodite. Comparison with other trunk limbs with different burial styles suggests that the original transverse section close to the distal tip of this podomere was subelliptical. Podomeres 3, 4, and 5 are faintly tapering tubes of similar outline. Podomere 6 appears to be a slender tubular segment, more than three times longer than wide. Podomere 7 is a short tubular sec-

Fig. 12. Eoredlichia intermedia (Lv 1940). Explanatory drawing of NWUS 92-1013B (Fig. 11). Vcntral vicw of incompletc carapacc with adhering fragmenlS of ventral appendages. Visible are series of imbricatcly arranged exopodites with their lamellae roughly parallel to the dorsal carapace. The exopodites of the anatomically right flank arc nearly in place, whereas exopodites of the sinistral side (ex I) are overturned and now cover the axial area ventrally. The differing orientation is also indicated by differences in the imbrication. This is additionally confimled by the differing orientation of the broken edges, which in tum confirm the inverse imbrication of the exopodites with the posterior parts of the exopodite 'combs' overlying the anterior blade of the exopodite of the posteriorly adjacent segment. The wavy pattern of the (anatomically) right exopodites (exr) is a result of compaction. Abbreviations: c, caecal features on the ocular platform; d, doublure; ex!, exopodites of the sinistral flank; exr, exopodite combs of the dextraillank.

tion, which tapers into a thorn- or claw-like terminal spine that sits slightly oblique to its tip. It is noteworthy that the lengths of the podomeres do not gradually decrease distally. A well-preserved biramous appendage with endopodite and exopodite in one plane is found on the right side of the anterior thorax in specimen NWUS 93100 I (PI. I, figs. I, 4). Because the appendage is clearly displaced, it is impossible to know whether it belongs to the posterior part of the cephalon or to the anterior part of the thorax. The endopodite of this segment has a tubular shape that is thick proximally

Rcdliehiacean trilobites from Chengjiang

and tapers gradually toward the distal end. Its joints are faint and hardly recognizable. Next to the endopodite lies an exopodite, which probably belongs to the posteriorly adjacent appendage. This exopodite is clearly shorter than the endopodite and lacks a recognizable shaft. It has a complex cross-section with a gently curved anterior margin and a shallowly bilobate posterior margin. Attached to the large and partly covered inner lobe is a conspicuous fringe of long filaments, which are directed obliquely backward. The smaller distal lobe is lingulate and barely differentiated from the proximal lobe. It bears a fringe of short and subradially arranged filaments at its lateral border. The base of the exopodite is covered by the pleurae, which strongly deformed the internal lobe during compaction. The mode of deformation indicates that the exopodite was relatively soft. The arrangement of the exopodites in this specimen suggests that the exopodite was carried inclined with a slight to moderate slope forward. As a result, adjacent exopodites overlapped, and the posterior fringe overlayed the anterior part of the exopodite in the posteriorly neighbouring segment. This mode of imbrication for Eored/ichia intermedia is confirmed by the series ofexopodites seen in NWUS 92-1013B (Figs. II, 12). The thoracic exopodites of the anterior thoracic segments in NWUS 93-100 I are similar to those described above. However, those of posterior segments differ markedly. A change in the morphology occurs most probably at the ninth thoracic segment, which significantly differs from the others by having a long axial spine. The exopodites of the posterior thoracic segments have a broadly elliptical, blade-like shaft with a fringe of long filaments (Fig. 13). Proximally, these filaments are perpendicular to the axis, but gradually turn outwards at the distal third.

Fig. 13. Eor.dlic},ia in/urn.dia (Lv 1940). NWUS 93-1001; sample horizon D2, Detail showing cxopodites of posterior thoracic segments with broadly elliptical, blade-like shan and attached posterior fringes of long ftIa-ments. Magnification 5x.

217

Endopodites and exopodites have usually parallel axes, except in notably distorted specimens. Their common direction suggests a stiff connection of the exopodite with the basal podomere of the endopodite and hence a harmonized movement. 3. Hypostome The general style of attachment of the hypostome in "true" redlichiids has been termed conterminant (FORTEY, 1990) and is characterized by connection of the hypostome to the doublure by an extension of the rostral plate. This type of attachment can also be observed in Eored/ichia intermedia. As a consequence, hypostomes are found comparatively infrequently (FORTEY, 1990). Nevertheless, the hypostome with its conterminous attachment or attached soft-parts can be detected by preparation from the dorsal side. Earlier notes on the hypostome of E. intermedia have been presented by ZHANG & LIN (in ZHANG et aI., 1980). In the description of the genus Eored/ichia (p. 151), these authors mentioned that the hypostome has two pairs of comparatively long spines; a note that was not indicated by their figures, and may refer to the recovery of a fragmentary hypos tome of Eored/ichia yaoyingensis (KOBAYASHI, 1944) (ZHANG, 1962, PI. I, fig. 2c). However, these spines can be detected in the material studied herein. Specimen NWUS 93-1006 represents an early holaspid (15 mm long, 15 thoracic tergites), in which the hypostome lies beneath the frontal through third glabellar lobes (PI. I, figs. 3, 6). It has a subtrapezoidal outline with an almost straight anterior border, which is slightly wider than the posterior border. The anterior wings are divided into two parts. The posterior wings extend into posteroventrally directed spines. The lateral border broadens into a triangular plate, which extends into posteroventrally directed spines. The posterior lobe of the median body is crescent-shaped and extends anteroventrally. The anterior lobe is conspicuously convex towards the ventral side but hidden by the matrix. Specimen NWUS 93-100 I represents a later holaspid (46 mm long, 15 thoracic tergites). It shows a hypostome with similar morphology to that described for NWUS 93-1006. However, the spines visible at the posterior wings are comparatively small, although they may not be entirely preserved. Small spines are also visible at the lateral border slightly posterior to its midlength. However, the lateral border does not show a conspicuous triangular extension (PI. I, fig. 7). This specimen is also in accordance with a remarkable Irend: The hypostome has a progressively smaller size

218

SHU, GEYER, CHEN & ZHANG

compared to the glabella with growing overall size of the individuals. The conterminant condition as the primitive mode of hypostomal attachment in the redlichiids is easily

ger of these parts is termed the »crop« and the smaller, posterior part is called »proventriculus«. However, it is difficult to locate the boundary between anterior and median guts.

recognizable at Eoredlichia inlermedia. However, the rostral plate and hypostome are probably fused and, hence, lack a functional hypostomal suture. A so-called »interrostrohypostomal plate«, which has been proposed for the sternite between the hypostome and the rostral plate in redlichiid trilobites (see ZHANG & liN, 1980), is probably also present in Eoredlichia inlermedia. This plate is possibly larger than in other, stratigraphically younger species of the Redlichiacea. The slight dorsoventral deformation (due to compaction) usually led to a direct contact of the hypostome with the overlying dorsal part of the cephalic exoskeleton. Consequently, the shape of the hypostome is frequently impressed on the glabella and vis-

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No reliably identified alimentary canal has yet been described from trilobites. Identification of an alimentary canal in two specimens of Deanaspis goldfussi (BARRANDE 1846)* from the Ordovician of Bohemia. However, interpretation the axial structures, first presented by BARRANDE (1852: pI. 30, figs. 38, 39; as »Trinucleus Goldfussi Barr.«) and refigured in the Treatise (HARRINGTON in MOORE, 1959: fig. 72; as Onnia ornala), do not appear conclusive. Trilobites are supposed to possess an alimentary canal that was built more-or-Iess like those of other arthropod groups. Hence it should have consisted of three parts termed »anterior«, »median«, and »posterior gut«. The anterior and posterior guts were derived, as in extant groups, embryologically from ectodermal tissue at the anterior and posterior sections and possessed limited digestive abilities. The mid-gut, in contrast, originated from endodermal tissue. It usually bears digestive glands and is the principal location where digestion and absorption take place. For the trilobites, it is generally accepted that the anterior gut, as »stomach«, was located between the hypostome and the dorsal cephalic exoskeleton underneath the glabella. Nevertheless, the anterior digestive tract with its weak digestive abilities can be subdivided into two parts. The anterior and lar-

* Remarks on the correctness of the nomenclature of the specific name gold!ussi; arc found until recently (SHAW, 1995). However, BARRANDE himself corrected his original, erroreous genitive ending (BARRANDE, 1852).

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Fig. 14. Eoredlichia intermedia (Lv 1940). Explanatory drawing of

NWUS 92-1023B (see Fig. 15A). Ventral view of partial carapace showing base of median spine on tcrgilc 9, articulating half-rings, and adhering remains of supposed midgut diverticula (black).

A number of specimens of E. inlermedia show paired dark markings that are preserved as colored spots, usually with little relief that would clearly distinguish them from the surrounding soft tissue. These spots usually have dark to reddish brown or dark grey color and have been found in the axial region. In specimen NWUS 9 I-I 00 IA, there are seven pairs of spots recognizable. The anteriormost of these marks is located at the second glabellar lobe, the posteriormost at the axial ring of the fourth thoracic segment (Figs. 14, 15A, 15B, PI. 1, fig. 8). Commonly, the pairs of markings are roughly symmetrical to each other but asymmetrical with respect to the sagittal line of the dorsal exoskeleton. In NWUS 9 I-1 00 IA, they are clearly shifted to the right (in anatomical view). However, the markings have never been observed to overlap the pairs of scars, which are supposed to represent muscle attachment sites (compare HUPE, 1953b; STcJ>RMER, 1959). These spots can therefore not be

219

Rcdlichiacean trilobites from Chengjiang

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,

\

Fig, 15, Eoredlichia infermedia (Lv 1940), A, NWUS 92-1 023B; sample horizon MJ . Ventral view of partial carapace showing base of median spine on tergile 9 and adhering remains of supposed mid-gut diverticula. Magnification 1.5x. B. NWUS 941041 A; sample X2 . Ventral view of partial carapace with adhering remains of supposed mid-gut diverticula. Magnification 2x. C. NWUS 94-1041 B; sample X2 . Counterpart of NWUS 94-1041 A (Fig. 15B). Dorsal view of internal mold with adhering remains of supposed mid-gut diverticula. Note slighl differences in the extension of the colored markings. Magnification 2x. equated with muscle imprints. The asymmetrical position of the marks resulted from a post-mortem deformation of the soft-parts with respect to the dorsal exoskeleton. During this deformation, the alimentary canal and other attached organs would have been shifted from their sagittal position, A few of these spots are faintly branched and appear to have a composite shape. Hence, it appears likely that they were connected to the digestive tract and represent lateral or dorsolateral outgrowths of the gut, which are generally termed» lateral diverticula«. Their with form is best described as branched tubules, Comparison with the mid-gut of modern Arachnida further suggests that these organs functioned as the rest of the mid-gut and may have been places where the major part of digestion and absorption of nutritions occured. Indeed, a light-colored tubular structure can be identified between and/or ventral to the series of colored markings. This structure is interpreted as the digestive tract. In places, the structure appears to show a series of lumps, which might represent partially digested nutrients. During deformation, the displacement of the viscera at the axial part was limited by the musculature of the limbs. These muscles were attached at pits immediately below the axial furrows as seen on Fig. 15B. As a result, organs located in the axial region could not be dislocated laterally beyond those pits. The apparent

lack of colored markings beyond these scars confornls with the proposed anatomy. If the interpretation presented above is correct, the alimentary canal behind the fourth tergite may represent the posterior gut. It should additionally be noted that impressions of the supposed posterior gut on the interior surface of the dorsal exoskeleton are not visible behind the seventh thoracic tergite. This fact may be a taphonomic result as a further dislocation of the axial organs after burial of the individuals. The mid-gut as reconstructed herein (i. e., the ventriculus with paired digestive tubules) is tubular in shape and not developed as a gastric pouch (as in further developed arthropods). It appears to be approximately equal in length to the posterior digestive tract; a fact that is commonly seen in most of the Recent arthropods. 5. Functional morphology and mode of life Dorsal exoskeleton. Eoredlichia inlermedia has the typical morphology of redlichiid trilobites and shows no indications of any adaptations to a specialized mode of life, Special attention should be paid to the overall shape of the cephalon and its joints with the thorax: The cephala have a posterior margin that consists of two sections of roughly equal lengths. The proximal section (roughly identical to the posterior border of the cranidium) is more-or-Iess straight; the distal section

220

SIIU, GEYER, CHEN

(belonging to the librigena) curves conspicuously forward to meet the base of the genal spine at about onethird the cephalic length in front of the posterior end. This configuration is usually seen in primitive redlichiaceans. In accordance with this configuration, a distinct fulcral socket is located at mid-length on the proximal section of the posterior border. Together with the corresponding process of anterior thoracic tergite, it creates a joint, which is located in a relatively adaxial position, as is the rule in primitive redlichiaceans. Particularly noteworthy is the presence of both fulcral joints and comparatively well developed flanges on thoracic tergite 2 and posteriorly. These devices permitted a precise inclination, but limited its extenSlOn. In accordance, the sizes and positions of the facets of the thoracic tergites also suggest limited enrollment abilities. The facets are of different width and deflection and this indicates differences in the possible inclinations of neighbouring tergites. For the joints between tergites 2 and 3, 3 and 4, 9 and 10, and 10 and II, respectively, the possible inclination is more than 20° each. Remarkably, the development of the axial rings indicates a flexibility of the thorax that allowed concave curvature at a few joints, such as at the anteriormost thorax and at the posterior thorax. Other possible concave inclinations of adjacent tergites, as at midlength, were impossible due to the bulbuous swellings that acted as stopping devices. Nevertheless, E. intermedia had a comparatively wider range of flexibility that included the ability to assume an s-shaped curvature of the thorax. However, these possible inclinations did not enable the animal to perform complete spherical or disk-enrollment. The possibility of concave curvature of the thoracic portions may have brought the enormous spine of tergite 9 into a defensive position. The overall morphology of the thorax, with its long, prominent spine and the slightly diminished size of the opisthothorax, resembles the form of a number of trilobites from quite different systematic groups (e.g., Triarthrus (T) rougensis PARKS 1921; compare LUDVIGSEN & TUFFNELL, 1994: PI. 2, fig. I). The occurrence of that type of morphology in different higher taxa, as well as a differing thoracic morphology in the same genus, indicates a minor systematic significance for suprageneric taxa but a distinct functional habit (see also discussion above under Pararedlichiidae). Caeca. The caecal features on the ocular platform and the lateral border furrow form a dense net that reflects the vessels under the dorsal cephalic cover. Of note are

& lUANG

the facial lines (sensu ZHANG, 1962) that emerge from the center of the eye and turning obliquely forward and outward. According to analogous structures, these ridges may have housed the visual nerves or nerves for yet unknown sensory organs. Nonetheless, equivalent structures are present in several olenelloid trilobites (e.g., Olenellus, Bristolia, or Elliptocephala). An especially nice example for Bristolia bristolensis (RESSER) was figured by PALMER & REPINA (1993: Fig. 13), where a main vessel commences at the center of the eye and runs outward and slightly backward to meet the lateral border at about the position of the genal spine. An equivalent double ridge similar to that in Eoredlichia intermedia is seen in Elliptocephala asaphoides EMMONS, where it emerges from the center of the eye and runs outward and backward to meet the genal angle (see PALMER & REPINA, 1993: Fig. 6.7). Appendages. The anterior endopodites have faint joints that apparently allowed a comparatively limited mobility as suggested by the relatively weakly defined joints (that are not due to imperfect preservation). Distinct pivot and hinge joints were not developed. Of note is the unusually long and distinctly conical shape of podomere 2. Its length restricted the possible degree of motion of the limbs towards the anterior and posterior and most probably did not allow fine-motoric, precisely directed movements of the exopodite. However, the podomere lengths do not gradually decrease distally, and a faint division of the endopodite into functional units does not appear to have been developed. These features suggest that a levator-depressor muscle system, as reconstructed for other trilobites (e.g., Olenoides; compare WHITTINGTON, 1980), may not have been developed in Eoredlichia. The endopodites resemble vaguely and superficially the endopodites of Agnostus pisiformis (see MOLLER & WALOSSEK, 1987); a feature that led to the challenging reinterpretation of the Agnostida and their systematic and phylogenetic relationships (MOLLER & WALOSSEK, 1987; WALOSSEK & MOLLER, 1990; WALOSSEK, 1993). These branches in Eoredlichia intermedia are herein interpreted as allowing a comparatively awkward crawling. Endopodites of the posterior thoracic segments, in contrast, are more similar in morphology to those of Olenoides serratus from the Burgess Shale (WHITTINGTON, 1975). The spines of these endopodites may have served as a grasping function to carry its prey forward along the ventral midline to the oral openmg. One problem that arises from the trilobite limbs and that has not yet been addressed to our knowledge

Rcdlichiaccan lrilobitcs from Chcng,jiang

should be discussed briefly: As the limbs are borne close to the midline of the body, the leg branches are directed laterally and have a considerable length to ensure stability of the organism on the substratum as clearly documented at E. inlermedia. However, this increased lengths of the endopodites would create a marked overstepping of the distal parts of the limbs if the leg branches were to swing at a greater rate. Especially in the earlier trilobites with their relatively great number of thoracic segments, the arrangment of ventral limbs was comparatively tight. Interference between the endopodites would have been a frequent problem if not a general program for the limb coordination did not serve to organize locomotion or if the endopodites had much mobility while swinging forth and back. In analogy with other primitive arthropods, we may assume that an advanced program for coordinated leg movement was not yet developed in redlichiacean trilobites, but there is no evidence for that assumption. In contrast, WHITI"INGTON (1975) restored the probable gait of the Middle Cambrian corynexochoid Olenoides serratus. However, the latter proposal can be proved directly. The endopodites at Eoredlichia intermedia show a comparatively weak sclerotization, poorly developed joints, and an imperfect differentiation of the podomeres. The tubelike appearance is similar to primitive types of limbs and differs considerably from other described limbs of trilobites, such as those of Triarthrus eatoni (CISNE, 1975, 1981), Olenoides serralus (WHITTINGTON, 1975), and Ceraurus pleurexanlhemlls (STRMER, 1939) where the podomeres show an insect-like habit with significantly individual morphology. The morphology of the endopodite suggests a limited mobility. It seems unlikely that these endopodites allowed fast movement. Endopodites and exopodites of Eoredlichia inlermedia usually have parallel axes, except in notably distorted specimens. Their shared orientation suggests both a stiff connection of the exopodite with the basal podomere of the endopodite and, hence, a harmonized movement. As a result, action of the endopodites induced a metachronous movement of the exopodites. In contrast to more advanced trilobites, such as Cerallrlls, Phacops or Triarlhrlls, the proximal podomeres of the exopodites of Eoredlichia inlermedia were small and movement of the exopodite independent from that of the endopodite can be excluded. Especially noteworthy is the morphologic plasticity of the exopodites; this permits a critical evaluation of the exopodite function. Much has been written on this

221

topic, and we refrain from presenting a new summary but refer to that presented by BERGSTROM (1969). The crucial point is the identification of the exopodite either as a (I) breathing organ or an organ used for (2) food-collecting or (3) swimming. The anatomy of the exopodite of Eoredlichia inlermedia is far from adequately reconstructed, but some indication of its functional purposes is available and summarized in the following paragraphs. (I) Respiration requires adequate ventilation, an enlarged breathing surface, mantling of the gills with a permeable membrane that permits gas diffusion, and protection against mechanical damage by sediment particles. As we reconstruct a stiff connection of the limb rami, continuous movement of the endopodites would have forced the exopodites to move as well, and this created sufficient ventilation. However, neither of the two varieties of the exopodites at Eoredlichia inlermedia shows a conspicuously large area composed of the filaments in question. The fringe of filaments on the anterior limbs differs, in particular, considerably from the true gill-blades of Recent arthropods. The thread-shaped, setae-like habit of the filaments suggests rigidity, which is additionally confirmed by the absence of clear post-mortem deformation of the filaments. Therefore, the cuticle, which covered the filaments appears to have been fairly strong. It would have protected the gills from mechanical damage but inhibited the gas diffusion as well. Additional protective structures, however, are absent. AIthough TIEGS & MANTON (1958) suggested that the outer rami of the trilobite limbs were of a size and shape capable of allowing respiratory circulation (see also MANTON, 1977, for further explanation), a breathing function of the exopodites of Eoredlichia inlermedia appears to be unlikely. (2) Food-collecting of early trilobites with a large hypostome was more-or-Iess synonymous with filtering of nutrients because conspicuously en larged gnathobases are absent. Apart from water currents that enabled a necessary suspension, the animal needed devices for filtering, removing the food particles from the filter, and transport to the mouth. An active, as well as a passive, water current can be envisaged for Eoredlichia inlermedia and needs no further discussion here. However, the specific shape of the anterior exopodites merits special attention. The fringe of filaments on the proximal lobe generally resembles filtering devices known from Recent crustaceans and is also comparable to that described from Olenoides serratus (compare STRMER, 1939, and WHITTINGTON, 1975), which has

222

SHU, GEYER, CHEN

been related to filter-feeding (BERGSTROM, 1969). The outer lobe, consequently, may be compared with that of O/enoides serratus, which, however, is strikingly smaller. This outer lobe may have improved the specific pathways of water currents underneath the trilobite (i.e., within the filter chamber). However, nothing useful can be determed from the studied material to contribute to the problem of cleaning devices and food transport. (3) A large surface, the basic prerequisite of a swimming function, is present in both extreme variations of the Eored/ichia exopodite. As pointed out by BERGSTROM (1969), the metachronous movement of limbs in filter-feeding trilobites created a water inflow from below, allowed lift of the animal, and may have helped in swimming. The reconstruction of the biramous appendages of Eored/ichia (as described above) assumes slightly forwardly inclined exopodites that overlapped by imbrication. Metachronous movement that expelled water laterally would have resulted in a posterolateral propulsive effect that may have been used in swimming. It appears especially noteworthy that the notable differences in the sagittal width of the blades agree with the predicted anteroposterion differences in propulsion. However, the tight connection of exopodites with endopodite movement, as well as the dense arrangement of the blades, make an efficient swimming ability unlikely. In summary, we assume that the anatomy of the exopodites of Eored/ichia intermedia proffers a function for both filtering and limited swimming abilities. Alimentary canal. In contrast with Naraoia, the structure and preservation of the alimentary canal and the ventral appendages give no direct evidence for the mode of life of Eored/ichia intermedia and Yunnanocepha/us yunnanensis. Identification of internal structures related to the alimentary canal remain, a priori, hypothetical even when they are observable. Hence, the description presented above led to a number of functional interpretations and will not be repeated here. The preserved lateral outgrows of the gut suggest tubular diverticula that had the same function as the mid-gut epithelium for subsidiary digestion and absorption because the necessary surface area was not available on the relatively narrow gut. The extensions of the gut allowed a high relationship of surface/volume so that a faster processing of the nutritients could occur. This anatomy resembles that known, for example, from primitive Arachnida.

&

ZHANG

Family Yunnanocephalidae HUPE 1953 Yunnanocepha/us KOBAYASHI 1936 Type species: Ptychoparia yunnanensis

MANSUY

1912.

Yunnanocepha/us yunnanensis (MANSUY 1912) ·1912 Ptychoparia yunnanensis nov. sp. - MANSUY, Etude geologique du Yun-Nan oriental, p. 31, PI. IV, fig. 4a-b. 1936 Yunnanocephalus yunnanensis. - KOBA YA5HI, On the Parabolinella fauna, p. 101. 1940 Pseudoptychoparia yunnanensis. - DING, [Evaluation of Lower Cambrian trilobites 1. 1941 Pseudoptychoparia yunnanensis (Mansuy). - Lv, Lower Cambrian stratigraphy, p. 85-86, PI. I, fig. 10. 1944 Yunnanocephalus yunnanensis (MANSUV).- KOBA. YASHI, On the Cambrian formations in Yunnan and Haut-Tonkin, p. 125, 132, PI. IX, fig. I. 1980 Yunnanocephalus yunnanensis (Mansuy).- ZHU, Cambrian trilobite faunas of Southwestern China, p. 248, PI. 80, figs. 10-II, PI. 81, figs. 1-3. ? 1980 Yunnanocephalus kunyangensis Zhu et Zhou (sp. nov.). - Zuu & ZI-IOU in ZHU, Cambrian trilobite faunas of Southwestern China, p. 249, PI. 81, fig. 4, 1'1. 82, fig. I. ? 1980 Yunnanocephalus latus Zhang et Zhu (sp. nov.). ZHANG & ZHU in ZHU, Cambrian trilobite faunas of Southwestern China, p. 249, PI. 80, lig. 12, PI. 81, fig. 5, PI. 82, fig. 2. 1981 Yllnnanocephallls planifrons (sp. nov.). - Lua, Trilobites from the Chiungchussu formation, p. 337, 339, PI. II, fig. 9. ? 1981 Yunnanocephalus subparallelus (sp. nov.). - Lua, Trilobites from the Chiungehussu formation, p. 337, 339, 1'1. II, fig. 8. 1982 Yllnnanocephalus yunnanensis (Mansuy). - Lua in Lua et aI., The Sinian-Cambrian boundary in Eastern Yunnan, p. 43, 45. 1982 Yunnanocephalus planifrons Luo.• Lua in Lua el aI., The Sinian-Cambrian boundary in Eastern Yunnan, p. 45, PI. 28, fig. 15 [specimen identical with hololype]. ? 1982 Yunnanocephalus subparallelus Luo. - Lua in Lua et aI., The Sinian-Cambrian boundary in Eastern Yunnan, p. 43, PI. 28, fig. 161specimen identical with holotype ]. ? 1982 Yunnanocephalus kunyangensis Zhu et Zhou. - Luo in Lua et aI., The Sinian-Cambrian boundary in Eastern Yunnan, p. 45. 1984 Yunnanocephalus planifrons Luo. - HE et aI., 13iotic characteristics of the Sinian-Cambrian boundary, fig. 7-2, PI. II, fig. 17lspceimen identical with holotype]. ? 1984 Yunnanocephalus subparalellus lsic] Luo.· Lua, The Qiongzhusian trilobite sequence, PI. 16, fig. 8 lspeeimen identical with holotypej. 1984 Yunnanocephalus planifrons Luo. - Lua, The Qiongzhusian trilobite sequence, p. 76, PI. 16, fig. 9 Ispecimen identical with holotype'j. ? 1984 Yunnanocephalus kunyangensis Zhu et Zhou. - Lua, The Qiongzhusian trilobite sequence, PI. 16, figs. lOIl Ispecimen on fig. II identical with holotype J. 1987 Yllnnanocephalus yllnnanensis (Mansuy). - ZliANG, Early Cambrian Chengjiang fauna, p. 229, PI. I, figs.

Redlichiaccan trilobites from Chengjiang

1-4, PI. II, figs. 4-5. v 1993 Yunnanocephalus yunnanensis. - SHU ct aI., New im-

portant findings, p. 100, 10 I, text-fig. 2B. See ZHU (1980) and ZHANG (1987) for additional synonymy. Studied material from Chcngjiang. Locality Xiaolantian, sample

horizon X,: NWUS 94-J047A, NWUS 94-1068A,B; sample horizon X,: NWUS 94-1020, NWUS 94-1056A, NWUS 94-1061. Locality Maotianshan. sample horizon M2: NWUS 91-10 I; sample horizon M,: NWUS 93-1003, NWUS 93-1004. Locality Dapodou, sample

horizon D,: NWUS 92-1014; sample horizon D,: NWUS 931005A,B. I. Dorsal exoskeleton Cephalon. The cephalon of this well-known species has been described by a number of authors (e.g., MANSUY, 1912; KOBAYASI-II, 1944; ZI'IU, 1980), and most of the morphological features need not to be repeated here. Yunnanocephalus yunnanensis is commonly referred to as lacking genal spines. The rounded genal angle, which should be distant from the posterior end of the facial suture, gives evidence for this interpretation. A number of specimens of the species, however, •

•

223

have a distinct spine, which sits at the most distal part of the cranidial border or is even dissected in its distal third by the facial suture. Hence, this spine has to be regarded as the intergenal spine (Fig. 17A). As a consequence, the fulcral joint is developed at the posterior border and is in a very proximal position. The eye ridges are often clearly bilobate, with a narrower posterior and a thicker and more prominent anterior lobe. In well-preserved specimens, the anterior lobe can be identified as consisting of two lobes as well, the anterior of which is usually extremely faint. The eye ridges are usually much shallower at the sides of the frontal lobes, where they meet the dorsal furrows. However, the division of the lobes into single faint ridges is recognizable in well-preserved specimens. Moreover, it can be shown that the anteriormost branches run along the glabellar front and even have a straight ridge that runs obliquely forward from either side to meet at about midlength of the preglabellar field - a site that is reconstructed at the anterior border of the hypostome on the ventral side (see below). In accordance with that reconstruction, the plectrum-like faint ridge, which has been observed in a few specimens and which depicts the position of the rostral plate on the ventral side, ends at the junction of the described lobes, which are connected with the eye ridges. A common preservational effect is that the hypostome is squeezed against the cranidium during compaction, and its outline is being counterfeit dorsally at the anterior part of the glabella (Figs. 17A, 19A, 19B). A shallow and faint caecal ridge extends from about midlength of the eye ridges to the anterolateral border. Such a ridge - although narrower but better defined has also been observed in Eoredlichia intermedia. The ocular platform and the lateral border furrow are occasionally densely covered with caecal features that depict the arrangement of the underlying vessels (Fig. 18B). An additional taphonomic effect is the dislocation of the Iibrigenae, which are often slightly detached from the cranidium and preserved in an oblique position with the palpebral section almost in place.

Fig. 16. Yunnanocephalus yunnanensis (MANSUY 1912). Schematic drawing of a medium sized adult dorsal carapace.

Thorax. The thorax consists of 14 segments in holaspids. The rhachis is rather convex in transverse section and generally tapers progressively toward the posterior, but shows a slightly greater decrease in width along the thoracic tergites 4 to 9 than at the anteriormost and posteriormost tergites. Therefore, the axial furrows are slightly bent. The axial rings of the anterior 3 and sometimes 4

224

Suu, GEYER, (I·IEN &

Fig. J 7. }'rmnanocephalus yunnonensis (MANSUY 1912). Latex cast of WUS 94-10680; sample horizon >So A. Dorsal vicw of complete dorsal carapace showing intcrgcnal spines, imprint of the

hypostomc on the anterior pan of the glabella and fulcral joints. Magnification 9x. B. Oblique posterior view showing pygidiurn wiLh poslcrovcntral boss below the posterior tip of the axis. Magnifica-

tion 12x.

tergites are devoid of well developed median nodes or spines, but nodes develop from tergite 4 or 5 on and become more and more prominent posteriorly except for the axial rings oftergites 13 and 14. The axial rings of tergite lOis sagittally narrower than the anterior ones, and the axial rings oftergites I I to 14 are further reduced in width. A transverse tripartition of the axial rings can be seen in dorsal view due to the development of anterolateral nodes, which are comparatively well defined by shallow furrows. The much wider median section has a slightly backset anterior rim that allows a view of the relatively wide furrow to the ante-

ZUANG

rior. A faint, transverse depression close to the posterior margin of the median section of the axial ring occasionally shows the margins of an underlying doublure. However, that tripartition is strongly reduced to the posterior due to the reduction of the lateral nodes. The margin of the axial ring of tergite I is conspicuously curved in dorsal view; the anterior rim of the median section of the tergites 2,3, II, and 14 are conspicuously bent backwards. In some specimens, the shell is removed at the axial rings and shows the exfoliated articulating half-rings. These half-rings are comparatively narrow but prominent. The posteriormost tergites carry a small node that fits into the almost crest-like node of the corresponding axial ring. In the anterior half of the thorax, the pleurae are extended into acute, stout spines with a slightly convex anterior rim and an almost straight to faintly concave posterior margin. These pleural spines are slightly denected posteriorly in the anterior tergites but become in accordance with the general change of the pleurae progressively bent posteriorly from about segment 6 on. As the axial rings, the pleurae are conspicuously narrower from about segment 10 backwards and show progressively falcate tips. Nevertheless, the pleural tips of tergites 12 or 13 to 14 possess a progressively sigmoidal posterior margin. The pleurae are very short in tergites 13 and 14. As a consequence, tergites 10 to 14 form a part of the dorsal exoskeleton that is slightly differentiated in dorsal view from the anterior part of the thorax (Fig. 17A), as is similar to but slightly less differentiated than in Eoredlichia inlermedia. It is obvious that this morphological differentiation defines a functional unit. The pleural furrows are straight and relatively short in the anterior three tergites and tergites 10 to 14, but faintly curved from tergites 4 to 9. They reach a maximum width slightly proximal to the position where the pleurae are denected ventrally. The distal end of the pleural furrow just fades. Fulcral joints (sensu BERG· STROM, 1973) are comparatively well developed (Fig. 17A). Fulcral processes are developed at about onethird the (transverse) length at the anterior pleurae, and their positions grade progressively towards the axial furrows. As a result, the joints are located very close to the axial furrows from about the mid length of the thorax and almost meet the axial furrows at the posteriormost tergites. The fulcral processes fit into corresponding sockets, which are quite well marked. The fulcral joints mark a begin of the ventral denection of the pleurae, which was approximately 30° at

Rcdlichiaccan trilobites from Chcngjiang

!'"':!~LO---

....... -

225

Fig. 18. Yunnanocephalus yunnanen-

sis (MANSUY 1912). Qiongzhusi section, Qiongzhusi Formation, sample CH 2.

A. PIWG 95Xlla; dorsal vIew of small cranidium with rounded frontal lobe of glabella; Magnification 6x. B. PIWG 95X12; detail of large cranidium showing caecal features on

fixigenae and preglabellar Magnification 9x.

the living animal. Dorsal furrow processes are very weakly developed. Distal to the fulcral joints are rather well developed facets that marked the area of overlap during enrollment. An exception is tergite 10, where the facets are almost absent. These facets extend anteriorly into a stoutly triangular and upward flexed tongue. Posteriorly, these facets are defined by a shallow ridge, which acted as a stopping device. The first thoracic tergite has slightly shorter (transversely) pleurae, a shorter but slender spine, an anterior fulcral joint that is in a slightly more proximal position, and a relatively large facet. The surface of the tergites is smooth. Faint furrows more-or-Iess parallel to the anterior and posterior margins of the pleurae indicate underlying doublures. Patterns that portray a few underlying vessels may be preserved at the the anterior or posterior rim of the pleural furrow (Fig. 17A). As in E. in/ermedia, sagittal furrows at the base of the pleural spines are a common feature on the thorax of Y. yunnGnensis. They are a taphonomic artefact and result from compaction of the sediments. In addition to small cracks that are occasionally visible, this interpretation is also suggested by the change in deflection that can be seen beyond these furrows (Fig. 178). Pygidium. The pygidium of Yunnanocephalus yunnanensis consists mainly of a convex, subquadrate pygidial axis with curved sides. The axis is about 70 percent of the maximum width of the pygidium, which is roughly at midlength. Two axial rings are visibly anteriorly, both defined by laterally rather distinct, but medially obsolescent furrows, the second being slightly less clearly visible than the anterior one. These two axial rings include about half of the axis. The posterior part of the axis shows two rather faint, exsagillal furrows, which slightly converge posteriorly.

field;

The pleural fields are narrow and subtriangular. They increase in width obliquely posterior from the anterior margin and are defined anterolaterally by the rather prominent and strongly backward flexed border. The border diverges slightly inward and faintly ventrally to form a slight curve marginally and terminates in a faint spine-like tip. The short distance between this tip and the lateral margin of the axis is composed of the strongly ventrally deflected posterior margin of the pleural fields. This means that the posterior margin of the axis extends slightly beyond the pleural fields. Especially noteworthy is the presence of a ventral boss below the posterior tip of the axis; this is best seen in posterior view (Fig. 178). Remarkably, this boss tapers in width ventrally, and its dorsoventral relief is comparable to or slightly greater than that of the overlying axis. 2. Appendages Adult individuals of Yunnanocephalus yunnanensis are usually much smaller than those of Eoredlichia in/ermedia. In addition, the layers that yield Y yunnanensis are commonly slightly coarser in grain size than those with E. inlermedia. As a result, soft parts usually are less well preserved, and preparation is more difficult, although a number of complete specimens with an indication of soft-parts have been discovered. Antennae. The antennae of Yunnanocephalus Yllnnanensis were found on six specimens from the Chengjiang locality. They emerge from beneath the cephalic shield at the anterior rim of the cephalic margin and usually lie anterior to the axial furrows. This position appears to be relatively constant (except for specimens that suffered post-mortem deformation). The course of the antennae can be followed beneath the cephalic shield in one specimen (NWUS 93-1003A),

226

SHU, GEYER, CI'IEN

&

lUANG

which shows a distinct and more-or-Iess parallel ar-

slightly in front of the cephalic margin (this is espe-

rangement of the proximal portions that run from the

cially visible in Fig. 190). The distal parts of the flag-

antennal base to the cephalic rim (PI. I, fig. 9). Al-

ella are usually straight and diverge strongly (Figs.

though the attachment site of the antennal base has not

198, 190), curved flagellae occur rarely (Fig. 19A).

been precisely detected, it can be seen that the antennae

The proximal

were attached relatively close to the midline and bear a

faintly from the base (PI. I, fig. 9). A slight reduction

short basal section, which diverges from the base. The

in width can be seen at the curvature of the flagellum,

section below the cephalic shield appears to be rela-

and the distal sections are narrower and taper progres-

tively stiff. A particularly mobile section lies at or

sively in width toward the tips (Fig. 190). •


RMER (1939). G. Phacops sp.; trunk limb; redrawn from MOLLER & WALOSSEK (1987: Fig. 27DI), modified after BERGSTROM (1969). Abbreviations: cox, coxa; en, endopodite; ex, exopodite; g, digestive tract.

clearly different arthropod groups (compare WALOSSEK & MOLLER, 1990) or groups with strongly derived appendage anatomy:

Exopodites with blade-like lobes differentiated into a proximal and a distal part; the posterior margin of the larger proximal lobe bears I.

Eored/ichia-type.

Redlichiaccan lrilobites from Chengjiang

long lamellar filaments; free margins of smaller distal lobe with short setae. Known from Eoredlichia, Olenoides, and Kootenia. It is noteworthy that this type is fairly consistent with the limb morphology known from Naraoia. 2. Triarthrlls-type. Exopodites with long lamellae directly attached to the shaft; small, spoon-shaped distal lobe lies at the end of shaft. Known from Triarthrus and Cryptolithlls. 3. Cerallrlls-type. Exopodites broom-like, proximal part consists of several podomeres; lamellae attached only to distal lobe. Known from Cerallrlls and Phacops. These three types of limbs reflect both a developmental series and a functional pattern, and variations within the Eoredlichia type (e.g., as in Olenoides) indicates evolutionary refinement as well as functional adaptation. Although the data base is extremely nar-

235

row, the three types of limbs appears to coincide moreor-less with high-ranked taxa defined by other criteria. Trilobites with Eoredlichia-type limbs appear to share a primitive, conterminant attachment of the hypostome (sensu FORTEY, 1990), and belong to the traditional orders Redlichiida and Corynexochida. Triarthrllstype limbs may generally accompanied by a natant or impendent hypostome attachment. Cerallrlls-type limbs are accompanied by conterminant or impendent hypostome attachment. Limb morphology cannot, per se, depict a systematic position, and additional information is needed to reconstruct a refined morpholgical evolution of trilobite appendages. Nevertheless, integrated analysis of dorsal exoskeletal morphology, enrollment mechanism, hypostome attachment, and limb morphology may help to overcome the general deficiencies of present trilobite classifications.

Acknowledgements We are indebted to E. LANDING, Albany, for criticism of the paper and improvement of the language. Special thanks are due to A. R. PALMER, Boulder, who provided information about taxonomic and nomenclatural problems of Eoredlichia. Field work for this article has been financially supported by the National Natural Science Foundation of the People's Republic of China. Special thanks from D.-G. SHU are given to the Ale-

xander von Humboldt Foundation, Bonn, for a research grant, which helped to complete this article. Moreover, the Alexander von Humboldt Foundation provided financial support for the publication of this article. Ultimately, the preparation of the article was made possible by a Heisenberg grant of the Deutsche Forschungsgemeinschaft awarded to G. GEYER.

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