an unusual new sinuitid mollusc (bellerophontoidea ...

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chuan. Professional Papers in Paleontology and Stratigraphy, 2: 7889. SIEMIRADZKI, J. 1920. Systematic catalogue of the paleontological collections of the Dzieduszyck Museum in Lvov. Rozpravy Wiadewski Muzeum Dzieduszyck, 6: 15 1-1 78. SPRIESTERSBACH, J. 1 942. Lenneschiefer (Stratigraphie, Fazies, und Fauna). Abhandlungen des Reichsamts fur Bodenforschung, 203: 1219. STRWE,W. 196 1. Zur Stratigraphie der siidlichen Eifler Kalkmulden (Devon: Emsium, Eifelium, Givetium). SenckenbergianaLethaea, 42: 291-345. . 1964a. Stromungs-Orientierung bei bodenverwachsenen, schlosstragenden Brachiopoden. Natur und Museum, 94: 5 15-529. . 1964b. Mimatrypa n. g. (Atrypidae: Palaferellinae). Senckenbergiana Lethaea, 45: 433-440. -. 1978. Fixo-sessile Brachiopoden aus dem Rheinischen Devon: Schuchertellopsis (Krejcigrafella)und Auchmerella (Strophomenida). Senckenbergiana Lethaea, 59: 93-1 15. . 1980. Zur Palaijkologie fixo-sessiler articulater Brachiopoden aus dem Rheinischen Gebirge. Senckenbergianalethaea, 60: 399-433. VERNEUIL, E. 1845. Paltontologie, mollusques, brachiopodes, p. 17-

395 . In R. I. Murchison, E. De Verneuil, and A. De Keyserling, Gtologie de la Russie $Europe et des montagnes de I'Oural, 2(3), Paltontologie. John Murray, London and Paris. WEDDIGE,K. 1977. Die Conodonten der Eifel-Stufe im Typusgebiet und in benachbarten Faziesgebieten. Senckenbergiana Lethaea, 58: 271-419. WILLIAMS,A., AND C. H.C. BRUNTON.1993. Role of shell structure in the classification of the orthotetidine brachiopods. Palaeontology, 36: 931-966. Xu, HANKUI. 199 1. Early and Middle Devonian boundary strata of Hoboksar, west Junggar, and their brachiopods. Acta Palaeontologica Sinica, 30: 307-333. ZHANG,YAN. 1981. Early Devonian brachiopods from the Zhusilenghairhan region, western Nei-Mongol. Acta Palaeontologica Sinica, 20: 383-392. . 1983. Parakarpinskia, a new genus of Brachiopoda from the Lower and Middle Devonian in Qinling. Acta Paleontologica Sinica, 22: 587-592. 30 OCTOBER ACCEPTED 1995

J. Paleont., 70(4), 1996,pp. 602-609 Copyright O 1996,The Paleontological Society 0022-3360/96/0070-0602$03.00

AN UNUSUAL NEW SINUITID MOLLUSC (BELLEROPHONTOIDEA,

GASTROPODA) FROM THE ORDOVICIAN OF SPAIN

JIRI FRYDA AND J U A N CARLOS GUTIERREZ-MARCO

~ e s k ?geologick? ustav, Klarov 3/ 131, 118 2 1 Praha 1, Czech Republic, and

UEI Paleontologia, Instituto de Geologia Economics (CSIC-UCM),

Facultad de Ciencias Geologicas, 28040 Madrid, Spain

ABSTRACT-Hispanosinuites peeli new genus and species from the Lower Oretan shales (Middle Ordovician) of central Spain is described and placed in the new subfamily Hispanosinuitinae of the family Sinuitidae. This new subfamily is considered to represent a highly specialized phylogenetic lineage, which probably separated from the morphological range of the genus Sinuites during the Early Ordovician. The outer shell surface of Hispanosinuitespeeli is entirely covered by secondary shell layers, which are interpreted as perinductura, inductura and coinductura. The similarity of these shell deposits in Hispanosinuitespeeliand species of Euphemites suggests that these layers were secreted by mantle flaps having the same form in both genera. Hispanosinuites peeli is interpreted as a mobile mollusc with an internal shell adapted to an infaunal mode of life. Discovery of this unusual mollusc reopens the question of the phylogenetic relations of the families Sinuitidae and Euphemitidae, which are oAen assigned to different molluscan classes. INTRODUCTION

T

HE CLASS-LEVELassignment of bellerophontoidean molluscs

has been discussed frequently during the past 50 years. The unknown nature of the soft parts of these molluscs, with their coiled, bilaterally symmetrical shell, has divided paleontologists, who have variously argued that bellerophontiform molluscs were untorted, exogastrically oriented monoplacophorans, o r torted, endogastrically oriented gastropods, o r a polyphyletic combination of both (Wahlman, 1992). O u r limited knowledge of the soft-part morphology of these molluscs is based mainly o n interpretations of muscle scar patterns and the general and apertural shapes of their shells. W e describe below a new genus of bellerophontoidean, which may represent a phylogenetic lineage connecting the families Sinuitidae and Euphemitidae. These two families are often placed in different molluscan classes (Walhman, 1992). OCCURRENCE AND AVAILABLE MATERIAL

Bellerophontoidean molluscs are common fossils i n some Ordovician formations of southwestern Europe. They are especial-

ly c o m m o n in those thick shale sequences with subordinate sandstones ("Tristani Beds") that overlie ubiquitous Arenig strata such as the Armorican Quartzite. Nevertheless, previous studies of this peculiar fossil group are few a n d many of these are obsolete. With the exception of the work of Yochelson (in Babin et al., 1982), few Lower Ordovician species from Montagne Noire (southeastern France) are accurately described o r r e viewed. References to some British s ~ e c i e sof "Be/leroohon." such as "B. " bilobatus Sowerby, "B."hcutus Sowerby, o r "B." trilobatus Sowerby, were fairly frequent in earlier works o n the "Tristani Beds" (both in Neseuretus shale and homalonotid sandstone facies) of Spain, western France and Portugal, but the species were rarely described o r figured (Verneuil a n d ~ a r r a n d e , 1856: Tromelin and Lebesconte. 1876). Discoverv ofdifferences within the aforementioned taxa'led to'the erectidn of some new and obscure taxa, such as "Bellerophon " alixi Rouault, 185 1, "B. " deslongchampsi D'Orbigny, 1840, "B. " duriensis Sharpe, 1849, "B. " lebescontei Tromelin, 1877, and "B. "lhuissieri Rouault, 185 1; none were adequately described o r figured. The only recognizable species from the bulk of previous studies o n preCaradoc bellerophontoideans are "Bellerophon" sacheri Tromelin a n d Lebesconte, 1876, (described as "Bucania" sacheri by Barrois, 189 l), and "Protowarthia" hispanica Born, 19 18,

FR YDA AND GUTZERREZ-MARCO-ORDO VZCZAN GASTROPOD listed by GutiCrrez-Marco (1984) as Sinuites (Sinuites) hispanicus (Born). Due to this imprecise and unresolved taxonomic scenario, a review of the Spanish Middle Ordovician gastropods has been undertaken by the authors, beginning with several thousand specimens collected by the Spanish team throughout the last eighteen years. Most of the material comes from Central Iberian zone localities, but some is from the Cantabrian and West Asturian-Leonese zones of the Hesperian Massif (Figure 1). Bellerophontoidean remains are generally poorly preserved as weakly to intensely deformed internal molds, but some tens of them show relevant diagnostic features. Among this material, only three s~ecimensfrom a single locality in the Toledo Mounts secondary shell deposits of great significance ( ~ i ~ u r1)e preserve to all sinuitids, and they are described here as Hispanosinuites peeli new genus and species. The studied specimens come from a field exposure 5200 m southwest of Navas de Estena (northern Ciudad Real province, Spain), west of the "Cuesta de Valderuelo" and close to the road between this town and Retuerta de Bullaque toward the east (Figure 1). These outcrops expose a bed of dark, fermginous shales with siliceous nodules, 80-100 m above the base of the Navas de Estena Formation. The occurrence of the trilobites Neseuretus (N.) avus Hamman and Asuphellus toledanus (Gil Cid), together with the rostroconch Tolmachovia babini nomen nudum, with certain bivalves and echinoderms, confirms a Lower Oretan age (ca. early "Llanvirn") for the type locality of Hispanosinuites peeli new genus and species; this is equivalent to the Didymograptus artus graptolite biozone or the Placoparia cambriensis local trilobite biozone. More information about biostratiera~hvand correlation of com~arablelevels in the Navas de &tena:~uadalerzas syncline (Toledo Mounts country) can be found in Gutitrrez-Marco et al. (1984), Rhbano (1989), and San JosC et al. (1 992). The type locality of Hispanosinuites corresponds to relatively deep-water paleoenvironments of the Central Iberian shelf, slightly below storm wave base. Deposition at this locality occurred during the maximum development of the Llanvirn transgression. Associations of trilobites and molluscs in this area from lower Oretan to lower Dobrotivh rocks display some differences with their equivalents in much shallower facies of the southern part of the Central Iberian shelf (Rabano, 1989). All of these fossils are typical representatives of cold-water faunas, and they characterize the development of a "Mediterranean" paleoprovince along the southern margin of Gondwanaland during most of the Ordovician period. SYSTEMATIC PALEONTOLOGY

Class GASTROPODA Cuvier, 1797 Subclass PROSOBRANCHLA Milne Edwards, 1848 Remarks.-The class-level assignment of sinuitid molluscs has been frequently discussed during the past 50 years, as summarized by Wahlman (1992). However, the question of whether the sinuitid molluscs were untorted, exogastrically oriented molluscs belonging to the class Monoplacophora or torted, endogastrically oriented gastropods is not still resolved. Superfamily BELLEROPHONTOIDEA McCoy, 185 1 Family SINUI~DAE Dall in Eastman, 19 13 Subfamily HISPANOSINLTITINAE new subfamily Diagnosis. -Sinuitid mollusc with outer shell surface entirely covered by secondary shell deposits. Anterior apertural margin with wide sinus. Discussion. -The last complete revisions of the classification of the superfamily Bellerophontoidea M'Coy, 185 1, were Knight et al. (1960), Horn? (1 963), and Runnegar and Jell (1 976). During the past 35 years, the number of genera assigned to this superfamily has approximately doubled. Also, the taxonomic position and the generic composition of the family Sinuitidae have been changed since the classification of Knight et al. (1960).

603

FIGUREI -Geological sketch map of the southern flank of the Navas de Estena-Guadalerzas Syncline, showing the position of the type locality of Hispanosinuitespeeli new genus and species, near the town of Navas de Estena (black asterisk). Lithostratigraphy: a, Lower Cambrian basement; b, conglomerates and sandstones (Upper Tremadoc to Lowermost Arenig); c, sandstone alternation ("Intermediate beds", Lower Arenig); d, Armorican Quartzite (Arenig); e, Marjaliza Formation (Upper Arenig); f, Navas de Estena Formation (Oretan-Dobrotiva: ca. "Llanvirn-Llandeilo"); g, Late Cenozoic/Quatemary cover. (After geological map of Spain 1/50.000 scale, sheets 709 and 710). Upper right: Location of the former area in the Iberian Peninsula. Numbers correspond to the following zones: 1, Cantabrian; 2, West Asturian-Leonese/Iberian Cordillera: 3. Galician-Trasmontan: 4. Central Iberian (dotted); 5, Ossa ~ o r e n a6; , South Portuguese.

The most important events influencing the higher-level taxonomic position of sinuitids were discoveries of paired muscle scars in the Middle Devonian Sinuitopsis acutilira (Hall) (Rollins and Batten, 1968), the Late Ordovician Sinuites cancellatus (Hall) (Knight, 1947; Peel, 1980; Runnegar, 198 l), and the Late Silurian Sylvestrosphaera lemchei Peel, 1980. One group of paleontologists, (e.g., Peel, 1980; Runnegar, 198 l , 1983; Wahlman, 1992) interpreted these discoveries as evidence for untorted, exogastrical orientation in these genera. For this reason, these authors transferred the above-mentioned genera, and thus the family Sinuitidae, to the class Monoplacophora. Nevertheless, the higher-level taxonomic position of the family Sinuitidae is still uncertain and requires further investigation. The familylevel position of the majority of the genera earlier assigned to the family Sinuitidae (see Knight et al., 1960) has become questionable because their muscle scar patterns are unknown. The shell morphology of Hispanosinuites peeli is very similar to genera of the subfamily Sinuitinae, especially to the type genus Sinuites Koken, 1896. All morphological characters of the shell of H. peeli (the general shell form, the shape of the aperture, and the presence of the wide sinus in anterior apertural margin) correspond well to what have been used as diagnostic characters of the subfamily Sinuitinae. The form of muscle scars of Hispanosinuites peeli is unknown; however, this character is also unknown for the majority of species of the type genus Sinuites,

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including the type species of this genus, Sinuites bilobatus (Sowerby, 1839). The development of secondary shell deposits on the entire outer shell surface is the only significant difference between Hispanosinuites peeli and all other representatives of the subfamily Sinuitinae. Secondary shell deposits were previously described in some representatives of the subfamily Sinuitinae [e.g., Sinuites cancellat us (Hall, 184 7), Sinuites granistriatus (Ulrich, 1897), and Sinuites (Strangulites) strangulatus (Perner, 1903)], but these secondary deposits are limited to the parietal and part of umbilical regions (see Knight, 194 1; Horn?, 1990; Wahlman, 1992). In our opinion, the Middle Ordovician genus Hispanosinuites represents a highly specialized phylogenetic lineage separated from the morphologic range of the genus Sinuites during the Early Ordovician. For this reason, we establish the new subfamily Hispanosinuitinae in the family Sinuitidae. We believe that this new subfamily is evolutionarily more closely related to the subfamily Sinuitinae than are all other subfamilies previously established in the family Sinuitidae. The subfamily Euphemitidae Knight, 1956, previously assigned to the family Sinuitidae (as subfamily; see Knight et al., 1960), also contains molluscs with an outer shell surface entirely covered by secondary shell deposits. However, the DevonianPermian euphemitids represent a highly specialized group, and their phylogenetic relationship to other groups of bellerophontoidean molluscs is uncertain. The shells of the representatives of the subfamilies Sinuitinae and Hispanosinuitinae differ from those of euphemitids in bearing a wide sinus in the anterior apertural margin. Shells of euphemitids bear a very narrow sinus or slit which generates a selenizone (Harper and Rollins, 1985; Gordon and Yochelson, 1987). Genus HISPANOSINUITES new genus Type species. -Hispanosinuites peeli new species from the Lower Oretan (ca. early "Llanvirn": Middle Ordovician), Navas de Estena Formation at Navas de Estena, Ciudad Real province, Spain. Diagnosis. -Medium-sized sinuitid molluscs with isostrophical, laterally depressed shell; outer shell surface entirely covered by secondary shell deposits; anterior apertural margin with wide V-shaped sinus; transverse ornamentation on inductural surface; perinductural surface smooth. Discussion. -Among sinuitid genera, Hispanosinuites new genus most closely approaches the family type genus Sinuites Koken, 1896, in terms of the general form of its shell and wide sinus on the aperture. It is easily distinguished from all other genera of the family Sinuitidae by the presence of secondary shell deposits entirely covering the outer shell surface. It differs from representatives of the family Euphemitidae in the form of the apertural margin. Etymology. -The name Hispanosinuites was formed by combining the Latin name of the Iberian Peninsula and the genus name Sinuites. Included species.-The new genus is presently known only from the type species Hispanosinuites peeli new species.

HISPANOSINUITES PEELI new species Figures 2.1-2.13, 3.1 Diagnosis. -Same as the genus by monotypy. Description. -1sostrophicaly coiled, cryptomphalous, involute, laterally depressed shell; length to width ratio approximately 1.4. Maximum shell length slightly exceeds 25 m m (the holotype). Dorsal part of whorl shallowly arched, without development of keel; lateral sides of whorl symmetrically convex, slightly arched to umbilical region, which is completely filled with secondary shell deposits. Aperture not well preserved in studied specimens, but form may be reconstructed from deformed parts of aperture and relic of growth lines; aperture with V-shaped sinus of Sinuites-type with nearly straight sides. Lateral lobes short, subtrigonal. Growth lines obscured by secondary shell deposits, visible only on youngest part of outer shell surface. Main part of outer shell surface smooth. Between onehalf and three-quarters of whorl back from the aperture, this smooth, outer shell surface abruptly covered by secondary shell deposits with very characteristic "wrinkled" pattern (Figure 2.3, 2.7). Boundary between smooth dorsal surface and wrinkled surface forms shallow, wide, U-shaped curve that crosses dorsum of the shell. Curve culminate at, and is symmetrical about dorsal plane of symmetry (Figures 2.3, 3.1). At its most lateral points, boundary line slightly changes direction, continues adaperturally following boundary between dorsal, umbilical surfaces of whorl. Ornamentation of wrinkled shell deposits on dorsal surface of whorl differs from that on umbilical surface. Dorsal surface covered by small wrinkles that cross dorsum generally in same manner as boundary line between smooth and wrinkled surfaces (i.e., in transverse direction). Course of wrinkles becomes more irregular on latero-dorsal, lateral surfaces, where wrinkles often branch and cross (Figure 2.7, 2.10, 2.13). Umbilical surface covered by wrinkles of approximately same size as those on dorsal surface; wrinkles arranged in spiral direction. Sizes and distances between wrinkles decreases with increasing distance from shell axis (Figure 2.7, 2.1 1, 2.12). Umbilical region filled with additional shell deposits that cover shell layer with wrinkled surface and reach approximately to half of height of umbilical wall. Surface of umbilical deposits are smooth (Figure 2.1, 2.2, 2.7). Thickness of shell about 0.3 m m in dorsal part, about 0.7 m m in umbilical wall of whorl. Juvenile part and structure of the primary shell are unknown. Etymology. -H. peeli-The species is named in honor of Dr. John S. Peel (Uppsala University, Sweden), for his contributions to our present understanding of bellerophontiform molluscs. Material examined. -DPM 2504 (holotype) and DPM 25052506 (paratypes). Specimens are housed in the Department of Paleontology, Complutense University of Madrid, Spain. Occurrence. -Lower Oretan shales (ca. early "Llanvirn") of the Navas de Estena-Guadalerzas syncline, Central Iberian zone of the Hesperian Massif, Spain. A COMPARISON OF THE SECONDARY SHELL DEPOSITS OF HISPANOSINUITES AND EUPHEMITES

The presence of secondary shell deposits entirely covering the outer shell surface is a characteristic of bellerophontoidean fam-

FIGURE2-1-13, Hispanosinuites peeli new genus and species from the Lower Oretan shales (Middle Ordovician) of central Spain; 1-2, DPM 2305, x 2.5; 1, lateral view, 2, oblique view; 3, 5, 6 DPM 2304, x 2.5; 3, dorsal view showing the boundary between inductura and perinductura, 5, oblique view, 6, lateral view; 4, 9 DPM 2306; 4, oblique view, x 2.5, 9, detail of 4 showing the inductural layer in umbilical area, x 5.7; 7, 8, 10, 11, 12, 13, DPM 2305; 7, lateral view showing the coinductural secondary shell layer (smooth) covering inductural layer (wrinkled), x 7.5; 8, the boundary between the perinductural (smooth) and inductural (wrinkled) layers, x 16.0; 10, contact of dorsal and umbilical types of inductura, x 9.8; 11, the boundary between coinductural (smooth) and inductural (wrinkled) layers, x 15; 12, umbilical view, x 7.5; 13,

contact of dorsal and umbilical types of inductura,

x

15.

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coinductura -

\

inductura /

FIGURE 3-Sketch of dorsal views showing an arrangement of the secondary shell deposits in I, Hispanosinuites peeli, new genus and species and 2, Euphemites.

ily Euphemitidae Knight, 1956. The shell structure of the representatives of this family has been studied and interpreted by many authors (Weller, 1930; Moore, 194 1; Yochelson, 1960; MacClintock, 1967; Harper and Rollins, 1985; etc.). Moore (194 1) described secondary shell deposits in Euphemites Warthin, 1930, in detail and used the terms "inductura," "perinductura" and "coinductura." The inductura is a secondary shell layer extending from the inner side of the aperture over the parietal region, columellar lip, and part or all of the outer shell surface. In Euphemites, Moore (194 1) used the term inductura for layers on the outer shell surface bearing numerous spiral costae. This author concluded that the inductura was secreted by a forward-growing posterior flap of the mantle. The perinductura is a secondary shell layer secreted by the mantle flap and reflected back over the outer apertural lip. This shell layer obscures the growth lines and is the lowest of three outer shell layers. In Euphemites, the perinductura is the layer on the outer shell surface and is either smooth and unornamented or bears nodes or nodose ridges. The coinductura is a secondary shell layer extending over the inner lip within the aperture and covering only a small part of the inductura. Yochelson (1960) suggested that the coinductura was secreted by the same part of the mantle as the inductura, in contrast with Moore's (194 1) opinion that there was no obvious correlation between the coinductura and inductura. The similar development of secondary shell deposits of Hispanosinuites peeli allows the use of the same terms for their description (Figure 3). The smooth layer covering the main part of outer shell surface of Hispanosinuites peeli is interpreted as perinductura and the layer with a transversally wrinkled surface as inductura. The interpretation of the shell layer developed in the umbilical region that covers the layer with the wrinkled pattern (i.e., inductura) is not so definite. This layer covers part of the umbilical region and continues to the parietal region (Figure 2.7). For this reason, we interpret this layer as coinductura. A comparison of the form of perinductura-inductura boundaries of Hispanosinuites and Euphemites is very interesting because one group ofpaleontologists (see Wahlman, 1992) has suggested that the families Sinuitidae and Euphemitidae belong to different molluscan classes-the first to the class Monoplacophora and the second to the class Gastropoda. In both Hispanosinuites and Euphemites, the perinductura-inductura boundary line forms a shallow, wide U-shaped curve on the

dorsum (Figures 2.3, 3). In the lateral and umbilical parts of the shell of Hispanosinuites, the inductural layer continues more toward the aperture, and the perinductura-inductura boundary line is more distinct than in species of Euphemites (see e.g., Harper and Rollins, 1985; Gordon and Yochelson, 1987). The form of perinductura-inductura boundary in the lateral and umbilical regions is variable in Euphemites species; it is a specieslevel character (Gordon and Yochelson, 1987). Also, the positions of perinductura-inductura boundary in both genera is the same. In Euphemites, this boundary lies on the dorsum between one-quarter and three-quarters of a whorl (Harper and Rollins, 1985), and in Hispanosinuitespeeli, between one-half and threequarters of a whorl back from the aperture. There are, thus, no essential differences in the form and the position of the perinductura-inductura boundary between Hispanosinuites and Euphemites. The similarity of the form of the perinductura-inductura boundaries is significant considering that Hispanosinuites has a quite different form of anterior apertural margin than Euphemites. The aperture of Hispanosinuites peeli has a wide, V-shaped sinus, and that of Euphemites has a narrow sinus or slit that generates a selenizone. There are, however, differences in the type of ornamentation of the inductural shell layer. In Euphemites, this layer bears numerous, very distinct spiral costae that were interpreted as "guides" to control the posterior mantle flap during extension and retraction (Harper and Rollins, 1985). In Hispanosinuites peeli, the surface of the inductural layer bears transversely arranged wrinkles on the dorsal part and spirally arranged wrinkles in the umbilical region. Nevertheless, we assume that the secondary shell deposits were secreted by the mantle flaps having the same form in both genera. Mode of life. -Thirty years ago, many paleontologists generally regarded representatives of the suborder Bellerophontina as grazing and browsing herbivores limited to hard bottoms in clear water. The reason for this interpretation was the comparison of these fossils to modern archaeogastropods and the capability of bipectinate aspidobranch gills of allegedly related archaeogastropods (Yonge, 1947). During the past 30 years, many authors (e.g., Horn?, 1963; Peel, 1972, 1974, 1975, 1977; Linsley, 1977, 1978a; Berg-Madsen and Peel, 1978; Harper and Rollins, 1982, 1985; Wahlmann, 1992) have suggested that bellerophontoideans occupied a wide range of depositional environments (from shallow intertidal to deep offshore environments with clastic or carbonate sediments, and from hard-bottom to fine grained, soft-bottom facies). Also, a number of different modes of life (epifaunal deposit feeders on soft-bottom substrates, grazers among algal foliage, bottom-dwelling detritus feeders, scavengers, or predators, and an infaunal existence) were suggested for some groups of bellerophontoideans. These interpretations were recently summarized and discussed by Wahlman (1992). The shell of Hispanosinuites peeli is unusual in connecting the typical characters of representatives of sinuitids (general shell and apertural forms) and euphemitids (secondary shell deposits on whole outer shell surface). Hispanosinuites peeli is nearly identical in general shell and apertural forms to some species of genus Sinuites. The arrangement of secondary shell deposits of Hispanosinuites (course of the perinductura-inductura boundary and its distance from apertural margin) is most similar to some species ofEuphemites. The comparison of modes of life of both mentioned genera may give some suggestion of the life mode of Hispanosinuites. The Ordovician species of Sinuites from the Cincinnati arch region studied by Wahlman (1992) were most common and diverse from deeper water, muddy environments. This author suggested that some species of Sinuites were deposit feeders on

FR YDA AND GUTZERREZ-MARCO- ORDOVICIAN GASTROPOD a soft bottom. The more common occurrences of some Ordovician species of Sinuites in deeper, muddy environments than in nearshore facies were also described by Pickerill and Brenchley (1979) and by Hurst (1979). On the other hand, Titus and Cameron (1976) cited some Ordovician species of Sinuites as common elements of lagoonal and nearshore shoal facies. Wahlman (1992) described a great concentration of Sinuites planodorsutus in an argillaceouslimestone lens in the Kope Formation (Ordovician, Cincinnati arch region), and he suggested two possible interpretations: concentration on a food source or postmortem concentration by predatory nautiloids. These great local concentrations of the shells of Sinuites probably are not exceptional. We know similar great concentrations of the shells of two species of Sinuites from the Middle Ordovician (Sarka and Dobrotiva Formations) of the Prague Basin (Bohemia) and of undetermined sinuitids in Lower Oretan shales of the AlgodorMilagro syncline in central Spain. Concentration of shells occur from the shallow, outer shelf (Spain) to relatively deep, offshore environments (Bohemia), always in fine clastic facies. Sinuitids are associated with inshore dalmanitid-calymenid faunas (including the trilobite Neseuretus) and with deeper mesopelagic assemblages of the cyclopygid biofacies (see Cocks and Fortey, 1988, for composition and terminology). Byers and Galvin (1979) studied two contemporaneous communities from the Ordovician strata of Wisconsin, and they considered some Ordovician species of Sinuites to be opportunistic. These interpretations suggest a high level of niche diversity in species of Sinuites. The mode of life of Euphemites was studied in detail by Harper and Rollins (1985). These authors interpreted Euphemites as a mollusc with an internal shell adapted to an infaunal mode of life. Functional analyses of shell form also suggested that both Euphemites and Sinuites were among the most mobile of the bellerophontoideans (e.g., Linsley, 1978b; Wahlmann, 1992). Based on the absence of apertural flare, extensive secondary shell deposits, a relatively very thin shell, and absence of extensive collabral ornamentation (compare with Harper and Rollins, 1985) Hispanosinuitespeeli may be interpreted as a mobile mollusc (low Raup's D parameter), most probably with an internal shell adapted to an infaunal mode of life. This interpretation is not at variance with the mode of occurrence of Hispanosinuitespeeli. This mollusc lived in a soft, siliciclastic substrate together with bivalves, rostroconchs, trilobites, brachiopods, and pelmatozoan echinoderms (see GutiCrrez-Marco et al., 1984). The bivalves from this benthic assemblage were interpreted partly as infaunal deposit feeders [Praenucula costae (Sharpe, 1853); P. sharpei Babin and GutiCrrez-Marco, 19911 or as shallow infaunal filter feeders (Glyptarca? lusitanica (Sharpe, 1853); Coxiconcha britannica (Rouault, 1851); Redonia deshayesi (Rouault, 1851); Babinka prima Barrande, 18811 by Babin and GutiCrrez-Marco (199 1). CONCLUSIONS

The representatives of the family Sinuitidae together with other bellerophontiform molluscs are among the most frequently discussed Paleozoic molluscs. Their uncommon shell morphologies together with the form of the muscle scars have divided paleontologists, who have disputed whether the bellerophontiforrn molluscs were untorted, exogastrically oriented, or torted, endogastrically oriented molluscs. The origin of these molluscs and early history of the phylum Mollusca continues to be debated (e.g., Wahlman, 1992; Peel, 1993). The poor knowledge of the morphology of the soft parts of bellerophontiform molluscs is the main reason for these discussions. Observations from the current study pertaining to this problem are summarized as follows.

1. The Middle Ordovician Hispanosinuites peeli represents a highly specialized phylogenetic line which probably separated from the morphological range of the genus Sinuites during the Early Ordovician. We believe that the new subfamily Hispanosinuitinae is evolutionarily most closely related to the subfamily Sinuitinae than are all other subfamilies earlier established in the family Sinuitidae. The reasons for such interpretation are not only similarities of the general shell and apertural forms, but also the presence of the limited secondary shell deposits in some representatives of the subfamily Sinuitinae. The similarity of ornamentation and form (i.e., spirally arranged wrinkles) of the secondary shell deposits in the umbilical region of Sinuites cancellatus (Hall, 1847) (see plate 6, figure 3a in Knight, 194I), together with the ornamentation and the configuration of inductura in the umbilical region of Hispanosinuites peeli (Figure 2.1, 2.7), suggests that these inductural deposits were secreted by similar mantle flaps in both molluscs. 2. The secondary shell deposits of the genera Hispanosinuites and Euphemites are conspicuously similar in position of the perinductura-inductura boundary (between one-half and threequarters of whorl back from the aperture), its form (shallow, wide U-shaped arch on dorsum), and ornamentation type (smooth surface of the perinductural layer). We assume that the secondary shell deposits were secreted by homologous mantle flaps in both genera. This assumption reopens the question of the phylogenetic relations of the families Sinuitidae and Euphemitidae, which some paleontologists place in different molluscan classes (see e.g., Wahlman, 1992 but also Knight et al., 1960, and Gordon and Yochelson, 1987). 3. Hispanosinuites peeli is interpreted as a mobile mollusc with an internal shell, most probably adapted to an infaunal mode of life such as that of euphemitid molluscs (Harper and Rollins, 1985). This suggests a high level of niche diversity in sinuitid molluscs, which is consistent with their long geologic range.

This paper was camed out within the framework and with the financial support of the Spanish Comision Interministerial de Ciencia y Tecnologia, National Programe on R+D, 19921995, project nr. AMB92-1037-C02-01. Exchange expenses of one of the authors (JCGM) were financed by current cooperation CSIC-AVHR project "Biostratigraphical correlation between the Iberian and Bohemian Ordovician." We thank D. M. Rohr (Sul Ross State University, Texas) for language correction. We are also indebted to the reviewers, R. D. Hoare and an anonymous reviewer for their critical and constructive remarks.

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J. Paleont., 70(4), 1996, pp. 609-611 Copyright O 1996, The Paleontological Society

0022-3360/96/0070-0609603.00

CLARIFICATION OF NA UTILUS PRAEPOMPILIUS

SHIMANSKY FROM THE LATE

EOCENE OF KAZAKHSTAN

W. B. SAUNDERS,' V. N. SHIMANSKY,2 AND 0 . V. AMITROV2 'Department of Geology, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010 and 2PaleontologicalInstitute, Russian Academy of Sciences, Profsoyuznaya 123, 1647 Moscow, Russia ABSTRACT-Thediscovery of a specimen of Nautilus praepompilius Shimansky, 1957, from the Chegan Formation of Kazakhstan confirms that this species is assignable to Nautilus, and that this extant genus extends back to the late Eocene. It is morphologically closest to Nautilus pompilius Linnaeus. The nepionic constriction shows that the hatching size was ca. 23 mm dia, close to that for Nautilus pompilius (ca. 26 mm dia). INTRODUCTION

N

IS currently thought to include five or six living species (Saunders, 1987; Ward, 1987), but the ancestry of the genus has been clouded by the near non-existent Tertiary record for the genus. Teichert and Matsumoto (1987) ably summarized what is presently known of the ancestry of Nautilus, placing emphasis on a species based on a single specimen reportedly from the early Oligocene of Kazakhstan, Nautiluspraepompilius Shimansky, 1957. However, because some morphological details of N. praepompilius were not available, in particular, the suture outline, its relationship to Nautilus has been uncertain. An additional specimen of this species has recently become available for study, along with new data concerning additional occurrences and stratigraphic information, permitting a more accurate age assignment, description of new morphological details (including growth- and suture lines and hatching size), and clarification of its taxonomic relationship to other species. AUTILUS

DESCRIPTION

The second specimen of Nautilus praepompilius (Figure 1.11.4) is remarkably close to the holotype in size and preservation. It is a phragmocone 53.7 m m maximum diameter, with a whorl width ca. 32 m m (W/D=.60); the complete shell would have been ca. 90-100 m m diameter with an intact body chamber. The preservation is such that the inner series of chambers were not filled and the siphuncle and septa1 necks are preserved intact; both appear identical to those of extant Nautilus. The abnormally thick appearance of the siphuncle (Figurel.1) is due to partial encrustation by diagenetic deposits of crystalline carbonate. The estimated size of the umbilicus is ca. 5 m m dia. (U/D .09). What appears to be an umbilical callus (Figure 1.3, 1.4) may actually be secondary crystalline carbonate percipitated within the umbilicus of the outer whorl. This renders unclear

whether N. praepompilius actually had an umbilical callus, for this feature may not develop until ca. 85 m m dia. in some species (e.g., N. pompilius has a complete callus by ca. 90 m m dia., whereas in N. belauensis an umbilical callus is not present until ca. 105-1 10 m m dia.). The nepionic constriction in ectocochliate cephalopods is an apertural discontinuity which marks embryonic hatching (see Arnold, et al., 1987). It is partially exposed in this specimen (Figurel.4), marked by a number of characteristic features: 1) slight constriction of the aperture; 2) a series of shell breaks along the former margin; and 3) cessation of faint longitudinal lirae (spaced 2-3/mm). The nepionic constriction occurs at an estimated diameter of ca. 23 mm, and 17 m m width. Considering the broader whorls of N. praepompilius, these figures are reasonably close to the mean nevionic size for extant Nautilus (26 m m diameter, 16 m m width) reported by Arnold, et al. (1987). The suture of N. praepompilius, reconstructed from disassembled camerae, includes a broad ventral salient, a broad, shallow lateral lobe, a distinct umbilical lobe, and a broad dorsal lobe accented by a prominent annular flexure (Figure 2.1). Growth lines are excellently preserved and show a broad hyponomic sinus, strong lateral salient, and an almost imperceptible ocular sinus (Figure 3.2). Material and age. -The exact locality of the holotype of N. praepompilius (PIN 1264/1) is not certain; it is known to have come from the middle Chegan Formation, North Precipice, Ustjurt (Ust-Urt) Plateau, ca. 180 km west of the north Aral Sea, Kazakhstan. Its age was originally reported as early Oligocene, but restudy of the molluscan fauna indicates that the Chegan Formation is middle?- late Eocene (Bartonian?-Prabonian Stages; Amitrov, 1994; see also Lukovic, 1926). The second specimen (PIN 1264/ 10; Figure 1.1- 1.4) was obtained on the north coast ofthe Aral Sea, ca. 260 km to the east, in greenish clays with interbedded concretions rich in molluscs, in the lower part of the Chegan Formation. Search of the Paleontological