New raphiophorid trilobites from the Ordovician of ...

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strong affinities with the fauna from Digger Island. (Victoria) (Jell 1985; Webby & Edgecombe in. Webby et al. 2000), and with the Takaka terrane. (New Zealand) ...
New raphiophorid trilobites from the Ordovician of Argentina and their biogeographic implications N. EMILIO VACCARI, BEATRIZ G. WAISFELD, BRIAN D.E. CHATTERTON & GREGORY D. EDGECOMBE VACCARI, N.E., WAISFELD, B.G., CHATTERTON, B.D.E. &. EDGECOMBE, G.D. 2006:07:29. New raphiophorid trilobites from the Ordovician of Argentina and their biogeographic implications. Memoirs of the Association of Australasian Palaeontologists 32, 353-374. ISSN 0810-8889. The raphiophorid trilobites Lehnertia nawisapa gen. et sp. nov. and Pytine wirayasqa sp. nov. are described from the Lower and Middle Ordovician of Argentina. Lehnertia gen. nov. is a member of Endymioniinae that includes L. nawisapa, from the Las Chacritas Formation (Darriwilian) in the Precordillera of San Juan Province, and L. embolion, from the Nora Formation (Darriwilian) in the Georgina Basin, Australia. An extension of the cephalic doublure as a long, pointed spine in Lehnertia is regarded as convergent with a similar spine in Alsataspididae. Silicified material of L. nawisapa includes a growth series from protaspides to holaspides, recording the development of the ocular structures and an increase in the relative size of the eyes late in ontogeny. Lehnertia is most closely allied to Pytine Fortey, 1975; both genera include species with and without ocular structures. Pytine wirayasqa sp. nov. is found in the Acoite Formation (early Arenig) in the Cordillera Oriental, Jujuy Province. In addition to its type from Spitsbergen and the new species from Argentina, Pytine includes early Arenig-Darriwilian species from the North and South China blocks, Baltica, and East Gondwana (Canning Basin, Australia). Lehnertia provides further evidence for East Gondwanan influence on Precordilleran faunas in the Darriwilian. A reevaluation of the trilobite fauna of the Cordillera Oriental suggests East Gondwanan connections since the Early Tremadocian. N. Emilio Vaccari ([email protected]) and Beatriz G. Waisfeld ([email protected]. edu), CONICET, CIPAL (Centro de Investigaciones Paleobiológicas), F.C.E.F y N. Universidad Nacional de Córdoba, Av. Vélez Sársfield 299, X5000JJC Córdoba, Argentina; Brian D.E. Chatterton, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada; Gregory D. Edgecombe, Australian Museum, 6 College Street, Sydney, NSW 2010, Australia. Received 29 March 2006. Keywords: Trilobita, Ordovician, Argentina, Raphiophoridae, new genus

TRILOBITE FAUNAS from the Ordovician of Argentina are abundant and diverse (Waisfeld & Vaccari 2003). In this contribution we describe two new raphiophorid trilobites, selected for their particular biogeographic signature, emphasising close relationships with eastern Gondwana faunas. These raphiophorids come from two different regions with dissimilar geological histories. One of them, Lehnertia nawisapa gen. et sp. nov., comes from the Precordillera terrane, while the other, Pytine wirayasqa sp. nov., comes from the Cordillera Oriental, on the South American Gondwanan margin. Lehnertia nawisapa gen. et sp. nov. comes from the Quebrada de La Tuna (Sierra de La Trampa), 42 km south of San José de Jáchal, San Juan Province (see locality information and location map in Chatterton et al. 1998). The 58 m thick succession of nodular limestones has

previously been regarded as the upper member of the San Juan Formation (Espisúa 1968; Astini 1994), but then reassigned to the lower member of the Gualcamayo Formation (Carrera & Astini 1998), and subsequently to the Las Chacritas Formation (Peralta et al. 1999). The age of the Las Chacritas Formation is early Darriwilian; the unit spans the whole Eoplacognathus pseudoplanus conodont Zone, with a conodont association from the uppermost levels suggesting the base of the succeeding Eoplacognathus suecicus Zone (Albanesi & Astini 2000). This unit conformably overlies the San Juan Formation (upper Tremadoc - lower Darriwilian) on a hardground surface, and is overlain by the basal conglomerates of the La Chilca Formation (Upper OrdovicianLower Silurian). According to Astini (1994) and Carrera & Astini (1998), the lowermost part of the succession consists of black shales deposited

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Fig. 1. Location map for Pytine wirayasqa sp. nov. A, general location of Ordovician basins and terranes on southern South American margin. The white square on the Cordillera Oriental refers to area detailed in the geological map; B, geological map with details of main units exposed in the Purmamarca area. The asterisk indicates the fossil locality at La Ciénaga.

under reduced oxygenation conditions and low sedimentation rate during incipient flooding. A rapid shallowing and the re-establishment of the carbonate system under normal sedimentation conditions in open marine settings is suggested by the increase in bioturbation, and the abundance and diversity of the fauna. Pytine wirayasqa sp. nov. comes from La Ciénaga, 5 km west of Purmamarca (latitude 23º 41’ 52.6” S, longitude 65º 33’ 24.1” W), Tumbaya Department, Jujuy Province, in the Argentine Cordillera Oriental (Fig. 1). The Purmamarca area is structurally complex, and

Ordovician successions occur as tectonically truncated packages within several thrust sheets that form the Tertiary structure of the region (cf. Harrington in Harrington & Leanza 1957; Astini 2003). The discontinuous shale succession with occasionally interbedded calcareous sandstone beds and calcareous lenses toward the top was referred to the Cieneguillas Shales/Sepulturas Limestones by Harrington (in Harrington & Leanza 1957). Both units cannot be distinguished in the field and are broadly similar to the Acoite Formation, which is widespread in other parts of the basin. Hence, we refer the succession

AAP Memoir 32 (2006) exposed at La Ciénaga to the Acoite Formation. The age of the succession at this locality is not yet accurately constrained. Rao et al. (1994) studied conodont and graptolite associations and suggested an early and middle Arenig age. Brussa et al. (2003) indicated that available data point to an early Arenig age, possibly correlative with the T. akzharensis graptolite Zone of the North American scheme (Williams & Stevens 1988). Aceñolaza (2003) suggested a late early Arenig age on the basis of the association of Pliomeridius sulcatus Leanza & Baldis with the conodont Gothodus crassulus andinus (Rao, Hünicken & Ortega) (= Baltoniodus crassulus andinus). A similar association referred to that age was documented by Rao (1999) in the Sepulturas Formation (Espinazo del Diablo, Aguilar area). According to our data, Pytine wirayasqa sp. nov. co-occurs with Thysanopyge sp. and Pliomeridius sp. The co-occurrence of the latter genera is infrequent in the Northwest Basin, as they belong to distinct, ecologically and environmentally segregated assemblages (the Thysanopyge and Famatinolithus Faunas, respectively, cf. Waisfeld et al. 2003). The association of Thysanopyge sp. with Pliomeridius sp. is so far documented in the upper part of the Acoite Formation cropping out in the Río La Huerta (Santa Victoria area, northern Cordillera Oriental), within the uppermost part of the Baltograptus deflexus Zone (Toro & Waisfeld 1998). Thus, the trilobite association of the succession exposed at La Ciénaga might be correlated with the upper part of the Acoite Formation at the Santa Victoria area. BIOGEOGRAPHIC IMPLICATIONS Precordillera The geological evolution of the Precordillera terrane has received considerable attention during the past decade. Several alternative hypotheses have been proposed to explain the strikingly different tectono-sedimentary nature of the successions of the Precordillera in comparison to coeval successions exposed along the protoAndean margin of South America. Some authors regard the Precordillera as autochthonous (González Bonorino & González Bonorino 1991) or parautochthonous to the southwestern margin of Gondwana (Aceñolaza & Toselli 1989; Baldis et al. 1989; Aceñolaza et al. 2002; Finney et al. 2005). Based upon stratigraphic (Ramos et al. 1986; Astini et al. 1995; Thomas & Astini 1996; among others), palaeomagnetic (Rapalini & Astini 1998), biogeographic (Benedetto 1993, 1998; Vaccari 1994), and geochronologic (Thomas et al. 2004) evidence, other authors endorsed a hypothesis of allochthony of the Precordillera. In this latter framework, the Precordillera is regarded

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as a far-travelled microplate that initially rifted from the southeastern margin of Laurentia in the Early Cambrian and, after an interval of drifting and isolation in the Iapetus Ocean, accreted to the proto-Andean margin of South America during the Mid-Late Ordovician (Benedetto 2004, and references therein). Although there is a general agreement in considering the Precordillera as an exotic terrane, the timing of its disconnection from Laurentia and its collision with the protoAndean margin still remain controversial (Dalziel et al. 1994; Astini et al. 1995; Keller & Dickerson 1996; Keller 1999; Benedetto 2004). In this scenario, the biogeographic affinities of the trilobite fauna of the Precordillera are critical for understanding its drifting history. The presence of the endymioniinid Lehnertia in the Darriwilian of the Precordillera and of the Georgina Basin (central Australia) accounts for a faunal connection between both areas. Characteristic Laurentian elements such as the bathyurids Peltabellia and Uromystrum (Vaccari 1995; Waisfeld & Vaccari 2003) associated with Leiostegium occur in the upper Tremadoc-early Arenig (lower part of the San Juan Formation). Taxa with undoubtedly eastern Laurentian affinities such as Ceratocara (Chatterton et al. 1997), Stenoblepharum (Edgecombe et al. 1997), Frencrinuroides (Edgecombe et al. 1998), and Telephina (Chatterton et al. 1999) persist until the Caradoc. The first non Laurentian element is Benedettia Toro & Monaldi, 1980 (Prioniodos elegans Zone), an endemic pliomerid that is closely related to the Australian (Canning Basin) Canningella Legg, 1976 (Vaccari 2003). Particularly significant is the leiostegiid Annamitella. This genus exhibits a relatively wide geographic distribution, documented in China (South China block and Tarim), Vietnam, Kazakhstan, Australia, eastern Newfoundland, Iapetus terranes (Wales, Ireland, and Norway), the Famatina terrane, and the Western Puna volcanic-arc adjacent to the Gondwanan margin of South America. The absence of Annamitella in the carbonate platform of North America and Siberia has been interpreted as a result of facies controls (Fortey & Shergold 1984; Webby & Edgecombe in Webby et al. 2000). However, Annamitella is the commonest trilobite in middle Arenig to Darriwilian successions of the Precordillera (San Juan, Gualcamayo and Las Chacritas Formations), represented by A. harringtoni, A. tellecheai, and A. forteyi (Vaccari 1993). These successions correspond to the last stages of the carbonate cycle that commenced in the Early Cambrian, and display broadly similar facies to those developed contemporaneously on the Laurentian margin (Astini et al. 1995; Cañas

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1999; Keller 1999, among others). Accordingly, the record of Annamitella in the Precordillera and its absence in Laurentia might result from biogeographic controls rather than facies controls, and might support a clear separation of the Precordillera from Laurentia. The occurrence of Lehnertia in the Darriwilian in a distal ramp setting in the Precordillera and in the inshore, cratonic environment of central Australia (Georgina Basin) gives further support to previous ideas suggesting that the Precordillera received eastern Gondwanan elements by this time, endorsed by the presence of particular Phacopida (e.g., Prosopiscus and Pliomerina; Edgecombe et al. 1999) and shumardiids (e.g. Kweichowilla; Waisfeld et al. 2001). Recently, Paterson (2004) proposed an alternative explanation for the dispersal of Prosopiscus, taking into account its earliest records in the Bendigonian of Australia. He suggested that Prosopiscus could have had non-adult like larvae, and that a life strategy involving planktonic larvae and metamorphosis (Life-strategy II of Chatterton & Speyer 1997) might have favored its dispersal. In sum, trilobite evidence from the Precordillera suggests a close relationship with Laurentia until the upper Tremadoc-lower Arenig (bathyurid fauna in the lower part of the San Juan Formation), and a mixture of elements with different biogeographic affinities after the lower Arenig (Benedetto et al. 1995; Edgecombe et al. 1999). Hence the Precordillera, being distant enough from Laurentia, was not biogeographically isolated and began to receive immigrants from Gondwana and Baltica. Arenig and Darriwilian trilobite faunas do not show a pattern of endemic radiations consistent with isolation. In contrast, the Precordillera was exchanging biota with other terranes and palaeocontinents. Cordillera Oriental Siliciclastic successions of the Cordillera Oriental of Argentina and Bolivia represent the Gondwanan margin of South America, excluding the Famatina and Precordillera terranes, as well as the volcanic island-arc of the Western Puna (Las Vicuñas and Aguada de la Perdiz Formations) (see Fig. 1A). Arenig trilobite faunas of the Argentine and Bolivian Cordillera Oriental include a mixture of endemic elements (Thysanopyge and Famatinolithus faunas), cold water West Gondwanan forms (e.g., Colpocoryphe, Neseuretus, Ogyginus, Ampyx reyesi), and warm water elements (e.g., Carolinites, Psilocara, and a new taxon close to Emanuelaspis) recording a wider exchange with lower latitudes mainly in relatively deep inner-shelf settings (cf. Waisfeld

AAP Memoir 32 (2006) 1995; Waisfeld et al. 2003). Ampyx reyesi Benedetto & Malanca from the Arenig of the Acoite Formation and Rhombampyx lamasi (Harrington & Leanza) from the upper Tremadoc of the Parcha Formation are the only raphiophorids previously described; Pytine wirayasqa sp. nov. is the third representative of the family known for the Cordillera Oriental. Ampyx reyesi resembles raphiophorids from south Wales (cf. Fortey & Owens 1987). Species of Rhombampyx have been recorded from Laurentia (Spitsbergen and Nevada), Baltica, and South China (Hunan and Hubei) (cf. Nielsen 1995). Pytine as here revised, occurs in Spitsbergen (on the margin of the Laurentian craton fide Cocks & Torsvik 2002), East Gondwana (Canning Basin, Australia), the North and South China blocks, and probably in Baltica (Sweden). Hence, both Rhombampyx and Pytine show biogeographic affinities with warm water faunas. The record of Carolinites in the Argentine and in southern Bolivian Cordillera Oriental (Dean 1989; Waisfeld 1995; Aceñolaza et al. 1999; Waisfeld & Vaccari 2003) is particularly significant. This genus was previously considered to exhibit a pan-equatorial distribution (Fortey & Shergold 1984); however, McCormick & Fortey (1999) have recently extended its range to a palaeolatitudinal belt between 30ºN and 30ºS. This distribution is consistent with the palaeogeographic position of the South American margin in recent reconstructions (Cocks & Torsvik 2002; Fortey & Cocks 2003). Western Argentinian trilobite faunas have been included in the Asaphopsis Province, a name used by Whittington & Hughes (1972) with reference to warm water trilobite faunas from Australia and South America. However, these authors did not make a distinction among different Argentine basins (Precordillera, Famatina, and Cordillera Oriental). Later authors (e.g., Fortey & Shergold 1984; Webby et al. 2000), probably following Přibyl & Vaněk (1980, p. 39), assumed that forms like Hungioides occur on the South American Gondwanan margin (Cordillera Oriental of Argentina and southern Bolivia), and continued to refer the Argentine trilobite fauna to the Asaphopsis Province. However, key elements of this province, such as Hungioides and Gogoella, are so far restricted to the Famatina island-arc, where a mixture of East and West Gondwanan elements occur (Vaccari 1995; Waisfeld 1998). Webby & Edgecombe (in Webby et al. 2000) also noted that the Asaphopsis Province was imprecisely defined, taking into account the lack of detailed studies on Australian faunas at the time of Whittington & Hughes’ (1972) work. Fortey & Cocks (2003) also placed the South

AAP Memoir 32 (2006) American Gondwanan margin in an intermediate position on the basis of the occurrence of cold water West Gondwanan and warm water East Gondwanan faunas. Characteristic Upper Tremadoc and Arenig warm water forms include, aside from Carolinites, Rhombampyx and Pytine of relatively wide geographic distribution, the asaphid Kayseraspis, and a new taxon close to Emanuelaspis (Waisfeld 1995, and unpublished data). A similar situation is documented among earlier Ordovician trilobite faunas that exhibit strong affinities with the fauna from Digger Island (Victoria) (Jell 1985; Webby & Edgecombe in Webby et al. 2000), and with the Takaka terrane (New Zealand) (Wright et al. 1994; Webby & Edgecombe in Webby et al. 2000). In the volcanic arc of the Western Puna, adjacent to the Gondwanan margin, Moya et al. (1993) suggested that trilobite species of the Las Vicuñas Formation resemble the Tiñú Formation from Oaxaca, Mexico (Robison & Pantoja Alor 1968). Vaccari & Waisfeld (2000) and Waisfeld & Vaccari (2003) recorded a new species of Amzasskiella, a widespread East Gondwanan element occurring in China, Australia and New Zealand, and also in Kazakhstan and Siberia. Amzasskiella has been recently documented in the early Tremadoc of the Cordillera Oriental (Casayok Formation, unpublished data). This record, along with the occurrence of Onychopyge, Leiostegium and Australoharpes, supports a close link between the western Puna and the Cordillera Oriental. These elements reinforce the connection between the faunas of the proto-Andean margin of South America with East Gondwana, as early as the early Tremadoc. SYSTEMATIC PALAEONTOLOGY Superfamily TRINUCLEOIDEA Hawle & Corda, 1847 Discussion. Traditionally, Alsataspididae Turner, 1940, Hapalopleuridae Harrington & Leanza, 1957, and Orometopidae Hupé, 1955, are considered the primitive groups of Trinucleoidea. Jell & Adrain (2003) included the three groups together within the Alsataspididae. Previous authors (e.g., Fortey & Shergold 1984), considered Hapalopleuridae and Orometopidae to be synonymous, and accommodated Seleneceme Clark, 1924, Falanaspis Tjernvik, 1956, and Hapalopleura longicornis Harrington & Leanza, 1957, in Alsataspididae, on the basis of the frontal spine emerging from the cephalic doublure. Ludvigsen et al. (1989) argued that the presence of an inflated baccula in Orometopidae

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(including Orometopus Brøgger, 1896, and Pagometopus Henningsmoen, 1959) justifies its separation from the Hapalopleuridae. Fortey & Owens (1991) suggested that Hapalopleuridae and Alsataspididae are a group of primitive multisegmented Trinucleoidea, and should be regarded as synonymous. Hence, they regarded Orometopidae as a separate family. In their discussion of the position of Skljarella Petrunina, 1973, they placed the genus in the Orometopidae because of cranidial features, although they noted that the thorax and pygidium are similar to Araiopleura Harrington & Leanza, 1957, a typical hapalopleurid. Peng (1992) considered Proaraiopleura Zhang, 1981 a synonym of Skljarella, which he placed within the Hapalopleuridae, with Bao & Jago (2000) following this assignment. We agree that Skljarella should be removed from Orometopidae; it is better placed within the Alsataspididae (= Hapalopleuridae; = Jegorovaidae). We regard Orometopidae (including Orometopus, Pagometopus?, Pyrometopus Přibyl & Vaněk, 1980, and Jiangxiaspis Zhang in Qiu et al. 1983) as a valid group that can be separated from the Alsataspididae based on the drastic reduction in the number of thoracic segments (six in Pyrometopus, and five in Jiangxiaspis), and the triangular pygidium with the same configuration as in the Raphiophoridae and Trinucleidae. Both features (reduction of segments and triangular pygidium) are apomorphic characters in the Trinucleoidea (cf. Fortey & Chatterton 1988; Fortey & Owens 1991) and might be considered as synapomorphies that link Orometopidae, Raphiophoridae, Trinucleidae and Dionididae. In contrast to this situation, all the Alsataspididae bear 10 to 40 thoracic segments and a tiny pygidium that is difficult to distinguish from the thorax. Family RAPHIOPHORIDAE Angelin, 1854 Discussion. Fortey (1975, p. 64-65) provided a detailed discussion of the Raphiophoridae and emphasised the great morphological variability of the group. He considered the Endymioniidae Raymond, 1920 as a subfamily of the Raphiophoridae, and the Ampyxinellinae Koroleva, 1959 as synonymous with the Raphiophorinae. Fortey (1975) suggested that the position of the median node in the posterior half of the glabella among the Endymioniinae separates this subfamily from the Raphiophorinae. Zhang (1979) erected the subfamily Taklamakaniinae to include a group of raphiophorids with only three thoracic segments, but Zhou et al. (1995) considered this to be a polyphyletic assemblage

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within the Raphiophorinae. Zhou et al. (1995) suggested a revised concept of Endymioniinae, accommodating Ampyxinellinae Koroleva, 1959 within it. They considered that variation in the number of thoracic segments and presence/ absence of ocular tubercles does not justify the subfamilial separation. This view is followed here. A revision of the Raphiophoridae, involving a detailed phylogenetic analysis, is needed in order to understand relationships among the genera and suprageneric groups. Such an analysis is beyond the scope of this contribution, which concentrates on those taxa considered most closely related to Lehnertia gen. nov. Subfamily ENDYMIONIINAE Raymond, 1920 Lehnertia gen. nov. Type species. Lehnertia nawisapa gen. et sp. nov., from the Las Chacritas Formation (Darriwilian), Quebrada de La Tuna, 42 km south of San José de Jáchal, San Juan Province, Argentina. Species assigned. Nambeetella embolion Fortey & Shergold, 1984. Diagnosis. Endymioniinae with cephalic doublure extended forward and slightly downward into long, sharp, pointed spine; glabella strongly inflated; preglabellar field pointed forward and arched medially. Pygidium with axis extended on to posterior border; border wide, steeply down-turned. Discussion. The most distinctive feature of this genus is the extension forward of the cephalic doublure into a long, sharp, pointed spine. Fortey & Shergold (1984) considered this feature distinctive enough that it was unlikely to have evolved more than once, and in consequence they broadened their diagnosis of the Alsataspididae to include Nambeetella embolion and “Hapalopleura” longicornis Harrington & Leanza, together with Falanaspis and Seleneceme, more typical members of this family. Later, Laurie & Shergold (1996) excluded embolion from Nambeetella, and the latter from the Alsataspididae, since the type species of that genus lacks a doublural spine. Laurie & Shergold further suggested that embolion should be included in a new genus. We include embolion in Lehnertia gen. nov. because of its many similarities to the type species Lehnertia nawisapa sp. nov., including: very similar spinose projections of the cephalic doublure; the preglabellar region projecting forward and arched medially; similar cranidial

AAP Memoir 32 (2006) outline; very similar pygidia, including the same shape of the axis, and a wide, steeply downturned border. Differences between these two species are listed under the discussion of L. nawisapa. The precise number of thoracic segments is unknown in Lehnertia. However, taking into account the shape of the pygidium, and the morphology of the incompletely preserved thorax, Lehnertia should be excluded from the Alsataspididae. The genus is better accommodated within the clade of advanced trinucleoids (orometopids, raphiophorids, trinucleids, and dionidids). The inclusion of Lehnertia in the Raphiophoridae is supported by the cranidial outline, the course of the facial suture, and the long, narrow free cheeks. The presence of the anterior projection of the cephalic doublure as a spine represents a homoplasy, also present in some Alsataspididae The glabellar shape and convexity of Lehnertia is reminiscent of those Raphiophorinae in which the glabella does not protrude beyond the anterior cranidial border, and which have a node on the anterior half of the glabella and lack a frontal spine (e.g., Globampyx Fortey, 1975, or Mendolaspis Rusconi, 1951). However, Lehnertia exhibits a glabellar node on the posterior part of the glabella, a distinctive backward widening of the axial furrows, ocular tubercles, and relatively coarse anastomosing lines on the genal fields. These features resemble the Endymioniinae. The presence of an anterior median spine emerging from the cephalic doublure is a unique feature among the raphiophorids. However, in many other respects Lehnertia closely resembles Pytine Fortey, 1975. Lehnertia shares with Pytine, as well as with other endymioniinids, the backward widening of the axial furrows. Both Lehnertia nawisapa sp. nov. and P. graia Fortey, 1975, exhibit three pairs of glabellar impressions, S1 and S2 as subcircular apodemes, and S3 as short and shallow furrows. Also, both species share a distinctive surface sculpture of the cranidium (reticulate pattern on the glabella and anastomosing ridges on the genal fields). Pygidia of both genera are closely similar, with a wide border, sloping downward abruptly, covered with anastomosing terrace lines, and an axis extending onto the border. Accordingly, we regard Lehnertia as a member of the Endymioniinae most closely allied to Pytine. The poorly known genus Carinocranium Dean, 1989, from Zone J of the Outram Formation, at Wilcox Pass, Alberta, Canada, resembles Lehnertia in some respects. Carinocranium cariniferum (Dean, 1989, p. 17, pl. 1, figs 12-16) is similar to L. nawisapa in the shape and convexity of the glabella, strongly raised immediately anterior to the occipital furrow, and

AAP Memoir 32 (2006) also in the presence of ocular ridges. The latter run from the axial furrows toward the anterior part of the cranidium in Carinocranium; in contrast, they are slightly directed backward in L. nawisapa. Carinocranium is also comparable with Pytine graia in the presence of the short transverse furrows on genae adjacent to the axial furrows, and in the development of prominent bacculae. Regarding other Endymioniinae, Lehnertia broadly resembles species of Miaopopsis Lu, 1965 (in Lu et al. 1965), such as the type species M. whittardi (Yi, 1957) (see Peng et al. 2001, pl. 3, figs 1-17). The Chinese species exhibits a posteriorly convex glabella, posteriorly expanded axial furrows, and a glabellar tubercle in a similar location to that of L. nawisapa. Miaopopsis whittardi possesses a pair of sinuous ridges obliquely crossing the genal fields, directed from the axial furrows to the genal angle. A pair of relatively faint ridges is also present in L. nawisapa, developed between the prominent eyes (Fig. 5I), although this feature is obscured in most specimens by the raised ocular structures. Lehnertia differs from Miaopopsis in the absence of bacculae, the presence of the anterior cephalic spine and in the morphology of the pygidium, much shorter (sag.) and with a broader and steeply downward sloping border. Etymology. This genus is named for Oliver Lehnert, amigo and conodont worker, who contributed important biostratigraphic information on the carbonate successions of the Argentine Precordillera. Lehnertia nawisapa gen. et sp. nov. (Figs 2–7) Diagnosis. Lehnertia with glabella strongly convex, greatly elevated immediately anterior to SO, prominent stalked eyes, and ocular ridges. Free cheeks with a prominent sagittal embayment at base of anterior cranidial spine, and gentle flexure at posterior margin of doublure. Pygidium 2.5 times as wide as long, axis extended onto posterior border; six axial rings, second ring continuing onto pleural field; anterior three ring furrows with apodemal depressions abaxially; border wide, steeply downturned and moderately arched behind axis. Type material. Holotype cranidium CEGHUNC 22254 (Fig. 5I-L); paratypes CEGH-UNC 22224-22253, 22255-22272, 22281-22283, 22395-22396. All from Las Chacritas Formation (Darriwilian), Quebrada de La Tuna, 42 km south of San José de Jáchal, San Juan Province, Argentina. Holotype and most paratypes from 33.6 m above base of Las Chacritas Formation

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(horizon LT 14). Description. Cranidium subtriangular, 1.8-2.2 times as wide as long. Cranidial anterior border short subtriangular process, upturned in lateral view, border furrow faint medially at anterior process, deepening anterolaterally and laterally, running parallel to cranidial margin (Fig. 7A, G). Glabella oval in outline, 0.8 as wide as long, highly convex (sag., tr.), expanding gently in width with angle of about 50º, then tapering forward, very highly elevated immediately anterior to occipital ring, sloping steeply downwards anteriorly, and not overhanging anterior border. Highest part of glabella bears prominent tubercle, dorsally directed, placed just behind transverse midline of glabella. Three pairs of lateral glabellar furrows on posterior part of glabella: S1 and S2 deep, subcircular impressions, S3 shallow and short (Fig. 7B). Axial furrows well impressed, shallow anterolateral fossula located anterior to point of maximum width of glabella; axial furrow deepens and strongly widens posterior to fossula in depressed, subtriangular area. Axial and preglabellar furrows narrower and shallower anterior to fossula. Occipital furrow rather shallow, occipital ring nearly straight, low, narrow, indistinctly defined laterally. Fixed cheeks with prominent transverse and exsagittal convexity, steeply sloping downwards anteriorly and laterally, postocular fixigenal field sloping almost vertically. Low ridge runs anteriorly from stalked eye to point slightly forward of posterolateral corner of cranidium (Figs 5I, 7G, H); this genal ridge then merges with strong ridge at base of genal spine (Fig. 5E). Stalked eyes, subcircular in dorsal view, inclined outward in anterior view, palpebral area strongly raised. Visual surface more convex in profile but not distinctly different in texture from adjacent cheek. Eye ridges well-developed, proximal part opposite anterior edge of S2, distal part opposite its posterior edge. Posterior border furrow faint proximally, fairly broad, flexed forward, ending in apodemal pit. Posterior border transversely directed, maintaining constant width (exsag.), expanding at some distance in from apodemal pit. Two low ridges, diverging from axial furrows, cross genal fields; one of them runs anteriorly to eye, other runs parallel to abaxial margins of posterior expansion of axial furrows and posterior border furrow. Anterior cranidial margin upturned in anterior view, strongly elevated medially. Facial suture runs across cephalic border on “sutural ridge”, parallel to margin, describes sagittal inflexion at base of anterior cephalic spine, and strongly curves backward and inward at posterior corner of cranidium, crossing posterior

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Fig. 2. Lehnertia nawisapa gen. et sp. nov. from Las Chacritas Formation at La Tuna section, San Juan Province. All specimens are from a horizon 33.6 m above base of Las Chacritas Formation (LT 14). A, B, dorsal view of protaspis (P1), paratype CEGH UNC 22224, x69; B, paratype CEGH UNC 22225, x69; C, D, dorsal view of protaspis (P2), paratype CEGH UNC 22226, x69; D, paratype CEGH UNC 22227, x69; E, dorsal view of articulated meraspid degree 0, paratype CEGH UNC 22228, x60; F, dorsal view of transitory pygidium, paratype CEGH UNC 22229, x60; G-I, dorsal views of meraspid cranidia, G, paratype CEGH UNC 22230, x60; H, paratype CEGH-UNC 22231, x60; I, paratype CEGH UNC 22232, x60; J, dorsal view of enrolled moult of meraspid degree 0, paratype CEGH 22233, x60; K, dorsal view of small transitory pygidium, paratype CEGH UNC 22234, x60; L, dorsal view of cranidium, paratype CEGH UNC 22235, x60; M, dorsal view of enrolled moult of meraspid degree 0, paratype CEGH UNC 22236, x60.

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Fig. 3. Lehnertia nawisapa gen. et sp. nov. from Las Chacritas Formation at La Tuna section, San Juan Province. All specimens are from a horizon 33.6 m above base of Las Chacritas Formation (LT 14). A, B, dorsal and anterodorsal views of meraspid cranidium, paratype CEGH UNC 22281, x48; C-H, dorsal and anterior views of meraspid cranidia, C, D, paratype CEGH UNC 22282, x44; E, F, paratype CEGH UNC 22283, x42; G, H, paratype CEGH UNC 22395, x29.4; I, stalked eye, paratype CEGH UNC 22396, x48.

border. Free cheeks united in single piece by narrow doublure, produced into stout median spine. Median spine parallel-sided proximally, sharpens strongly distally. Free cheeks in dorsal view narrow, concave strips running around margin of cranidium, limited abaxially by low rim (Figs 5F, 7I). Strong, long, stout based genal spine, at least twice sagittal length of cranidium, with flat cross section, bearing narrow dorsal ridge. Doublure divided along its length by ridge leaving external and wider depressed band and narrower internal one, ridge prolonged along genal spine (Fig. 7J). Doublure upturned and slightly embayed about

mid-line, showing deep ventral groove behind spine seen as strong dorsal ridge (Figs 5F, 6L, 7K). Surface sculpture of reticulate pattern concentrically arranged around median glabellar node, reaching anterior margin of glabella in small specimens (Fig. 5C, D); glabella smooth adjacent to axial furrows (Fig. 7G, H). Fine anastomosing ridges and pits on anterior and lateral parts of genal fields. Hypostome 1.2 times longer than wide, anterior margin curved forward, posterior margin transverse; maximum width about half hypostomal length; middle body transversely

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Fig. 4. Lehnertia nawisapa gen. et sp. nov. from Las Chacritas Formation at La Tuna section, San Juan Province. All specimens are from a horizon 33.6 m above base of Las Chacritas Formation (LT 14). A, ventral view of protaspis (P1), paratype CEGH UNC 22237, x90; B, ventral view of meraspid, paratype CEGH UNC 22238, x30; C, ventral view of protaspis (P2), paratype CEGH UNC 22239, x95; D-I, ventral views of incomplete fused free cheeks, D, paratype CEGH UNC 22240, x65, I, paratype CEGH UNC 22245, x85; E-H, dorsal views of incomplete fused free cheeks, E, paratype CEGH UNC 22241, x50, F, paratype CEGH UNC 22242, x48, G, paratype CEGH UNC 22243, x19, H, paratype CEGH UNC 22244, x25; J,K, dorsal view of pygidium; J, paratype CEGH UNC 22246, x21; K, paratype CEGH UNC 22247, x16.

convex, suboval, surrounded by narrow borders; middle furrows as shallow depressions located behind transverse line at maximum width of hypostome. Thorax incompletely known, at least four segments (Fig. 6I), tapering gently to pygidium. Axis convex, very gently tapering backward, axial rings about 0.7 width of pleurae, slightly narrower and flexed forward distally; crescentic

articulating half ring with sagittal length similar to that of axial rings; ring furrows deepen laterally to form distal apodemes; tip of pleurae truncated, with downturned edge; pleural furrows shallow and wide, broader distally. Pygidium subtriangular, 2.5 times as wide as long. Axis raised well above pleurae, occupying 0.3 pygidial width at anterior margin, tapering gently posteriorly (angle enclosed by axial

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Fig. 5. Lehnertia nawisapa gen. et sp. nov. from Las Chacritas Formation at La Tuna section, San Juan Province. All specimens are from a horizon 33.6 m above base of Las Chacritas Formation (LT 14). A, B, anterior and dorsal views of cranidium, paratype CEGH UNC 22248, x11; C, D, anterior and dorsal views of cranidium, paratype CEGH UNC 22249, x11; E, dorsolateral view of cranidium, paratype CEGH UNC 22252, x11; F, dorsal view of incomplete fused free cheeks, paratype CEGH UNC 22251, x11; G, dorsolateral view of broken cephalon, paratype CEGH UNC 22250, x8; H, lateral view of cranidium, paratype CEGH UNC 22253, x11; I-L, dorsal, lateral, anterior and posterior views of cranidium, holotype CEGH UNC 22254, x11.

furrows about 35º) and extending onto posterior border. Six axial rings, first two more distinct; anterior three ring furrows deep, reaching axial furrows, with apodemal depressions abaxially; posterior ring furrows progressively shallowing.

Axial rings transverse; second ring continues onto pleural field. Pleural field subtriangular, flat, edged distally by narrow, convex rim. One pair of pleural ribs prominent and slightly backward directed, other pairs barely discernible; pleural

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furrows broad and deep, interpleural furrows shallow. Border wide, steeply downturned and moderately arched behind axis, with closely spaced subparallel to anastomosing terrace lines also covering distal rim. Description of ontogeny. Two protaspid instars are recognized for Lehnertia. The first protaspid (P1) stage (Figs 2A, B, 4A) is subovoid in shape, has two pairs of sharply pointed, subconical, marginal spines. Posteroventrally directed pair close together and slightly divergent; anterolateral pair is directed outward from anterolateral extremities. Axial furrows are shallow to indistinct, and glabella is represented as a slightly convex lobe, dying out posteriorly, with no indication of occipital furrow. Sculpture is finely reticulate. Anterior margin is gently curved forward in ventral view. Doublure is relatively narrow, gradually widening toward rear. Posterior branch of facial suture cuts the doublure slightly forward of midlength. Hypostome and free cheeks are unknown. The second protaspid stage (P2) (Figs 2C, D, 4C) is larger than P1, and similar in overall shape. Glabella becomes more distinct, parallel sided, rounded anteriorly, with independent convexity and better impressed axial, preglabellar, and occipital furrows. Posteromedian spines are crossed over, and longer than in P1; lateral pair is slightly more strongly directed forward. Anterior margin is gently concave outward in ventral view. Posterior branch of facial suture crosses doublure farther back than in P1, in posterior third, and then turns forward. Changes associated with metamorphosis between P2 and M0 (Fig. 2E, J, M) include development of much more inflated glabella, and more distinct axial furrows widening backward as flat, subtriangular areas adjacent to posterior part of glabella. Marginal spines disappear. Free cheeks extend in strong, long and curved genal spines. Transitory pygidium exhibits scarcely discernible axis and posterior indentation medially (Fig. 2E). Earlier meraspid degrees (Figs 2 and 3) show a gradual increase in cranidial convexity; in addition, the cranidial margin becomes more upturned in anterior view. The ocular structures appear during meraspid development. Although it is not possible to determine precisely at which meraspid instar these structures originate, sizes of the available specimens suggest an intermediate meraspid degree for their appearance (Figs 2L, 3A-H). This late development of the ocular structures during the meraspis period is peculiar within the Trilobita as a whole. Later meraspid degrees show increase in

AAP Memoir 32 (2006) glabellar convexity. Median glabellar node behind midlength of glabella, ocular ridges, and shallow anterior fossula become more distinct; backward expansion of axial furrows becomes more apparent by deepening of axial furrows and by increase in convexity of genal fields. Ocular structures increase in size and height. Cranidial anterior border insinuates as short subtriangular process, and becomes more pronounced in later stages. Sculpture of fine anastomosing ridges on anterior and lateral margins of genal fields becomes more pronounced. Free cheeks show increase in size of anterior cranidial spine; posterior margin of doublure behind base of anterior spine becomes gently flexed, and dorsal transverse ridge more distinct. Transitory pygidium becomes wider (tr.) and shorter (sag.); axis, axial rings and pleural ribs become better defined; and median posterior indentation progressively disappears. Holaspid growth stages show development of ocular structures: strong eye ridges and prominent stalked eyes. Some specimens show pitting between terrace lines of sculpture. Facial sutures become more sinuous and concave posterolaterally, and fixed cheeks are consequently shorter (exsag.). Glabellar tubercle becomes much more prominent and distinct. Discussion. Lehnertia nawisapa sp. nov. differs from L. embolion (Fortey & Shergold, 1984) from the upper part of the Nora Formation (Darriwilian) in the Georgina Basin, western Queensland (Fortey & Shergold 1984, p. 353, pl. 45, figs 1822) in the development of stalked eyes, presence of ocular ridges, a glabella that is strongly convex posteriorly, and a wider and shorter pygidium. In L. nawisapa the free cheeks exhibit a prominent embayment at the base of the anterior cranidial spine, and a gentle flexure at the posterior margin of the doublure. The Australian species shows the inverse condition, with a slight flexure at the base of the anterior cranidial spine, and a marked embayment at the posterior margin of the doublure (Fortey & Shergold 1984, pl. 45, fig. 19). We assign relatively little taxonomic weight to the presence or absence of ocular structures within Lehnertia. Despite their pronounced expression in adults of L. nawisapa, the eye ridges and eye stalks originate surprisingly late in ontogeny (wholly lacking in early meraspid stages). In addition, ocular structures are variably absent or present in the closely allied genus Pytine if Jiuxiella is considered a synonym (see discussion of Pytine below). Discussion of ontogeny. Two types of trinucleoid protaspides are found at horizon LT 14 and other horizons that yield Lehnertia nawisapa. One of

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Fig. 6. Lehnertia nawisapa gen. et sp. nov. from Las Chacritas Formation at La Tuna section, San Juan Province. All specimens are from a horizon 33.6 m above base of Las Chacritas Formation (LT 14). A, B, D, dorsal, posterior and lateral view of pygidium, paratype CEGH UNC 22255, x11; C, F, dorsal and posterior views of pygidium, paratype CEGH UNC 22256, x11; E, dorsal view of cranidium and two pleura, paratype CEGH UNC 22257, x11.8; G, ventral view of hypostome, paratype CEGH-UNC 22258, x12; H, dorsal view of pleura, paratype CEGH UNC 22259, x11; I, dorsal view of pygidium, paratype CEGH UNC 22260, x11; J, dorsal view of thorax and pygidium, paratype CEGH UNC 22261, x13; K, dorsal view of pygidium, paratype CEGH UNC 22262, x11; L, ventral view of incomplete fused free cheeks, paratype CEGH UNC 22263, x12; M, dorsal view of pygidium, paratype CEGH UNC 22264, x11; N, ventral view of cranidium, paratype CEGH UNC 22265, x12.

these types has three prominent radiating pairs of marginal spines in stage P2, the posteriormost pair of marginal spines is widely separated as in Ampyx virginiensis Cooper, 1953 (see below), and it also occurs abundantly with Ampyx in the base of the section (LT1 and LT2). This type

clearly belongs to Ampyx, and neither adults of Lehnertia nawisapa nor the second type of trinucleoid protaspid occurs in these samples. The second protaspid type, which is here assigned to Lehnertia, is abundant at horizon LT 14, in which Lehnertia is the most common trinucleoid.

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Fig. 7. Lehnertia nawisapa gen. et sp. nov. from Las Chacritas Formation at La Tuna section, San Juan Province. A-C, dorsal, lateral and views of cranidium, paratype CEGH UNC 22266, x6.5; D-F, dorsal, anterior and lateral views of cranidium, paratype CEGH UNC 22267, x5.8; G, H, dorsal and anterior views of cranidium, paratype CEGH UNC 22268, x5.3; I, dorsal view of incomplete fused free cheeks, paratype CEGH UNC 22269, x7.6; J, K, ventral views of incomplete fused free cheeks, J, paratype CEGH UNC 22270, x3.5; K, paratype CEGH UNC 22271, x3; L, dorsal view of cranidium, paratype CEGH UNC 22272, x6.2.

Among the raphiophorids, larval stages and later growth series are known for Lonchodomas chaziensis Shaw (Shaw 1968; Chatterton et al. 1994), and Ampyx virginiensis Cooper (Whittington 1959). Protaspides of Ampyxoides inermis Fortey, 1975, or Globampyx trinucleoides Fortey, 1975, were figured by Fortey & Chatterton (1988). Meraspid stages were also documented for Ampyxina powelli (Raymond, 1920) by

Whittington (1959). The presence of two protaspid stages is the general condition among Raphiophoridae and Trinucleidae (Chatterton et al. 1994). Protaspides of L. nawisapa are similar in most respects to those documented by Chatterton et al. (1994, figs 7-9) for Lonchodomas chaziensis Shaw. Protaspides from the latter species differ from protaspides of L. nawisapa in the presence

AAP Memoir 32 (2006) of two small swellings anteriorly, adjacent to the axial furrows. This feature is also present in protaspides of Ampyxoides and Globampyx (Fortey & Chatterton 1988, pl. 19, figs 11, 12). In contrast, protaspides of Ampyx virginiensis Cooper (in Whittington 1959, pl. 30, figs 2130), like those of L. nawisapa, lack anterior swellings. The first protaspis stage (P1) of Lonchodomas chaziensis exhibits a glabella that is slightly better defined laterally than that of L. nawisapa. In addition, the anterolateral spines are longer, the posterior spines are more ventrally directed, and the doublure is wider. A distinct, fine, third pair of marginal spines is definitely present in Lonchodomas. This spine pair, if present in L. nawisapa, is not large enough to be seen in our specimens (they cannot be discriminated from the quartz crystals that replace the original calcite of the protaspid exoskeleton). Stage P2 of L. chaziensis possesses longer anteromedian spines, a wider doublure, and an anterior median margin that is less concave in ventral view than protaspid stage P2 of L. nawisapa. The glabella of L. chaziensis is slightly more prominent, bears a distinct preoccipital glabellar tubercle, and the axis is extended behind SO, ending in a pointed extreme posteriorly. In contrast, in L. nawisapa the preoccipital glabellar node is obscured, and no inflated region is evident behind SO. Protaspides of Ampyx virginiensis differ from those of L. nawisapa in the more subrounded shape, and in the longer and far apart posteromedian spines. Larger protaspides of A. virginiensis (Whittington 1959, pl. 30, figs 21-24, 27) differ from L. nawisapa in the presence of a gently convex lobe backward from the occipital furrow, slightly wider than the basal part of the glabella. The meraspid period of L. nawisapa shows broadly similar trends to those documented by Chatterton et al. (1994) for L. chaziensis and for Ampyxina powelli (Raymond, 1920) by Whittington (1959). Etymology. Ñawisapa is a Quechua word for ‘big eyes’. Pytine Fortey, 1975 1977 Jiuxiella; Liu in Zhou et al., p. 250. 1979 Miboshania; Zhang & Zhou in Zhang, p. 232. Type species. Pytine graia Fortey, 1975, from the Olenidsletta Member, Valhallfonna Formation (late Arenig), north Ny Friesland, Spitsbergen; by original designation.

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Species assigned. Jiuxiella laevigata Liu in Zhou et al., 1977; Miboshania corrugata Zhang & Zhou in Zhang, 1979; Jiuxiella jiangxiensis Qiu in Qiu et al., 1983; partim Nambeetella fitzroyensis Legg, 1976, of Laurie & Shergold, 1996; Ampyx brevicauda Wiman, 1905 sensu Hoel 1999; Pytine wirayasqa sp. nov. Discussion. Fortey (1975) erected Pytine as a monotypic genus for P. graia Fortey, a raphiophorid from the late Arenig of Spitsbergen with a broad cephalon, prominent bacculae within the axial furrows, a distinctive sculpture of anastomosing ridges, and a short (sag.) and wide (tr.) pygidium. Hoel (1999) placed Ampyx brevicauda Wiman, 1905, from the ‘Shumardia Shale’ [Megistaspis (Paramegistaspis) planilimbata Zone] of Sweden, in Pytine. This species bears a strong, backwardly directed glabellar spine (Wiman 1905, pl. 2, fig. 17; Hoel 1999, fig. 12G). The Swedish form resembles Pytine graia in the presence of the bacculae, a transverse furrow on the cheek, shape of the pygidium, and ornamentation. In P.? brevicauda the course of the facial suture is sinuous, strongly curved inward posteriorly. This species differs in this feature from P. graia and the other species here referred to the genus, in which the facial suture has a less inflected course around the lateral and anterolateral margins of the cranidium. Jiuxiella Liu in Zhou et al., 1977, based on J. laevigata Liu in Zhou et al., 1977, from the early Darriwilian of western Hunan, China, closely resembles Pytine in the configuration of the cranidium, presence of prominent bacculae, and shape of the pygidium. Synonymy of Jiuxiella and Miboshania Zhang & Zhou in Zhang, 1979, based on the early Darriwilian M. corrugata Zhang & Zhou in Zhang, 1979, from Ningxia Province, was proposed by Zhou in Zhou et al. (1982), and is accepted here. This synonymy means that species of Jiuxiella occur on both the North China block (J. corrugata) and the South China block (J. laevigata and J. jiangxiensis). Zhou et al. (2001, fig. 4J) referred the type species of Jiuxiella, J. laevigata, to Pytine; however, no discussion on this assignment was provided by the authors. Only P. graia and J. laevigata (see Liu in Zhou et al. 1977, pl. 74, figs 10-13; Liu 1982, pl. 232, figs 8, 9) are known from complete specimens. The Chinese species possesses six thoracic segments, in contrast to seven segments in P. graia. Ocular tubercles are present in each of J. laevigata, J. corrugata (Zhang 1979, pl. 1, figs 4-8; Zhou & Zhang in Zhou et al. 1982, pl. 69, figs 15-17), and the early Arenig J. jiangxiensis (Qiu in Qiu et al. 1983, pl. 81, fig. 5) from Jiangxi Province. As was

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Fig. 8. Pytine wirayasqa sp. nov. from the Acoite Formation at La Ciénaga section, Purmamarca, Jujuy Province. A-D, dorsal, anterior, lateral and posterior views of cranidium, holotype CEGH-UNC 22273, x10; E, F, dorsal and lateral views of cranidium, paratype CEGH-UNC 22274, x7.7; G-I, dorsal, anterior and posterior views of cranidium, paratype CEGH-UNC 22275, x8.7; J, dorsal view of cranidium, paratype CEGH-UNC 22276, x5.3; K, dorsal view of external latex cast of pygidium, paratype CEGH-UNC 22277, x6.9; L, dorsal view of pygidium, paratype CEGH-UNC 22277, x6.9; M, dorsal view of cranidium, paratype CEGH-UNC 22278, x10.8; N, dorsal view of pygidium, paratype CEGH-UNC 22279, x8.6; O, ventral view of incomplete fused free cheeks, paratype CEGH-UNC 22280, x6.1.

discussed above concerning ocular structures in Lehnertia, the presence or absence of this feature appears to be labile in the Endymioniinae and, hence, neither the presence of ocular tubercles nor the presence of six thoracic segments justifies Jiuxiella as a separate genus, and we follow Zhou et al. (2001) in regarding it as a junior synonym of Pytine. Nambeetella Legg, 1976, based on N. fitzroyensis Legg (1976, pl. 6, figs 14, 18) from the Emanuel Formation (Bendigonian Be2, early

Arenig) of the Canning Basin, Western Australia, was originally erected to include a raphiophorid species lacking a frontal glabellar spine, and the glabella not protruding beyond the anterior margin of the cephalon. Laurie & Shergold (1996) referred juvenile material (cranidia 0.63-1.77 mm and pygidia 0.59-1.26 mm) to N. fitzroyensis, from the type locality of this species. These authors figured two morphotypes of pygidia exhibiting different length/width ratios and segmentation. Possibly only the morphotype illustrated in

AAP Memoir 32 (2006) their pl. 14, fig. 26 is conspecific with the type material figured by Legg (1976). Cranidia differ from N. fitzroyensis in the presence of prominent bacculae. Laurie & Shergold (1996) pointed out that the presence of bacculae, the cranidial and pygidial sculpture, and the pygidial axis extending onto the wide border in their studied material suggest that Nambeetella and Pytine are closely related. Hoel (1999) referred part of this material to Pytine brevicauda (Wiman). We do not agree with this specific assignment, not the least because the Australian material lacks the long median glabellar spine seen in Swedish specimens (Hoel 1999, fig. 12G); however, the presence of bacculae and the configuration of the pygidial axis, the border, and the length/width ratios (see Laurie & Shergold 1996, pl. 14, figs 27-31) suggest that the juvenile specimens figured by Laurie & Shergold (1996) are not conspecific with N. fitzroyensis, and may correspond to a new species of Pytine. Until better material of N. fitzroyensis is available, this monotypic genus should be restricted to the type material figured by Legg (1976). Pytine wirayasqa sp. nov. (Fig. 8) Diagnosis. Pytine with small bacculae, glabella strongly inflated anteriorly, glabellar node located close to midlength of glabella; preglabellar field about equally long (sag.) as anterior cranidial border, anterior border wide (tr.), about twice maximum width of glabella. Pygidium three times as wide (tr.) as long (sag.), pygidial axis extended onto posterior border, six axial rings, anteriormost two distinct, four pairs of apodemes defining posterior ones; pleural field with three ribs; faint, sinuous ridge between border and pleural field. Type material. Holotype cranidium CEGH-UNC 22273 (Fig. 8A-D); paratypes CEGH 2227422280. All from Acoite Formation (early Arenig), La Ciénaga, 5 km west of Purmamarca, Jujuy Province, Argentina. Description. Cranidium semicircular in outline, slightly arcuate anteriorly, 2.3 times wider than long (sag.), up to 2.8 times wider than long in juveniles. Glabella expanded forward, highly convex (sag., tr.), with highest point coincident with position of glabellar node, anterior half sloping very steeply downwards in profile, not extended beyond anterior border; glabellar node close to midlength of glabella. Three pairs of lateral glabellar impressions, of which S1 is deepest, subcircular, S2 subtriangular, slightly deeper proximally, S3 weak and short distance anterior to mid-point (sag.) of glabella. Occipital

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ring narrow, of uniform width (sag., exsag.), and convex backward (tr.). Distinct fossula anterior to point of maximum width of glabella; preglabellar furrow narrow, well impressed; axial furrows widen backward behind fossula, becoming broader and slightly shallower adjacent to posterior part of glabella; low, subtriangular bacculae adjacent to L1. Fixed cheeks slightly convex, gently sloping downwards laterally and anteriorly, merging in short (sag.) preglabellar field; gentle change in slope defining shallow depression at similar position to transverse furrow on cheek of P. graia. Posterior border furrow distally, distal third slightly widens and curves backward, ending in deep pit; posterior border widening adaxially. Facial suture runs along lateral margin of cranidium, intersecting anterior cranidial border at point opposite (exsag.) one third of posterior border width, and meeting in front of anterior border. Cephalic sculpture pronounced on external surface. Anastomosing ridges on anterior portion of glabella, and reticulated ridges roughly concentric to median node. Fine ridges on preglabellar field and anterolateral areas of fixigena, subparallel to cranidial margin, reticulate pattern on rest of genal lobes, coarser toward axial furrows. Cephalic doublure partially preserved, bearing fairly strong ridge and at least two fine ridges abaxially. Hypostome and thorax unknown. Pygidium subtriangular, three times as wide (tr.) as long (sag.), axis 0.15-17 maximum pygidial width, gently tapering, extended onto posterior border; two anterior axial rings distinct, posterior rings effaced, defined by four pairs of apodemes; pleural fields with three ribs, wide and shallow pleural furrows, broadening and flexed backward distally; sinuous, faint ridge between border and pleural fields. Posterior border sloping downward abruptly; posterior margin curved backward behind axis. Sculpture of very fine lines on pleural fields, and fine anastomosing lines on border. Discussion. Pytine wirayasqa sp. nov. shares with the type species P. graia (Fortey 1975, pl. 23, fig. 7; pl. 31, figs 1-11; fig. 10) a backward widening of the axial furrows, the presence of three pairs of glabellar impressions, a similar position of the median tubercle, and similar surface sculpture. The Argentine species differs from P. graia in having a more convex glabella, smaller bacculae, a wider (tr.) anterior border, and a wider (tr.) pygidium, with broader pleural fields, and a narrower border. Pytine wirayasqa resembles the Western Australian species of Pytine figured by Laurie & Shergold (1996, pl. 14, figs 14-25, 27-31) in the

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overall convexity of the cranidium. However, P. wirayasqa is distinguished from the Australian species in the smaller and more posteriorly placed median node, smaller bacculae, more numerous pygidial axial rings, and a less distinct and sinuous ridge between the pleural field and the border. The Chinese species Pytine laevigata, P. corrugata, and P. jiangxiensis are easily distinguished from P. wirayasqa by their larger bacculae, and particularly in the presence of ocular tubercles. Pytine? brevicauda (Wiman 1905, pl. 1, figs 19, 20; Hoel 1999, figs 12, 13) is similar to P. wirayasqa in the cheek sculpture, and in the glabellar convexity; however, the Argentine species exhibits smaller bacculae, lacks the prominent glabellar spine, and the pygidium is wider (tr.), bearing more numerous axial rings, and the pleural fields are more distinctly segmented. Etymology. In Quechua, wirayasqa means ‘engorged’, in reference to the swollen glabella. ACKNOWLEDGEMENTS Vaccari and Waisfeld acknowledge support from CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), and ANCyT (Agencia Nacional de Promoción Científica y Tecnológica: PICT 2003, 07/11741 and PICT 2000 07/8920). Chatterton was funded by an operating grant from the Natural Sciences and Engineering Research Council of Canada (NSERC). We thank J.M. Adrain and R.A. Fortey for constructive suggestions that improved the manuscript. REFERENCES

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