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Apa 1188.Qxd AMEGHINIANA (Rev. Asoc. Paleontol. Argent.) - 42 (2): 501-504. Buenos Aires, 30-06-2005 ISSN 0002-7014 NOTA PALEONTOLÓGICA A new temnospondyl record from the Upper Triassic of Argentina Claudia A. MARSICANO Introduction tion; UCMP, University of California Museum of Paleontology, Berkeley (USA). The Brachyopoidea is a group of Mesozoic tem- nospondyls with flat, parabolic skulls that were re- cently reviewed and considered to include Systematic paleontology Brachyopoidea and Chigutisauridae (Warren and Marsicano, 2000; Yates and Warren, 2000, Damiani TEMNOSPONDYLI Zittel, 1887-1890 and Kitching, 2003). Brachyopids have been record- BRACHYOPOIDEA Lydekker, 1885, sensu Warren ed from several different localities both in and Marsicano, 2000 Gondwana (excluding South America) and Laurasia Brachyopidae? indet. (Warren and Marsicano, 2000) during the Early- Figure 1 Middle Triassic. After the Middle Triassic, they are absent from the fossil record for several million years Material. MCNAM-PV 3195, an incomplete left mandible. until they are recorded in the Middle-Late Jurassic of China (Dong, 1985) and Mongolia (Shishkin, 1991). Locality and Horizon. Quebrada de la Mina, In contrast, chigutisaurid temnospondyls appear to Potrerillos locality, western Mendoza, Argentina; be restricted to Gondwana. They are known from the Cacheuta Formation, Late Triassic (Morel et al., Lower Triassic, Lower Jurassic and Lower 2002). Cretaceous of Australia (Warren, 1981; Warren and Description. The specimen (MCNACM-PV-3195) Hutchinson, 1983; Warren et al., 1997), the Upper corresponds to the anterior part of a left mandible, Triassic of Argentina (Bonaparte, 1975; Marsicano, from the symphysis to the level of the anterior coro- 1993, 1999) and India (Sengupta, 1995), and from the noid (figure 1). The fragment is poorly preserved Upper Triassic and Lower Jurassic of South Africa and somewhat distorted although it clearly shows (Warren and Damiani, 1999). that the mandible was very low anteriorly with the This paper describes a new temnospondyl speci- symphysis anteroposteriorly expanded; the outline men consisting of an incomplete left mandible, pre- suggests that it was associated with a parabolic skull. served from the symphysis to the level of the anteri- On the labial and ventral surface, a ridge-and-groove or coronoid, found in strata assigned to the Late sculpture covers the dentary and splenial, which be- Triassic Cacheuta Formation at the Potrerillos locali- comes more pitted anteriorly in the symphyseal area. ty in western Argentina (Marsicano et al., 2000). The On the dentary, just underneath the tooth row, runs mandible is here considered to be a putative brachy- the oral sulcus, one of the two main sensory canals opid and, therefore, it would be the first occurrence usually found in temnospondyl mandibles (Jupp of this group in South America and the youngest for and Warren, 1986); it finishes at the level where the Gondwana. symphysis becomes anteroposteriorly expanded. Abbreviations-MCNAM-PV, Museo de Ciencias The sutures are quite well preserved so that it Naturales y Antropológicas Juan Cornelio Moyano was possible to trace them with confidence. The con- of Mendoza (Argentina), paleovertebrados collec- tact between the dentary and splenial is on the ven- tral surface of the ramus and not visible in labial view. This contact finishes posterior to the symph- ysis, which is thus only formed by the dentary. Laboratorio de Paleontología de Vertebrados, Dto. de Ciencias Lingually the surface is poorly preserved although Geológicas, Universidad de Buenos Aires, Ciudad Universitaria Pabellón II, C1428DHE Ciudad Autónoma de Buenos Aires, the splenial-dentary contact is visible low in the Argentina. <[email protected]> mandible and runs into a longitudinal groove which ©Asociación Paleontológica Argentina AMGHB2-0002-7014/05$00.00+.50 502 C.A. Marsicano Figure 1. Left mandible MCNAM-PV 3195. A, photograph and drawing in occlusal view; B, photograph and drawing in ventral view; C, photograph and drawing in lingual view; D, photograph and drawing in labial view. Scale bar = 1 cm. Abbreviations: d, dentary; sp, splenial; ac, anterior coronoid; o, oral sulcus / Mandíbula izquierda MCNAM-PV 3195. A, fotografìa y dibujo en vista oclusal; B, fotografìa y dibujo en vista ventral; C, fotografìa y dibujo en vista lingual; D, fotografìa y dibujo en vista labial. Escala = 1 cm. Abreviaciones: d, dentario; sp, esplenial; ac, coronoide anterior; o, surco oral. finishes ventral to the symphyseal tusk. Above this contrast, the dentary teeth are oval in section close to groove, the dentary is expanded and forms a round- their bases and become more rounded towards their ed shelf just medially to the tooth row. Posteriorly in tips. Eight dentary teeth are preserved and alternate lingual view, a small part of the anterior coronoid is with replacement pits; the teeth decrease in size to- present and forms a V-shaped wedge between the wards the symphyseal area and the larger ones dentary and the splenial. markedly curved inwards. When compared to the In the symphysis, the expanded shelf of the den- overall size of the mandible, the teeth are relatively tary accommodates the symphyseal tusk, which is large and few in number. rounded in cross section at the level of its base. In Discussion. Parabolic-shaped jaws have been previ- AMEGHINIANA 42 (2), 2005 Late Triassic temnospondyl from South America 503 ously described in the Mesozoic groups Plagio- other known brachyopid mandibles as Bathignathus sauridea and Brachyopoidea. Plagiosaurids are Tria- (Damiani and Jeannot, 2002) and QMF 14483 ssic temnospondyls with parabolic mandibles with a (Damiani and Warren, 1996). Moreover, the presence low symphysis. Nevertheless, the absence of sym- of relatively few large recurved teeth that decrease in physeal tusks and the presence of pustular ornament size anteriorly is shared by all Gondwanan bra- in most plagiosaurids (Jupp and Warren, 1986) pre- chopid mandibles (see Warren, 1981; Damiani and cludes the specimen from Potrerillos from belonging Warren, 1996; Damiani and Jeannot, 2002; Damiani to that group. and Kitching, 2003). Within Brachyopoidea, chigutisaurids also have In summary, despite the fragmentary nature of parabolic mandibles and, moreover, they are repre- the material described herein, the structure of the sented in the same levels and locality by some speci- mandibular symphysis and the size and distribution mens of size similar to the material described herein of the teeth allow us to conclude that it belongs to a (e.g. P. mendozensis, see Marsicano, 1999). Never- brachyopoid, possibly a brachyopid rather than a theless, known chigutisaurids do not present symph- chigutisaurid. ysis comparably low and broad, and teeth as large and few in number as the new specimen from Potrerillos. The only known chigutisaurid where Paleogeographic significance these features are also present is Koolosuchus (Warren et al., 1997), represented by a very large specimen The earliest brachyopid records are from the from the Cretaceous of Australia. The mandibular Lower Triassic of Australia: the Arcadia Formation of symphysis in Koolosuchus, however, is formed by the Queensland, the Knocklofty Formation of Tasmania, dentary and the splenial, thus differing from the con- the Narrabeen Group of the Sydney Basin, and the dition in the specimen from Mendoza. Blina Shale of Western Australia (Warren, 1981; With respect to the brachyopids, all described Damiani and Warren, 1996; Warren and Marsicano, mandibles have a parabolic shape with an expanded 1998). In contrast, the lower Middle Triassic record is and low anterior region (e.g. Warren, 1981; Damiani much more dispersed, including other Gondwanan and Warren, 1996; Damiani and Kitching, 2003), in- and Laurasian areas, as the upper Beaufort Group of cluding undescribed mandible fragments assigned to South Africa (Warren and Marsicano, 2000; Damiani Batrachosuchus sp. (UCMP 140589) from South Africa and Jeannot, 2002; Damiani and Kitching, 2003), the (see Warren and Marsicano, 2000). Brachyopoid Denwa Formation of India (Sengupta, 2003) and the mandibles are not particularly abundant in the fossil Moenkopi Formation of Arizona (Welles and Estes, record and most of the described material comes 1969; Warren and Marsicano, 2000). The youngest from the Lower-Middle Triassic of Africa and brachyopid records are again more restricted as they Australia. Mandibular remains assigned to Batra- are only known from the Asian part of Laurasia chosuchus sp. (Watson, 1956; Colbert and Cosgriff, (Middle Jurassic of the Sichuan Province, China, and 1974; Warren and Marsicano, 2000) and B. concordi Upper Jurassic of southwestern Mongolia). It is evi- (Chernin, 1977) were recovered from southern dent that the brachyopid fossil record was hitherto Africa. Additionally, new fairly complete brachyopid characterized by a noteworthy gap of more than 50 mandibles associated with skull material (Vanastega million years, representing most of the Triassic and plurimidens Damiani and Kitching, 2003 and the Early Jurassic. Recently, a brachyopid phyloge- Bathignathus poikilops Damiani and Jeannot, 2002) netic hypothesis was combined with the known tem- were recently described from the same area. The poral distribution of the group and remarkable ghost known Australian material includes three rather linages were suggested in the resulting calibrated complete mandibular rami all from the Lower cladogram (Damiani and Kitching, 2003). Triassic of Queensland
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