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A New Lower Permian Trematopid (Temnospondyli: Dissorophoidea) from Richards Spur, Oklahoma

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A New Lower Permian Trematopid (Temnospondyli: Dissorophoidea) from Richards Spur, Oklahoma Zoological Journal of the Linnean Society, 2011, 161, 789–815. With 15 figures A new Lower Permian trematopid (Temnospondyli: Dissorophoidea) from Richards Spur, Oklahoma BRENDAN P. POLLEY and ROBERT R. REISZ* Department of Biology, University of Toronto, Mississauga Campus, 3359 Mississauga Road North, Mississauga, Ontario, Canada L5L 1C6 Received 31 January 2010; revised 16 March 2010; accepted for publication 23 March 2010 A new trematopid amphibian, Acheloma dunni, is reported based on excellently preserved cranial and postcranial elements recovered from the Lower Permian fissure fill deposits of the Dolese Brothers Co. limestone quarry near Richards Spur, Oklahoma. The new taxon is characterized by lateral exposures of the palatine (l.e.p.) and ectopterygoid (l.e.e.), which are clearly visible externally and completely enclosed within the suborbital elements. This large, terrestrial carnivore may represent the top predator of the Richards Spur assemblage. A phylogenetic analysis including 12 taxa and 53 cranial characters yielded a single most parsimonious tree, placing Ach. dunni within the monophyletic Trematopidae as the sister taxon to Acheloma cumminsi. Furthermore, the analysis includes the enigmatic Ecolsonia and Actiobates within Trematopidae, forming a clade with the Upper Pennsyl- vanian Anconastes and the Lower Permian Tambachia. The study comprehensively analyses all valid and aberrant forms of Trematopidae. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 789–815. doi: 10.1111/j.1096-3642.2010.00668.x ADDITIONAL KEYWORDS: Amphibia – Olsoniformes – Tetrapoda – Trematopidae. INTRODUCTION Formation of the Clear Fork Group of Texas (Olson, 1991). This assignment has been further supported by The Dolese limestone quarry, situated near Richards biostratigraphical evidence based on the fauna recov- Spur, Oklahoma is home to the most diverse known ered from the South Grandfield locality of southern assemblage of Palaeozoic terrestrial tetrapods. Oklahoma (Daly, 1973; Sullivan, Reisz & May, 2000; Regular excavation of Ordovician Arbuckle limestone Maddin, Evans & Reisz, 2006). has continually yielded fossil-rich clays and conglom- The Richards Spur assemblage represents a dra- erates (Olson, 1991). Although often disarticulated, matic departure from contemporary Early Permian fossil material is abundant and well preserved, rep- faunas. Whereas the majority of North American resenting a great variety of taxa (Reisz, 2007; localities typically yield faunal samples consistent Fröbisch & Reisz, 2008). A large proportion of this with aquatic, semi-aquatic, and terrestrial forms of fossil material (Daly, 1973; Olson, 1991) has been lowland, deltaic environments (Olson, 1956), the assigned to the small terrestrial eureptile, Captorhi- Richards Spur assemblage is comprised exclusively of nus aguti. Olson (1991) interpreted the relative abun- small and medium-sized terrestrial forms. This dance of C. aguti material as indicative of an Early unique faunal composition has led to the suggestion Permian age for the faunal assemblage. More specifi- that the locality has preserved a predominantly arid, cally, he inferred that the fauna of Richards Spur upland assemblage (Sullivan et al., 2000; Anderson & was contemporaneous with the Leonardian Arroyo Reisz, 2003; Schoch, 2009). Skeletal elements of larger taxa have been reported from Richards Spur, corroborating the hypothesis that the distinct compo- *Corresponding author. E-mail: [email protected] sition of the fossil assemblage may have been the © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 789–815 789 790 B. P. POLLEY and R. R. REISZ product of palaeoecological factors, rather than tapho- atops thomasi; however, the family remained largely nomic biases (Sullivan et al., 2000). These large unexamined until Olson’s (1941) comprehensive remains include isolated elements assignable to a study. In his review, he erected several new species of varanopid (Maddin et al., 2006), the sphenacodontid Acheloma and Trematops: Acheloma pricei, Acheloma Thrausmosaurus (Evans, Maddin & Reisz, 2009), the whitei, and Trematops willistoni. He later expanded dissorophid Cacops (Sullivan et al., 2000; Reisz, the family by describing Trematopsis seltini (Olson, Schoch & Anderson, 2009), a large trematopid sug- 1956) and Trematops stonei (Olson, 1970). The type gested to be Acheloma (Bolt, 1974a; Schultze & specimen of Trematopsis was later found to be a Chorn, 1983; Sullivan et al., 2000), Seymouria (Sulli- junior synonym of Cacops (Milner, 1985b). Moreover, van & Reisz, 1999), and an unidentified eryopid, Olson was first to recognize the close affinities possibly Eryops (Olson, 1991). between trematopids and the diverse group of terres- Similar to the typical smaller taxa, the large forms trially adapted amphibians of the family Disso- recovered from Richards Spur appear to represent rophidae. Dissorophids span a greater temporal and taxa that were primarily terrestrial. As early geographical range than trematopids and are distin- amniotes, there is little doubt that the varanopid and guished from trematopids by the possession of sphenacodontid were well suited for life on land. armoured dermal plates associated with the neural Dissorophids and trematopids, collectively forming spines and the absence of an elongated external naris the clade Olsoniformes (Anderson et al., 2008), are (Olson, 1941; Carroll, 1964a; DeMar, 1966b; DeMar, considered the most terrestrial representatives of late 1968). Palaeozoic temnospondyl amphibians (Bolt, 1969; Subsequent authors also recognized the close rela- Berman, Reisz & Eberth, 1987; Sumida, Berman & tionship of trematopids and dissorophids (Vaughn, Martens, 1998; Dilkes & Brown, 2007; Markey & 1969; Berman, Reisz & Eberth, 1985, 1987; Dilkes, Marshall, 2007; Schoch, 2009). Likewise, authors 1990; Daly, 1994; Sumida et al., 1998; Anderson et al., agree that Seymouria was principally terrestrial, 2008). However, because ingroup relationships of both dependent on an aquatic habitat only during repro- families remained largely unresolved, several taxo- duction and very early growth stages (Sullivan & nomic problems arose when forms seemingly possess- Reisz, 1999; Berman, 2000; Klembara et al., 2007; ing a combination of trematopid and dissorophid Schoch, 2009). Although it may be argued that ery- characters were discovered and described. Mordex opids may have been aquatic or semi-aquatic, the calliprepes and Parioxys ferricolus were both origi- identification of the skull fragment as Eryops is nally described as trematopids (Romer, 1947). Mordex doubtful, and the fragment is not diagnostic. In fact, was later synonymized with Amphibamus (Carroll, we propose that it is more appropriate to designate 1964a) only to be resurrected as a dissorophid with a the skull fragment as Temnospondyli incertae sedis. trematopid-like elongated external naris (Milner, Described here is a new large trematopid skull 1986). Presently, Mordex is in the process of once (OMNH 73281) collected from Richards Spur in 2006. again being reclassified as a basal trematopid (Milner, Although trematopids were previously known from 2007). Parioxys is still considered closely related to Richards Spur on the basis of isolated, fragmentary dissorophids, but has been removed from Trematopi- elements, the newly recovered skull is nearly com- dae and placed within its own family, Parioxyidae plete, showing little distortion. This material repre- (Mustafa, 1955; Carroll, 1964b). sents the largest recorded taxon of the Richards Spur Longiscitula houghae (DeMar, 1966a) was origi- assemblage, rivalling the varanopid described by nally described as possessing both a trematopid-like Maddin et al. (2006) in size. Trematopids form a external naris and the distinctive dermal armour of monophyletic clade of poorly understood temno- dissorophids. Re-examination of the type specimen spondyl amphibians known from the Late Pennsylva- revealed the apparent elongated external naris was nian and Early Permian of North America and central an artefact of preservation (Bolt, 1974c). Milner Germany (Berman et al., 1987; Dilkes, 1990; Sumida (2003) eventually synonymized L. houghae with Dis- et al., 1998). The taxonomic history of Trematopidae sorophus multicinctus. The enigmatic Ecolsonia cut- is long and complex. Whereas the monophyly of the lerensis was described as sharing affinities with clade has remained largely unquestioned, the group dissorophids but was tentatively assigned to Trem- as a whole has yet to be subjected to rigorous phylo- atopidae by Vaughn (1969) based on its elongated genetic analysis. external naris and lack of exostoses and armour. Trematopidae as erected by Williston (1910) Berman et al. (1985) argued the skull proportions and included only two taxa known from Lower Permian structure of the otic notch of Ecolsonia were in fact type specimens: Acheloma cumminsi (Cope, 1882) and indicative of dissorophid affinities, and that its elon- Trematops milleri (Williston, 1909). Mehl (1926) gated external naris evolved convergently. Daly described an additional species of Trematops, Trem- (1994) incorporated Ecolsonia into her study of disso- © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 789–815 NEW LOWER PERMIAN TREMATOPID 791 rophoid relationships but was unable to resolve its premaxilla and maxilla obscured by matrix and a assignment (Sumida et al., 1998). Eaton (1973)
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