A Review of Neusibatrachus Wilferti, an Early Cretaceous Frog from the Montsec Range, Northeastern Spain

A review of Neusibatrachus wilferti, an Early Cretaceous frog from the Montsec Range, northeastern Spain ANA M. BÁEZ and BORJA SANCHIZ Báez, A.M. and Sanchiz, B. 2007. A review of Neusibatrachus wilferti, an Early Cretaceous frog from the Montsec Range, northeastern Spain. Acta Palaeontologica Polonica 52 (3): 477–487. Neusibatrachus wilferti is an anuran from the late Berriasian–early Valanginian fossiliferous lacustrine limestones that are exposed in the eastern part of the Montsec Range, province of Lleida, Spain. It was originally described by Seiffert in 1972 and its phylogenetic position has since been discussed. Neusibatrachus has been considered an undeterminable fos− sil, an abnormal individual, or a primitive palaeobatrachid. Here we redescribe the only available specimen, and clarify features, such as absence of palatines, nine presacrals, and procoelous vertebral centra, that have been the subject of previ− ous debates. We consider the specimen to be a postmetamorphic individual and make developmental interpretations of some of its characters. In particular, we provide evidence of a living anuran (Rana iberica) that resembles Neusibatrachus in the development of intervertebral articulations. Neusibatrachus is considered a valid genus, which differs from other anurans, except for the pipoids, in the joint presence of an azygous frontoparietal and a parasphenoid lacking the subotic alae, although it differs from the pipoids in having nine presacral vertebrae. Morphological evidence indicates that Neusi− batrachus is related to Xenoanura, the pipoid branch in the living Amphibia Tree of Life based on molecular data. More− over, it might be a member of the pipoid clade proper, which presently includes the Pipidae, Rhinophrynidae, and several fossil taxa, including the Palaeobatrachidae, although the evidence is not conclusive. Key words: Amphibia, Anura, Pipoidea, Palaeobatrachidae, Neusibatrachus, Cretaceous, Montsec, Spain. Ana M. Báez [[email protected]], CONICET, Department of Geology, Facultad de Ciencias Exactas, Universidad de Buenos Aires, Ciudad Universitaria, 1428 Buenos Aires, Argentina; Borja Sanchiz [[email protected]], Museo Nacional de Ciencias Naturales, CSIC. J. Gutiérrez Abascal 2, E−28006, Madrid, Spain. Introduction servat−Lagerstätten) have yielded numerous, exceptionally well preserved remains of plants, invertebrates and verte− Recent analyses based on morphological (Báez and Harrison brates, collected since the beginning of last century (Barale et 2005; Trueb and Báez 2006), developmental (Haas 2003), al. 1984; Martínez−Delclòs 1991; Andreu et al. 1996). The and molecular (Roelants and Bossuyt 2005; Frost et al. 2006) frog bearing bed is part of the La Pedrera de Rúbies Litho− evidence have substantiated the monophyly of the anuran graphic Limestones, which consist of laminated carbonates group composed of the crown taxa Pipidae Gray, 1825 and representing open lacustrine conditions (Lacasa and Martí− Rhinophrynidae Günther, 1859 “1858”, for which the node− nez 1986; Gibert et al. 2000). These deposits are part of the based Pipoidea was applied by Ford and Cannatella (1993). sedimentary filling of a complex basin that developed be− This name is possibly a junior synonym of Xenoanura as pro− tween the European and Iberian plates in relation to the open− posed by Savage (1973) to include Pipidae, Rhinophrynidae, ing of the Bay of Biscay (Souquet 1988). The age of the and Palaeobatrachidae Cope, 1865, the latter undergoing ex− fossil−bearing beds was previously determined to be late tinction in the Pleistocene. A number of fossil taxa, including Berriasian to early Valanginian, according to the evidence the palaeobatrachids, appear as stem−rhinophrynids and provided by ostracods (Peybernes and Oertli 1972; Brenner stem−pipids, although their taxonomic placements are still et al. 1974; Whalley and Jarzembowski 1985) and pollen unstable (Gao and Chen 2004; Báez et al. in press). (Barale et al. 1984). Seiffert (1972) erected the anuran genus and species Seiffert (1972) considered Neusibatrachus to be a repre− Neusibatrachus wilferti on the basis of a single specimen sentative of a stock ancestral to both palaeobatrachids, an preserved on two slabs as part and counterpart and acid pre− extinct group of “archaeobatrachians”, and neobatrachian pared (Fig. 1). The specimen was discovered in a quarry (La ranids. He noted the resemblance of Neusibatrachus to pala− Pedrera de Meià, or La Pedrera de Rúbies, or La Pedrera fos− eobatrachids with both having an azygous frontoparietal, sil site) at the well−known fossil locality of Santa Maria de parasphenoid lacking subotic alae, and long metacarpals. Meià, in the lithographic limestones that crop out in the east− However, he also mentioned that Neusibatrachus has dentate ern part of the Serra del Montsec, province of Lleida, north− vomers and femora and tibiofibulae of similar length, traits eastern Spain. These lacustrine conservation deposits (Kon− that he considered present in ranids but not in palaeobatra− Acta Palaeontol. Pol. 52 (3): 477–487, 2007 http://app.pan.pl/acta52/app52−477.pdf 478 ACTA PALAEONTOLOGICA POLONICA 52 (3), 2007 chids. Subsequently, Estes and Reig (1973) commented that having 9 presacral vertebrae. It differs from Rhadinosteous the putative ranid features of Neusibatrachus also occur in and rhinophrynids in having the atlas formed by fusion of many other anuran groups. These authors considered Neusi− Vertebrae I and II, and metacarpals exceeding 75% the batrachus an undoubted palaeobatrachid, although more pri− length of the radioulna. It differs from all known pipimorphs mitive than the Tertiary representatives in the absence of a in the presence of a complete maxillary arch and can be fur− synsacrum and processus rostriformis on the coracoid, and ther distinguished from crown pipids in the presence of a the presence of a complete maxillary arch and free ribs T−shaped squamosal, pedicellate teeth, a parahyoid bone, on some presacral vertebrae. Špinar (1975) also advocated and a bicondylar articulation between sacrum and urostyle. It a close relationship between Neusibatrachus wilferti and also differs from Thoraciliacus and Cordicephalus in its nar− palaeobatrachids, suggesting that this species was in the di− rower braincase, a frontoparietal forming a flat dorsal table, rect ancestry of the group. Despite all these arguments, and tiny scapular cleft and it can be distinguished from Sanchiz (in Sanchiz and Roček 1996, 1998) considered Neu− palaeobatrachids in having a T−shaped squamosal lacking sibatrachus as a junior synonym of Eodiscoglossus san− processes on the ventral ramus, an articulation for the lower tonjae Villalta, 1956, a putative discoglossid taxon described jaw at the midlevel of the otic capsules, a monovertebral sa− from the same deposits (Hecht 1970; Vergnaud−Grazzini and crum, slightly expanded sacral diapophyses, and a coracoid Wenz 1975), although no reasons were given other than lacking a conspicuous rostral process and having a slightly judging it an abnormally developed specimen. More re− expanded sternal end. cently, a parsimony analysis of several extinct anuran taxa by Neusibatrachus wilferti Seiffert, 1972 Gao and Chen (2004) has shown Neusibatrachus nested within the pipoid clade. In their analysis, character states for Holotype: FUB 33A, B. Neusibatrachus were scored according to Seiffert’s (1972) Type locality and age: Santa Maria de Meià, province of Lleida, Spain; description and from comments on its features made by late Berriasian–early Valanginian. Vergnaud−Grazzini and Wenz (1975) and Roček (2000). However, our personal examination of the holotype of Neu− sibatrachus wilferti housed in the Freie Universität, Berlin, Description revealed that some features were misinterpreted by earlier authors. In addition, this specimen presents a very peculiar The only known specimen of Neusibatrachus wilferti (Fig. set of anatomical features and is not referable to Eodisco− 1) is about 21 mm in snout−vent length. Because the speci− glossus or to any other known anuran taxon. Herein, we men is irregularly split into two parts (FUB 33A, B), im− redescribe and analyze several anatomical and developmen− pressions and/or fragments of individual elements are pre− tal aspects of Neusibatrachus, and consider its relationships served on both slabs and, thus, descriptions of most bones to living and extinct anurans in the context of recent phylo− are composite. genetic hypotheses. The pipoid affinities of Neusibatrachus were corroborated in a phylogenetic analysis in which the Cranial skeleton characters for this taxon were recored according to the new observations (Báez et al. in press). The skull is wider than it is long. The preorbital region is no− Institutional abbreviations.—FUB, Freie Universität, Berlin, tably short; its anteroposterior length is slightly less than Germany; KU, Natural History Museum, The University of one−fifth the total length of the skull (Fig. 2). Kansas, Lawrence, Kansas, USA; MNHU, Museum für The nasals are poorly preserved although their impres− Naturkunde der Humboldt−Universität, Berlin, Germany; sions indicate that they were delicate, relatively narrow MNCN, Museo Nacional de Ciencias Naturales, Madrid, winglike bones that incompletely roofed the nasal capsules Spain; PMHU, Paläontologisches Museum, Humboldt−Uni− (Fig. 2). These bones were adjacent but not in contact along versität, Berlin, Germany. the skull midline. The anterior margins of the nasals are slightly concave,

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