PELAGOSAURUS TYPUS BRONN, 1841 (MESOEUCROCODYLIA: THALATTOSUCHIA) FROM THE UPPER LIAS (TOARCIAN, LOWER JURASSIC) OF SOMERSET, ENGLAND STEPHANIE E. PIERCE and MICHAEL J. BENTON Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol, BS8 1RJ, United Kingdom, S.Pierce@bristol.ac.uk, Mike.Benton@bristol.ac.uk ABSTRACT—The thalattosuchian crocodyliform Pelagosaurus typus Bronn, 1841 is fully documented and described from the Upper Lias (Toarcian, Lower Jurassic) of England. The material under study is part of a historical collection made by Charles Moore (1814–1881) at Strawberry Bank (Ilminster, Somerset, England) around 1848. Apomomorphic features of the genus include: sculpturing on almost the entire skull and mandible with extensive sculpturing on the prefrontal, lachrymal, frontal, parietal, temporal arcade and the posterior extent of the mandible; 30 piercing teeth on each side of the upper and lower jaws; small, shallow, egg-shaped antorbital fenestra present within the lachrymal and maxilla; supratemporal fenestrae short anteroposteriorly; paired frontal; anterior margin of internal choana tapers ante- riorly between the paired palatines; and presence of a choanal septum on the palatine and pterygoid. Pelagosaurus was a small, exceedingly long-snouted, gracile crocodyliform whose diet probably consisted of small fishes, crustaceans and possibly insects. The small-bodied fish Leptolepis is confirmed as part of its diet as a specimen is found in the rib cage of a small juvenile Pelagosaurus. Laterally placed eyes suggest that this species actively pursued its prey rather than sitting and waiting at the water surface. The phylogenetic position of Pelagosaurus has been debated. Pelagosaurus possesses the majority of teleosaurid apomorphies, including: four premaxillary teeth; small prefrontal; lachrymal visible in dorsal aspect; presence of mandibular fenestrae; dermal armor; and a straight tail; however, these are all plesiomorphic for the Crocodyliformes in general. There also appear to be problems when defining the proposed metriorhynchid features of Pelagosaurus (i.e., broad nasal, large frontal, lateral orbit, sclerotic ring and arrangement of prefrontal-lachrymal). Moreover, characters that have been used in past cladistic analyses are either incorrect or too simplistic. Accordingly, Pelagosaurus is considered to belong to the Thalattosuchia incertae sedis until a more thorough phylogenetic investigation is conducted. INTRODUCTION One of the most intriguing groups to evolve during the Meso- zoic was the Thalattosuchia, longirostrine marine crocodyli- forms. The two thalattosuchian families, the Teleosauridae and Metriorhynchidae, appear in abundance in the Lower Jurassic of Western Europe (Carroll, 1988). These crocodiles diversified and dispersed throughout the Jurassic with specimens recorded from Russia (Hua et al., 1998), South America (Gasparini and Dellapé, 1976; Gasparini and Díaz, 1977; Vignaud and Gaspa- rini, 1995, Gasparini et al., 2000, 2005), North Africa (Fara et al., 2002), Mexico (Frey et al., 2002), and Cuba (Gasparini and Itur- ralde-Vinent, 2001). The teleosaurs were large nearshore ani- mals characterised by extreme elongation of the snout, extensive dermal armor, and a ‘generalised’ postcranial skeleton. Con- versely, the metriorhynchids were smaller offshore animals that became highly adapted to an aquatic lifestyle with loss of dermal armor, paddle-like limbs, and a caudal tail fin. Thalattosuchians form an important part of an exceptional assemblage of marine reptiles that have been recovered from the Upper Lias (Toarcian; Lower Jurassic) of England and Western Europe (Benton and Taylor, 1984; Walkden et al., 1987). Nota- bly common in the marine fauna of Germany and France is the monotypic genus Pelagosaurus Bronn, 1841 (Westphal, 1961, 1962). This animal was originally described by Eudes- Deslongchamps (1863; 1877) based on incomplete cranial and postcranial remains from Normandy, France. Since these initial investigations, few authors have examined the anatomy of Pela- gosaurus in any detail (Duffin, 1979b). Most studies have focused on a select number of morphological characters (e.g., position of orbits) in order to resolve the phylogenetic affinity of Pelago- saurus within the Thalattosuchia; however, little consensus has been achieved (e.g., Westphal, 1962; Buffetaut, 1982; Clark, 1994). Thus, an up-to-date description of Pelagosaurus seems warranted and will provide a valuable source of information to- wards unravelling thalattosuchian systematics. Although common in Western Europe, Pelagosaurus has gone almost unnoticed in the English Toarcian. Duffin (1979a, b) was the first to highlight a collection of beautifully preserved speci- mens from the Ilminster succession of the Upper Lias (Fig. 1) discovered by Charles Moore around 1848 (cf. Moore, 1852). Twenty-four specimens referable to Pelagosaurus typus are pres- ent in the Moore Collection (Bath Royal Literary and Scientific Institute, BRLSI) making it the most significant collection of Pelagosaurus material in England and indeed in Western Eu- rope. Remarkably, this material has never been properly de- scribed or figured. Moore’s (1852) first reference to the Pelagosaurus material was in a comprehensive paper about the paleontology of the Middle and Upper Lias. He drew attention to three particularly well-preserved individuals (one of which is a “baby Saurian”) and assigned them to the genus Teleosaurus. In subsequent papers, Moore placed the Ilminster specimens in the species Teleosaurus temporalis (Moore, 1866, 1870). The true taxonomic identity, however, was not realized until Eudes-Deslongchamps (in a lost manuscript) described the juvenile and proposed the name Pelagosaurus moorei (Wilson, 1893; Duffin, 1979a,b). Fol- lowing this account, the crocodyliforms of the Ilminster succes- sion were referred to two species of Pelagosaurus, P. moorei, and P. typus (Moore, 1879; Wilson, 1893; Woodward, 1893; Arkell, 1933); however, no further detailed examination of the material was ever undertaken. Duffin (1978), in an account of the vertebrate faunas collected by Charles Moore, remarks that recent reviews of fossil croco- dyliforms failed to mention the existence of these spectacular Pelagosaurus specimens (Westphal, 1961, 1962; Steel, 1973). Duffin (1979a) undertook a historical review of the material col- lected by Moore, providing a detailed literature survey. Further- more, in a companion paper, Duffin (1979b) presented a descrip- tion of the juvenile’s skull and reassigned the material to Pela- gosaurus typus. In the same article, Duffin (1979b:477) states, “the complete collection will be dealt with thoroughly in a later paper....” This, however, was never realized. Journal of Vertebrate Paleontology 26(3):621–635, September 2006 © 2006 by the Society of Vertebrate Paleontology 621