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A NEW GENUS of RHYNCHOSAUR from the MIDDLE TRIASSIC of SOUTH-WEST ENGLAND by DAVID W

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A NEW GENUS of RHYNCHOSAUR from the MIDDLE TRIASSIC of SOUTH-WEST ENGLAND by DAVID W [Palaeontology, Vol. 51, Part 1, 2008, pp. 95–115] A NEW GENUS OF RHYNCHOSAUR FROM THE MIDDLE TRIASSIC OF SOUTH-WEST ENGLAND by DAVID W. E. HONE* and MICHAEL J. BENTON* *Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK; e-mail: [email protected] Bayerische Staatssammlung fu¨r Pala¨ontologie und Geologie, Richard-Wagner-Straße 10, D-80333 Mu¨nchen, Germany; e-mail: [email protected] Typescript received 16 October 2006; accepted in revised form 15 January 2007 Abstract: We present a description of new cranial and odapedontinae, the clade of Late Triassic rhynchosaurs. The postcranial material representing a new genus of rhyncho- new cladistic analysis, for which many more characters were saur (Diapsida, Archosauromorpha) from the Otter Sand- coded for Fodonyx than before (a rise from 39 to 75 per stone Formation (Mid Triassic) of Devon, south-west cent), counter-intuitively produced less well-resolved results: England. The taxon had been named Rhynchosaurus spenceri the new codings of previously uncoded characters intro- Benton, 1990, but cladistic analysis of the clade, and one duced conflict so that Fodonyx turns out to be less like the autapomorphy, show that it does not belong to Rhyncho- Late Triassic rhynchosaur clade than had been assumed saurus, and a new generic name is required. We propose before. the name Fodonyx for this genus. A cladistic analysis of the Rhynchosauria confirms the main discoveries of previous Key words: Rhynchosaur, Triassic, Otter Sandstone Forma- analyses, and that Fodonyx is sister group to the Hyper- tion, Devon, Archosauromorpha. Rhynchosaurs were terrestrial, herbivorous basal the existing genus Rhynchosaurus Owen, 1842. The new archosauromorphs of the Early–Late Triassic. Large claws specific name was established since R. spenceri differed on the hind feet suggest the ability to dig well and the from all other then-known rhynchosaurs, but the heavy jaws and interlocking tooth-plates imply a diet of remains were too incomplete to determine whether it tough vegetation and tubers (Benton 1983). Rhynchosaurs belonged to a distinct genus or not. Indeed, R. spenceri enjoyed a near-global distribution, having been found in was excluded from the cladistic analysis by Benton Great Britain (Benton 1983, 1990), South Africa (Dilkes (1990) because so many parts of the skeleton were 1998), Zimbabwe (Raath et al. 1992), Tanzania, Madagas- unknown, and hence uncoded in the character matrix. car (Buffetaut 1983), India (Chatterjee 1974), Brazil (Lan- This approach was criticized by Wilkinson and Benton ger and Schultz 2000), Argentina, Canada and the United (1995): excluding a taxon from cladistic analysis simply States (Lucas et al., 2002; Nesbitt and Whatley 2004). because it is incompletely coded is inappropriate. On There are currently some 15 valid species of rhynchosaur, including R. spenceri in a repeat of Benton’s (1990) cla- recognised after recent revision and recognition of synon- distic analysis, they found that it fell between the other ymies, as well as a further five unnamed, or tentatively two species of Rhynchosaurus, R. articeps and R. brodiei, named, taxa based on incomplete remains from other on the one hand, and the Late Triassic clade on the locations (Benton 1983, 1990; Hunt and Lucas 1991; other. Langer and Schultz (2000) found the same thing, Langer and Schultz 2000). and indicated that R. spenceri was definitively not a Cladistic analyses of the phylogeny of rhynchosaurs member of the genus Rhynchosaurus. (Benton 1983, 1985, 1990; Evans 1988; Dilkes 1995, 1998; The aims of this paper are to present new material of Wilkinson and Benton 1995; Langer et al. 2000a; Langer the Devon rhynchosaur, concentrating in particular on a and Schultz 2000) have revealed a common pattern: two new partial skeleton and a new skull, and to place this in basal forms, Mesosuchus and Howesia from the Lower Tri- the context of a thorough phylogenetic analysis of rhyn- assic of South Africa, then a number of Mid Triassic chosaur relationships. Our conclusion is that the Devon forms, principally Rhynchosaurus and Stenaulorhynchus, rhynchosaur cannot remain a species of Rhynchosaurus and a crown clade of Late Triassic forms, species of Hyp- and has to be assigned to a new genus. erodapedon and Scaphonyx. The Devon rhynchosaur was named Rhynchosaurus Institutional abbreviations. BRSUG, Bristol University, Depart- spenceri by Benton (1990), a new species assigned to ment of Geology; EXEMS, Royal Albert Museum, Exeter. ª The Palaeontological Association doi: 10.1111/j.1475-4983.2007.00739.x 95 96 PALAEONTOLOGY, VOLUME 51 SYSTEMATIC PALAEONTOLOGY fossils, correlate with late Anisian and latest Anisian magnetoz- ones on the marine standard. Subclass DIAPSIDA Osborn, 1903 Infraclass ARCHOSAUROMORPHA Huene, 1946 Revised diagnosis. Fodonyx has a single apomorphy that Order RHYNCHOSAURIA Osborn, 1903 distinguishes it from other rhynchosaurs: the paraoccipital Family RHYNCHOSAURIDAE Huxley, 1859 processes, when seen in posterior view, angle ventrally. In all other rhynchosaurs, these processes are either horizontal Genus FODONYX gen. nov. or are raised dorsally. The cladistic analysis also confirms that Fodonyx is distinct from any other known rhyncho- Fodonyx spenceri (Benton, 1990) saur. Fodonyx differs from Rhynchosaurus (as represented Text-figures 1–7 by R. articeps and R. brodiei) in having the orbits orientated more dorsally than laterally, a major diagonal crest on the [Full synonymy list to 1990 in Benton 1990] jugal that reaches the anterior portion of the orbit, and 1993 Rhynchosaurus spenceri Benton, 1990; Benton et al., ornamentation on the external surface of the jugal with pp. 167–170. crests and bosses dorsal to this diagonal crest, in having the 1994 Rhynchosaurus spenceri Benton, 1990; Benton et al., frontal longitudinal groove almost the same depth through- pp. 145–146. out, a basipterygoid process that is broader than long, and 1995 Rhynchosaurus spenceri Benton, 1990; Wilkinson and chevron bones that taper distally. Fodonyx lacks the charac- Benton, pp. 141–147. ters of the Late Triassic Hyperodapedontinae (see below). 1997 Rhynchosaurus spenceri Benton, 1990; Benton, pp. 145–147. 2000 ‘Rhynchosaurus’ spenceri Benton, 1990; Langer and Schultz, pp. 647–648. MORPHOLOGY OF THE SKULL 2000 ‘Rhynchosaurus’ spenceri Benton, 1990; Langer et al., pp. 120, 123–127. Introduction Derivation of name. The new generic name Fodonyx is modelled A new rhynchosaur skull was found in spring 1999 by on the name Scaphonyx, given to the Brazilian rhynchosaur by Mark Hounslow at Pennington Point, about 20 m east of Woodward (1907), and meaning ‘spade claw’: Latin, fodere,to the River Sid outfall (National Grid reference SY 130873). dig, and Greek, onyx, claw, hence meaning ‘digging claw’, in It was in situ (many fossils have come previously from reference to the large unguals present on the foot. fallen blocks) at the base of the cliff, and found at a time when much of the beach gravel had been swept away. Holotype. EXEMS 60 ⁄ 1985.292, a partial skull and mandible, Stratigraphically, the skull was found about 3 m below including the floor of the orbit and the palate of the right side, the top of Andy Newell’s Unit C, the Pennington Point a partial palate of the left side, the posterior right-hand angle of Member of Gallois, and layer 21 of Hounslow and McIn- the skull, and both mandibles (Benton 1990, figs 28–29, 31, 36i– j, 37f–g). tosh (2003). According to the magnetostratigraphy of these authors, the age of this horizon is within the late Referred material. Material listed by Benton (1990, pp. 221– Illyrian (latest Anisian), equivalent to the lower part of 222) as well as EXEMS 79 ⁄ 1992 (a partial postcranial skele- the Tethyian P. trammeri (conodont) Zone. ton; Benton et al. 1993), BRSUG 27200 (a nearly complete This skull (BRSUG 27200) was prepared by Remmert skull), EXEMS 60 ⁄ 1985.20 (isolated right jugal); EXEMS Schouten in the Bristol Palaeontology Laboratories in 60 ⁄ 1985.48 and BRSUG 26874 (two isolated parietals); BRSUG 2004 and 2005. The sandstone was removed from the 26875 (partial dorsal vertebra); EXEMS 60 ⁄ 1985.324 (partial dorsal and right-hand sides and the whole of the palate toe with ungual). was exposed. The orbital and temporal regions on the right-hand side were prepared deep into the specimen. Locality and horizon. Various sites along the South Devon coast Sandstone was left in parts of the left-hand side in order from Ladram Bay to Port Royal, Sidmouth (maps and map ref- to keep the specimen stable. erences in Benton 1990, 1997; Benton et al. 1993, 1994), all in The skull is typically rhynchosaurian, triangular in the upper half of the Otter Sandstone Formation (Sherwood Sandstone Group). The unit is dated as Anisian on the basis of shape in dorsal view, with large subcircular temporal faunal comparisons and matching with palynologically dated fenestrae and orbits, a large midline naris, hooked ‘tusk’- units in the English Midlands (Benton et al. 1994). This has like premaxillae, and broad maxillary tooth plates. The since been confirmed by magnetostratigraphy (Hounslow and skull was probably rather lower than assumed by Benton McIntosh 2003), who found that the lower parts of the Otter (1990), whose reconstruction was based on materials that Sandstone Formation correspond to the early and mid Anisian, lacked the skull roof. It is nearly complete and has the and the upper parts, which contain the majority of the macro- HONE AND BENTON: NEW GENUS OF MID TRIASSIC RHYNCHOSAUR FROM ENGLAND 97 lower jaws in place (Text-figs 1–2). The posterior ventral The prefrontal is large and borders the anterodorsal margin of corners of the skull, including both quadrates, the qua- the orbit, forming a thick, angular ‘eyebrow ridge’. Medially, the dratojugals and parts of the jugals are missing. The skull prefrontal is bounded by the nasals and frontals, but it does not roof has been depressed slightly, causing movement meet the postfrontal.
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