A Re‐evaluation of Small Tetrapods from the Middle Triassic Otter Sandstone Formation of Devon, England

Abstract

ABSTRACT. Material of small sauropsids from the Otter Sandstone Formation of east Devon (Sherwood Sandstone Group; Middle Triassic; Anisian) includes remains that were formerly attributed to a primitive procolophonid. In the light of new specimens, this material is instead found to contain remains of a diapsid and a procolophonine procolophonid. Among these fossils, the medium-sized procolophonine, Kapes bentoni sp. nov., is the ®rst record of this Russian genus in the British Triassic. Coartaredens isaaci gen. et sp. nov. is a small diapsid tentatively assigned to Lepidosauromorpha. The heterodont lower dentition of Coartaredens comprises a row of large, conical posterior teeth and tightly packed, procumbent incisiforms. Two additional specimens are distinguished on the basis of distinctive dentary remains. One of these is of possible procolophonid af®nity, while the dentition of the second resembles that of the aberrant Early Triassic parareptilian genus Sclerosaurus.KEY WORDS: Procolophonia, Procolophonidae, Parareptilia, Lepidosauromorpha, Anisian, Otter Sandstone.H U X L E Y (1869) was the ®rst to report the occurrence of vertebrates in the Triassic of Devon, with the discovery of a rhynchosaur dentary [BGS (GSM) 90494]. Whitaker (1869) recorded that this specimen was collected from a`brecciated horizon' in the lower part of the Otter Sandstone Formation, exposed in the cliff on the east bank of the mouth of the River Otter. At High Peak, a coastal locality about 2 km west of Sidmouth (National Grid Reference SY 104858), Whitaker (1869) distinguished`red sandstone' overlain by`red marl' of the New Red Sandstone, which in turn is overlain by Cretaceous Upper Greensand. From this section, additional ®nds of fossil tetrapods were made during the 1870s and 1880s. Seeley (1876) described a jaw and other bones of the temnospondyl Mastodonsaurus lavisi, and a possible Hyperodapedon ( Rhynchosaurus) tooth plate, while Metcalfe (1884) ®gured remains of Rhynchosaurus, Mastodonsaurus jaws, and other elements. Further remains, including ®sh scales and coprolites, were reported by Carter (1888). Ussher (1876), Metcalfe (1884), Irving (1888Irving ( , 1892Irving ( , 1893, Hull (1892) and Woodward and Ussher (1911) also discussed the stratigraphy and dating of the coastal section near Sidmouth, with particular attention to vertebrate material.After a long collecting hiatus, a large collection of vertebrate material was made by one of us (PSS) during the years 1982±1985, principally from the north-eastern region of the exposure from Ladram Bay towards Sidmouth (Spencer and Isaac 1983), but also from various localities from Danger Point, near the mouth of the River Otter, eastwards to Port Royal, at the mouth of the River Sid. Spencer and Isaac (1983), Benton (1990), Milner et al. (1990, Benton et al. (1993Benton et al. ( , 1994, and Benton and Gower (1997) described much of this new tetrapod and ®sh material, greatly enlarging the faunal list.Procolophonids were initially reported from the Otter Sandstone by Spencer and Isa...

The Middle Triassic procolophonid Kapes bentoni: computed tomography of the skull and skeleton

“…Otter Sandstone succession (left, adapted from Gallois ) and geological sketch map of the coast around Sidmouth, Devon (right), showing distribution of recorded procolophonid fossils: A, EXEMS 60/1985.87, Procolophonidae incertae sedis , partial dentary; EXEMS 60/1985.9, Kapes bentoni , doubtfully referred interclavicle (Spencer & Storrs ). B, BRSUG 29950‐13, K. bentoni , skull and partial postcranium (this paper).…”

“…Anisian (including perhaps late Olenekian) procolophonids include Theledectes , Thelephon , Thelerpeton and Teratophon from the Burgersdorp Formation of South Africa, Eumetabolodon bathycephalus and Pentaedrusaurus from the upper Heshanggou Formation of northern China, Neoprocolophon from the middle or upper Ermaying Formation, northern China, and Sclerosaurus from the upper Buntsandstein of Switzerland. Most interesting biogeographically is the genus Kapes , known from several species from the Yarenskian (Olenekian) and Donguz (Anisian) gorizonts of Russia (Ivakhnenko , ; Novikov ; Spencer & Benton ; Novikov & Sues ), and the Anisian Otter Sandstone (= Helsby Sandstone Formation) of Devon, UK (Spencer & Storrs ). Of these Russian taxa, and after some nomenclatural confusion and proliferation (reviewed, Spencer & Benton ; Spencer & Storrs ), the most secure and complete material belongs to Kapes majmesculae (Ochev ) from the Donguz Svita of the south Urals, of which there is an excellent skull housed in the Paleontological Institute, Moscow, PIN 4365/40, and described by Novikov & Sues ().…”

“…Most interesting biogeographically is the genus Kapes , known from several species from the Yarenskian (Olenekian) and Donguz (Anisian) gorizonts of Russia (Ivakhnenko , ; Novikov ; Spencer & Benton ; Novikov & Sues ), and the Anisian Otter Sandstone (= Helsby Sandstone Formation) of Devon, UK (Spencer & Storrs ). Of these Russian taxa, and after some nomenclatural confusion and proliferation (reviewed, Spencer & Benton ; Spencer & Storrs ), the most secure and complete material belongs to Kapes majmesculae (Ochev ) from the Donguz Svita of the south Urals, of which there is an excellent skull housed in the Paleontological Institute, Moscow, PIN 4365/40, and described by Novikov & Sues ().…”

“…The identification of the genus Kapes in the UK by Spencer & Storrs () provided an important geographical link between the terrestrial red beds of Russia and those of western Europe, at a time when the intervening Germanic basin was flooded by the Muschelkalk Sea, and from which such terrestrial fauna is largely unknown.…”

“…These authors noted the difficulties of discriminating procolophonids from some enigmatic diapsids such as Anisodontosaurus when only jaw fragments were available. Spencer & Storrs () further discriminated Otter Sandstone procolophonids from other clades and presented some of their earlier jaw material as well as the holotype of a new species, Kapes bentoni , a partial snout, comprising the maxillae and partial premaxillae, palate and mandibles. This was an important discovery that has been widely accepted, but it was too incomplete to be coded for the seminal cladistic analysis of procolophonid phylogeny by Cisneros ().…”