Diphydontosaurus undetermined

Whiteside, David I. & Duffin, Christopher J., 2017, Late Triassic terrestrial microvertebrates from Charles Moore’s ‘ Microlestes’ quarry, Holwell, Somerset, UK, Zoological Journal of the Linnean Society 179 (3), pp. 677-705 : 691-693

DIPHYDONTOSAURUS SP. INDET

Remarks: There are other specimens probably referable to Diphydontosaurus sp. , the most likely of which is the jugal BATGM DW5a ( Fig. 6A, B). It has an unadorned lateral side and resembles that of D. avonis , being the same size and with a large central foramen in similar position to the specimens from Tytherington fissure 2 ( Whiteside, 1986: fig. 15a, b).

RHYNCHOCEPHALIA GEN. ET SP. INDET

Remarks: The basioccipital specimen BATGM C35 ( Fig. 6C, D) is about 40% larger than the paratype of D. avonis ( Whiteside, 1986: fig. 26), and is slightly smaller than in Gephyrosaurus . The Holwell specimen has the dorsal midline ridge that is typically found in those genera (and in other rhynchocephalians), but it is more pronounced. Other features such as the basal tubera ( Fig. 6C) are similar. The specimen is broken at the posterior lateral edges in dorsal view, and it is likely that the basioccipital was fused to the exoccipital, as found in larger specimens of Diphydontosaurus ,

A C D G J K L B E F H I M N O P Q R S T U V W X Y Z AA BB CC

© 2017 The Linnean Society of London, Zoological Journal of the Linnean Society, 2017, 179, 677–705 Planocephalosaurus , and Gephyrosauru s, compared with the separate elements of adult Clevosaurus ( Fraser, 1988) . The basioccipital is therefore from an indeterminate rhynchocephalian.

The vertebra BATGM C35 ( Fig. 6E – I), a dorsal, was illustrated by Owen (1860), who was unsure of its affinities and tentatively indicated that it may be saurian. The vertebra is amphicoelous and notochordal, with a morphology indistinguishable from that of Diphydontosaurus in the Tytherington collection at BRSUG; however, the Holwell specimen is double the size of the dorsal vertebra of D. avonis , but is similar in size and morphology to that of G. bridensis illustrated by Evans (1981: fig. 6). The affinities of this dorsal vertebra are likely to be within the Gephyrosauridae . There are specimens of a scapula (BATGM 42a; Fig. 6J – L), interclavicle (BATGM C42b; Fig. 6M, N), chevron (BATGM 42c; Fig. 6O, P), and an ungual phalanx (BATGM DW5a; Fig. 6Q, R) that all have a morphology and size that indicates an affinity with the larger species in the Gephyrosauridae , most likely with Gephyrosaurus . Judging from the angle of the articulation surfaces, the ornamented articular complex BATGM C42e ( Fig. 6S, T) is a right bone, with a pronounced condyle in two parts separated by a prominent ridge for articulation with the quadrate. The nature of this condyle suggests that the animal had an orthal shear bite similar to that found in Clevosaurus .

Two other jugals, BATGM 42d and BATGM DWc, are possibly from the same unidentified taxon ( Fig. 6U – Z). These bones have an ornamented lateral surface that is reminiscent of Gephyrosaurus . Cranial bones include an unidentified bone that possibly formed part of the paraoccipital process: e.g. an opisthotic (BATGM 42j; Fig. 6 AA).

INFRACLASS LEPIDOSAUROMORPHA BENTON, 1983 GEN. ET SP. INDET

Remarks: An ectopterygoid, labelled BATGM 42g ( Fig. 6 BB, CC) is also recorded, but the pterygoid process and facets of this bone are too complex to be considered as a known rhynchocephalian. This specimen is difficult to assign to a particular family, and we consider it to be an indeterminate Lepidosauromorpha.

INFRACLASS ARCHOSAUROMORPHA VON HUENE, 1946 FAMILY TRILOPHOSAURIDAE GREGORY, 1945 GENUS VARIODENS ROBINSON, 1957 B

Type species by monotypy: Variodens inopinatus Robinson, 1957b , from a fissure filling in Emborough quarry, Somerset, UK.

Holotype: NHMUK PV R36850 .