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| Pendraig milnerae Spiekman, Ezcurra, Butler, Fraser & Maidment, 2021 Life reconstruction by James Robbins. |
Abstract
We describe a new small-bodied coelophysoid theropod dinosaur, Pendraig milnerae gen. et sp. nov, from the Late Triassic fissure fill deposits of Pant-y-ffynnon in southern Wales. The species is represented by the holotype, consisting of an articulated pelvic girdle, sacrum and posterior dorsal vertebrae, and an associated left femur, and by two referred specimens, comprising an isolated dorsal vertebra and a partial left ischium. Our phylogenetic analysis recovers P. milnerae as a non-coelophysid coelophysoid theropod, representing the first-named unambiguous theropod from the Triassic of the UK. Recently, it has been suggested that Pant-y-ffynnon and other nearby Late Triassic to Early Jurassic fissure fill faunas might have been subjected to insular dwarfism. To test this hypothesis for P. milnerae, we performed an ancestral state reconstruction analysis of body size in early neotheropods. Although our results indicate that a reduced body size is autapomorphic for P. milnerae, some other coelophysoid taxa show a similar size reduction, and there is, therefore, ambiguous evidence to indicate that this species was subjected to dwarfism. Our analyses further indicate that, in contrast with averostran-line neotheropods, which increased in body size during the Triassic, coelophysoids underwent a small body size decrease early in their evolution.
Keywords: Coelophysoidea, Theropoda, body size evolution, Pendraig, osteology, Triassic
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| Figure 1. Holotype NHMUK PV R 37591 pelvis and vertebrae of Pendraig milnerae gen. et sp. nov. in (a) left lateral view and (b) right lateral view. atr, antitrochanter; bf, brevis fossa; bfr, brevis fossa rim; bs, brevis shelf; dv, dorsal vertebra; iss, ischial shaft; nc, neural canal; no, notch; obf, obturator foramen; poap, postacetabular process; prap, preacetabular process; puf, pubic fenestra; pus, pubic shaft; ras, rib attachment scar; ri, rim; sac, supra-acetabular crest; sv, sacral vertebra. |
Systematic palaeontology
Archosauria Cope, 1869–1870
Dinosauria Owen, 1842
Theropoda Marsh, 1881
Neotheropoda Bakker, 1986
Coelophysoidea Nopcsa, 1928
Pendraig milnerae gen. et sp. nov.
Etymology: Pendraig from the Welsh Pen (head, chief or top) and Draig (dragon), literally meaning ‘chief dragon’ but used in a figurative sense in Medieval Welsh to mean ‘chief warrior’. The anglicized form, Pendragon, was the epithet of Uther, father of King Arthur in medieval legend. Milnerae, in honour of Dr Angela C. Milner (1947–2021), in recognition of her major contributions to vertebrate palaeontology, including as one of the leading experts on British theropod dinosaur fossils, and to the Natural History Museum, London, where the type specimen is held.
Diagnosis. Pendraig milnerae is a small-sized non-averostran theropod (estimated femoral length: 10.21 cm; lower 95% CI: 8.60 cm; upper 95% CI: 12.08 cm; see below) that differs from other dinosaurs in the following unique combination of character states present in the holotype (autapomorphies indicated with an asterisk): posteriormost dorsal vertebrae with a strongly elongated centrum (centrum length ca 2.6 times its anterior height), ilium with a distinctly anteroventrally slanting dorsal margin of the preacetabular process, and posterodorsal margin of the postacetabular process curving abruptly posteroventrally and, as a result, the posteroventral end of the process is formed by an acute angle of approximately 65° in lateral view*; pubis with pubic fenestra; ischium with well-developed obturator plate but without posteroventral projection forming a deep U-shaped or V-shaped notch with the shaft; and femur with fourth trochanter posteriorly developed to a height similar to the mid-depth of the shaft at that level. In addition, the referred middle–posterior dorsal vertebra differs from other early neotheropods in the absence of an accessory hyposphene–hypantrum articulation, and the presence of an anteriorly expanded neural spine*.
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| Figure 9. Life reconstruction of Pendraig milnerae gen. et sp. nov. among the fissures of Pant-y-ffynnon and three individuals of the rhynchocephalian lepidosaur Clevosaurus cambrica during the Late Triassic. Artwork by James Robbins. |
Stephan N. F. Spiekman, Martín D. Ezcurra, Richard J. Butler, Nicholas C. Fraser and Susannah C. R. Maidment. 2021. Pendraig milnerae, A New Small-sized Coelophysoid Theropod from the Late Triassic of Wales. Royal Society Open Science. 8(10); DOI: 10.1098/rsos.210915
