R script and supporting information files for performing the regression analysis from Pendraig milnerae, a new small-sized coelophysoid theropod from the Late Triassic of Wales

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.

我们记述了产自威尔士南部潘特-菲农（Pant-y-ffynnon）晚三叠世裂隙充填沉积物中的一种小型腔骨龙超科（coelophysoid）兽脚类（theropod）恐龙新属新种*Pendraig milnerae* gen. et sp. nov.。该物种的正模标本包含一具铰接保存的腰带骨、荐椎及后部背椎，以及一块关联的左侧股骨；另有两件归入标本，分别为一块孤立的背椎与部分左侧坐骨。我们的系统发育分析显示，*P. milnerae*属于非腔骨龙科的腔骨龙超科兽脚类，是英国三叠纪地层中首个被正式命名的确定兽脚类恐龙。近期有研究提出，潘特-菲农及附近其他晚三叠世至早侏罗世裂隙充填动物群可能经历了岛屿矮化（insular dwarfism）。为验证该假说是否适用于*P. milnerae*，我们对早期新兽脚类（neotheropods）的体型开展了祖先状态重建分析。尽管研究结果表明体型缩小是*P. milnerae*的特有衍征，但其他部分腔骨龙超科类群也出现了类似的体型缩减，因此尚无确凿证据表明该物种经历了矮化作用。我们的分析还显示，与三叠纪时期体型逐渐增大的阿韦龙兽类支系（averostran-line）新兽脚类不同，腔骨龙超科在演化早期经历了体型小型化的过程。