R script and supporting information files for performing the ancestral state reconstruction analyses 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.

本研究记述了产自威尔士南部潘特-芬农（Pant-y-ffynnon）晚三叠世裂隙充填沉积中的一种新型小型腔骨龙超科（coelophysoid）兽脚类（theropod）恐龙，将其确立为新属新种彭德拉伊格·米尔纳（Pendraig milnerae gen. et sp. nov.）。该物种的化石材料包括一件正模标本，由关节连接的腰带、荐椎、后部背椎以及关联的左股骨组成；另有两件归入标本，分别为一枚孤立背椎与部分左坐骨。我们的系统发育分析结果显示，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明确兽脚类恐龙。近期有研究指出，潘特-芬农及周边晚三叠世至早侏罗世的裂隙充填沉积动物群可能曾发生岛屿矮化（insular dwarfism）现象。为验证该假说是否适用于P. milnerae，我们针对早期新兽脚类（neotheropods）的体型开展了祖先性状重建分析。尽管分析结果表明体型缩小是P. milnerae的独有衍征（autapomorphic），但其他部分腔骨龙超科类群也呈现出类似的体型缩减趋势，因此目前尚无明确证据支持该物种曾经历矮化作用。本研究进一步分析显示，与三叠纪时期体型逐渐增大的阿韦龙斯坦支系（averostran-line）新兽脚类不同，腔骨龙超科在演化早期便经历了体型小型化的过程。