Data from: New heterodontosaurid remains from the Cañadón Asfalto Formation: cursoriality and the functional importance of the pes in small heterodontosaurids

New ornithischian remains reported here (MPEF-PV 3826) include two complete metatarsi with associated phalanges and caudal vertebrae, from the late Toarcian levels of the Cañadón Asfalto Formation. We conclude that these fossil remains represent a bipedal heterodontosaurid but lacks diagnostic characters to identify it at the species level, although they probably represent pedal remains of Manidens condorensis, known from the same locality. Histological features suggest a subadult ontogenetic stage for the individual. A cluster analysis based on pedal measurements identifies similarities of this specimen with heterodontosaurid taxa. The inclusion of the new material in a phylogenetic analysis with expanded character sampling on pedal remains confirms the described specimen as a heterodontosaurid. Finally, uncommon features of the digits (length proportions among non ungual phalanges of digit III, and claw features) are also quantitatively compared to several ornithischians, theropods, and birds, suggesting that this may represent a bipedal cursorial heterodontosaurid with gracile and grasping feet and long digits. In particular the elongated non-terminal pedal phalanges and morphology of digit III resemble features present in arboreal birds, a unique condition found so far among ornithischians.

本次报道的新鸟臀目（Ornithischian）化石标本（编号MPEF-PV 3826）包含两件完整的跖骨，以及与之关联的趾骨与尾椎，产自卡尼翁阿斯法托组（Cañadón Asfalto Formation）的托阿尔阶（Toarcian）晚期地层。研究认定，这批化石遗存属于双足型异齿龙类（Heterodontosaurid），但缺乏可供物种级鉴定的诊断特征，不过它们大概率与同一化石点产出的曼氏异齿龙（Manidens condorensis）的足部化石同属一类。组织学特征显示该个体处于亚成体的个体发育阶段。基于足部测量数据的聚类分析表明，该标本与异齿龙类类群存在相似性。将该新材料纳入针对足部化石特征采样范围得到扩展的系统发育分析后，进一步确认该标本属于异齿龙类。此外，研究还定量对比了该标本的趾部特有特征——第三趾非末端趾骨的长度比例与爪部形态——与多种鸟臀目、兽脚类及鸟类的对应特征，结果显示该类群可能是一种双足型适于奔跑的异齿龙类，拥有纤细且兼具抓握能力的足部与修长的趾骨。尤为特别的是，其非末端足部趾骨修长以及第三趾的形态，与树栖鸟类的特征高度相似，这在目前已知的鸟臀目类群中为独一无二的情况。