A new long and narrow‐snouted ichthyosaur illuminates a complex faunal turnover during an undersampled Early Jurassic (Pliensbachian) interval

Ichthyosaurian faunas before and after the Pliensbachian stage of the Early Jurassic are known from numerous, often complete fossils. The two faunas are very different taxonomically, with only one of the pre‐Pliensbachian genera, but none of the species, persisting into the post‐Pliensbachian (Toarcian). Pliensbachian ichthyosaurs are rare, yet this interval represents a critical and poorly understood time in ichthyosaurian evolution just c. 10 myr after the end‐Triassic mass extinction. Thus, a new ichthyosaur from the mid‐Pliensbachian of the Dorset coast of the UK, the most complete ichthyosaur known from that stage, is significant. Xiphodracon goldencapensis gen. et sp. nov. is characterized by a distinct combination of characters and several autapomorphies, including: a unique lacrimal with prong‐like projections on its anterior edge, a prefrontal with projections that interdigitate with the nasal and lacrimal, a wedge‐shaped external naris with an anterodorsal constriction that forms a distinct foramen (shaped by the nasal, lacrimal and prefrontal), and a maxilla that forms almost the entire border of the external naris. Phylogenetic analyses indicate that X. goldencapensis is more closely related to the late Pliensbachian to Toarcian genus Hauffiopteryx than to earlier genera that continued into the Pliensbachian (e.g. Leptonectes, Ichthyosaurus), and forms a distinct clade (Hauffiopterygia nov.) within a monophyletic Leptonectidae. This indicates that a substantial faunal turnover in diversity occurred towards the end of the early Pliensbachian, leading to a major shift in composition towards a more typical Toarcian ichthyosaur fauna.