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| Xiphodracon goldencapensis Lomax, Massare & Maxwell, 2025 Artwork by Bob Nicholls |
Abstract
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.
Keywords: Ichthyosauria, Pliensbachian, Leptonectidae, Lower Jurassic, faunal turnover, Xiphodracon
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| The holotype and only known specimen of the hauffiopterygian leptonectid, Xiphodracon goldencapensis (ROM VP52596) from Golden Cap, between Charmouth and Seatown, Dorset, UK. The skeleton is exposed in ventrolateral view. The skull has been fully prepared free of matrix whereas most of the skeleton is still in matrix. The left (upper) forefin has been prepared so that it is three-dimensionally preserved and projects upwards. Scale bar represents 20 cm. Skull of Xiphodracon goldencapensis (ROM VP52596). Photograph (A) and interpretative illustration (B) in left lateral view. C, photograph of the right lateral view. Note the unusual, multi-prong projections on the anterodorsal margin of the lacrimal and similar but smaller interdigitating structures on the prefrontal (see also Fig. 4). Abbreviations: an, angular; den, dentary; ju, jugal; la, lacrimal; mx, maxilla; n, nasal; p, parietal; pmx, premaxilla; po, postorbital; prf, prefrontal; ptf, postfrontal; qj, quadratojugal; sp, splenial; st, supratemporal. Scale bar represents 10 cm. |
SYSTEMATIC PALAEONTOLOGY
ICHTHYOSAURIA de Blainville 1835
PARVIPELVIA Motani 1999a
LEPTONECTIDAE Maisch 1998
HAUFFIOPTERYGIA nov.
Diagnosis: Mid-sized ichthyosaurs <3.5 m in length, characterized by a lack of contact between the nasal and postfrontal; participation of the prefrontal in the external narial opening; forefin with four digits; proximal limb elements polygonal; bicapitate dorsal ribs; lateral gastral elements extending at least two-thirds of the length of the dorsal region; and a rod-like ischium and pubis.
Genus Xiphodracon nov.
Derivation of name: Sword-like dragon. Xipho- derived from ancient Greek xiphos meaning ‘sword or sword shaped’ in reference to the long, narrow and sword-like snout, and -dracon, ancient Greek (drakōn) and Latin (dracō) for ‘dragon’, in reference to ichthyosaurs having been informally and colloquially referred to as ‘sea dragons’ for over 200 years.
Xiphodracon goldencapensis sp. nov.
Derivation of name: Sword-like dragon from Golden Cap. The species epithet goldencapensis refers to the location of discovery at Golden Cap, Dorset, England, UK.
Holotype: ROM VP52596, an almost complete skeleton comprising a three-dimensionally preserved skull, mandible and teeth, pectoral girdle, both forefins, pelvic girdle, parts of both hindfins, and most of the axial skeleton. A cast of ROM VP52596 is in the collections of the State Museum of Natural History Stuttgart, catalogued as SMNS 97790.
Type locality & horizon: East of Golden Cap, between Charmouth and Seatown, Dorset, UK, from the Early Jurassic, early Pliensbachian. Lias Group, Lower Lias Subgroup, Charmouth Mudstone Formation, Green Ammonite Member, Bed 122c (c. 1.5–2 m above Bed 121); Davoei Zone, Maculatum Subzone.
Diagnosis: A mid-sized, c. 3 m hauffiopterygian leptonectid with the following autapomorphies: anterodorsal border of triradiate lacrimal rugosely striated with prominent prong-like projections on its anterior edge; prefrontal anterior process with projecting structures that interdigitate with similar structures on nasal and dorsal lacrimal; posterodorsal foramen connected to the external naris; posterodorsal foramen formed by the nasal, prefrontal and lacrimal; small flange on the nasal and lacrimal forming a constriction that connects the foramen to the narial opening; anterodorsal part of the maxilla ‘split’ by the subnarial process of the premaxilla, creating dorsal and ventral processes; maxilla comprising almost entire ventral margin of naris, which is unique among Early Jurassic ichthyosaurs.
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Artwork by Bob Nicholls |
Dean R. Lomax, Judy A. Massare and Erin E. Maxwell. 2025. A New long and narrow-snouted ichthyosaur illuminates a complex faunal turnover during an undersampled Early Jurassic (Pliensbachian) interval. Papers in Palaeontology. DOI: doi.org/10.1002/spp2.70038 [09 October 2025]
