 |
| Pararhincodon torquis Dearden, Johanson, O’Neill, Miles, Bernard, Clark, Underwood & Rücklin, 2025 Artwork by Julio Lacerda |
Abstract
A rich fossil record of teeth shows that many living shark families’ origins lie deep in the Mesozoic. Skeletal fossils of the sharks to whom these teeth belonged are far rarer and when they are preserved are often flattened, hindering understanding of the evolutionary radiation of living shark groups. Here we use computed tomography to describe two articulated Upper Cretaceous shark skeletons from the Chalk of the UK preserving three-dimensional neurocrania, visceral cartilages, pectoral skeletons and vertebrae. These fossils display skeletal anatomies characteristic of the Parascylliidae, a family of Orectolobiformes now endemic to Australia and the Indo Pacific. However, they differ in having a more heavily mineralized braincase and a tri-basal pectoral fin endoskeleton, while their teeth can be attributed to a new species of the problematic taxon Pararhincodon. Phylogenetic analysis of these new fossils confirms that Pararhincodon is a stem-group parascylliid, providing insight into the evolution of parascylliids’ distinctive anatomy during the late Mesozoic–Cenozoic shift in orectolobiform biodiversity from the Northern Atlantic to the Indo Pacific. Meanwhile both Pararhincodon and extant parascylliids have a distinctive vertebral morphology previously described only in Carcharhiniformes, contributing a skeletal perspective to the picture emerging from macroevolutionary analyses of coastal, small-bodied origins for galeomorphs.
Keywords: Elasmobranchii, Orectolobiformes, Galeomorphii, CT scanning, Cretaceous
Class. Chondrichthyes Huxley, 1880
Subclass. Elasmobranchii Bonaparte, 1838
Superorder. Galeomorphii Compagno, 1973
Order. Orectolobiformes Applegate, 1972
Family. Parascylliidae Gill, 1862
Genus: Pararhincodon Herman in Cappetta, 1976
Pararhincodon torquis n. sp.
Holotype specimen: NHMUK PV P 73821 a
Diagnosis of species: Very small, strongly asymmetrical teeth. Cusp triangular with sharp cutting edge, strongly bent lingually and distally. Lateral cusplet on distal edge of tooth, absent on mesial edge which is developed into slight shoulder. Base of cusp has a labial bulge and the medial section is developed into a low labial protuberance. Parallel folds present at the base of the cusp, some of which travel up the cusp’s face. Root flat and developed into mesial and distal lobes with deep, open nutrient groove.
Derivation of name: From torc, a metal collar associated with cultures from the European Iron Age.
Richard P. Dearden, Zerina Johanson, Helen L. O’Neill, Kieran Miles, Emma L. Bernard, Brett Clark, Charlie J. Underwood and Martin Rücklin. 2025. Three-dimensional Fossils of a Cretaceous Collared Carpet Shark (Parascylliidae, Orectolobiformes) shed light on Skeletal Evolution in galeomorphs. R. Soc. Open Sci. 12: 242011. DOI: doi.org/10.1098/rsos.242011 [30 April 2025]
