A new specimen of Palvennia hoybergeti: implications for cranial and pectoral girdle anatomy in ophthalmosaurid ichthyosaurs.

Lene Liebe Delsett,Jørn Harald Hurum,Patrick Scott Druckenmiller,Aubrey Jane Roberts

doi:10.7717/peerj.5776

Lene Liebe Delsett, Jørn Harald Hurum + Show 2 more

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https://doi.org/10.7717/peerj.5776

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Abstract

The Late Jurassic Slottsmøya Member Lagerstätte on Spitsbergen preserves a diverse array of marine reptiles, including four named taxa of ophthalmosaurid ichthyosaurs. One of these, Palvennia hoybergeti, is based on the single holotype specimen (SVB 1451) with an incomplete skull. A newly discovered specimen (PMO 222.669) with a disarticulated but largely complete skull and anterior postcranium is described, which considerably expands our knowledge of this taxon. Two additional new ophthalmosaurid specimens with pectoral girdles from the same member are described. The taxonomic utility of the ophthalmosaurid pectoral girdle is contentious, and an assessment of seven pectoral girdles from the Slottsmøya Member provides a basis for addressing this question via a 2D landmark principal component analysis of baracromian coracoids. The analysis reveals a taxonomic signal in the coracoids but also highlights the degree of individual variation. Commonly used phylogenetic characters do not fully encapsulate the degree of variation seen in coracoids and in some cases combine analogous features.

Highlights

Ichthyopterygia was one of the major secondarily aquatic vertebrate clades that existed during the Mesozoic
Taxonomic referral of the new material PMO 222.669 is referred to P. hoybergeti, an ophthalmosaurid previously described from the Slottsmøya Member Lagerstätte (SML) (Druckenmiller et al, 2012)
Given that the preservation of this element is far better in PMO 222.669, these differences are ascribed to taphonomic artefacts or it could result from individual variation (Maisch, 1997) and the mention of these traits have been removed from the diagnosis

Summary

Introduction

Ichthyopterygia was one of the major secondarily aquatic vertebrate clades that existed during the Mesozoic. Fossils are found from the Early Triassic (Olenekian) to the early Late Cretaceous (Cenomanian). The Late Jurassic was an interval with great species richness of thunnosaurian ichthyosaurs that evolved an elongated skull with an enormous eye and forefins larger than hindfins (Bardet, 1992; Motani, 2005; Fischer et al, 2016). 1 and 2), is well known for its abundance of marine reptile remains (ichthyosaurs and plesiosaurians) from the latest Jurassic and the earliest Cretaceous (Hurum et al, 2012; Delsett et al, 2016). Four new monospecific ophthalmosaurid genera and three undetermined species of ophthalmosaurids have recently been described. How to cite this article Delsett et al (2018), A new specimen of Palvennia hoybergeti: implications for cranial and pectoral girdle anatomy in ophthalmosaurid ichthyosaurs.

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