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

A large new Middle Jurassic ichthyosaur shows the importance of body size evolution in the origin of the Ophthalmosauria

The Middle Jurassic is an important time period for the evolutionary history of marine reptiles as it represented a transitional phase for many clades. Notably, in ichthyosaurs, many early parvipelvian taxa went extinct. The Middle Jurassic saw the emergence of the derived Ophthalmosauria, ultimately becoming the dominant ichthyosaurian clade by the end of the epoch. Even though this is an important period in the evolutionary history of Ophthalmosauria, our understanding remains limited in terms of morphology and taxonomy due to the scarcity of vertebrate-bearing strata. Here we present a large new ichthyosaur from the Bajocian of Switzerland, represented by an almost complete skull with 3D-preserved bones, the (inter)clavicles and a large portion of the postcranial skeleton. After CT- and surface scanning, we reconstructed the 3D in vivo morphology. Our morphological observations and phylogenetic analyses show that the new taxon named Argovisaurus martafernandezi is nested at the base of the Ophthalmosauria. The holotype and only known specimen of Argovisaurus likely represents an adult individual. Bajocian members of the Ophthalmosauria (Mollesaurus and Argovisaurus) were large-bodied animals, a trait typically associated with the more derived Platypterygiinae. This hints at the importance of a large body size early in ophthalmosaurian evolution.LSID: urn:lsid:zoobank.org:act:C3312628-1544-4B87-BBE3-B12346A30BE3LSID: urn:lsid:zoobank.org:act:23C2BD71-8CF0-4D99-848A-0D631518415B.

The soft tissue and skeletal anatomy of two Late Jurassic ichthyosaur specimens from the Solnhofen archipelago

Ichthyosaurs from the Solnhofen Lagerstätte are among the only examples of soft tissue preservation in the major Middle Jurassic-middle Cretaceous family Ophthalmosauridae. However, few such specimens are currently described, and the taphonomical pathways for the preservation of soft tissue are not well understood. In order to answer this, two new ichthyosaur specimens, one nearly complete and one isolated tail, are described here. The nearly complete specimen is assigned to Aegirosaurus sp. It is accompanied by large amounts of incrustation pseudomorphs (epimorphs) of soft tissue preserved as apatite. It also preserves a nearly complete gastral basket, for the first time in ophthalmosaurids. Soft tissue samples were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) analysis. The analyses confirm the presence of apatite, with phosphate most likely derived from the body itself.

Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution

The Late Jurassic ichthyosaur Nannopterygius is among the poorest known, with the only skeleton, NHMUK PV 46497, on display in the Natural History Museum, London and, therefore, difficult to access. This holotype specimen is here reassessed. The newly obtained data have enabled the identification of several additional specimens of Nannopterygius in museum collections across the UK. Furthermore, all the material of Russian ichthyosaurs previously referred to genera Paraophthalmosaurus and Yasykovia, and considered as junior synonyms of Ophthalmosaurus in the majority of subsequent works, are also reassessed. Both these genera are synonymized with Nannopterygius with preservation of the two from six originally erected species: Nannopterygius saveljeviensis comb. nov. and Nannopterygius yasykovi comb. nov. Additionally, a new species from the Berriasian of Arctic (Svalbard and Franz Josef Land) is proposed. To resolve the phylogenetic relations within Ophthalmosauria, a revised dataset, including 44 taxa and 134 characters, 20 of which are new, was compiled. The results of a phylogenetic analysis places Nannopterygius spp. as sister to Arthropterygius spp. within Ophthalmosaurinae. Thus, the lineage of Nannopterygius was among several ophthalmosaurine lineages that crossed the Jurassic–Cretaceous boundary and, similarly to Arthropterygius, survived the Jurassic–Cretaceous transition at high latitudes.

A new ichthyosaur from the Late Jurassic of north-west Patagonia (Argentina) and its significance for the evolution of the narial complex of the ophthalmosaurids

Ophthalmosaurids were highly derived and the youngest clade of ichthyosaurs. Their evolutionary history comprises ~76 Myr (from the early Middle Jurassic to the final extinction of the group at the Cenomanian–Turonian boundary). Fossil records indicate that soon after they emerged they achieved a widespread geographical distribution. Analyses of disparity based on craniodental morphologies, and the co-occurrence of different bone histology and microstructure among the members of the group, indicate that ophthalmosaurids are not only taxonomically but also ecologically diverse. A region of the skull that is particularly complex among ophthalmosaurid taxa is the external nares and surrounding areas, but there have been few attempts to explore this topic. We describe a new ophthalmosaurid from the Late Jurassic of Patagonia (Argentina) in the genus Arthropterygius and analyse its phylogenetic relationships. A detailed exploration of the skull, using computed tomography, reveals the division of the external nares by means of a stout bony pillar. This condition was previously known only in some Cretaceous forms and, within a phylogenetic framework, its distribution among ophthalmosaurids indicates that this morphology was the result of convergent evolution. Based on available data on extant (and some extinct) forms, we explore putative soft structures involved in the narial region. We propose that the division of the external nares (complete or partly osseous) was related functionally to the separation of the air passage from the outlet of nasal salt glands in such a way that the salt glands could be evacuated underwater, while the air passage could be closed by a valvular system.

A prevalence of Arthropterygius (Ichthyosauria: Ophthalmosauridae) in the Late Jurassic-earliest Cretaceous of the Boreal Realm

The ichthyosaur genus Arthropterygius Maxwell, 2010 is considered as rare and poorly known. However, considering the existing uncertainty regarding its position in respect to ophthalmosaurid subfamilies in recent phylogenies, it is among the key taxa for understanding the evolution of derived Late Jurassic and Early Cretaceous ichthyosaurs. Recently excavated unique material from the Berriassian of Franz Josef Land (Russian Extreme North) and examination of historical collections in Russian museums provided numerous specimens referable to Arthropterygius. The new data combined with personal examination of ichthyosaurs Palvennia, Janusaurus, and Keilhauia from Svalbard give us reason to refer all these taxa to Arthropterygius. Therefore, we recognize four species within the genus: Arthropterigius chrisorum (Russell, 1994), A. volgensis (Kasansky, 1903) comb. nov., A. hoybergeti (Druckenmiller et al., 2012) comb. nov., and A. lundi (Roberts et al., 2014) comb. nov. Three of the species are found both in the Arctic and in the European Russia. This allows the suggestion that Arthropterygius was common and widespread in the Boreal Realm during the Late Jurassic and earliest Cretaceous. The results of our multivariate analysis of ophthalmosaurid humeral morphology indicate that at least some ophthalmosaurid genera and species, including Arthropterygius, could be easily recognized based solely on humeral morphology. Our phylogenetic analyses place the clade of Arthropterygius close to the base of Ophthalmosauria as a sister group either to ophthalmosaurines or to platypterygiines. Although its position is still uncertain, this is the best supported clade of ophthalmosaurids (Bremer support value of 5, Bootstrap and Jackknife values exceeding 80) that further augments our taxonomic decision.