Topic
Janusaurus
About: Janusaurus is a research topic. Over the lifetime, 2 publications have been published within this topic receiving 63 citations.
Papers
TL;DR: The paleobiogeographical implications of this result suggest the presence of a single clade of Boreal ophthalmosaurid ichthyosaurs that existed during the latest Jurassic, a pattern also reflected in the high degree of endemicity among some Boreal invertebrates, particularly ammonoids.
Abstract: Abundant new ichthyosaur material has recently been documented in the Slottsmoya Member of the Agardhfjellet Formation from the Svalbard archipelago of Norway. Here we describe a partial skeleton of a new taxon, Janusaurus lundi, that includes much of the skull and representative portions of the postcranium. The new taxon is diagnosed by a suite of cranial character states including a very gracile stapedial shaft, the presence of a dorsal process on the prearticular and autapomorphic postcranial features such as the presence of an interclavicular trough and a conspicuous anterodorsal process of the ilium. The peculiar morphology of the ilia indicates a previously unrecognized degree of morphological variation in the pelvic girdle of ophthalmosaurids. We also present a large species level phylogenetic analysis of ophthalmosaurids including new and undescribed ichthyosaur material from the Upper Jurassic of Svalbard. Our results recover all Svalbard taxa in a single unresolved polytomy nested within Ophthalmosaurinae, which considerably increases the taxonomic composition of this clade. The paleobiogeographical implications of this result suggest the presence of a single clade of Boreal ophthalmosaurid ichthyosaurs that existed during the latest Jurassic, a pattern also reflected in the high degree of endemicity among some Boreal invertebrates, particularly ammonoids. Recent and ongoing descriptions of marine reptiles from the Slottsmoya Member Lagerstatte provide important new data to test hypotheses of marine amniote faunal turnover at the Jurassic-Cretaceous boundary.
TL;DR: The phylogenetic analyses place the clade of Arthropterygius close to the base of Ophthalmosauria as a sister group either to ophthalmosurines or to platypterygiines, and indicate that at least some ophthalMosaurid genera and species, including Arthropologygius, could be easily recognized based solely on humeral morphology.
Abstract: 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.
Performance Metrics
| Year | Papers |
|---|---|
| 2019 | 1 |
| 2014 | 1 |