A basal thunnosaurian from Iraq reveals disparate phylogenetic origins for Cretaceous ichthyosaurs

Fischer, Valentin; Naish, Darren; Liston, Jeff; Appleby, Robert M; Riding, James B.; Brindley, Stephen; Godefroit, Pascal

doi:10.31233/osf.io/wnam4

Cited by 7 publications

(23 citation statements)

References 14 publications

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“…2A; Nicholls & Manabe 2001;Fröbisch et al 2006;Sander et al 2011), Mixosauridae (Fig. 2B;Jiang et al 2005;Jiang et al 2006;Chen & Cheng 2010), and Parvipelvia and Thunnosauria (Figs 2C-E;Fernández 2007;Druckenmiller & Maxwell 2010;Fischer et al 2012;Fischer et al 2013). The analysis by Fröbisch et al (2013) was the first to Bayesian inference rather than parsimony (Fig.…”

Section: Introductionmentioning

confidence: 98%

A new phylogeny of ichthyosaurs (Reptilia: Diapsida)

Moon

2017

Journal of Systematic Palaeontology

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The largest phylogenetic analysis of ichthyosaurs to date is presented, with 114 ingroup taxa coded at species level. Completeness of the taxa included varied from >98% to <2%; ten taxa were removed a priori using Concatabominations, due to incompleteness and taxonomic uncertainty. The data were analysed using three widely used optimisation criteria: maximum parsimony, maximum likelihood, and Bayesian inference; while similar, each criterion produced different topologies, support, and levels of resolution. Maximum parsimony found a well-resolved consensus tree with minor improvement from a posteriori pruning of unstable taxa; however, general support remains low. Tree resolution was reduced more by taxa that lacked codings from phylogenetically important regions of the tree, rather than by those that simply lacked many codings. Resolution present in the most likely tree is poorly supported; sister relationships cannot be confirmed, although similarities are found to the most parsimonious tree. Bayesian inference found poorly resolved consensus trees. While more resolved, an equal-distribution rate prior is significantly worse than the null gammadistribution rate prior for morphological data, but suggests rate heterogeneity across ichthyosaur phylogeny. Tree comparisons under each analytical criterion failed to select a single best tree, however, the Bayesian inference tree with gamma-distribution rate prior is selected as the best tree based on recent analyses showing improved accuracy using this criterion. Unequivocally resolved clades include Ichthyopterygia, Ichthyosauria, Shastasauria, Euichthyosauria, Parvipelvia, and Neoichthyosauria, but with variation in their taxonomic components. Mixosauridae and Ophthalmosauridae are similarly recovered, but their definitions are modified to stem-based definitions to prevent substantial variation of included taxa. Several genera are not monophyletic: Brachypterygius,

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Section: Introductionmentioning

confidence: 98%

A new phylogeny of ichthyosaurs (Reptilia: Diapsida)

Moon

2017

Journal of Systematic Palaeontology

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“…) and, among marine reptiles, ichthyosaurs survived the transition relatively unscathed (Fischer et al . , ). Marine and semi‐aquatic crocodylomorphs, on the other hand, demonstrate high rates of extinction and turnover during this transition (Mannion et al .…”

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confidence: 99%

Increased pliosaurid dental disparity across the Jurassic–Cretaceous transition

et al. 2018

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Pliosaurid marine reptiles played important roles in marine food chains from the Middle Jurassic to the middle Cretaceous, frequently as apex predators. The evolution of pliosaurids during the later parts of the Early Cretaceous has recently been illuminated by discoveries from Russia (Hauterivian) and Colombia (Barremian). However, knowledge of pliosaurids representing the Jurassic–Cretaceous transition (late Tithonian – Valanginian), is still largely incomplete, especially during the earliest Cretaceous. As such, the effect on pliosaurids of hypothesized faunal turnover during the Jurassic–Cretaceous boundary interval is poorly understood. We report pliosaurid teeth from the upper Volgian (Tithonian, Upper Jurassic) of the Kheta river basin (Eastern Siberia, Russia), to the Berriasian and Valanginian (Lower Cretaceous) of the Volga region (European Russia). These assemblages have yielded a series of distinct tooth morphotypes, including the first reports of conical‐toothed pliosaurids from the latest Jurassic and earliest Cretaceous. This challenges the hypothesis that only one lineage of pliosaurids crossed the Jurassic–Cretaceous boundary. It appears that conical‐toothed pliosaurids co‐existed with their trihedral‐toothed relatives for at least 25 million years during the latest Jurassic and earliest Cretaceous. In fact, our quantitative analyses indicate that pliosaurids reached their maximal dental disparity during this interval, showing little evidence of turnover associated with the Jurassic–Cretaceous transition. Instead, disparity decreased later in the Early Cretaceous, with the disappearance of trihedral‐toothed forms in the Barremian.

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“…The latter is a sister taxon to Ichthyosaurus (Fischer et al . ), but only forefin and scapula characters could be coded on our matrix (17% of the characters). Macgowania , although Late Triassic in age, had originally been assigned to the genus Ichthyosaurus (McGowan ).…”

Section: Resultsmentioning

confidence: 99%

“…() and Fischer et al . (). In addition, 17 characters were added in this study to include other differences in morphology among species of Ichthyosaurus , bringing the total to 58: 23 cranial and 35 postcranial characters (Lomax & Massare , appendix).…”

Section: Phylogenetic Analysismentioning

confidence: 97%

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Two new species of Ichthyosaurus from the lowermost Jurassic (Hettangian) of Somerset, England

Lomax

Massare

2016

Papers in Palaeontology

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All specimens of Ichthyosaurus from the Lower Jurassic of Somerset were previously identified as I. communis, an abundant and extremely variable species. Here, two new species of Ichthyosaurus are recognized from multiple specimens. The species are assigned to Ichthyosaurus on the basis of the humerus, pectoral girdle and forefin morphologies. I. larkini sp. nov. is distinguished by a broad jugal with a blunt anterior end that extends as far forward as the middle of the external naris, separating the maxilla and lacrimal; and a unique combination of other features. I. somersetensis sp. nov. is distinguished by a jugal with a nearly straight dorsal ramus that lacks a right-angle dorsal bend; a high, narrow, crescentic postorbital that forms almost all of the posterior margin of the orbit and separates the jugal dorsal ramus from the orbit; and an ilium that is wide relative to its length, more oblong than rib-like. The identifications are supported by a phylogenetic analysis which finds the new species more closely related to each other than to other species of the genus. We also identify a squamosal in both species, which confirms that it is present in the genus. This study suggests that hindfin morphology has some taxonomic utility, at least within the genus. The new species increases the diversity of Ichthyosaurus to six species, three of which are found in the Hettangian of Somerset.

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A basal thunnosaurian from Iraq reveals disparate phylogenetic origins for Cretaceous ichthyosaurs

Cited by 7 publications

References 14 publications

A new phylogeny of ichthyosaurs (Reptilia: Diapsida)

A new phylogeny of ichthyosaurs (Reptilia: Diapsida)

Increased pliosaurid dental disparity across the Jurassic–Cretaceous transition

Two new species of Ichthyosaurus from the lowermost Jurassic (Hettangian) of Somerset, England

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