Trophic niche ontogeny and palaeoecology of early <scp>T</scp>oarcian <i><scp>S</scp>tenopterygius</i> (<scp>R</scp>eptilia: <scp>I</scp>chthyosauria)

Dick, Daniel G.; Schweigert, Günter; Maxwell, Erin E.

doi:10.1111/pala.12232

Cited by 29 publications

(40 citation statements)

References 21 publications

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“…• Maiaspondylus lindoei Maxwell & Caldwell, 2006: material is only known for this taxon from juveniles (Maxwell & Caldwell 2003. Ontogenetic changes in morphology are known to occur in ichthyosaurs, and may affect the coding (McGowan 1973;Motani & You 1998;Dick et al 2016), although potentially only to a limited degree in the few identifiable in utero remains of Cretaceous ichthyosaurs (Kear & Zammit 2014). Here M. lindoei is conservatively excluded due to its juvenile nature and incompleteness.…”

Section: Resultsmentioning

confidence: 99%

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: Resultsmentioning

confidence: 99%

A new phylogeny of ichthyosaurs (Reptilia: Diapsida)

Moon

2017

Journal of Systematic Palaeontology

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“…Hooklets have been reported in specimens of Ichthyosaurus (Pollard 1968;Lomax 2010) and although most were initially thought to have been from belemnites they also belong to phragmoteuthids (Valente et al 2010;Lomax and Massare 2015). The presence of cephalopod hooklets in the stomach contents of the studied specimen differs from what was found by Dick et al (2016) for small juvenile specimens of Stenopterygius. They found that small juveniles had only fish scales in their stomach contents, whereas large adults had only cephalopod hooklets, therefore showing a size-related trophic niche shift through ontogeny.…”

Section: Stomach Contentsmentioning

confidence: 63%

The first known neonateIchthyosaurus communisskeleton: a rediscovered specimen from the Lower Jurassic, UK

et al. 2017

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Numerous specimens of Ichthyosaurus are known, but only very few small examples (total body length of < 1 m) have been assigned beyond Ichthyosaurus sp. Here, we report on a very small specimen (preflexural length of 560 mm) that can be unequivocally assigned to Ichthyosaurus communis due to possessing a unique combination of diagnostic skull and postcranial characters that are found in larger examples of the species. Furthermore, the specimen is identified as a neonate because of the small size, large sclerotic ring relative to the orbital region, and poorly ossified (highly cancellous) bones of the skull and postcranium. It is not an embryo as it is not preserved within an adult specimen and stomach contents are clearly evident. This is therefore the first neonate Ichthyosaurus communis skeleton to be described. The specimen, in the Lapworth Museum of Geology, University of Birmingham, has no provenance data associated with it. A microfossil analysis of the matrix in which the ichthyosaur skeleton is preserved strongly suggests a stratigraphic range of uppermost Hettangian to lowermost Sinemurian age (Lower Jurassic), but does not provide any geographical information.

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“…The taxonomic value of tooth morphology (size and shape) of Early Jurassic ichthyosaurs has been questioned. Recent contributions have shown that size and shape of teeth change during ontogeny, at least in Stenopterygius (Dick and Maxwell, 2015;Dick et al, 2016). In the case of Ichthyosaurus communis and I. intermedius, historically differentiated on the basis of tooth morphology, Massare and Lomax (2017) recognized different morphologies, although they pointed out that tooth features were not reliable to distinguish these two species.…”

Section: Systematic Palaeontologymentioning

confidence: 99%