First evidence of centralia in Ichthyopterygia reiterating bias from paedomorphic characters on marine reptile phylogenetic reconstruction

Jiang²,

Chen

et al. 2014

Nature

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107

146

The incompleteness of the fossil record obscures the origin of many of the more derived clades of vertebrates. One such group is the Ichthyopterygia, a clade of obligatory marine reptiles that appeared in the Early Triassic epoch, without any known intermediates. Here we describe a basal ichthyosauriform from the upper Lower Triassic (about 248 million years ago) of China, whose primitive skeleton indicates possible amphibious habits. It is smaller than ichthyopterygians and had unusually large flippers that probably allowed limited terrestrial locomotion. It also retained characteristics of terrestrial diapsid reptiles, including a short snout and body trunk. Unlike more-derived ichthyosauriforms, it was probably a suction feeder. The new species supports the sister-group relationships between ichthyosauriforms and Hupehsuchia, the two forming the Ichthyosauromorpha. Basal ichthyosauromorphs are known exclusively from south China, suggesting that the clade originated in the region, which formed a warm and humid tropical archipelago in the Early Triassic. The oldest unequivocal record of a sauropterygian is also from the same stratigraphic unit of the region.

Section: Research Lettermentioning

confidence: 87%

Section: Research Lettermentioning

confidence: 99%

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A basal ichthyosauriform with a short snout from the Lower Triassic of China

Jiang²,

Chen

et al. 2014

Nature

Self Cite

107

146

“…( b ) Carpus length relative to body size. The carpus length is measured as the distance between the radius and the second metacarpal, whereas length of the second caudal vertebra is used as the proxy for body size, following a previous work 41 . ( c ) Maximum diameter of the upper temporal fenestra (UTF) relative to a body size proxy.…”

Section: Figurementioning

confidence: 99%

A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction

Jiang

Huang

et al. 2016

Sci Rep

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Contrary to the fast radiation of most metazoans after the end-Permian mass extinction, it is believed that early marine reptiles evolved slowly during the same time interval. However, emerging discoveries of Early Triassic marine reptiles are questioning this traditional view. Here we present an aberrant basal ichthyosauriform with a hitherto unknown body design that suggests a fast radiation of early marine reptiles. The new species is larger than coeval marine reptiles and has an extremely small head and a long tail without a fluke. Its heavily-built body bears flattened and overlapping gastral elements reminiscent of hupehsuchians. A phylogenetic analysis places the new species at the base of ichthyosauriforms, as the sister taxon of Cartorhynchus with which it shares a short snout with rostrally extended nasals. It now appears that ichthyosauriforms evolved rapidly within the first one million years of their evolution, in the Spathian (Early Triassic), and their true diversity has yet to be fully uncovered. Early ichthyosauromorphs quickly became extinct near the Early-Middle Triassic boundary, during the last large environmental perturbation after the end-Permian extinction involving redox fluctuations, sea level changes and volcanism. Marine reptile faunas shifted from ichthyosauromorph-dominated to sauropterygian-dominated composition after the perturbation.

“…Most of the newly prepared skeletons resemble Chaohusaurus chaoxianensis in that their mesopodia are poorly ossified and elongated 12 compared to those of the type species C . geishanensis 13 .…”

Section: Introductionmentioning

confidence: 99%

Separating sexual dimorphism from other morphological variation in a specimen complex of fossil marine reptiles (Reptilia, Ichthyosauriformes, Chaohusaurus)

Huang

Jiang

et al. 2018

Sci Rep

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The Early Triassic Chaohu Fauna from Anhui Province, China, contains the oldest record of Mesozoic marine reptiles, such as Cartorhynchus and Sclerocormus. Most specimens from the fauna belong to the ichthyosauriform Chaohusaurus, more specifically resembling C. chaoxianensis. However, a wide range of morphological variation exists within about 40 skeletons that have been prepared, likely reflecting mixed signals from both sexual and taxonomic differences. We test whether the sexual and taxonomic signals are separable based on quantification, aided by the knowledge of sexual dimorphism in extant marine tetrapods. There are two different suites of dimorphism that divide the specimens differently from each other yet consistently within each suite, resulting in four morphotypes in combination, likely representing two sexes of two taxa. Presumed males have larger ‘organ of prehension’ sensu Darwin, specifically limbs in the present case, for a given body length. This sexing criterion is supported by the only specimen of a gravid female, which belongs to the morphotype with short limbs. Males also have larger skulls for the trunk length compared to females. This study demonstrates that sexual and taxonomic signals are separable in fossil reptiles, with a sufficient sample size and careful analyses.