The anatomy of the palate in Early Triassic <i>Chaohusaurus brevifemoralis</i> (Reptilia: Ichthyosauriformes) based on digital reconstruction

Yin, Ya-Lei; Ji, Cheng; Zhou, Min

doi:10.7717/peerj.11727

Cited by 8 publications

(5 citation statements)

References 49 publications

(111 reference statements)

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“…An ossified epipterygoid is often observed in basal ichthyosaurians, such as Chaohusaurus brevifemoralis and Besanosaurus leptorhynchus , as well as in Ichthyosaurus communis 37 , 42 , 45 , 46 . As it is often obscured in slab mounted specimens, it is difficult to discern how variable the ossification of the epipterygoid is in Stenopterygius .…”

Section: Resultsmentioning

confidence: 99%

Ontogenetic variation in the skull of Stenopterygius quadriscissus with an emphasis on prenatal development

Miedema

Maxwell

2022

Sci Rep

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The availability of a large sample size from a range of ontogenetic stages makes Stenopterygius quadriscissus a good model to study ontogenetic variation in a fossil sauropsid. We qualitatively examined pre- and postnatal ontogenetic changes in the cranium of S. quadriscissus. The prenatal ossification sequence is similar to other diapsids, exhibiting delayed chondrocranial ossification compared to the dermatocranium. In the dermatocranium, the circumorbital area is more ossified earlier in development relative to other elements, especially those of the skull roof where ossification is comparatively weaker across prenatal stages. Perinatally all cranial elements are ossified, and many scarf and step joints are already closed. We propose four prenatal and three postnatal stages in S. quadriscissus on the basis of relative ossification, size and qualitative cranial characters pertaining to the jugal, parietal, frontal, pterygoid and surangular. These will provide a basis for determining ontogenetic stages in other ichthyosaurs. Moreover, our postnatal observations aid in refining ontogenetic characters for phylogenetic studies. Lastly, we observed that the antimeric sutures of the midline of the skull roof are open perinatally and that fusion of the midline only appears in the adult stage. We hypothesize that the loose connection of the midline functions as a fontanelle, limiting potential damage during birth.

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Section: Resultsmentioning

confidence: 99%

Ontogenetic variation in the skull of Stenopterygius quadriscissus with an emphasis on prenatal development

Miedema

Maxwell

2022

Sci Rep

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“…No ossified epipterygoid was found across the sample. Ossified epipterygoids are found sporadically in other non-ophthalmosaurid ichthyosaurs (Bindellini et al, 2021 ; McGowan, 1973 ; Miedema & Maxwell, 2022 ; Yin et al, 2021 ), but the element is difficult to observe especially in articulated 2D-prepared specimens. It is therefore possible an ossified epipterygoid was also present in Mixosaurus cornalianus .…”

Section: Resultsmentioning

confidence: 99%

Ontogenetic variation in the cranium of Mixosaurus cornalianus, with implications for the evolution of ichthyosaurian cranial development

Miedema,

Bindellini,

Dal Sasso

et al. 2023

Swiss J Palaeontol

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Relatively complete ontogenetic series are comparatively rare in the vertebrate fossil record. This can create biases in our understanding of morphology and evolution, since immaturity can represent a source of unrecognized intraspecific variation in both skeletal anatomy and ecology. In the extinct marine reptile clade Ichthyopterygia, ontogenetic series were widely studied only in some Jurassic genera, while the ontogeny of the oldest and most basal members of the clade is very poorly understood. Here, we investigate cranial ontogeny in Mixosaurus cornalianus, from the Middle Triassic Besano Formation of the Swiss and Italian Alps. This small-bodied taxon is represented by a wealth of material from multiple size classes, including fetal material. This allows us to assess ontogenetic changes in cranial morphology, and identify stages in the ontogenetic trajectory where divergence with more derived ichthyosaurs has occurred. Early ontogenetic stages of Mixosaurus show developmental patterns that are reminiscent of the presumed ancestral (early diverging sauropsid) condition. This is prominently visible in the late fetal stage in both the basioccipital, which shows morphology akin to basal tubera, and in the postorbital, which has a triradiate head. The ontogenetic trajectory of at least some of the cranial elements of Mixosaurus is therefore likely still very akin to the ancestral condition, even though the adult cranium diverges from the standard diapsid morphology.

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“…Furthermore, W. problematicus possesses numerous large teeth on the transverse process of the pterygoid. By contrast, most ichthyosaurs lack pterygoid dentition [33], with potentially only ‘vestigial’ pterygoid teeth being present in stem ichthyosauriform Utatsusaurus [34]. However, to ascertain the presence of denticles on the pterygoid in that taxon more evidence is required.…”

Section: Discussionmentioning

confidence: 99%

To glide or to swim? A reinvestigation of the enigmatic Wapitisaurus problematicus (Reptilia) from the Early Triassic of British Columbia, Canada

Bastiaans,

Buffa,

Scheyer

2023

R. Soc. open sci.

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Wapitisaurus problematicus was initially described as a member of the Weigeltisauridae, a clade of Late Permian gliding reptiles from Eurasia and Madagascar. However, the poor preservation of the holotype and only known specimen, from the lower Sulphur Mountain Formation at Ganoid Ridge (British Columbia, Canada), raised doubts about this assignment. Here, we redescribe W. problematicus and reassess its systematic position among diapsid reptiles. Comparison with all known weigeltisaurids, as well as contemporaneous reptiles from the Sulphur Mountain Formation, indicates that the taxon instead represents a thalattosauroid thalattosauriform, with noted similarities to Thalattosaurus and Paralonectes . This reidentification restricts weigeltisaurids to the Late Permian, with no occurrence in North America. Wapitisaurus problematicus potentially represents one of the oldest thalattosauriforms and increases our understanding of their diversity and disparity during the late Early and Middle Triassic. The close morphological similarities with later (thalattosauroid) thalattosauriforms and their high abundance in (shallow) marine settings may indicate an earlier invasion of this realm than previously assumed. This parallels observations in early ichthyopterygians with widespread opportunistic trophic niche diversification occurring relatively rapidly after the end-Permian mass extinction event.

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The anatomy of the palate in Early Triassic Chaohusaurus brevifemoralis (Reptilia: Ichthyosauriformes) based on digital reconstruction

Cited by 8 publications

References 49 publications

Ontogenetic variation in the skull of Stenopterygius quadriscissus with an emphasis on prenatal development

Ontogenetic variation in the skull of Stenopterygius quadriscissus with an emphasis on prenatal development

Ontogenetic variation in the cranium of Mixosaurus cornalianus, with implications for the evolution of ichthyosaurian cranial development

To glide or to swim? A reinvestigation of the enigmatic Wapitisaurus problematicus (Reptilia) from the Early Triassic of British Columbia, Canada

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