Field of Science

New Ichtyosaur Material from the Middle Triassic of China

First Triassic themed paper of 2011.

Liu, J., Aitchison, J.C.,Sun, Y.-Y., Zhang, Q.-Y., Zhou, C.-Y., and T. Lv. 2011. New Mixosaurid Ichthyosaur Specimen from the Middle Triassic of SW China: Further Evidence for the Diapsid Origin of Ichthyosaurs. Journal of Paleontology 85(1):32-36. doi: 10.1666/09-131.1

Abstract - Recent cladistic analyses have all suggested a diapsid origin of ichthyosaurs. However, an intermediate evolutionary stage of the lower temporal region of ichthyosaurian skull between basal diapsids and derived ichthyosaurs has been absent from the fossil record. Here we describe the cranial skeleton of a new mixosaurid ichthyosaur specimen with a well-preserved lower temporal region from the Anisian Guanling Formation of eastern Yunnan. It is characterized by the most primitive lower temporal region within known ichthyosaurs. The primitive characters of the lower temporal region include both external and internal separation between the jugal and the quadratojugal, an anterior process of the quadratojugal, an apparent posteroventral process of the jugal, and a large lower temporal opening surrounded by the jugal, the postorbital, the squamosal, and the quadratojugal. The lower temporal region of this specimen provides the most direct evidence to the diapsid origin of ichthyosaurs. It also suggests that the disappearance of the lower temporal fenestra is caused initially by the reduction of the lower temporal arcade rather than the enlargement of the surrounding bones.

7 comments:

  1. That's great! Can I receive a pdf copy of this paper?

    My e-mail address is frisk89@hotmail.it

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  2. Sometime after I'm doing with grad school apps, I'm going to need to sit down and read this paper, Maisch's paper and the other primitive ichthyosaur descriptions, heh. I'm pretty sure I have all the literature, just lacking in the time to look it over. If only I could have multiple copies of myself to delegate tasks to, I'd get soooooo much more done!

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  3. Incredible! It is always awesome when theories are finally proved. I will definitely be looking forward to reading this paper. Thanks for the notification!

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  4. 3rd comment reads like spam. Disregard.

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  5. What about what Maisch (2010) said at the end of his very good review of ichthyosaur material?

    http://www.palaeodiversity.org/pdf/03/Palaeodiversity_Bd3_Maisch.pdf

    "if ichthyosaurs were the sister-group of neodiapsids, their ghost-lineage would be much longer, because in that case the terminus post quem non for their origin would be the Upper Carboniferous. If they were the sister-group of procolophonians and pareiasaurs (ignoring the turtles for that matter), it only reached back to the Middle Permian. With regard to the fact that the oldest known ichthyosaurs are still Smithian in age, this argument may have at least some weight, as ghost-lineages tend to become less and less credible the longer they get."

    Is this supposed to mean that ichthyosaurs really originated in the carboniferous? And what's the phylogenetic definition of Ichthyosauria? Im a bit confused

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  6. don't worry about it. Maisch's statement is only relevant in the light of his own work. A thorough consideration of this recent paper (and others), primitive ichthyosaur character states, etc and a more expansive analysis of early sauropsids (and other amniotes) is needed to resolve this.

    Upper Carboniferous seems reasonable for that, but it doesn't mean it really happened. We don't have a thorough enough evaluation of all the data that is relevant to this. this really early divergence date is only relevant if that position is correct.

    best wishes,

    nick

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