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Rib of a Triassic Marine Reptile?


Crazyhen

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This fossil is from Guanling, Guizhou of China, of Triassic Formation.  Many marine reptile fossils were found there.  This one looks like a rib bone of a marine reptile?

IMG_0807.JPG

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Hard to say without properly preparing the piece, but I must say the shape certainly looks suggestive. Certain other aspects do look a bit off, however, such as the depression in the middle of the rib. For while ichthyosaurs do have such a depression central to their ribs, this is rarely as deep and wide as seen in this specimen, nor are the ribs generally as wide in ichthyosaurs as this specimen appears to be. For comparison, here are some ichthyosaur rib cages from through the ages:

 

445364012_Besanosaurusleptorhyncusribcage.thumb.jpg.4e7731463fb0d01078d2518e0591d561.jpg290049932_Eurhinosauruslongirostrisribcage.thumb.jpg.34618000cd8ec705a79c56b42f1eaac8.jpg809535859_Stenoptetrygiusquadriscissusribcage.thumb.jpg.910427196c67fea8d291d96c86f377e4.jpg

 

195022945_Ophthalmosaurusincenicusribcage.thumb.jpg.469a23d2fcdfa932fadc80e82d00b6ed.jpg1162677617_Temnodontosaurustrigonodonribcage.jpg.a76d0d56428b5912771f7e2c6d7d142c.jpg

 

Rib cages of the Middle Triassic Besanosaurus leptorhyncus (cast at the Museo Civico dei Fossili di Besano, Besano); Lower Jurassic Eurhinosaurus longirostris (Naturmuseum Senckenberg, Frankfurt); Lower Jurassic Stenopterygius quadriscissus (Paläontologische Sammlung MUT Tübingen); Ophthalmosaurus incenicus (Paläontologische Sammlung MUT Tübingen); and Temnodontosaurus trigonodon (Museum am Löwentor, Stuttgart)

 

Neither plesiosaurs, nothosaurs nor Placodus gigas seem to share this feature of a depression along the surface of their ribs, their ribs generally being more solid and robust - though it does appear that in certain infrequent cases the dorsal edge of pl(es)iosaur ribs can be somewhat thickened towards the proximal rib end, as is the case in the P. philarchus specimen below.

 

1905204839_Peloneustesphilarchusribcage.thumb.jpg.de3332fc63f25cdbcc908cc8df7a5796.jpg1580155926_Simosaurusgaillardoti.thumb.jpg.ee0bce5272c68be97bab350e75c4ea5d.jpg1926940065_PlacodusgigasSenckenbergdorsalandlumbarvertebrae.thumb.jpg.67f569472b2733632079efbef6e56369.jpg

Rib cages of Peloneustes philarchus (Paläontologische Sammlung MUT Tübingen); the nothosaur Simosaurus gaillardoti (Naturmuseum Senckenberg, Frankfurt); and Placodus gigas (Naturmuseum Senckenberg, Frankfurt)

 

Ribs from Blezingeria ichthyospondyla also don't seem to have a depression as exhibited in the fossil under discussion (source of below image):

 

Blezingeria_Muschelkalkmuseum_Hagdorn.jpg.e1b60079cc3d5079acd21e01586d0c26.jpg

 

So while the depression is not a common feature of marine reptile ribs, I think the specimen presented here still has very good potential to be one (that is, while it branches to form the depression, the branches reconnect, suggesting it's a single bone and not something plantlike), probably ichthyopterygian in nature - although we certainly cannot rule out any other of the lesser-known Triassic marine reptiles, with which I myself am less familiar too. The width of the rib and it's shallow curvature remain odd, but I don't think we'd necessarily need to consider them abnormal either.

 

Hope this helps!

  • I found this Informative 1

'There's nothing like millions of years of really frustrating trial and error to give a species moral fibre and, in some cases, backbone' -- Terry Pratchett

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Many thanks for the detailed account.  The Shastasaurus is the biggest ichthyosaur found there, and I suspect that it’s a rib bone of Shastasaurus.

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That sounds about right, Shastasaurus :) Would be pretty cool if it is that indeed! :dinothumb:

  • Thank You 1

'There's nothing like millions of years of really frustrating trial and error to give a species moral fibre and, in some cases, backbone' -- Terry Pratchett

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