A Giant Mesosaur

Cymbospondylus is a primitive Triassic ichthyosaur of enormous length, approximately ten meters. It is also, due to its geneology a giant mesosaur. All ichthyosaurs and thalattosaurs are derived from mesosaurs. Cymbospondylus is one of the few ichthyosaurs to retain the long, sinuous body shape of mesosaurs.

Figure 1. Cymbospondylus overall in situ.

Figure 1. Cymbospondylus overall in situ. Overall, a very similar morphology to any basal mesosaur with the addition of flippers transformed from limbs.

Despite the Size Difference
Actually an order or two of magnitude larger in size, the giant ichthyosaur Cymbospondylus (Leidy 1868) kept the basic proportions of Stereosternum, but with a shorter neck and limbs transformed into flippers.

Stereosternum, a basal mesosaur

Figure 2. Stereosternum, a basal mesosaur

A comparison of skulls helps make the point.
The long premaxilla, the posteriorly shifted nares, the size of the supratemporal are obvious shared traits with Wumengosaurus acting as a transitional taxon. Details at reptileevolution.com.

Figure 2. A comparison of mesosaur skulls. Stereosternum at the base. Wumengosaurus with a very distinct upper temporal fenestra. And Cymbospondylus with upper temporal fenestra more dorsally oriented.

Figure 2. A comparison of mesosaur skulls. Stereosternum at the base. Wumengosaurus with a very distinct upper temporal fenestra. And giant Cymbospondylus (not to scale) with upper temporal fenestra more dorsally oriented, not quite visible in lateral view.

No other taxa are closer in the large reptile tree to thalattosaurs and ichthyosaurs than mesosaurs.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Leidy J 1868. Notice of some reptilian remains from Nevada: Proceedings of the American Philosophical Society, v. 20, p. 177-178.

5 thoughts on “A Giant Mesosaur

  1. Wasn´t there a recently discovered, new (I think) species of Cymbospondylus described by the press (unsurprisingly) as “T-Rex of Triassic seas” and said to have had large serrated teeth to feed on large sea reptiles?
    I never heard anything else about it (even though, I believe, it had a small note published about it on National Geographic).

  2. Pingback: ICHTYOSAURIERS « Tsjok's blog

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