Platecarpus and its fluke

Platecarpus tympaniticus (LACM 128319) in it's full glory. See high res version here

Paleontology is mostly bare bones, but on occasion we are treated with discovery of exceptional specimen that brings us that much closer on how the animal looked and lived when it was still alive. I love those specimens. To see a skin impression, or halo of feathers, or to see insect in amber and to realise that what you are seeing are details of an animal that once lived and breathed in this planet millions of years ago...it's simply amazing.

This time the treat is a mosasaur. A complete articulated specimen of Platecarpus tympaniticus from famous niobrara chalk formation that preserves possible remains of retina, numerous skin impressions (including parts of the facial scalation), cartilaginous rings that supported the windpipe, possible remains of internal organs, last meal (partially digested fish bones) and partial body outline. Amazing stuff. But what really got peoples attention was the tail.

The tail is distinctly kinked downward in similar fashion that is seen in other extinct marine reptiles like ichthyosaurs and thalattosuchian crocodiles. Not only that but the length pattern of individual vertebral bodies in the tail is typical for animals that have (dun dun dunh!) a two-lobed tail fluke.

Yes indeed, this animal had tail fluke. Now this isn't the first case of mosasaur with such thing to be reported. The first one was Plotosaurus. A very derived form, so the tail fluke in this animals was thought to be anomalous and typical for only this mosasaur. Now Platecarpus is more typical mosasaur indicating that two-lobed tail fluke is far more widely present among mosasaurids.

Furthermore this means that these mosasaurs were far better adapted to swimming than previously thought. Unfortunately we don't know the exact shape of the whole tail fluke. Apparently the outline was possibly present , but was destroyed before the preparator realised that there was soft tissue preserved.


It would be interesting to see how the tail vertebral metrics of mosasaurs match against some ichthyosaurs. Ichthyosaurs have pretty nice fossil record that documents the evolution of aquatic adaptations including the fluke, so comparison between Ichthyosaurs and mosasaurs could shed some light to how far mosasaurids got with this whole fluke thing, and perhaps give an indication of the fluke shape. Should be rather interesting indeed.

Ofcourse the cherry on top of this whole thing is the fact that it was published in PLOS.
Open access and high res photos. Awesome.

Lindgren J, Caldwell MW, Konishi T, Chiappe LM (2010) Convergent Evolution in Aquatic Tetrapods: Insights from an Exceptional Fossil Mosasaur. PLoS ONE 5(8): e11998. doi:10.1371/journal.pone.0011998