Creature Feature 7

I hope everyone had a great weekend, and I hope you are all ready for this week's Creature Feature!
This week, I will be talking about Champsosaurus natator.

Champsosaurus may look like a cross between a lizard and a crocodile, but it is not closely related to either. In fact, Champsosaurus was neither a squamate nor an archosaur - it was a member of the now-extinct sauropsid lineage called Choristodera. While the phylogenetic positioning of this group is still uncertain, most recent analyses place it within Archosauromorpha (Lee, 2013).

While it is not closely related to crocodilians, its superficial resemblance to the modern gharial is due to convergent evolution - this creature was highly aquatic, using its long, narrow jaws to catch fish that shared its environment, though in early life it likely fed on arthropods, amphibians, and slow-swimming fish (Katsura, 2010). It is thought that this creature swam much like modern crocodilians or Amblyrhynchus cristatus, using its tail to propel itself forward while pinning its arms close to its body to minimize drag. The jaws widened significantly at the base, where strong jaw muscles attached (Lambert et al., 2001).

Champsosaurus had a flexible neck and long nasal passages, with external openings at the tip of the snout [as opposed to crocodilians, with external nares on the dorsal ends of the rostrum) - this, combined with a well-developed secondary palate, is thought to be indicative of a 'snorkeling'-esque resting posture. In other words, unlike crocodilians, where the head lies parallel to the surface with the nares and eyes just above the surface and the body sinking down, Champsosaurus would rest on the bottom, angling its snout towards the surface so it could breathe (Katsura, 2010).

Champsosaurus was specialized for its aquatic lifestyle to the point where the only part of its life cycle that still required land was reproduction. In fact, it is thought that males were unable to walk on land at all; it is thought that the specimens with fused sacral vertebrae and more robust limbs represent females, with features allowing them to come to land for the purpose of laying their eggs (Katsura, 2007).

Well, I hope this has given you a bit more information on the fascinating Champsosaurus! It's a pity that this fascinating lineage of creatures went extinct - I would've loved to see these creatures in the wild!

Acknowledgements:
Lee, M. S. Y. 2013. Turtle origins: Insights from phylogenetic retrofitting and molecular scaffolds. Journal of Evolutionary Biology 26 (12): 2729.
Katsura, Y. 2010. Ontogenetic change of bone microstructures and its ethological implication in Champsosaurus (Diapsida, Choristodera). Historical Biology, 22 (4), 380-386.
D. Lambert, D.Naish, E.Wyse. 2001. Encyclopedia of Dinosaurs and prehistoric life. Dorling Kindersley Limited, London. p. 77.
Katsura, Y. 2007. Fusion of sacrals and anatomy in Champsosaurus (Diapsida, Choristodera). Historical Biology, 19 (3), 263-271.