Spec DinoVember 8: River Monster

Ctenodectes fluvius is the only known freshwater ichthyosaur. However, while the freshwater members of other Mesozoic sea reptile groups-- the plesiosaurs and mosasaurs-- were in general not so different from their marine counterparts, Ctenodectes is a very strange-looking animal. It lives in the shallow, muddy rivers of what is now eastern North America in the late Jurassic, about 150 million years ago, and its bizarre appearance is a result both of adaptation to this habitat, and the simple fact that it is not closely related to other ichthyosaurs. Ctenodectes is a basal ichthyosaur, more closely related to such Triassic animals as Cymbospondylus, with their snake-like bodies. These primitive ichthyosaurs mostly became extinct at the end of the Triassic, with only their sleek whale-like descendants surviving. Now, the freshwater-dwelling Ctenodectes is the only one left. About the size of a bottlenose dolphin, it feeds by scooping up riverbed mud in its mouth and using its hundreds of needle-like teeth to filter out tiny invertebrates. Due to the murky water it lives in, its vision is very poor, and its eyes are almost vestigial. Instead it finds its way around mainly through touch and hearing. Like all ichthyosaurs, however, Ctenodectes is viviparous, with females giving birth to a single baby every three to four years.