Concavispina biseridens (Zhao et al. 2013) is a new thalattosaur (Fig. 1) that nests with the two Xinpusaurus specimens (Figs. 2, 3), but at the base of their clade. Rather than having a sharp-pointed rostrum, Concavispina had a broad, nearly spoon-bill premaxilla. The low blunt maxillary teeth appeared in two rows on each side, an inner and right next to it, an outer. The rostrum and mandible both tilted up. One can imagine this genus was a bottom-feeder, crushing small prey items with that bill and teeth, convergent, perhaps, with the living platypus (Ornithorhynchus anatinus).
Atypical for thalattosaurs, many of the vertebral spines were embayed dorsally, producing two spikes per spine fore and aft. This concave dorsal spine trait inspired the generic name. The twin teeth inspired the specific name. By convergence, there is an almost pre-snake-like morphology here, with such small limbs and so many ribs. Curious that so many sacral transverse processes were present on that odd-shaped ilium. I count five.
Concavispina is certainly a derived taxon, but it nests at the base of the even more derived sword-bills in the genus Xinpusaurus. Odd that all three of these oddballs nest so close to the base of the thalattosauria, just outside of Ichthyosauria and another platypus-like oddball (apparently by convergence), Hupehsuchus (Fig. 4). All these taxa had their origins near the derived mesosaur, Wumengosaurus, which we looked at earlier.
We’ll take a closer look a Hupehsuchus and Xinpusaurus in future posts.
And what was it about Utatsusaurus that helped transform it, over time, into the variety of ichthyosaurs we now recognize?
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.
Zhao L-J, Liu J, Li C and He T 2013. A new thalattosaur, Concavispina biseridens gen. et sp. nov. from Guanling, Guizhou, China. Vertebrata PalAsiatica 24-28.