Concavispina – A Platypus of the Triassic

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). 

Concavispina biseridens, a new thalattosaur with twin blunt teeth and a wide, platypus-like bill.

Figure 1. Click to enlarge. Concavispina biseridens, a new thalattosaur with twin blunt teeth and a wide, platypus-like bill. The forelimbs were tiny. The hind limbs were weak. At least five sacral vertebrae locked the pelvis to the spine. The narrow clavicle was taller than the short scapula. Here the jugal is broken into several pieces, but extended to the quadrate in life. The mandible appears to have curved upwards, matching the premaxilla. Here the specimen, including its ribs and gastralia, are traced in situ following crushing. Not much shifted prior to burial, but the premaxilla and cruciform interclavicle twisted from transverse to parasagittal during crushing. 

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.

Xinpusaurus suni, the short rostrum species.

Figure 2. Xinpusaurus suni, the short rostrum species.

Xinpusaurus kohi, the swordbill species.

Figure 3. Xinpusaurus kohi, the swordbill species.

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.

Hupesuchus, a close relative of Concavispina and ichthyosaurs.

Figure 4. Hupesuchus, a close relative of Concavispina and ichthyosaurs, but not a thalattosaur and not far from Wumengosaurus.

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.

References
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.

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