Dinocephalosaurus orientalis (Li, Rieppel and LaBarbera 2004) Late Ladinian, Middle Triassic ~228 mya, was orginally considered a marine sister to Tanystropheus with limbs nearly transformed into paddles of similar size. Phylogenetic analysis places it closer to a specimen of Macrocemus, T2472. Dinocephalosaurus was not a protorosaur, as originally described. In the large study it was not related to Protorosaurus. Rather Dinocephalosaurus was a tritosaur lizard.
The skull was described as crushed, but it was actually quite flat in life with dorsally directed orbits. The ribs were also much wider than deep. Both of these are characters found in bottom dwellers, not free-swimmers.
The cervical (25) and dorsal (33) counts are the highest among tanystropheids. The limbs were short but the hands and feet were relatively large, paddle-like and probably webbed.
Sucking in Fish?
This animal was originally described (Li, Rieppel and LaBarbera 2004) as capable of sucking in fish by expanding its neck cervicals to create an inrush of water.
Wikipedia reports, "Dinocephalosaurus also had a unique strike capability, where it could increase the volume of its esophagus by flaring out its cervical ribs, creating a vacuum. This is thought to be true because each of the cervical vertebrae had very pronounced transverse processes for muscle attachment and all of the cervical ribs articulated near the anterior end of the cervical vertebrae. This action would also prevent the Dinocephalosaurus from creating a pressure wave alerting the fish that they were being attacked. The Dinocephalosaurus could then grab its prey and hold onto it with the fangs in its upper and lower jaw. This reptile was then thought to have swallowed its prey whole."
The neck cervicals were bound to one another along their lengths and thus were restrained from any motion other than to slide along their lengths, as in other tetrapods. Moreover, the esophagus does not expand in size in any tetrapod. It changes shape only by peristalsis, moving food toward the stomach in a series of wave-like, worm-like contractions. Sucking in sea food is a trait of frogfish, but they expand their jaws with their gills shut. The blue whale also expands its jaws and throat to engulf massive amounts of food-laden sea water, but its esophagus does not change diameter.
Think About It.
Why would a reptile need fish-trap teeth if its prey were bypassing the teeth while being vacuumed down the throat? Macrocnemus and Tanystropheus has similar neck ribs for support of the long neck, so there's nothing special there in Dinocephalosaurus. The neck ribs were architectural structures giving support to the mechanical crane-like neck in similar fashion.
Let's Pretend the Neck Ribs Could Rotate on Their Articulation Points.
The articular points don't move, so all you get is a series of rotating ribs creating zigzags, not a voluminous vacuum. If the ribs do expand does that mean the support function decays? And what muscles are leveraged to pull the neck ribs open? Every rib is straight so the pull of any muscle on any rib would be only along the axis of the rib. Are the ribs articulated as little balls and sockets? No. Nothing about the vacuum hypothesis makes sense.