The Myth of Suction Feeding in Dinocephalosaurus

Dinocephalosaurus

Figure 1. Reconstruction of Dinocephalosaurus. Click for more info.

Dinocephalosaurus orientalis (Li, Rieppel and LaBarbera 2004, Figs. 1 and 2) Late Ladinian, Middle Triassic ~228 mya, was orginally considered a marine sister to Tanystropheus with limbs nearly transformed into paddles. Phylogenetic analysis places it closer to a specimen of MacrocemusT2472. 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.

From Wiki:
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.”

This is So Wrong.
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.

Dinocephalosaurus underwater feeding and breathing

Figure 2. Dinocephalosaurus waiting on the bottom, feeding at mid-levels and inhaling a throat bubble at the surface which can be passed to the lungs only after resuming the waiting/resting position.

If Not Vacuuming Fish, What Then?
Instead Dinocephalosaurus would have been a stealthy bottom-dweller with eyes able to look dorsally. When fish came within its strike-zone, the long neck could raise the toothy skull to snare one (Fig. 2). In this hypothesis, everything works like it looks like it should work, convergent with Plesiosaurus.

Bottom-Dwelling Respiration
Respiration would have been a two-step process: raising the head to the surface to gather a bubble in the gular sac, then sinking the head to the bottom before passing the bubble horizontally back to the lungs. Otherwise, if the neck was vertical and underwater, the difference in water pressure would have prevented dorsal rib expansion and inhalation to move the air bubble down by expansion of the lungs, as smaller reptile, like turtles, practice.

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
Li C, Rieppel O and LaBarbera MC 2004. A Triassic aquatic protorosaur with an extremely long neck. Science 305:1931.
Peters D, Demes B and Krause DW 2005. Suction feeding in Triassic Protorosaur? Science, 308: 1112-1113.

wiki/Dinocephalosaurus

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