Lepidosaurian epipterygoids in basal pterosaurs

In 1998 lepidosaurian epipterygoids
were found in the basal lepidosaur tritosaur, Huehuecuetzpalli (Fig. 1, Reynoso 1998; slender magenta bones inside the cheek area).

Figure 2. Huehuecuetzpalli has a tall, narrow epipterygoid, as in other lepidosaurs, and just a pore of an antorbital fenestra in the maxilla.

Figure 1. Huehuecuetzpalli has a tall, narrow epipterygoid, as in other lepidosaurs, and just a pore of an antorbital fenestra in the maxilla.

About two years ago
previously overlooked lepidosaurian epipterygoids were identified here in a more derived lepiodaur tritosaur, Macrocnmeus (Fig. 2, slender green bones in the orbit area) for the first time.

Figure 1. Macrocnemus fuyuanensis (GMPKU-P-3001) in situ and as traced by the original authors, (middle) flipped with colors applied to bones, and (above) bone colors moved about to form a reconstruction. Darker yellow and darker green are medial views of premaxilla and maxilla. Note the long ascending process of the premaxilla and the palatal elements seen through the various openings all overlooked by those with firsthand access to the fossil. Epipterygoids are lepidosaur synapomorphies not present in protorosaurs.

Figure 2. Macrocnemus fuyuanensis (GMPKU-P-3001) in situ and as traced by the original authors, (middle) flipped with colors applied to bones, and (above) bone colors moved about to form a reconstruction. Darker yellow and darker green are medial views of premaxilla and maxilla. Note the long ascending process of the premaxilla and the palatal elements seen through the various openings all overlooked by those with firsthand access to the fossil. Epipterygoids are lepidosaur synapomorphies not present in protorosaurs.

Until now,
no one has ever positively identified lepidosaurian (slender strut-like) epipterygoids in a pterosaur. In the large reptile tree (LRT, 1737+ taxa) and the large pterosaur tree (LPT, 251 taxa) Bergamodactylus (MPUM 6009) nests as the basalmost pterosaur. Here is the skull in situ with DGS colors applied, as traced by Wild 1978 (above), and reconstructed in lateral and palatal views (below) based on the DGS tracings.

Figure 3. Bergamodactylus skull in situ and reconstructed. Wild 1978 tracing above.

Figure 3. Bergamodactylus skull in situ and reconstructed. Wild 1978 tracing above. Note the break-up of the jugal. Note the fusion of the ectopterygoids with the palatines producing ectopalaatines.

The lepidosaurian epipterygoids of Bergamodactylus
(slender bright green struts in the cheek/orbit area in figure 3), or any pterosaur over the last 200 years, are identified here for the first time, further confirming the lepidosaurian status of pterosaurs (Peters 2007, the LRT). Sorry I missed these little struts earlier. When you don’t think to look for them, you can overlook them.

Figure 5. Eudimorphodon epipterygoids (slender green struts).

Figure 4. Eudimorphodon epipterygoids (slender green struts).

Now you may wonder how many other pterosaurs
have overlooked epipterygoids? A quick look at Eudimorphodon reveals epipterygoids (Fig. 4, bright green struts). Other Triassic pterosaurs include:

  1. Austriadactylus SMNS 56342: slender strut present
  2. Austriadactuylus SC 332466: slender strut present
  3. Raeticodactylus : slender strut is present (identified on link as a stapes)
  4. Preondactylus: slender strut present
  5. Dimorphodon: amber strut over squamosal (Fig. 5 in situ image), 
  6. Seazzadactylus MFSN 21545: slender struts present, tentatively identified by Dalla Vecchia 2019, but as more than the slender struts they are) (Fig. 6).
The skull of Dimorphodon macronyx BMNH 41212.

Figure 5. The skull of Dimorphodon macronyx BMNH 41212. Above: in situ. Middle: Restored. Below: Palatal view. The slender yellow strut on top of the red squamosal in situ is a likely epipterygoid.

Figure 6. Seazzadactylus from Dalla Vecchia 2019. Here the epipterygoid struts are more correctly and less tentatively identified.

Figure 6. Seazzadactylus from Dalla Vecchia 2019. Here the epipterygoid struts are more correctly and less tentatively identified.

Hard to tell in anurognathids
where everything is crushed and strut-like. Hard to tell in other pterosaurs because the hyoids look just like epipterygoids. Given more time perhaps more examples will be documented that are obvious and irrefutable.

Added a few days later:

Added Figure. Here's the Triebold specimen of Pteranodon (NMC41-358) with epipterygoid splinters in bright green.

Added Figure. Here’s the Triebold specimen of Pteranodon (NMC41-358) with epipterygoid splinters in bright green.

Here’s the Triebold specimen of Pteranodon
(NMC41-358, added figure) with epipterygoid splinters in bright green. So start looking for the epipterygoid in every pterosaur. We’ll see if it is universal when more pterosaur specimens of all sorts are presented.


References
Dalla Vecchia FM 2019. Seazzadactylus venieri gen. et sp. nov., a new pterosaur (Diapsida: Pterosauria) from the Upper Triassic (Norian) of northeastern Italy. PeerJ 7:e7363 DOI 10.7717/peerj.7363
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

wiki/Bergamodactylus
wiki/Huehuecuetzpalli
wiki/Homoeosaurus
wiki/Bavarisaurus

Late-surviving sharovipterygids in Early Cretaceous Burmese amber

Earlier we looked at a
Oculudentavisa late-surviving cosesaur in Early Cretaceous Burmese amber. I noted it had just a few traits closer to another fenestrasaur, Sharovipteryx (Fig 2).

Figure 1. DGS tracings of two amber entombed Early Cretaceous sharovipterygids.

Figure 1. DGS tracings of two amber entombed Early Cretaceous sharovipterygids.

Today,
two unnumbered, unnamed, undescribed Early Cretaceous fenestrasaurs with even more sharovipterygid traits from the same Burmese amber. These specimens have huge eyes, a larger naris, a small antorbital fenestra, gracile postorbital bones, long cervicals with robust cervical ribs. That gray sickle-shaped area appears to represent the same sort of extendable hyoids seen in Sharovipteryx that extend the neck skin to form canard wing membranes or strakes (Fig. 2). Once again, these poor saps got their head stuck in the resin. The rest of the body was lost to the ages.

For comparison, a complete Sharovipteryx
(Fig. 2) is known from Late Triassic strata, coeval with the first pterosaurs, both derived from Cosesaurus, a lepidosaur tritosaur fenestrsaur.

Figure 3. Sharovipteryx reconstructed. Note the flattened torso.

Figure 3. Sharovipteryx reconstructed. Note the flattened torso.

References
No scale bar, No citation, No museum number, Owner unknown.

Phylogenetic bracketing and pterosaurs – part 1

Since pterosaurs (and other tritosaurs) nest between rhynchocephalians and squamates, there are a few traits they likely shared based on phylogenetic bracketing (unless specifically excepted based on fossil evidence). According to Evans (2003) these include:

(1) A derived skin structure with a specialized shedding mechanism involving distinct epidermal generations that are periodically lost and replaced, linked to
a cyclic alternation between a and b keratogenesis. — Ttritosaurs had scales. Pterosaurs also had pycnofibers, hair-like structures that first appear in Sharovipteryx. Unfortunately there is no evidence of skin shedding in any fossil lepidosaur.

(1A) The possession of a crest of projecting scales along the dorsal midline of the body and tail may also be unique to members of this group. — this reaches its acme with the tritosaur fenestrasaur, Longisquama.

(2) Paired male hemipenes housed in eversible pouches at the posterior corners of a transverse cloacal slit. These hemipenes are well developed in squamates and rudimentary in Sphenodon. — the fossil record does not include such structures.

(3) Notching of the tongue tip, possibly in relation to the development of the vomero-nasal system. — Barely notched in Iguana. I don’t see this in known rhynchochephalians or tritosaurs based on the division of the choanae into anterior and posterior fenestra, which appears in basal scleroglossans only.

(4) Separate centres of ossification in the epiphyses of the limb bones (a condition acquired independently in mammals and some birds). — This has never been noted in tritosaurs.

(5) Specialized mid-vertebral fracture planes in tail vertebrae to permit caudal autotomy facilitated by the organisation of associated soft tissue. — This has never been confirmed in any tritosaur, but then again, they are rare as fossils.

(6) A unique knee joint in which the fibula meets a lateral recess on the femur (not end to end as in many tetrapods) — This must be a very subtle trait. I see this trait in Tupinambis, Varanus and Bahndwivici, but not in very many other lepidosaurs.

(7) Specialized foot and ankle characters including a (a) hooked fifth metatarsal, (b) a specialized mesotarsal joint with a fused astragalocalcaneum and (c) an enlarged fourth distal tarsal. —  (a) The hook comes and goes. In basal rhynchocephalians, not present. It is present in Sphenodon through Mesosuchus, starts to fade with Rhynchosaurus and is gone in Hyperodapedon. Something of twisted fifth metatarsal present in most tritosaurs. Minor hook in basal squamata, becomes larger in Varanus, absent in snakes and other limbless lizards, of course. (b) In tritosaurs no ankles are fused except in drepanosaurs. (c) Also large in tritosaurs.

(8) Other soft tissue features include a sexual segment on the kidney; reduction or absence of the ciliary process in the eye; presence of a tenon (cartilaginous
disc) in the nictitating membrane and its attachment to the orbital wall. — These have never been observed in any lepidosaur fossil. But that doesn’t mean they weren’t there.

(9) In addition to these characters, all lepidosaurs show one of two kinds of tooth implantation, pleurodonty and acrodonty. — Basal tritosaurs have pleurodont teeth. Macrocnemus and later tritosaurs have thecodont teeth that happen to be much larger.

Part 2 is posted here.

References
Evans SE 2003.
At the feet of the dinosaurs: the origin, evolution and early diversification of squamate reptiles (Lepidosauria: Diapsida). Biological Reviews, Cambridge 78: 513–551.

 

Pulling Bavarisaurus out of the belly of Compsognathus

Figure 1. Click to enlarge. The little Jurassic lizard Bavariasaurus was found inside the belly of the little Jurassic dinosaur, Compsognathus. But it is not the same genus as the holotype.

Figure 1. The little Jurassic lizard Bavariasaurus was found inside the belly of the little Jurassic dinosaur, Compsognathus. Illustration by Franz Nopcsa 1903.

As everyone knows, one Jurassic lizard, Bavarisaurus macrodactylus (Figs. 1-4, = Homoesaurus macrodactylus Wagner 1852, Hoffstetter 1964; length: ~20cm, (Lower Tithonian), Solnhofen), was found inside the belly of a small Jurassic dinosaur, Compsognathus (BSPHM AS-1-563). All curled up like the good meal it was, Bavarisaurus has been added to various lepidosaur phylogenetic analyses, but, to my knowledge, it has not been reconstructed in the literature. However, Tracy Ford did a good job here.

Figure 2. Like Michelangelo removing the excess marble, I removed every trace of Compsognathus, leaving nothing but Bavarisaurus in step 1.

Figure 2. Like Michelangelo removing the excess marble, I removed every trace of Compsognathus, leaving nothing but Bavarisaurus in step 1.

Not sure how much good this will do, but I took all the bones I could see and segregated from the dinosaur bones (Fig. 2), then rearranged them as well as I could (Fig. 3). Seems like Bavarisaurus had quite a long tail when it is all stretched out! Looking at the maxilla and mandible you’ll notice the teeth don’t match. Small triangle-shaped teeth are on the dentary, but posteriorly-oriented narrow, sharp teeth appear on the maxilla. The presumes that I have the maxilla correctly oriented.

Figure 3. Click to enlarge. Moving the bones of Bavarisaurus into a reasonable reconstruction is step 2.

Figure 3. Click to enlarge. Moving the bones of Bavarisaurus into a reasonable reconstruction is step 2.

The next step was to tentatively nest the elements phylogenetically, then clean them up in a better presentation in dorsal and lateral views (Fig. 4). A final scoring of elements nests Bavarisaurus more securely.

Figure 2. Click to enlarge. Cleaned up reconstruction of the former Bavarisaurus (cololizard at present). Gray areas added based on sister taxa. This is a tritosaur.  Note the large naris bounded ventrally by the maxilla. The ventral pelvis is shallower. I don't understand the pterygoid morphology anteriorly. The upper and lower teeth don't match. That's a red flag, but it is the only data available.

Figure 2. Click to enlarge. Cleaned up reconstruction of the former Bavarisaurus (cololizard at present). Gray areas added based on sister taxa. This is a tritosaur.  Note the large naris bounded ventrally by the maxilla. The ventral pelvis is shallower. I don’t understand the pterygoid morphology anteriorly. The upper and lower teeth don’t match. That’s a red flag, but it is the only data available.

Bavarisaurus is another tritosaur. 
And that’s why it nests uncertainly at the base of the Squamata in prior analyses that did not include any or many other tritosaurs — because it doesn’t nest in the Squamata. In the large reptile tree Bavarisaurus nests between Meyasaurus and the Dahugou lizard + Lacertulus, not far removed from Dalinghosaurus, which it resembles by convergence.

So based on the presence of Lacertulus in the Late Permian, something very much like Bavarisaurus originated in the Permian and continued to the Late Jurassic where we find the first and last of this genus inside the ribcage of Compsognathus.

References
Evans SE, Raia P and Barbera C 2004. New lizards and rhynchocephalians from the Lower Cretaceous of southern. Italy. Acta Palaeontologica Polonica 49:393–408.
Hoffstetter R 1964. Les Sauria du Jurassique supérieur et specialement les Gekkota de Baviére et de Mandchourie. Senckenberger Biologische 45, 281–324.
Nopcsa F 1903. Neues ueber Compsognathus. Neues Jahrbuch fur Mineralogie, Geologie und Palaeontologie 16: 476-494.
Wagner A 1852. Neu-aufgefundene Saurier, Uberreste aus dem lithographischen Schiefern und dem obern Jurakalke: Abhandlungen der Bayerischen Akademieder Wissenschaften Mathematisch-naturwissenschafliche Kl, 3(6): 661-710.

Shifting extensor anchors in lepidosaurs and pterosaurs

Since muscles rarely fossilize and when they do only the major muscles are discernible, reconstructing pterosaur myology (muscle, tendons and ligaments) depends on analogy with living taxa and the correct identification of muscle scars. Papers on musculature in living taxa are also rare. Virginia Abdala, an expert in this niche, sent my papers from 1939 and 1946, along with her own work.

According to the large reptile tree, among living reptiles pterosaurs are most closely related to Sphenodon, a basal lepidosaur, and Varanus (Fig. 1) a living lizard (squamate), so we make comparisons to them. All traditional paleontologists, just so you know, think birds and crocs are the closest living relatives, but then they are not referencing the only study – ever-  that gives lizards a fair shake.

Extensors color coded from Haines 1939 and 1946 in Sphenodon (left) and Varanus (right). Note the shifts in muscle anchors.

Figure 1. Click to enlarge. Extensors color coded from Haines 1939 and 1946 in Sphenodon (left) and Varanus (right). Note the shifts in muscle anchors from the intermedium in Sphenodon to the Ulnare in Varanus, in which the intermedium is greatly reduced. This sets up the hypothesis that muscles and tendons do shift from bone to bone. The long extensor from the humerus (gray) connects only to the proximal metacarpals.

While most muscle anchors on these two lepidosaurs are the same, some shifts have taken place on the wrist anchors. In Sphenodon most of the extensor digitorum brevis anchors are on the intermedium, while in Varanus all have shifted to the ulnare. The intermedium, the former anchor, is a vestige in Varanus. Establishing those shifts sets us up for the possibility of shifting wrist extensor anchors in the phylogenetic ancestors of pterosaurs (Fig. 2). This is key, especially when you get to taxa in which the carpals are poorly ossified.

Metacarpal extensors in tritosaurs, fenestrasaurs and pterosaurs.

Figure 2. Click to enlarge. Metacarpal extensors in tritosaurs, fenestrasaurs and pterosaurs. Huehuecuetzpalli ossifies only the ulnare. Cosesaurus ossify the wrist elements and the two centralia migrate to the medial margin where they become known as the pteroid and preaxial carpal. Longisquama and pterosaurs co-ossify the distal carpals. For extinct taxa the metacarpal extensors are hypothetical.

A strange thing happens in Huehuecuetzpalli. Only the ulnare ossifies. The rest of the carpal elements, it appears from the evidence of phylogenetic bracketing (Fig. 2) are undergoing a transformation/migration. Basal tritosaurs. When the carpal elements re-ossify in Cosesaurus the two centralia are missing and a pteroid and preaxial carpal are present on the medial margin of the wrist (Fig. 3).

The origin of the pterosaur pteroid and preaxial carpal from lepidsoaur centralia.

Figure 3. Click to enlarge. The origin of the pterosaur pteroid and preaxial carpal from lepidsoaur centralia.

The shift in the two centralia corresponds to a shift in morphology elsewhere in the anatomy of Cosesaurus, including the development of a pterosaur-like pectoral girdle that enabled flapping. Huehuecuetzpalli does not demonstrate such changes, but it does have proportions similar to those of living lizards capable of bipedal locomotion, such as Chlamydosaurus, the frilled lizard.

No large extensors were anchored to the two centralia in Sphenodon or Varanus. In Sphenodon a small extensor was anchored to the medial centralia, but it attached to digit 1. Any large extensors that might have anchored on the preaxial carpal would have had to migrate there.

Digit extensors

Figure 5. Digit extensors anchored between the metacarpals had to migrate or disappear when the metacarpals became appressed. Here they have hypothetically migrate to the dorsal surfaces of the metacarpals.

The carpus of Dinocephalosaurus, a basal tritosaur close to Macrocnemus. Here only one centralia is ossified and it occurs on the medial wrist.

Figure 6. The right carpus dorsal view  of Dinocephalosaurus, a basal tritosaur close to Macrocnemus. Here only one centralia is ossified and it occurs on the medial wrist as a vestige.

More evidence of migration
In many basal tritosaur lepidosaurs more derived than Huehuecuetzpalli many of the carpals are poorly ossified. For instance, Tanystropheus ossifies the radiale, ulnare and distal tarsal 4. However in Dinocephalosaurus, a phylogenetic descendant of Macrocnemus you find a well ossified carpus that demonstrates the migration of the centralia to the medial wrist. In this case (Fig. 6), only one centralia is ossified.

On the other hand, in drepanosaurs (arboreal tritosaurs) basal members have poorly ossified carpals, but Drepanosaurus and Megalancosaurus ossify all the carpals with the exception of the radiale. The intermedium and ulnare become elongated. The centralia of derived drepanosaurs remain in the middle of the wrist.

Tomorrow we’ll see more pterosaur arms and muscles.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Haines RW 1939. A revision of the extensor muscles of the forearm in tetrapods. Journal of Anatomy 73:211-233.
Haines RW 1946.
 A revision of the movements of the forearm in tetrapods. Journal of Anatomy 80: 1-11.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods
Ichnos, 7: 11-41.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.

Cosesaurus pycnofibers, frills, membranes and hair

It is well known that pterosaurs were hairy
After all, Sordes is the “hairy devil.” The origin of pterosaur pycnofibers (ptero-hair) is the topic of this post. We covered the extradermal fibers on Sharovipteryx and Longisquama earlier here and here. Today we feature yet another hairy lizard and a sister to the ancestor of all three higher fenestrasaurs.

As reported earlier here and here, no one has done more work on the basal fenestrasaur, Cosesaurus aviceps than Dr. Paul Ellenberger (1993). Unfortunately Dr. Ellenberger’s bias towards birds blinded him to the pterosaur-like interpretations that would have revealed the prepubis, pteroid, quadrant-shaped coracoid and other pterosaur-like traits that he traced, but did not correctly interpret. On the other hand, Dr. Ellenberger did a good job of tracing the various extradermal membranes found around the sole specimen of Cosesaurus (Fig. 1). I use his illustration (Ellenberger 1993) to show that I am not the only one seeing these traces.

Cosesaurus fibers, frills and membranes. Here the same extradermal membranes found in Sharovipteryx, Longisquama and pterosaurs are found here.

Figure 1. Cosesaurus fibers, frills and membranes. Here the same extradermal membranes found in Sharovipteryx, Longisquama and pterosaurs are found here. I’m using Ellenberger’s interpretation because mine are sometimes considered suspect.

Skull and Dorsal Fibers/Frills
A single row of fibers grading into frills tops the cranium and extends to at least the sacral area. These are homologous to the same structures in Huehuecuetzpalli, Macrocnemus, Iguana and Sphenodon. These structures reach an acme with Longisquama.

Tail Fibers
Ellenberger considered these the quills of primitive feathers. These fibers ultimately coalesce to become a tail vane in derived pterosaurs.

Arm Fibers
Posterior to the ulna are fibers that ultimately become a wing membrane in Longisquama and pterosaurs.

Leg Fibers
Anterior to the knee are fibers that are homologous to pycnofibers of pterosaurs. These are likely decorative and insular.

Uropatagia
Posterior to the legs are decorative frill/membranes that ultimately become the gliding membranes in Sharovipteryx, Longisquama and, to a lesser extent, in pterosaurs.

Not sure if we’ll find fibers prior to Cosesaurus. Its seems that Langobardisaurus has been too thoroughly prepared to ever know this and it has scales. Jesairosaurus does not preserve hairs and it was a lethargic type rather than a hyper-active taxon like Cosesaurus (remember the flap over flapping?).

In letters to a previous post, J. Headden questioned the identity of fiber-like shapes found in the neck skin of Sharovipteryx. With Cosesaurus having fibers and Longisquama having fibers and pterosaurs having fibers, phylogenetic bracketing (in spite of or in support of the fossil evidence) indicates that Sharovipteryx also had fibers.

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
Ellenberger P 1993. 
Cosesaurus aviceps. Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.

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