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 running and flapping animation

Cosesaurus is the “Archaeopteryx” of pterosaurs, the “ur-flugsaurier,” the one that has so many pterosaur traits, yet does not have the key trait, wings. The large reptile tree indicates that Cosesaurus is closer to the origin of pterosaurs than is any archosaur in traditional studies.

Earlier we talked about how the pes of Cosesaurus matches narrow-gauge, digital, occasionally bipedal tracks with a hyper-flexed pedal digit 5 attributed to Rotodactylus. Those tracks document this sort of locomotion in this sort of reptile.

Earlier we also talked about the stem-like coronoid and strap-like scapula and sternal complex of Cosesaurus, all of which contributed to its ability to flap, based on similarities to birds and pterosaurs.

Earlier we talked about the important contributions of Dr. Paul Ellenberger, who, unfortunately, insisted that Cosesaurus was a pro-avian and was thus blinded to the possibility that Cosesaurus was a pro-pterosaur. Similarly modern paleontologist keep insisting that pterosaurs were archosaurs, blinding them to the possibility that pterosaurs were lizards.

Added a day later
And just so the point is not lost, no predecessor to the basal pterosaur, MPUM6009, could fly. They could leap, flap and glide, but the wings and pectoral girdle were not relatively large enough to sustain climbing flight. 

So, without further ado, I present a simple animation of Cosesaurus running and flapping based on Dr. Bruce Jayne’s treadmill lizards (Jayne’s video here).

Figure 1. Cosesaurus flapping - fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Figure 1. Click to enlarge and animate. Cosesaurus flapping – fast. Dr. Jayne’s treadmill lizards run extremely fast and the legs here, if just as fast, should appear as blurs. There should be some bounce in the tail and neck here, but the effort to produce that was not attempted.

Figure 2. Cosesaurus running and flapping - slow.

Figure 2. Click to enlarge. Cosesaurus running and flapping in slower motion. Pedal digit 5 would have impressed only while walking. Cosesaurus was also capable of quadrupedal locomotion, according to Rotodactylus tracks and the hands impressed in a digitigrade fashion.

In Summary
The elongate ilium and the addition of two sacrals for a total of four in Cosesaurus indicates a bipedal configuration, as is often the case with terrestrial reptiles. The prepubis may have contributed to this ability. The simple hinge (mesotarsal) ankle joint supports this. Unlike most lizards, members of the Tritosauria, like Cosesaurus and Huehuecuetzpalli, did not fuse the astragalus and calcaneum. The attenuated tail is a tritosaur/pterosaur trait. The pectoral girdle was pterosaurian, able to flap, but the arms were too short to fly. Even so a pteroid, preaxial carpal and trailing fibers were also pterosaurian traits (the fibers support the wing membrane in pterosaurs). Flapping was likely a secondary sexual behavior, designed to attract mates or drive off enemies, analogous, perhaps, to the frilled neck of the similar, but unrelated Australian frillneck lizard, which is also a capable biped, which does not flap its arms.

As in Dr. Jayne’s lizards
and despite a sprawling femur, the footfalls of Cosesaurus (Rotodactylus) were narrow-gauge and digitigrade, countering decades of traditional thinking regarding running lizards.

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 and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
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.
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.

wiki/Cosesaurus

New Langobardisaurus Confirms Earlier Findings

There’s a new Langobardisaurus (Figs. 1-3) with hollow limb bones courtesy of Saller, Renesto & Dalla Vecchia (2013). Langobardisaurus, with all of its oddities and wonders deservers a bit more PR. So, here ’tis.

The new Langobardisaurus. A little hard to see, but the neck curves up, left, down and behind the body, with the head emerging on the right.

Figure 1. The new Langobardisaurus. P10121. A little hard to see, but the neck curves up, left, down and behind the body, with the head emerging on the right. The hollow bones are crushed revealing their interiors. No soft tissue is preserved along with the fossil leaves shown here.

Here’s the abstract:
“A new specimen of the small protorosaurian reptile Langobardisaurus pandolfii is described. It was collected from the Seefeld Formation, of Late Triassic (Norian) age, in the Innsbruck area (Austria) and represents the first occurrence of Langobardisaurus outside Italy. Although preserved mostly as an impression, the find is significant

because it extends the palaeogeographic range of the genus and it is the second specimen known to date with the skull fully exposed. The preserved portions of the limb elements show that the bones are hollow, with a layer of compacta and without any trace of spongiosa. Reappraisal of all the specimens assigned to the genus Langobardisaurus reveals no significant differences between L. pandolfii and L. tonelloi, allowing to consider the latter as a junior synonym of the former.”

Not a protorosaur. Not an archosauromorph.
Saller, Renesto and Dalla Vecchia (2013) labeled Langobardisaurus a “small archosauromorph” basing this on conventional thinking linking Langobardisaurus to protorosaurs. We talked about this mistake earlier. The large reptile tree nests Langobardisaurus and its sisters with tritosaur lizards, descended from a sister to Huehuecuetzpalli and Lacertulus. Sister taxa in the large reptile tree include CosesaurusTanystropheusTanytrachelos and Macrocnemus. This clade includes several other long-necked bipeds with sprawling hind limbs (Renesto, Dalla Vecchia and Peters 2002). So Langobardisaurus was an occasional biped, lizard-style.

Saller, Renesto and Dalla Vecchia (2013) report, “All specimens of Langobardisaurus were found in a dark limestone and dolostone that formed in relatively small and deep marine basins surrounded by shallow-water carbonate platforms.” Langobardisaurs appear to be terrestrial reptiles, so their bodies appear to have been swept into these basins from river floods along with the plant debris seen in the fossil.

Figure 2. The skull of the new Langobardisaurus in situ, above, and reconstructed below, using the DGS technique. If there was no antorbital fenestra the rostrum was at least very weak. The left maxilla  itself was broken into several pieces. The skull looks like the other Langobardisaurus skulls, so is likely conspecific.

Figure 2. The skull of the new Langobardisaurus in situ, above, and reconstructed below, using the DGS technique. If there was no antorbital fenestra the rostrum was at least very weak and this taxon immediately preceded a taxon known to have an antorbital fenestra, Cosesaurus. The left maxilla itself was broken into several pieces. The skull looks like the other Langobardisaurus skulls, so is likely conspecific. The dentary is tipped with a tooth-like structure. Note the very tall coronoid process.

Antorbital fenestra
Langobardisaurus (Fig. 2) appears to have had an antorbital fenestra as it now appears in two specimens (Fig. 4) and in Pteromimus (Atanassov 2001), another langobardisaur with an antorbital fenestra.

Skull bones
The premaxilla is reported as edentulous with toothlike-projections erupting from it. Certainly this morphology was distinct and provided a mechanism for prey (insect) acquisition. Perhaps these were teeth fused to the jaws in the manner of sphenodontid teeth.

Most maxillary teeth had two or three cusps, but the posterior-most maxillary and dentary teeth were much longer than the others and bore many tiny cusps. These would have acted like linear molars.

The coronoid process was tall and robust, unlike other tritosaur lizards. No stomach contents tell us what Langobardisaurus ate. But the teeth and coronoid process tell us it was probably crunchy, requiring a certain amount of oral processing.

The pectoral girdle
Earlier we talked about the coracoid and strap-like scapula of Langobardisaurus, relabeled from earlier interpretations. Here (Fig. 3) those identifications are confirmed with similar morphologies and placements.

Figure 3. The pectoral girdle of the new Langobardisaurus highlighted in colors. These elements correspond to those of an earlier Langobardisaurus with an angled coronoid and a strap-like scapula.

Figure 3. The pectoral girdle of the new Langobardisaurus highlighted in colors. These elements correspond to those of an earlier Langobardisaurus with an angled coronoid and a strap-like scapula.

Hollow limbs
The hollow limb bones of Langobardisaurus are shared with members of the Fenestrasauria, including pterosaurs. So are the elongated nares, the large orbits, the elongated pedal 5.1 and the advancement of the sternum toward the clavicles.

Langobardisaurus tonelloi

Figure 4. Langobardisaurus tonelloi. The incomplete tail of this specimen was proabably longer based on other specimens. The the cosesaurid-type pectoral girdle. 

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.

Reference
Atanassov M 2001. Two new archosauromorphs from the Late Triassic of Texas. – Journal of Vertebrate Paleontology Abstracts 21(3): 30A.
Atanassov M 2002. Two new archosauromorphs from the Late Triassic of Texas. Dissertation.online abstract
Muscio G 1997. Preliminary note on a specimen of Prolacertiformes (Reptilia) from the Norian (Late Triassic) of Preone (Udine, north-eastern Italy). Gortania – Atti del Museo Friulano di Storia Naturale 18:33-40
Renesto S 1994. A new prolacertiform reptile from the Late Triassic of Northern Italy. Rivista di Paleontologia e Stratigrafia 100(2): 285-306.
Renesto S and Dalla Vecchia FM 2000. The unusual dentition and feeding habits of the Prolacertiform reptile Langobardisaurus (Late Triassic, Northern Italy). Journal of Vertebrate Paleontology 20: 3. 622-627.
Renesto S and Dalla Vecchia FM 2007. A revision of Langobardisaurus rossii Bizzarini and Muscio, 1995 from the Late Triassic of Friuli (Italy)*. Rivista di Paleontologia e Stratigrafia 113(2): 191-201. online pdf
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.
Saller F, Renesto S and Dalla Vecchia FM 2013. First record of Langobardisaurus (Diapsida, Protorosauria) from the Norian (Late Triassic) of Austria, and a revision of the genus. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen 268(1): 83-95
DOI: http://dx.doi.org/10.1127/0077-7749/2013/0319
Wild R 1980. Tanystropheus (Reptilia: Squamata) and its importance for stratigraphy. Mémoires de la Société Géologique de France, N.S. 139:201–206.

uninisubria/Langobardisaurus
wiki/Langobardisaurus

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.

Why an Increased Brain Capacity in Cosesaurus?

Derived from the basal lizard, Huehuecuetzpalli (Fig. 1), tritosaurs branched off in four distinct directions.

Huehuecuetzpalli

Figure 1. The mother of all pterosaurs, tanystropheids and drepanosaurs, Huehuecuetzpalli

Macrocnemus (Figs. 2-3) represents a long-necked terrestrial/marine clade culminating in Dinocephalosaurus and three other directions.

Jesairosaurus represents a long-necked, slow-moving arboreal clade culminating in the hook-tailed Megalancosaurus and Drepanosaurus.

Tanystropheus and kin going back to Huehuecuetzpalli.

Figure 2. Tanystropheus and kin going back to Huehuecuetzpalli.

Amotosaurus represents a long-necked terrestrial clade culminating in Langobardisaurus and Tanystropheus, some of which ventured into marine environs.

Cosesaurus (Fig. 3) represents a short-necked terrestrial clade culminating in Sharovipteryx, Longisquama and pterosaurs, which ventured into arboreal and aerial environs.

Among these four clades, Cosesaurus and kin appear to have had the larger cranium (red line in Fig. 1), both in length and depth. Why?

The answer is not neotony.
As demonstrated by Huehuecuetzpalli (Fig. 1) and pterosaurs, these taxa grew isometrically. Hatchlings and juveniles did not have larger eyes and a shorter rostrum. Now, with that said, what happened early on inside the egg, likely carried nearly to full term by the mother, is probably a different matter.

Clues to the answer for the bigger cranium and brain
may lie in the coracoids and pelvis of Cosesaurus.

Figure 1. Various tritosaur lizards shown to scale and their skulls portrayed to the same snout-occiput length. Red line represents the estimated cranial length. Note that in Cosesaurus, not only is the length longer, but the dorsal bulge is greater.

Figure 3. Various tritosaur lizards shown to scale and their skulls portrayed to the same snout-occiput length. Red line represents the estimated cranial length. Note that in Cosesaurus, not only is the length longer, but the dorsal bulge is greater.

Each of these taxa (Fig. 3) were quadrupeds, but Langobardisaurus and Cosesaurus were facultative bipeds in the manner of living lizards capable of bipedal locomotion. Narrow gauge, digitigrade and occasionally bipedal tracks with pedal digit 5 far behind the others are identified as Rotodactylus (Peabody 1948) tracks and they match the pedes of these two taxa (Peters 2000, Reneto et al. 2002).

The ilium in all four taxa (Fig. 1) are anteroposteriorly long, but more so in Cosesaurus. Such a morphology is associated with bipedal locomotion in various reptiles, like theropod dinosaurs. Bipedal capabilities free the forelimbs to do something other than support the body on the substrate.

In Langobardisaurus the manus remains small without much change from Macrocnemus.

However in Cosesaurus and Jesairosaurus the hand is relatively larger with longer medial metacarpals and longer medial digits. In Cosesaurus the anterior coracoid is eroded away by enlargement of the fenestrations until just the immobile quadrant-shaped posterior rim remains. This is an indicator of flapping, as we discussed earlier. In Cosesaurus the ulna is trailed by filaments (Ellenberger 1993, Peters 2009), the precursors of aktinofibrils in pterosaur wings. In Cosesaurus, such filaments would have only added to its retinue of extradermal decorations, but these could be animated by virtue of flapping. There was also a pteroid on Cosesaurus (Peters 2009, a former centralia, now migrated to the pre-axis of the radius), which in pterosaurs anchors and partially frames a propatagium, which is a flight membrane that also keeps the elbow from overextending.

Flapping, it would appear, was a social, territorial and secondary sexual trait and if so, Cosesaurus likely competed with other cosesaurs. The need for added coordination while a biped, while flapping excitedly to woo a mate, while watching out for competitors, while shrinking in overall size all may have served to increase the relative size of the cranium in Cosesaurus. The higher needs for coordination and social display seem to have supported the enlargement of the brain. At least that’s how it appears from here.

The relatively large size of the cranium is not continued in pterosaurs, which often, but not always (think: anurognathids) have an elongated rostrum to hyper-elongated rostrum (think ctenochasmatids, ornithocheirids and pteranodontids).

And birds?
In Archaeopteryx and its closest kin there is a similar and convergent expansion of the cranium that is otherwise not expressed in other nonvolant Meszoic bird-like taxa, like oviraptorids and veloceraptorids, but is present in Ichthyornis and living birds.

So, even in this regard, Cosesaurus can be considered “the Archaeopteryx of pterosaurs,” no matter the persistent rumors that such a creature remains unknown to science.

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 and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
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.
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.

wiki/Cosesaurus

Dinocephalosaurus – a star gazer, benthic feeder

Earlier we looked at the odd macrocnemid, Dinocephalosaurus (Fig. 1). This story opens with the first description of Dinocephalosaurus (Li et al. 2004), then follows with a response by Peters, Demes and Krause (2005) that disputed the swimming and sucking abilities originally ascribed, proposing instead a benthic ambush predation mode.

Dinocephalosaurus. Note the very narrow cranial portion of the skull and the very wide cheeks. That, by it self, opens the orbits dorsally. Sure there's some lateral exposure, but those eyes are looking up!

Figure 1. Dinocephalosaurus. Note the very narrow cranial portion of the skull and the very wide cheeks. That, by it self, opens the orbits dorsally. Sure there’s some lateral exposure, but those eyes are looking up!

Two of the original authors, LaBarbera and Rieppel (2005) reported in their reply: “We think it unlikely that Dinocephalosaurus was a benthic ambush predator. First, we would expect that the eyes in a benthic ambush predator would be dorsally located to monitor the overlying water (as seen in living frogfish and flatfish); the eyes of Dinocephalosaurus are anteriorlaterally positioned, apparently to monitor regions to the sides and in front of the snout.”

First of all, I disagree that frogfish and flatfish have the same sort of eye orientation. But be that as it may, one look at the skull of Dinocephalosaurus makes it easy to see the narrow inter orbital region (the frontals) as compared to the much wider skull. This alone produces an orbit that looks up. Sure there’s a lateral aspect, but the dorsal aspect is plainly present to an extent not seen in related Macrocnemus and Tanystropheus specimens.

LaBarbera and Rieppel (2005) report, “Dinocephalosaurus and suggests that the relative size of the limbs indicates a “poor swimmer.” We disagree. Two pairs of 30-cm-long, flipper-shaped f ins seem more than adequate to drive a 1-m-long body. Living sea lions (Zalophus californianus) have a similar ratio of flipper to body length.”

Big limbs, really, not so much… but look at how tiny the pectoral and pelvic girdles are. That’s where the muscles anchor. That’s where the strength originates. These are not the girdles of a strong and steady swimmer.

LaBarbera and Rieppel (2005) report, “In addition, Peters’ reconstruction would have Dinocephalosaurus capture prey by sweeping its neck through the water. We find this unlikely because (i) the cervical vertebrae lack neural processes that would improve the mechanical advantage of the (necessarily small) neck muscles to drive dorsiflexion, and (ii) such motion would generate high drag forces on the neck that would tend to drag the body of the animal  along the substrate in the direction opposite to the motion of the head. (The neck would act as an oar.)”

Let’s remind ourselves that the speed of “sweeping” the neck through the water is not an issue. The neck could have arisen slowly, not moving quickly until the last moment and then just the last few inches of neck would have been involved. So, no speed, no drag, no opposite motion, which was prevented in any case by the extreme width of the extremely flattened torso (a morphology ignored originally), and wide paddles.

Dinocephalosaurus in resting, feeding and breathing modes.

Figure 2. Dinocephalosaurus in resting, feeding and breathing modes. In breathing mode the throat sac would capture air that would not be inhaled until the neck was horizontal at the bottom of the shallow sea. Orbits on top of the skull support this hypothesis.

LaBabera and Rieppel (2005) report, “Peters rejects our hypothesis that Dinocephalosaurus may have employed suction feeding (driven by expansion of the cervical ribs) as a mode of prey capture on the basis that the cervical ribs are “bound to one another.” We know of no evidence to  suggest that the cervical ribs were bound to each other; indeed, the dispersal of the cervical ribs in the only available specimen would seem to indicate that tissues that surrounded the cervical ribs were quite liable to decay and thus unlikely to have been collagenous or cartilagenous.”

Well, they were bound together by their mutual length and overlapping proximity to each other (like uncooked spaghetti noodles), surrounded by skin. There’s nothing here more elaborate than anything seen in Tanystropheus and Macrocnemus, which do not have such expansion abilities. If the cervicals were able to rotate on some sort of axis, some sort of axis should be visible, but there’s nothing there. Expansion should have occurred in the cheeks or the stomach, two regions in which some small amount of expansion is already possible. The esophagus works by peristaltic motion, squeezing food toward the stomach. There little possibility for it to expand like the cheeks of a frogfish. The structure of the neck cervicals in Dinocephalosaurus, used to strengthen the extreme length of the neck, would be compromised by any lateral expansion.

If anything, let’s look for hyoids that might expand. Perhaps that’s where the confusion lies after all.

LaBabera and Rieppel (2005) report, “We have no direct evidence that Dinocephalosaurus used the cervical ribs to expand the throat, but that hypothesis is consistent with the observed morphology and we continue to search for additional tests of the hypothesis. If cervical ribs were used to power suction feeding in this animal, that function was certainly an exaptation.”

And we all appreciate this candor.

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.
LaBarbera M and Rieppel O 2005. Response. Science 308, p. 1113.
Peters D, Demes B and Krause DW 2005. Suction feeding in Triassic Protorosaur? Science, 308: 1112-1113.

wiki/Dinocephalosaurus

Huehuecuetzpalli in the eyes of Gauthier et al. 2012

Huehuecuetzpalli mixtecus (Reynoso 1998, Early Cretaceous, Middle to Late Albian, Fig. 1) is very primitive lepidosaur known from two closely associated specimens, one a juvenile, the other an adult. Huehuecuetzpalli has taken center stage here (at PterosaurHeresies) and at ReptileEvolution.com as a basal member of the Tritosauria. This third clade of squamates includes an odd assortment of drepanosaurs, tanystropheids and fenestrasaurs including pterosaurs that have been completely ignored and overlooked in all professional lizard studies.

Huehuecuetzpalli

Figure 1. The father of all pterosaurs and drepanosaurs, Huehuecuetzpalli, a basal lepidosaur.

A recent paper by Gauthier et al. (2012) considered Huehuecuetzpalli among the many lizards in its tree. A few quotes from that paper are worthy of attention. They nested Huehuecuetzpalli  alone between sphenodontids, like Gephyrosaurus and Sphenodon, and the Squamata (all other known lizards, divided by the Iguania and Scleroglossa (including snakes)).

Unfortunately Gauthier et al. (2012) did not reference the large reptile tree (or create their own more expansive tree of lizards) so they completely overlooked the tritosaurs as descendants of a sister to Huehuecuetzpalli. It should not have nested all alone. There was an opportunity missed that became yet another case of taxon exclusion. Below I make comments (in hot pink) on the small section of Gauthier (2012) regarding Huehuecuetzpalli.

Annotated Notes from Gauthier et al. (2012):

“Stem squamata – Given the antiquity of the squamate stem—which must extend deep into the Triassic (1)—surprisingly few stem fossils can be referred with any confidence to that great branch of the lepidosaur tree (2). Huehuecuetzpalli mixtecus, from the Early Cretaceous of Mexico, seems to be one of these (Reynoso 1998). This species is reasonably well known by the standards of Mesozoic lizard paleontology, as it is represented by two fairly complete skeletons, with some patches of skin impressions, of juvenile and nearly adult individuals. H. mixtecus apparently represents an entirely extinct side branch off the squamate stem (3). All major living clades of lizards— Iguania, Gekkota, Scincomorpha and Anguimorpha—diverged by the Late Jurassic (Estes 1983; Conrad 2008 (4)). Albian-age H. mixtecus must therefore have been separated from the surviving branch of the lizard tree by anywhere from 25 to 50 million years (5). Unsurprisingly, it displays several distinctive autapomorphies (see Appendix 4).

“Huehuecuetzpalli mixtecus is joined to the lizard crown by 20 unambiguous squamate synapomorphies (100% BP, 100% PP, 16 BS; see Appendix 4). Three of those are unique and unreversed on our tree: 177(1), 181(1) and 295(1). Among these diagnostic characters are many of those involved in the kinetic masticatory system unique to lizards (6). H. mixtecus is, however, also quite primitive in many ways; for example, skin impressions indicate that it retained a mid-dorsal row of spiny scales (7), a feature diagnostic of lepidosaurs that is retained today only among iguanian lizards and Sphenodon punctatus (scleroglossans generally lack the mid-dorsal scale row originally present in Reptilia; Gauthier, Kluge and Rowe 1988). The upper temporal arch of H. mixtecus displays a mixture of ancestral and derived traits; the postorbital, for example, still fits into a V-shaped recess on the lateral face of the squamosal as in diapsids ancestrally (8); Its squamosal is nevertheless distinctly lizard-like in having a peg at its posterior tip, on which pivots the mobile (streptostylic) quadrate uniquely diagnostic of crown lizards (Robinson 1967).(9)

“Crown Squamata – Huehuecuetzpalli mixtecus shares a few apomorphies characteristic of (at least some) iguanians, such as fused hourglass-shaped frontal bones and a small subtriangular postfrontal bone confined to the orbital rim (Reynoso 1998) (10). Nonetheless, it seems to lie well outside the lizard crown, because it lacks—so far as it is preserved—the 13 unambiguous synapomorphies that diagnose Squamata. … In any case, this morphological “long branch” simultaneously underscores our confidence in squamate monophyly while highlighting just how little we know about their evolutionary origins.(11)


Notes: (1) Actually the antiquity of the non-sphenodontid lepidosaurs extends back at least to Lacertulus of the Early Permian with more primitive taxa, like Homoeosaurus, and Dalinghosaurus (both ignored by Gauthier et al. 2012) surviving into later ages (Late Jurassic and Early Cretaceous respectively).”

(2) Listed above and look for others here.

(3) Indeed!

(4)  We can be confident of a much earlier Late Permian date for the tritosaur/squamate split due to the preponderance of fenestrasaur tracks in the Early Triassic (Peabody 1948).

(5) Add at least the entire Triassic to this number.

(6) This is reversed in some, but not all tritosaurs, principally by the shortening of the lateral temporal fenestra and the redevelopment of a quadratojugal with a loose connection to the quadrate.

(7) This dorsal series finds the acme of its expression in Longisquama.

(8) The Diapsida that Gauthier et al. 2012 is thinking of is diphyletic.

(9) See (6).

(10) As in tanystropheids and fenestrasaurs including pterosaurs.

(11) With the large reptile tree we actually know a very good set of sample ancestral taxa back to Ichthyostega (and we know its ancestors, so…, the list really extends as far back as you care to look.)


Besides the Tritosauria, Gauthier et al. (2012) excluded several fossil lepidosaurs that were key to understanding relationships in the large reptile tree. Without these their tree suffers by comparison despite its size. Taxon exclusion needs to become a thing of the past. Professional studies have suffered long enough.

 

References
Gauthier JA, Kearney M, Maisano JA, Rieppel O and Behlke ADB 2012. Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record. Bulletin of the Peabody Museum of Natural History 53(1):3–308.
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
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.

The Langobardisaurus Pteroid and Preaxial Carpal

The right manus of Langobardisaurus tonelloi.

Figure 1. Click to enlarge. The right manus of Langobardisaurus tonelloi. Left: Reconstructed. Middle: In situ. Right: Interpretation of elements in situ. Here a case can be made for the appearance of the pteroid and preaxial carpal, derived from the two former centralia. And if those are not bones but holes leading to the white matrix, no problem. No change either way to the family tree. Hard to tell when things are disarticulated like this. Or are they?

Peters (2009) described the pteroid and preaxial carpal of Cosesaurus, first viewed and illustrated (but misidentified) by Ellenberger (1993). Langobardisaurus nested in the large reptile tree as a sister to Cosesaurus, so it seemed appropriate to look for these bones in Langobardisaurus, a taxon we earlier noted had a similar pterosaur-like pectoral girdle, although the design is more primitive than in Cosesaurus and derived along its own way with enlarged clavicles.

In situ
The Langobardisaurus tonelloi skeleton is complete  and articulated. The manus is also complete and articulated, but some carpal elements were shifted (the loose ones) as well as the ungual of digit 5, which drifted closer to the tip of digit 4. The preaxial carpal and pisiform have drifted the least of the other carpals. The loose pteroid (in red, Fig. 1), drifted a little further. It has the same check mark shape seen in Cosesaurus, Sharovipteryx, Longisquama and pterosaurs.  And if those are not bones but holes leading to the white matrix, no problem. No change either way to the family tree. That simply means Langobardisaurus had no ossified centralia, like Tanystropheus, Tanytrachelos and Huehuecuetzpalli, the last of which had a completely unossified wrist. The lack of ossification is what enabled the centralia to migrate.

The ulna and radius have been slightly broken during crushing. The pteroid, lying atop the ulna, was previously overlooked. I found it, along with all the other listed details, using the much derided DGS technique employing Adobe Photoshop. In reality, I just looked more closely than others had done before. I also understood what to look for because I had reconstructed relatives.

Reconstruction
The distal carpals needed very little restoration. DC3 and 4 rotated as a set. The proximal carpals were strongly attached to the radius and ulna. The former centralia, the preaxial carpal and pteroid, were restored to the positions they have in Cosesaurus. Otherwise there is no room for them in the central carpus. In Sphenodon the medial centralia is pointed but straight. In Langobardisaurus the pteroid is check-marked shaped, as in Cosesaurus and pterosaurs. The pteroid and preaxial carpal, even in pterosaurs, have loose connections and commonly drift.

Langobardisaurus tonelloi

Figure 2. Langobardisaurus tonelloi. Looks more and more like a long-necked cosesaur.

Bipedalism and Flapping
Both Cosesaurus and Langobardisaurus have traits found in bipeds (Renesto, Dalla Vecchia and Peters 2002), although more developed in Cosesaurus (Ellenberger 1993, Peters 2000 a, b, 2002), supported by occasionally bipedal tracks, Rotodactylus, that match their manus and pedes. Both Cosesaurus and Langobardisaurus have a pterosaur-like pectoral girdle  distinct from their quadrupedal kin. Such a pectoral girdle suggests a flapping ability, as in pterosaurs. This secondary sexual character and behavior was a precursor to flight, but in the case of Langobardisaurus and Cosesaurus, it was just an attention-getting behavior, which reached an acme with Longisquama. Bipedalism lifts the manus off the substrate and permits evolutionary changes not associated with terrestrial locomotion.

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 1993Cosesaurus 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.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
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.
Muscio G 1997. Preliminary note on a specimen of Prolacertiformes (Reptilia) from the Norian (Late Triassic) of Preone (Udine, north-eastern Italy). Gortania – Atti del Museo Friulano di Storia Naturale 18:33-40
Renesto S 1994. A new prolacertiform reptile from the Late Triassic of Northern Italy. Rivista di Paleontologia e Stratigrafia 100(2): 285-306.
Renesto S and Dalla Vecchia FM 2000. The unusual dentition and feeding habits of the Prolacertiform reptile Langobardisaurus (Late Triassic, Northern Italy). Journal of Vertebrate Paleontology 20: 3. 622-627.
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.

Now it’s Langobardisaurus and the Origin of the Pterosaur Sternal Complex

Earlier we discussed the evolution of the pterosaurian sternal complex beginning with the plesiomorphic basal tritosaur lizard, Huehuecuetzpalli, and continuing through Cosesaurus (Fig. 1). Though flightless, Cosesaurus had all the elements of a pterosaurian sternal complex in place: 1) strap-like scapula; 2) quadrant-shaped coracoid with stem attached to interclavicle anterior to the transverse processes; 3) cruciform interclavicle; 4) transverse clavicles rimming the broad sternum; 5) sternum and interclavicle layered and coincident. In pterosaurs the clavicles extend posteriorly along an initially triangular sternum and in most pterosaurs the coracoid stem straightens out. So it looks like Cosesaurus was flapping, but not flying.

The evolutionary leap from Huehuecuetzpalli to Cosesaurus was great, but not insurmountable. Now we find a transitional taxon between these two to better bridge that gap and provide data on the order of changes.  Some surprises and unexpected wonders are here that should open all new chapters on the origin of vertebrate flapping and flight.

langobardisaurus-pectoral-girdle

Today we reexamine Langobardisaurus tonelloi (Figs. 1-3), a close relative of Cosesaurus, Tanytrachelos and the long-necked giant, Tanystropheus. Langobardisaurus demonstrates a transitional phase in the evolution of the fenestrasaurian/pterosaurian pectoral girdle. 

The anterior dorsal area of Langobardisaurus tonneloi with original designations noted in black and new interpretations in color overlays.

Figure 2. Click to enlarge. The anterior dorsal area of Langobardisaurus tonelloi with original designations noted in black and new interpretations in color overlays. The original clavicle is now rib #9. The original coracoid is now the broad clavicle. The original scapula is now the coracoid. The original rib #10 (on the right) is now the strap-like scapula. Rib #10 (on the left) and the sternum were identified correctly. See below for a reconstruction and comparison.

New Interpretations of the Langobardisaurus pectoral elements
Renesto’s tracing of L. tonelloi (Fig. 2) included his interpretations based on what was known of sister taxa at the time, all of which were thought to have a Tanystropheus/Macrocnemus-like pectoral girdle with short broad, elliptical elements. Now Cosesaurus (Fig. 1) offers new possibilities. Here colorized to re-identify the elements (Fig. 2), the original coracoid is now the broad clavicle. The original scapula is now the coracoid. The original rib #10 (on the right) is now the strap-like scapula. Rib #10 (on the left) and the sternum were identified correctly. See below for a reconstruction and comparison.

Langobardisaurus tonneloi reconstructed. Note the cosesaur-like pectoral girdle.

Figure 3. Langobardisaurus tonelloi reconstructed. Note the cosesaur-like pectoral girdle. Click to learn more. The pes is also fenestrasaurian/pterosaurian in character.

Distinct from Cosesaurus
The coracoid in L. tonelloi did not develop an elongated stem. Otherwise the Cosesaurus and Langobardisaurus shared many pectoral shapes and arrangements.

The Shift
In order for the fenestrasaur pectoral girdle to develop, the coracoids had to move anterior to the interclavicle transverse processes. Langobardisaurus gives us that transitional mid-point. Remember the sternal complex was chiefly transverse in orientation while the the scapula/coracoid was largely parasagittal.

Bipedalism Frees up the Forelimbs
How the muscles shifted and why they shifted is still to be determined. A study by Renesto, Dalla Vecchia and Peters (2002) described the bipedal abilities of Langobardisaurus. When the forelimbs rise off the substrate, they are free to do other tasks. There’s the opportunity.

The coracoids do not appear to be locked in place in Langobardisaurus as they were in Cosesaurus, so pterosaur-like, bird-like flapping was not so well developed.

Chlamydosaurus, the Austrlian frill-neck lizard

Fig. 4 Chlamydosaurus, the Austrlian frill-neck lizard with an erect spine and elevated tail. Click to see a YouTube movie.

Hypothesis
As small insectivores, langobardisaurs and cosesaurs might have made tasty meals for larger predators. If similar in their bipedal abilities to the living lizard, Chlamydosaurus (Fig. 4), then bluff and charge might have been in their repertoire. Lacking expanding neck skin, langobardisaurs and cosesaurs might have charged bipedally frantically waving their forelimbs. This might have also impressed the girl langobardisaurs and if that’s deemed sexy, well, folks, you just get more of the same generation after generation.

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
Muscio G 1997. 
Preliminary note on a specimen of Prolacertiformes (Reptilia) from the Norian (Late Triassic) of Preone (Udine, north-eastern Italy). Gortania – Atti del Museo Friulano di Storia Naturale 18:33-40
Renesto S 1994. A new prolacertiform reptile from the Late Triassic of Northern Italy. Rivista di Paleontologia e Stratigrafia 100(2): 285-306.
Renesto S and Dalla Vecchia FM 2000. The unusual dentition and feeding habits of the Prolacertiform reptile Langobardisaurus (Late Triassic, Northern Italy). Journal of Vertebrate Paleontology 20: 3. 622-627.
Renesto S and Dalla Vecchia FM 2007. A revision of Langobardisaurus rossii Bizzarini and Muscio, 1995 from the Late Triassic of Friuli (Italy)*. Rivista di Paleontologia e Stratigrafia 113(2): 191-201. online pdf
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.

wiki/Langobardisaurus

Hypothetical Tanystropheus Egg

Here’s how you paint yourself into a corner…
Huehuecuetzpalli and several pterosaur juveniles and embryos demonstrate that the tritosaurian lizards matured isometrically. In other words, just before hatching, tritosaurs had the proportions of adults. Among pterosaurs we’ve seen this in a juvenile Pteranodon, a juvenile Zhejiangopterus, a juvenile Tapejara, a juvenile Tupuxuara, the IVPP embryo, the JZMP embryo and Pterodaustro.

Now the question is…
If present in the giant, hyper-long-necked Tanystropheus, how in heck would you be able to fit that long neck inside an eggshell?

Juvenile?
Wild (1973) suggested that the smaller 4′ Tanystropheus with several tooth cusps was a juvenile of the 20′ giant with giant conical teeth, but at the time isometric growth had not been established for the Tritosauria. Now these two appear to be distinct species. Even if the smaller specimen is a juvenile, it still has an incredibly long neck, still difficult to fit inside an eggshell.

So, here we put the hypothesis to the test
(Prior to discovering Tanystropheus egg fossils, of course) let’s stuff Tanystropheus into an elliptical egg shape (Fig. 1).

A hypothetical Tanystropheus egg

Figure 1. A hypothetical Tanystropheus egg with an isometrically reduced adult reconfigured into an elliptical shape. No actual egg is known for Tanystropheus. Softer bones likely enabled the looser articulations here, particularly in the neck. Here the hyperelongated neck wraps around the body twice the long way. In the adult stiffening of the cervical ribs and the bony articulations of the cervicals would have prevented this sort of contortion. 

Other than a few very angled neck vertebrae, Tanystropheus fits okay. Are these angles too extreme? Did Tanystropheus embryos have shorter cervicals? We don’t know.

The Eggshell
As in pterosaurs the eggshell was likely an extremely thin leathery surface, more like a pillow case, not a hard ellipse, like a chicken egg. As in other tetrapod embryos, the bones and their articulations with each other were likely much softer and more flexible than in the adult, enabling this strange configuration, adopted only during the last few weeks prior to hatching as the embryo reached hatchling size.

By Land or By Sea?
Earlier we looked at a new hypothesis for vertical feeding in Tanystropheus based on stomach contents, its long neck and the crinoid-filled environment of Triassic seas. Whether Tanystropheus laid its eggs on land or in water may be immaterial if they, like pterosaurs and many other lizards, retained eggs within the mother until just prior to hatching. In that case the egg shell was more like a placenta, essentially producing a live birth. In that case, let’s look for babies near the pelvic region in future fossils.

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
Wild R 1973. Die Triasfauna der Tessiner Kalkalpen XXIII. Tanystropheus longobardicus(Bassani) (Neue Ergebnisse). – Schweizerische Paläontologische Abhandlungen 95: 1-16.

wiki/Tanystropheus