Snake and snake ancestor skulls in phylogenetic order

Updated February 24, 2015 with the addition of two basal snakes to the large reptile tree which united burrowing blind snakes with terrestrial sighted snakes. This is a major revision  and an embarrassing one, but one that depended on those two additions. 

Yesterday we talked about snake origins going back to the Jurassic (Caldwell et al. 2015), closer to the base of the origin of all autarchoglossans, including geckos, skinks and varanids – instead of being derived from varanids, one of the many traditional hypotheses for snake origins.

Here (Fig. 1) is a series of skulls showing three lineages that were shown in a cladogram yesterday: 1) the Shinisaurus/Heloderma clade; 2) the Varanus/Estesia clade that gave rise to mosasaurs; and 3) the Ardeosaurus clade that gave rise to all snakes, like BoaPachyrhachis and Leptotyphlops.

The origin of snakes alongside the origin of mosasaurs and the origin of Lanthanotus, all in phylogenetic order. Not to scale. Note the branching off of burrowing snakes.

The origin of snakes alongside the origin of mosasaurs and the origin of Lanthanotus, all in phylogenetic order. Not to scale. Note the branching off of burrowing snakes. Click to enlarge.

Some interesting convergent traits here (like pterygoid fangs on mosasaurs and terrestrial snakes), even among this small list of taxa. With the Middle Jurassic appearance of snakes, basal pre-snake taxa like Ardeosaurus must have originated much earlier, in the Permian or Triassic.

BTW, the snake pages at reptileevolution.com are updated now. More later.

References
Caldwell MW, Nyam RL, Placi A and Apesteguía S 2015. The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution. Nature Communications 6: 5996.[6996]
Conrad JL 2008. Phylogeny and systematics of Squamata (Reptilia) based on morphology. Bulletin of the American Museum of Natural History 310. online here.

Oldest known snakes: Caldwell et al. 2015

Updated February 15, 2014 with the addition of several basal snakes to the large reptile tree (498 taxa) that unites terrestrial snakes and burrowing snakes in one clade derived from basal gekkotans. 

Caldwell et al. (2015)
add 70 million years to the oldest known snakes previously known. Now snake origins go back to the Middle Jurassic/Early Cretaceous. These new fossils are not complete fossils — and they might have had legs. The few parts that are known (Fig. 1) indeed look like snake parts.

This is the paper for which Caldwell and Apesteguía asked me to delete and postpone my work on Jucarasepsp). However, as near as I can tell after reading the paper and supplementary information, Jucaraseps is not mentioned.

Figure 1. Maxillae from several Mid-to-Late Jurassic snakes discovered by Caldwell et al. 2015, including Parviraptor, Diabolosphis and Portualophis.. These are compared to Lanthanotus, an extant limbed precursor to burrowing snakes, like Cylindrophis. Also shown are Eichstaettisaurus, a limbed varanid precursor to terrestrial snakes along with the skulls of Adriosaurus, an elongate limbed pre-snake and Pachyrhachis, a Late Cretaceous snake with vestigial hind limbs and no forelimbs or pectoral girdle.

Figure 1. Maxillae from several Mid-to-Late Jurassic snakes discovered by Caldwell et al. 2015, including Parviraptor, Diabolosphis and Portualophis.. These are compared to Lanthanotus, an extant limbed precursor to burrowing snakes, like Cylindrophis. Also shown are Eichstaettisaurus, a limbed varanid precursor to terrestrial snakes along with the skulls of Adriosaurus, an elongate limbed pre-snake and Pachyrhachis, a Late Cretaceous snake with vestigial hind limbs and no forelimbs or pectoral girdle.

Unfortunately,
in the Caldwell et al. paper their phylogenetic analysis nests snakes with legless amphisbaenids (including Dibamus at their base), odd Sineoamphisbaena, mosasaurs (ncluding Adriosaurus at their base) and varanids (including Heloderma and Lanthanotus) as successively more distant outgroups. It may be that the legless traits swamped any skull differences — and they are legion — yet with many, many convergences.

In the large reptile tree Sineoamphisbaena and a variety of proto-amphisbaenids are derived from skinkomorphs, distinct from varanids, helodermatids and their allies. And certainly distinct from snakes.

The Caldwell et al. paper nested the odd to very odd burrowing snakes, such as tiny Leptotyphlopsin the midst of more traditional above ground snakes. In the large reptile tree Leptotyphlops nests as a very derived taxon.

Snakes are indeed difficult taxa to lump and split. There is a long history of attempts at nesting snakes within the Lepidosauria, many with distinctly different trees and distinct snake origin hypotheses.

An alternate tree
The large reptile tree did not recover the same topology. And the nesting of snakes has taken an odd twist from what I presented over the last four years.

Snakes evolved from the marine taxon, Adriosaurus, which evolved from the terrestrial taxa Jucaraseps and Eichstaettisaurus in order of increasing distance. That hasn’t changed.

What has changed is snake ancestors no longer evolve from basal varanids (which also gave rise to mosasaurs). So Adriosaurus is not a varanid in the new large reptile tree.

Now, according to the large reptile tree, the last common ancestor of traditional snakes through Eichstaettisaurus and Ardeosaurus is Tchingisaurus. So snakes are indeed an ancient clade, likely going back to the Triassic and the lineage of their ancestry goes back to the Middle Permian. Remember, the Ascendonanus nests within the iguanids, and it lived in the Early Permian, the earliest squamate specimen in this taxon list (Fig. 2), and it was more derived than the last common ancestor of skinks, geckos, varanids, snakes and helodermatids. This nesting also finds support in earlier nestings by Conrad (2008) that nested the snake ancestors Ardeosaurus and Eichstaettisaurus tentatively with geckos. In the large reptile tree these taxa now nest closer to geckos than to varanids.

Figure 2. Subset of the Large reptile tree focusing on snake origins within the Squamata.

Figure 2. Subset of the Large reptile tree focusing on snake origins within the Squamata.

Ardeosaurus and Eichstaettisaurus were Late Jurassic with origins probably much earlier. Jucaraseps was Early Cretaceous.

The longevity of several lepidosaur clades, including the extant Sphenodon, is remarkably distinct from the relatively shorter appearances of most archosauromorph, archosauriform, protorosaur and enaliosaur clades.

More on this topic later. I’ll rearrange the pages at reptileevolution.com to reflect these changes and add the taxa that made that happen. Science is a series of improvements.

 

References
Caldwell MW, Nyam RL, Placi A and Apesteguía S 2015. The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution. Nature Communications 6: 5996.[6996]
Conrad JL 2008. Phylogeny and systematics of Squamata (Reptilia) based on morphology. Bulletin of the American Museum of Natural History 310. online here.

A case of convergent discovery

I removed the Jucaraseps (Bolet and Evans 2012) post
for December 06, 2014 on request as a professional courtesy to colleagues Sebastian Apesteguia and Michael Caldwell who wrote:

From MC:
“check it out…somebody has picked it up.  Posted two days ago. [website link deleted]

From SA:
“Dear David, We are preparing the media release for the paper on jurassic snakes. If you keep the post, they will not give us the importance we need to present the news. Could you retire the article until dec 27 or 28? Our article will be published aprox in dec 29. I will appreciate your help on this.”

This is a case of convergent discovery.
|For those who blackwash everything I do, hope this case of convergent discovery turns you around, if even a little. For those of you who saw the Dec. 06 post, evidently you got a sneak preview of an upcoming paper.

The Jucaraseps post will reappear December 29. 
Bolet and Evans (2012) nested Jucaraseps with Eichstaettisaurus, which reptileevolution.com earlier (several years ago) nested with snakes.

References
Bolet A and Evans SE 2012. A tiny lizard (Lepidosauria, Squamata) from the lower Cretaceous of Spain. Palaeontology 55:491-500.

DGS finds Adriosaurus hand

Adriosaurus is a snake ancestor sister with a long sinuous body and tiny limbs. We looked at it earlier here, here and here. Today we’ll take a look at a new specimen SMNH 2158 (Caldwell and Palci 2010), one which evidently did not preserve the manus, but indeed it did. The bones were recovered using DGS, digital graphic segregation.

Figure 1. Adriosaurus manus recovered by DGS. Colorized digits are reconstructed here with continuous parallel interphalangeal lines.

Figure 1. Adriosaurus manus recovered by DGS. Colorized digits are reconstructed here with continuous parallel interphalangeal lines.

That the reconstruction of this tracing produces continuous parallel interphalangeal lines (PILs) and matches other Adriosaurus specimens appears to validate the method, again.

The DGS method 
has been disputed. While I agree that DGS should not be trusted, I think you all will agree, that a central tenet of Science is that nothing should be trusted. Trust is a hallmark of religion and politics. In Science everything should be tested. If an observation is scientifically valid it can be replicated by others using the same method. In this case I did not trust Caldwell and Palci that the manus was unossified or not visible and so tested their observations myself. Another test is whether the method delvers the same results as in other methods using other specimens. An interclavicle was also recovered mixed in with and largely beneath the other bones.

Figure 2. Adriosaurus, a snake ancestor sister.

Figure 2. Adriosaurus, a snake ancestor sister.

References
Caldwell MW and Palci A 2010. A new species of marine ophidiomorph lizard, Adriosaurus skrbinensis, from the upper Cretaceous of Slovenia. Journal of Vertebrate Paleontology 30:747-755.

DGS: pulling more data out of Eichstaettisaurus gouldi

We’ve looked at DGS (Digital Graphic Segregation) before here, here and here. Today another example, pulling more data from a published photo of a prehistoric reptile crushed flat on an Early Cretaceous matrix. It’s Eichstaettisaurus gouldi (Evans et al. 2004, Figs. 1-7), a pre-snake, which we looked at yesterday.

Figure 1. The hind limb and skull of Eichstaettisaurus gouldi according to Evans et al. 2004.

Figure 1. The hind limb and skull of Eichstaettisaurus gouldi according to Evans et al. 2004.

DGS is a method of tracing the bones (Figs. 2-6), then using the tracings to reconstruct the animal (Fig. 7). On the other hand, by using traditional methods, Evans et al. (2004) produced conventional tracings (Fig. 1).

Figure 2. Eichstaettisaurus gouldi in sintu and traced in color. Here the tail and other bones are identified.

Figure 2. Eichstaettisaurus gouldi in sintu and traced in color. Here the tail and other bones are identified.

Overall the specimen (Fig. 2) appears to lack most of its dorsal vertebrae and most of its tail. However, using DGS enables these areas to provide data.

Figure 3. Eichstaettisaurus gouldi pes in situ and traced in color. Compare to figure 1.

Figure 3. Eichstaettisaurus gouldi pes in situ and traced in color. Compare to figure 1. Impressions count in paleontology, not just bones.

Here (Fig. 3) the foot of E. gouldi is traced using colors for digits. Compare this data to the original tracings of Evans et al. (2014, Fig. 1). All of the elements are similar to those in sister taxa. All PILs (parallel interphalangeal lines) are continuous.

Figure 4. Eichstaettisaurus gouldi skull in situ and colorized.

Figure 4. Eichstaettisaurus gouldi skull in situ and colorized in ventral view.

Here (Fig. 4) is the skull in ventral view with elements identified (for mandible and palatal bones see below). Rather than a hyoid, as originally tentatively identified, a supratemporal (St) is positively identified here and there’s another one, too. Elements not originally identified include the prefrontal (Prf), postfrontal (Pof), lacrimal (La), nasal (Na), opisthotic, (Op) and supra occipital (So).

Figure 5. Eichstaettisaurus gouldi mandible in situ traced and colorized.

Figure 5. Eichstaettisaurus gouldi mandible in situ traced and colorized.

Here (Fig. 5) the mandible elements are digitally segregated. Here teeth are identified. In figure 1 no teeth are identified, but Evans et al. (2004) do note the presence of teeth in the text.

Figure 7. Eichstaettisaurus gouldi palate in situ and colorized.

Figure 6. Eichstaettisaurus gouldi palate in situ and colorized. More elements were found here using DGS than by personal examination of the specimen by the three authors, who should have thought it odd that in ventral view so few palatal elements could be identified ten years ago.

Here (Fig. 6) the palate elements are identified using DGS. They are few and far between. Evans et al. only identified the pterygoids, premaxilla and maxilla.

Figure 3. Eichstaettisaurus schroederi.

Figure 7. Eichstaettisaurus schroederi. Previous to 2004, the only known specimen of this genus. Proximal carpals are missing here, as they are missing in Adriosaurus.

Eichstaettisaurus schroederi (Fig. 7) has a more generalized (plesiomorphic) shape. The palate can be partly seen within the orbit, and the elements are more robust than in E. gouldi. 

 

Figure 1. Eichstaettisaurus gouldi. A transitional taxon in the lineage of terrestrial snakes.

Figure 8. Eichstaettisaurus gouldi. A transitional taxon in the lineage of terrestrial snakes. Here all the parts listed above are added to a reconstruction to ensure fit, both mechanically and phylogenetically. The scapula is assumed to have a soft dorsal extension, as in Varanus. The ribs are more slender than phylogenetic bracketing would indicate,  and the coracoids are triangular, the only autapomorphies I’ve found so far. Not sure about neural spines as these are buried in the matrix.

A reconstruction of E. gouldi (Fig. 8) demonstrates the validity of the DGS interpretations as all parts fit both mechanically and phylogenetically. See Varanus, ArdeosaurusAdriosaurus (Fig. 9) and Pachyrhachis for phylogenetic bracketing. Thus, all the parts are transitional morphologies between varanids and basal snakes. Even the anterior bowing of the radius is found in Adriosaurus.

Figure 1. Various specimens of Adriosaurus documenting the reduction of large clawed hands to small clawless paddles, then ultimately disappearing completely.

Figure 8. Various specimens of Adriosaurus documenting the reduction of large clawed hands to small clawless paddles, then ultimately disappearing completely. Note the curved radius and long pedal digits as in E. gouldi.

Eichstaettisaurus gouldi is the first taxon in the lineage of snakes to demonstrate an elongate torso and reduced limbs (though not by very much at this point). These become exaggerated in Adriosaurus and Pachyrhachis.

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.

The loss of hands in proto sea snakes documented in Adriosaurus

In contrast to widely-held traditional theories
that report snakes had a controversial single origin (Lee and Caldwell 2000, Lee and Scanlon 2002), the large reptile tree recovers a heretical two origins for modern snakes.

One set of snakes, led by the Gila monster, Heloderma, are largely burrowing forms, such as Cylindrophis, with increasingly odd jaws that ultimately rotate medially, like Leptotyphlops.

The other set of snakes, led by leggy Ardeosaurus and the elongated marine Adriosaurus (Fig. 1) ultimately led to non-burrowing snakes, like Boa and Pachyrhachis.

Today we’ll look at the reduction of the forelimbs in various species of Adriosaurus (Fig.1) as documented in Palci and Caldwell (2007).

Important to remember,
as noted by Palci and Caldwell, this forelimb reduction in Adriosaurus may be the sequence in which protosnakes lost their forelimbs, OR it may be a parallel and convergent sequence, since limb loss happens so often in elongated lepidosaurs (like skinks that evolve to become amphisbaenids).

Figure 1. Various specimens of Adriosaurus documenting the reduction of large clawed hands to small clawless paddles, then ultimately disappearing completely.

Figure 1. Click to enlarge. From Palci and Caldwell 2007, various specimens of Adriosaurus documenting the reduction of large clawed hands to small clawless paddles, then ultimately disappearing completely. Below, all the humeri are scaled to the same length.

Palci and Caldwell (2007) wisely reported, “Any attempts to understand the evolution of anatomy, such as that displayed by Adriosaurus microbrachis, will be brought up short by the limitations of a static system, that is, the limits of an individual, when the real goal is to understand the transformation of those systems within populations, and between species and other higher taxa.”

This blog and ReptileEvolution.com are devoted to showing and explaining the gradual accumulation of derived traits (which sometimes includes loss of bones). Sometimes no explanation is necessary as the series in Adriosaurus (Fig. 1) so grandly shows.

Interesting
that despite the major differences in fore limb morphology in these Adriosaurus specimens, all four are considered congeneric by Palci and Caldwell 2007.

Short note:
Earlier I posted three phylogenetic matrices on MorphoBank.org. Several interested parties downloaded work from there. Recently, however, the regents there decided they wanted to restrict posted matrices to those that had been peer-reviewed and published. So, my matrices are no longer available there. Nevertheless, anyone interested can always write to me directly through this website and request a matrix.

References
Lee MSY and Caldwell MW 2000. Adriosaurus and the affinities of mosasaurs, dolichosaurs, and snakes. Journal of Paleontology 74:915-937.
Lee MSY and Scanlon JD 2002. Snake phylogeny base on osteology, soft anatomy and ecology. Biological Reviews 77:333-401.
Palci A and Caldwell MW 2007. Vestigial forelimbs and axial elongation in a 95 million-year-old non-snake squamate. Journal of Vertebrate Paleontology 27(1):1-7.

The return of Najash – svp abstracts 2013

From the abstract
Apestguia and Garberoglio wrote: “La Buitrera is a fossiliferous locality from northern Patagonia, Argentina. It 
preserves superb small to mid-sized skeletons in a Gobi style, but evidencing subaereal exposure, scavenging, dissolution and shallow disarticulation. Skeletons are commonly well-defined and clearly separated from other. Lag deposits are present too, but as consequence of disarticulation of complete skeletons. Najash rionegrina is the only snake found in this locality. The phylogenetic approach positioned this species as the basalmost snake, bringing it into the large debate of snake origins. The species was primarily described based on one specimen consisting of a largely complete vertebral sequence of 122 vertebrae from axis to caudals, including pelvis, limbs and a dentary. As frequent in La Buitrera style, this specimen was largely articulated except for some displaced vertebrae (isolated within the jacket), the dentary some millimeters in front of the axis, and the fibula at less than one centimeter from the tibia. A recent work discussing the position of Najash proposed the exclusion of these elements for not being in anatomical contact. We reject this opinion. Full anatomical contact is rare in vertebrate paleontology. Concerning other elements, found isolated and at about 3 km (i.e., an isolated partial skull, a quadrate, an additional dentary and several vertebrae), included as referred material, debate is understandable. A recent visit to the locality resulted in the finding of two additional specimens, both provided with skull and bearing vertebrae that are indistinguishable from those described for the holotype. One of them bears an incomplete skull preserved almost exactly as the published one. The second skull, although still unprepared, bears an “anilioid” general aspect and preserves premaxilla, nasal, vomer, prefrontal, frontal, maxilla, jugal and postfrontal (both clearly differentiated), ectopterygoid, parietal, prootic, otoccipital, supraoccipital, supratemporal and quadrate. The lower jaw includes compound bone, angular and a dentary with two foramina. This new specimen makes a substantial contribution to make Najash rionegrina one of the better known basal snakes.”

Figure 1. The origin of snakes going back to the most primitive reptile, Cephalerpeton. To learn more about these taxa, find them on reptileevolution.com

Figure 1. Click to enlarge. The origin of snakes going back to the most primitive reptile, Cephalerpeton. To learn more about these taxa, find them on reptileevolution.com

Notes
Earlier we looked at the Najash pelvis. Now the skull is known and it has an “anilioid” aspect, confirming the hypothesis that Najash belongs to the burrowing clade of snakes, not the swimming clade. I’m looking forward to seeing more of this specimen.

The diphyletic snakes and their lineages.

Figure 2 The diphyletic snakes and their lineages. Here the squamosal is highlighted in tan and the supratemporal is in magenta to illustrate the homologies of these bones. The supratemporal on the right is a relatively tiny bone. The squamosal on the left is the tiny bone, further differentiating the two main clades of snakes.

References
Apestguia S and Garberoglio F 2013.
The return of Najash: new better preserved specimens change the face of the most basalmost snake. Journal of Vertebrate Paleontology abstracts 2013.

The Origin of Snakes Goes Way, Way Back

As we learned earlier, hypotheses on snake origins have suffered by not recognizing that living snakes are diphyletic. The tiny burrowing snakes (Scolecophidia, Aniliidae, Uropeltidae), like Cylindrophis, have a separate lineage through ancestors like Heloderma. The larger non-burrowing snakes (Macrostomata), like Pachyrhachis, have a lineage through Adriosaurus and Ardeosaurus (Fig. 1) according to the large reptile tree.

Wiki reports, “Based on comparative anatomy, there is consensus that snakes descended from lizards.”

Well, duh…

Figure 1. The origin of snakes going back to the most primitive reptile, Cephalerpeton. To learn more about these taxa, find them on reptileevolution.com

Figure 1. Click to enlarge. The origin of snakes – to scale – going back to the most primitive reptile, Cephalerpeton. To learn more about these taxa, find them on reptileevolution.com. Along the way several of these taxa were basal to new clades. The basal forms, many still unknown, are small and lizardy.

Wiki also reports, “The origin of snakes remains an unresolved issue. There are two main hypotheses competing for acceptance. 1) Burrowing lizard hypothesis; 2) Aquatic mosasaur hypothesis.”

As it turns out, based on the results of the large reptile tree, both are correct.

Wiki notes that Anilius is the most primitive known snake and the large reptile tree nests it closest to Lanthanotus, a sister to the ancestor of burrowing snakes. These are not directly related to boas, cobras and king snakes.

How far back can we trace the origin of snakes?
With the large reptile tree we can trace the origin of snakes back to Ichthyostega, but here (Fig. 1) we go back to the most primitive known reptile, Cephalerpeton. Because snakes are at one end of the lepidosaurormorph branch to get to snakes you pass through the basal taxa of all the other lepidosauromorphs, including diadectids, caseids, pareiasaurids, chelonians, gliding lepidosauriforms, lepidosaurs, tritosaurs (including pterosaurs and drepanosaurs) and squamates (including squamates). So, what we have are a series of mostly small lizardy forms (Fig. 1) that ultimately gave rise to a wide variety of derived forms. Several lizardy squamates lost their limbs. Snakes are just the most successful version of these.

What is Najash?
Described as a terrestrial Cretaceous protosnake with legs, Najash (Apesteguía and Zaher 2006) appears to share more pelvic traits with Heloderma than Adriosaurus, confirming our tree topology separating burrowers from the others, including swimmers.

Figure 2. The pelvis of the protosnake with legs, Najash, compared to Heloderma (burrower) and Adriosaurus (swimmer). Heloderma appears to share more traits with Najash.

Figure 2. The pelvis of the protosnake with legs, Najash, compared to Heloderma (burrower) and Adriosaurus (swimmer). Heloderma appears to share more traits with Najash, such as a curved ilium and ventrally narrowing pubis. The femur of Najash includes a very large process is not found in either candidate.

All it takes is another study with a similar gamut to confirm the diphyletic origin of living snakes.

References
Apesteguía S and Zaher H 2006. A Cretaceous terrestrial snake with robust hindlimbs and a sacrum. Nature 440: 1037-1040.

Adding Anilius, a Basal Snake, to the Large Reptile Tree

A recent paper on the phylogeny and prehistory of blind snakes (Vidal et al. 2010) listed Anilius (Fig. 1) as an outgroup taxon along with Tropidophis (dwarf boa), Elapidae (venomous snakes like the cobra) and Boa (the famous constrictor). Anilius is primitive enough to retain a vestigial pelvic girdle, visible as a pair of cloacal spurs, according to Wiki. Wiki also reports that Anilius “is considered to be the snake that most resembles the original and ancestral snake condition, such as a lizardlike skull.” Boa also retains a rudimentary pelvis and hind legs that externally appear as minor spurs.

Anilius skull

Figure 1. The skull of Anilius in dorsal and lateral views, courtesy of Digimorph.org. Elements here colorized and labeled. Click to enlarge. The post frontal is fused to the frontal. The jugal is fused to the maxilla. The supratemporal is tiny.

Anilius is medium-sized, reaching 27 inches (70 cm) in length. The eyes are covered beneath a clear scale.  It is a burrowing snake feeding on small reps, amphibians and even other blind snakes.

I wondered if this basal snake would change or enhance the current diphyletic nesting of snakes in the large reptile tree. After testing it nested between Lanthanotus (with legs) and Cylindrophis (without legs), nowhere near Boa, which nests with other larger non-burrowing snakes, like Pachyrhachis. The Vidal et al. (2010) nesting of Anilius at the base of the tree is due to the lack of more closely related more primitive taxa, a situation remedied by employing the large reptile tree.

The Vidal et al. (2010) study was quite remarkable and complete. However, deeper outgroup taxa were not employed and for good reason. The blind snakes are widely considered monophyletic.

Blind snake origins are distinct from that of other snakes when deeper outgroups are employed and Anilius appears to be closer to them than to non-burrowing snakes.

The Vidal et al. (2010) study postulated that the split between non-burrowing snakes (Alethinophidia, including Anilius) and the blind snakes (Scolecophidia) occurred sometime in the Jurassic, with taxa like Anilius likely little changed since then. This coincides with the breakup of Pangaea, which makes sense if burrowing blind snakes are going to spread world wide prior to the continental breakup. They prefer warm climes.

Bone Fusion
It’s important to recognize when bones fuse (Fig. 1) so we don’t consider certain bones “absent” in phylogenetic analysis. It’s also important to include lots of prehistoric taxa to discover where blind snakes do nest in the grand scheme of things.

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
Vidal N, Marin J, Morini M, Donnelllan S, Branch WR, Thomas R, Vences M, Wynn A, Cruaud C and Hedges SB 2010. Blindsnake evolutionary tree reveals long history on Gondwana. Biology Letters 2010 6, 558-561.

Tethysaurus, the odd mosasaur

Tethysaurus nopscai (Bardet et al. 2003) is a mosasaur of the Early Turonian (Late Cretaceous) from Morocco. Wiki puts its length at about 10 feet (3 meters), but the skull here is less than a foot long. I haven’t seen a complete specimen yet.

Tethysaurus

Figure 1. Tethysaurus based on and the private specimen shown below. Click to enlarge.

Haven’t seen the limbs either. 
I’m not able to make out limbs in the specimens I’ve seen (Fig. 2). Other mosasaurs have large paddles, but Aigialosaurus, a closer relative, has relatively smaller paddles.

The large reptile tree nests Tethysaurus with Aigialosaurus and both with Varanus, distinct from Adriosaurus and the origin of most snakes and Lanthanotus and the origin of pipe snakes. So the small forelimbs appear by convergence with pre-snakes.

Tethysaurus

Figure 2. Tethysaurus prepared by the Fossil Shack, image from Wiki. Click to enlarge.

Seems like one to several Tethysaurus specimens are known from the private market (Fig. 2). That doesn’t matter to me. I’d like to see more data on the tail and hind limb if possible.

Thanks to Chris Collinson for alerting me to the mistake I had made earlier based on a mislabeled metriorhynchid crocodilomorph (deleted now). The lateral and dorsal views I reconstructed were based on the skull presented by Bardet et al. (2003).

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
Bardet N, Pereda Suberbiola X and Jalil N-E 2003. A new mosasauroid (Squamata) from the Late Cretaceous (Turonian) of Morocco. Comptes Rendus Palevol 2:607-616.

wiki/Tethysaurus