Varanosaurus and the Ophiacodontidae

This post was updated on August 12, 2013 prompted by the addition of several taxa. 
Dr. Roger Benson (2012) recently proposed a family tree of basal synapsids (pelycosaurs) that was covered earlier. Benson (2012) added Varanosaurus as a late surviving member of the Ophiacodontia (Fig. 1) following Berman et al. (1995). The long rostrum and short cranial region of Varanosaurus (Fig. 2) is indeed shared with Ophiacodon. They are closely related, along with Apsisaurus. the ophiacodontid, Archaeothyris is basal to them.

Varanops and Varanodon nest in a different clade, with Elliotsmithia and Aerosaurus, taxa with the orbit at mid skull.

Figure 1. This time calibrated strict reduced consensus cladogram recovered by Benson 2012. This tree assumes the Varanopidae became extinct, whereas the large reptile tree found one part (yellow portion) of the Varanopid branch gave rise to diapsids, including living birds and crocs. Casesauria do not belong in this tree as they are related to Millerettids.  Therapsids arise from ophiacodontids in the large reptile tree.

Figure 1. This time calibrated strict reduced consensus cladogram recovered by Benson 2012. This tree assumes the Varanopidae became extinct, whereas the large reptile tree found one part (yellow portion) of the Varanopid branch gave rise to diapsids, including living birds and crocs. Casesauria do not belong in this tree as they are related to Millerettids. Therapsids arise from ophiacodontids in the large reptile tree.

Romer and Price (1940) published a reconstruction of Varanosaurus. However it differs in several respects from a complete skull image found on the web (Fig. 2). It is a distinct specimen, MCZ 1366.

Varanosaurus.

Figure 2. Above – Images from Romer and Price (1940) of the MCZ specimen. Middle – Photo image  of the FMNH specimen of Varanosaurus. Below – Tracing of the photo. This appears to be a distinct specimen and species, not just the result of crushing. Note the second lateral temporal fenestra, likely the result of an increase in the size of the jugal and squamosal.

Three Different Varanosaurus Specimens
Benson (2012) reports that the earlier Romer and Price (1940) specimen, MCZ 1366, is highly reconstructed. Berman et al. (1995) reported on FMNH PR 1760 (Fig. 2) and BSPHM 1901 XV 20 (Fig. 3.

Figure 3. The BSPHM specimen of Varanosaurus

Figure 4. A new nesting for the two new Varanosaurus specimens according to the large reptile tree. These two nest at the base of the main group of synapsids and close to the protodiapsids (synapsid taxa leading toward the diapsid, Petrolacosaurus). Note, Ophiacodon nests three nodes away.

Figure 4. A new nesting for the two new Varanosaurus specimens according to the large reptile tree, as outgroups to Ophiacodon and derived from a sister to Apsisaurus.

The large reptile tree includes several times more taxa than either the Benson (2012) tree or the Berman et al. (1995) tree. It recovered a tree in which both of the new Varanosaurus specimens were sisters to one another and nested with Apsisaurus at the base of the Ophiacondontidae. This clade includes therapsids and mammals. The Sphenacodontidae, formerly considered therapsid ancestors, is a sister clade to Ophiacodon and Apsisaurus (Fig. 4). Diapsids evolved from basal synapsids, like Heleosaurus.

The MCZ specimen was not tested.

So Varanosaurus was a late-surviving member of a basal synapsid clade. Varanosaurus had the proportions of a modern Varanus, the monitor lizard, and likely had a similar lifestyle.

Duplicating Results
Both the Berman (1995) and Benson (2012) studies could have benefitted by including more outgroup taxa (Fig. 4) and dropping Caseasauria, which are not related. Apsisaurus needs to be included.

References
Benson RBJ 2012. Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies. Journal of Systematic Palaeontology, iFirst 2012, 1-24.
Berman D S, Reisz RR, Bolt JR, and Scott D. 1995. The cranial anatomy and relationships of the synapsid Varanosaurus (Eupelycosauria: Ophiacodontidae) from the Early Permian of Texas and Oklahoma. Annals of Carnegie Museum 64: 99-133.
Romer AS and Price LW1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.

More Therapsid Palates

Yesterday I published a bad Biarmosuchus palate based on an erroneous illustration at Palaeos, another website devoted to prehistory. Today I’ll try to rectify that error and take the process another step forward.

There are two problems I’m trying to solve.
Was Archaeothyris closer to basal therapsids, like Nikkasaurus, than the traditional therapsid ancestors, the sphenacodonts?

And did Nikkasaurus + dicynodonts and kin split from biarmosuchids and kin at the base of the Therapsida, near Nikkasaurus?

At present, both of these heretical hypotheses are recovered by the large reptile tree. However neither Archaeothyris nor Nikkasaurus, preserve the palate, to my knowledge. So we have to look at what we do have: sisters and cousins. Complicating the matter is the evolution of a more 3-dimensional palate, with a deeper vomer (in palatal view) and an advancing secondary palate coming in from the sides. Further complicating the matter is a large amount of convergence, as you’ll see.

Six synapsid palates.

Figure 1. Six synapsid palates. Bones color-coded. With Biarmosuchus the sutures are not well-preserved, but this should be an improvement on my earlier attempt. Note the wide variety here, even in closely related taxa.

Ophiacodon and Haptodus
The palates of Ophiacodon and Haptodus are closer to one another in appearance than either is to the other four. The overall shape of the palate in Haptodus is closer to Biarmosuchus, but Ophiacodon is also much longer than the absent Archaeothyris (please remember the actual sister to the most primitive therapsids was not Archaeothyris, Ophiacodon nor Haptodus, but a missing taxon nesting close to all three and closer still to Nikkasaurus, a largely ignored late-surviving, but basal therapsid).

First problem: Ophiacodonts vs. Sphenacodonts
The palates of Haptodus and therapsids had a longer vomer and a longer pterygoid posterior to the transverse process. Ophiacodon and therapsids had smaller palatal teeth. The vomer contacted the pterygoid in Haptodous and therapsids. The interpterygoid vacuity was smaller in Ophiacodon and therapsids. The maxilla produced a slight medial shelf in Haptodus. The ventral skull was pinched in at the canines in Ophiacodon and therapsids.

Yes, it’s pretty clear, neither Ophiacodon nor Haptodus makes as good of a sister to Biarmosuchus than the imaginary missing taxon somewhere in between them…something like Nikkasaurus.

Second problem: A nearly diphyletic Therapsida
Other trees find dicynodonts to be sister to gorgonopsians and both derived from dinocephalians and biarmosuchians. The large reptile tree finds dicynodonts split from all other therapsids at the base of their clade.

Therapsids are known for their canine teeth, but there are no canine teeth in Endothidon (Fig. 1), Otsheria and Nikkasaurus.  Other dicynodonts had canine teeth, often their only teeth. Since dicynodonts were plant eaters, one wonders if canine teeth in dicynodonts were secondarily evolved, as it appears when one compares Tiarajudens to its sister, Anomocephalus. The sisters to dicynodonts, dromasaurs like Suminia and Galechirus, also lacked large canines.

A suborbital fenestra is present in Regisaurus, but not in Procynosuchus, or that other taxa here. Not sure about Biarmosuchus.

The quadrates were small in Biarmosuchus and Regisaurus, but they were larger in the pelycosaurs and dicynodonts.

The choanae opened ventrally in four the synapsids, but not in  Regisaurus and Endothiodon, which had something of a secondary palate, again, likely by convergence. The choanae were displaced posteriorly in both dicynodonts and Regisaurus, likely due to convergence.

The palates of the two figured dicynodonts are not close to one another in morphology. The large variety in these six palates provides no clear guidance with regard to basal therapsid affinities. The morphological distances between these taxa is great and the palate of a key taxon, Nikkasaurus, remains unknown.

When I learn more, we’ll come back to this subject. I do know that without Nikkasaurus resolution is lost at that node in the large reptile tree. Yes, its that close and Nikkasaurus is rarely included in other phylogenetic studies.

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.

New Evidence for a Therapsid/Ophiacodont Relationship in the Palate ??

The palates of Haptodus, Ophiacodon and Biarmosuchus.

Figure 1. The palates of Haptodus, Ophiacodon and Biarmosuchus. More traits are shared by the latter two to the exclusion of Haptodus. Okay, that’s wrong. I had a bad bit of data here for the Biarmosuchus skull. I went with a published image, then realized the mistakes I made here. Do-over in process.

Another short one. The picture tells the story (that was written Jun 17. And sometimes that story is wrong when the data is wrong. All the copy here in red was written the day after, the 18th. I’m trying to keep up a one-a-day blog schedule and fell into “well, isn’t that convenient” trap. Hopefully today we’ll put in a few fixes. Nuf sed. See next blog. Apologies. 

Addendum. Now I see that M. Mortimer has some comments as well. Looks like we have some house cleaning here. Let’s do it and see what comes of it. 

Most Azhdarchids Were Small

This is a short post (literally)
Everyone goes crazy over giant azhdarchids, but the fact is most were small to tiny (Fig. 1). The cause of gigantism is still unknown, but here, among these stork-like wading pterosaurs, it certainly enabled wading into deeper waters. It is also notable that there is isometric scaling going on here. The larger ones, like Quetzalcoatlus, are not much more robust than the tiny ones, like no. 42.

Azhdarchids and Obama

Figure 1. Click to enlarge. Here’s the 6 foot 1 inch President of the USA alongside several azhdarchids and their predecessors. Most were knee high. The earliest examples were cuff high. The tallest was twice as tall as our President. This image replaces an earlier one in which a smaller specimen of Zhejiangopterus was used.

I have a date tonight and have to get to work soon, hence the brevity of this post. We’re about three weeks away from our 365th heresy.

More tomorrow.

Addendum:
Thanks to Armchair Paleontologist for noting I earlier used a smaller Zhejiangopterus specimen. That was featured later here. And below, a selection of large azhdarchids, unfortunately none of them complete as fossils. 

The larger azhdarchids.

Figure 2. The larger azhdarchids.

The Question of Correlated Characters

Earlier, and on the Dinosaur Mailing List, David Marjanovic and Mickey Mortimer dismissed the phylogenetic analysis that produced the large reptile tree and the other trees (pterosaur, therapsid) due to their inclusion of purported correlated characters. I think this is short-sighted.

I’m here to tell you, it’s damn hard to avoid including correlated characters. For instance:

1. A long dorsal series of vertebrae is correlated to short to absent limbs.

2. A long canine tooth is correlated to a tall maxilla (that’s where the root is found) and often correlated to a deep dentary to protect it.

3. A large orbit is often correlated to a short rostrum, especially in taxa of relatively small overall size.

4. Unsharp, unconical teeth (they come in many shapes and sizes) are correlated to a broad or deep ribcage.

5. Wings of two sorts are correlated to a strap-like scapula and an elongated, locked-down coracoid.

6. A kinked tail is correlated to the development of flippers

7. A carapace is correlated to short fingers and toes.

8. Bipedal hind limbs and simple hinge ankle joints are correlated to reduced forelimbs, except in flying tetrapods.

9. An elongated neck is typically correlated to a small skull (with exceptions, of course).

10. A thick-boned skull is typically correlated with a thick-boned pelvis and hind limbs.

I’m sure you can think of others.

Caveat: There are exceptions to everything listed above. So don’t raise a finger immediately. I’m only asking, “how can you create a list of characters that does not include a certain amount of correlation?” Or even a lot of correlation? Evolution follows certain patterns. A dorsal fin will often appear in marine taxa. That happens. Correlation is everywhere.

Convergence in the Large Reptile Tree
The Consistency Index (CI) is a number that can be recovered in PAUP and it represents the amount of convergence in the matrix. In the large reptile tree the CI hovers near 0.1. Nearly every character finds at least two expressions somewhere on the tree. Mortimer and Marjanovic see this as a fault of the study. I see this as a fact recovered by the study. And it shows the strength of the study that the tree could separate the various convergent traits by maximizing parsimony.

Emphasizing Certain Traits
In the past, paleontologists have emphasized skull fenestrae and ankle traits in determining phylogenetic relationships. According to Mortimer and Marjanovic correlation is to be avoided because it over-emphasizes certain traits. The problem is, certain taxa are known from only a skull, so by default, skull traits are emphasized in the scoring of these taxa. Others are known from only other body parts and these are emphasized, by default. There’s nothing else you can do about it!

Like democracy, it’s not perfect, but it’s the best thing we have at present. Notably, neither Mortimer nor Marjanovic have been able to identify misnested genera within the large reptile tree without resorting to nebulous suprageneric taxa.

The large reptile tree is completely resolved and continues to be so as more taxa are added. All evolutionary pathways provide a gradual accumulation of traits, which is what we’re looking for as we attempt to model the original family tree of life.

Methods can always be faulted. There’s always a sniper in the bell tower. The results here speak for themselves. Even so, if errors are found, please bring them to my attention.

When a Lateral Temporal Fenestra Becomes an Upper Temporal Fenestra

It’s interesting.
Take a look at a cynodont or dicynodont skull (Fig. 1) and you get the impression that those two fenestra, nearly invisible in lateral view and touching each other in dorsal view, must be upper temporal fenestrae.

Basal Therapsida.

Figure 1. Click to enlarge. Basal Therapsida. Sorry for using the same figure twice within a week. Note the convergent enlargement of the lateral temporal fenestra in dicynodonts and dinocephalians, with the subsequent reduction in Tapinocephalia due to pachyostosis (bone thickening).

Placed into a phylogenetic framework…
It’s been known for decades that the lateral temporal fenestra in basal synapsids expanded dorsally and laterally, at first squeezing the cranium between its advancing margins. Then, as the brain expanded in mammals, the cranium rose above the lateral temporal fenestrae. There is still a crest marking the old midline boundary in many mammals. In humans the crest is absent, replaced by an even larger cranium.

Essentially the skull in mammals is inside out
In most reptiles, the jaw muscles and the braincase are inside the skull. In mammals the braincase and cheekbones are all that remains of the old reptile skull. The braincase and jaw muscles are on the outside.

Sorry, not alot of jaw-dropping news lately. Must be the summer collection season…

Dibamus and Boa Nestings PLUS the Problem with DNA

With regard to legless lizards, including snakes, blogger and paleontologist Mickey Mortimer mentioned in a recent comment here, “Vidal and David (2004) found that Uropeltis groups with Boa instead of Leptotyphlops by two nodes supported with 100% Bayesian posterior probability based on two nuclear genes.”

Curious about this, I added Boa constrictor to the large reptile tree (I’ll add it to the graphic tree when I get a few more taxa). To no surprise, Boa nested with Pachyrhachis, “the snake with (hind) legs.” Uropeltis did not group with Boa, but stayed with Leptotyphlops. Once again, DNA results did not match morphological results.

Scleroglossa
Morphology divides the Squamata into Iguania and all remaining squamates into a group named Scleroglossa. In the latter, the tongue is at least partly keratinized and flattened relative to iguanians (Estes et al., 1988). Members of the Iguania are mainly ambush predators, using visual prey discrimination and capture their prey by their sticky tongue., Members of the Scleroglossa use their tongue to seek out prey, but rely on their jaws to apprehend prey. The scleroglossan skull is less rigid (Vitt et al., 2003). This reaches an acme with snakes.

According to Rieppel (1988) there have been four main hypotheses as to the affinities of snakes:

1. With varanoids/mosasauroids (Cope, 1869; Nopcsa, 1923).
2. Independent of other squamates (Underwood, 1970).
3. With legless burrowing scincomorphs and dibamids (Senn and Northcutt, 1973).
4. With legless amphisbaenians (Rage, 1982).

Since 1988, Pachyrhachis, the snake with legs, was described. A fifth hypothesis (Palci A and Caldwell MW 2007) based on a derivation from the aquatic varanoid, Adriosaurus, appeared. Conrad (2008) sided with (3 and 4) in linking snakes to amphisbaenids, burrowing scincomorphs and dibamids.

The large reptile tree represents a sixth hypothesis in which most snakes were derived from a sister to Pachyrhachis, Adriosaurus and Ardeosaurus in that order. Other, less common, burrowing snakes (Cylindrophis, Uropeltis, Anomochilus and Leptotyphlops were derived from a sister to Lanthanotus, Heloderma and Cryptolacerta in that order.

Dibamus
Odd little Dibamus was tested and it nested between Spathorhynchus and Tamaulipasaurus two sisters of Bipes, Amphisbaena and other skinks. Not sure if fossil taxa have been included with other Dibamus studies, but I think not. Let me know if otherwise.

Legless Taxa
I have to admit, one of the reasons why my snakes don’t nest with my legless skinks is because virtually no post-cranial traits are used because I don’t have good data on post-crania. If leglessness is convergent, this works. If homoplastic, which appears doubtful, then it doesn’t.

DNA
DNA studies cannot pull data from fossils, so left with living taxa, some with a legacy going back to the Permian and beyond (before their eventual splits), we have to rely on morphological studies. We have to find a gradual accumulation of traits, something that DNA doesn’t give us, in reptiles at least. Mammals seem to fare better. Not sure why.

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
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(3): 747-755. doi:10.1080/02724631003762963.
Conrad JL 2008. Phylogeny and systematics of squamata (Reptilia) based on morphology. Bulletin of the American Museum of Natural History 310, 182 pp.
Estes R, de Queiroz K and Gauthier JA 1988. in Phylogenetic Relationships of the Lizard Families (eds Estes, R. & Pregill, G. K.) 119–281 (Stanford Univ. Press).
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. doi:10.1671/0272-4634(2007)27[1:VFAAEI]2.0.CO;2.
Seeley HG 1881. On remains of a small lizard from Neocomian rocks of Comen, near Trieste, preserved in the Geological Museum of the University of Vienna. Quarterly Journal of the Geological Society of London 37: 52-56.
Vidal N and David P 2004. New insights into the early history of snakes inferred from two nuclear genes. Mol. Phyl. Evol. 31:783-787.
Vidal N and Hedges SB 2002. Higher-level relationships of snakes inferred from four nuclear and mitochondrial genes. C. R. Biologies 325 (2002) 977–985.
Vidal N and Hedges SB 2004. Molecular evidence for a terrestrial origin of snakes. Biol. Lett. 2004;271:226–229.doi:10.1098/rsbl.2003.0151

Basal Synapsid Phylogeny – Benson 2012

A recent paper on basal synapsids (pelycosaurs) by Roger Benson (2012) reported, “Although cranial data support the current consensus that Caseasauria is the most basal clade, postcranial data and the full dataset suggest that a clade of Ophiacodontidae +Varanopidae occupies this position. Although relationships within higher clades are well supported, relationships among those clades are poorly supported.”

He also reported, “Sphenacodontia, encompasses all therapsids, including mammals.” While traditional, this needs to be rethought in light of the results of the large reptile tree which recovered therapsids from ophiacodonts close to Ophiacodon, Archaeothyris and Nikkasaurus through Stenocybus. (Sorry, not all images are up to date and include this taxon).

Roger Benson could have used the large reptile tree as a basis for taxon selection. Caseasauria are not related to Synapsida, for starters. Ophiacodonts produced therapsids. Taxon exclusion was the problem.

Figure 1. Click to enlarge. The Time calibrated strict reduced consensus cladogram recovered by Benson 2012. This tree assumes the Varanopidae became extinct, whereas the large reptile tree found this branch gave rise to diapsids, including living birds and crocs. The tree assumes that Casesauria are synapsids, but the large tree nests them with millerettids. The nesting of therapsids within Sphenacodontia is traditional, but lacking Nikkasaurus as a late-surviving basal therapsid obscures the relationship with Archaeothyris. The tree also lacks a series of outgroup taxa for the Synapsida.

Results of the Benson 2012 Tree
“The strict consensus of 15,552 MPTs is generally well resolved (Fig. 2A). The commonly recognized major clades of basal synapsids (e.g. Reisz 1980, 1986) are recovered. However, relationships among these clades differ from recent consensus because Ophiacodontidae and Varanopidae are the most basal synapsid clades, forming a polytomy with Archaeothyris, Echinerpeton, and a clade comprising Caseasauria + Ianthodon + Edaphosauridae + Sphenacodontia.” 

15, 552. That’s a lot of trees! I don’t see Stenocybus here, the basalmost therapsid in the large reptile tree.

The Importance of Nikkasaurus
In the large therapsid tree, removal of Nikkasaurus from the therapsid tree yields a polytomy between Ophiacodon, Edaphosaurus and Dimetrodon at the base of a diphyletic Therapsida. Removal of Nikkasaurus and Ophiacodon moves Edaphosaurus and Dimetrodon to the base of the Therapsida.

The Diphyletic Varanopidae
Benson 2012 recovered a clade of varanopids (Varanodon and Varanops) distinct from others (Heleosaurus, Mesenosaurus and Mycterosaurus. The large reptile tree also recovered this division. However the addition of several basal diapsids (Petrolacosaurus, Eudibamus, etc.) indicate these were basal synapsids, more basal than Archaeothyris, the earliest known synapsid, and not far from the Heleosaurus clade, which probably should not be included within the Varanopidae, despite a close relationship.

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
Benson RBJ 2012. Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies. Journal of Systematic Palaeontology, iFirst 2012, 1-24.

Is the Septomaxilla the Anterior Lacrimal in Synapsids?

In basal reptiles, the lacrimal bone extends from the naris to the orbit. This bone includes the tear duct that empties into the nasal cavity. The tear duct is the former second choana (the exit) in osteolepid rhipidistian fish.

In derived reptiles the lacrimal retreats from the naris but remains connected to the orbit.

In basal synapsids, the lacrimal continues to rim the naris. Among sphenacodontids, Haptodus and Edaphosaurus have this trait, but Sphenacodon and Dimetrodon do not. The nasal grows down further, touching the maxilla, covering the lacrimal.

Among protodiapsids, like Heleosaurus and Mesenosaurus, the maxilla rises to block the lacrimal from the naris.

Ophiacodon and the Origin of the Therapsida

Figure 1. Click to enlarge. Ophiacodon and its phylogenetic successors, the pelycosaurs and the therapsids. Note the extent of the lacrimal in blue.

In Ophiacodon it is not clear from available data whether or not the maxilla rises to block or overlie the lacrimal, but in all therapsids, including Nikkasaurus at the base, the maxilla overlaps the lacrimal, but not completely. Near the naris a part remains visible. Traditionally it is called the septomaxilla. Near the orbit the larger portion of the lacrimal remains visible. The interesting thing is the so-called septomaxilla always lines up with the lacrimal with the maxilla laminated over a portion of it.

In mammals the tear duct continues to empty into the nasal cavity.

Addendum: In Stenocybus we can see the septomaxilla taking over for a retreating lacrimal. So they are not the same bone.

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.

Do Snakes Have a Short Neck? Or Long?

One of the mysteries of herpetology and paleontology is just where do the cervicals end and the dorsals begin on a snake. It’s impossible to say in modern taxa (Fig.1). The cervicals blend imperceptibly with the dorsals. The question is complicated by the presence of two distinct clades of “snakes” in the large reptile tree.

The location of the thyroid and lung some 20+ cervicals back of the head appear to delineate where the dorsals begin in most snakes. I haven’t found much information on the post-crania or anatomy of the so-called “burrowing” snakes like Cylindrophis and Leptotyphlops. [help!!]

One clade of snakes arose from a sister to long-necked Adriosaurus (14 cervicals) that leads to Pachyrhachis (22 cervicals, Fig. 2) and Boa (unknown number, but likely about 22 based on the location of the thyroid and lungs, Fig. 1).

Boa constrictor.

Figure 1. Boa constrictor. Alternating green vertebrae are likely cervicals. Purple vertebra is a likely sacral.

Pachrhachis, the snake with legs.

Figure 2. Pachrhachis, the snake with legs. Alternating green vertebrae are likely cervicals.

Lee and Caldwell (1998) report, “In the case of Pachyrhachis, this also means the putative cervicals are diferentiated from the putative dorsals by a marked diverence in size, the shape of the neural spine, and the length, robustness and ossication of the associated ribs. The anterior region is well-preserved in both specimens and there is no sign of a pectoral girdle or forelimb. These elements were therefore absent: however, the cervical-dorsal boundary (vertebrae 20-22) presumably represented the approximate original position of the shoulder girdle and forelimb.”

Another clade arising from a sister to Heloderma (6 cervicals) and Lanthanotus (apparently more than 6 cervicals, but I have no data) that includes Cylindrophis through Leptotyphlops. (Any post-cranial data on these taxa would be gratefully appreciated). Dr. Nate Kley sent two references (Bergman 1953) that I’d like to see on Cylindrophis.

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
Bergman RAM 1953. The anatomy of Cylindrophis rufus (Laur.). I. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen, Series C 56:650–656.
Bergman RAM 1953. The anatomy of Cylindrophis rufus (Laur.). II. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen, Series C 56:657–666.
Lee MSY and Caldwell MW 1998. Anatomy and relationships of Pachyrhachis problematicus, a primitive snake with hindlimbs. Philosophical Transactions of the Royal Society London B 353:1521-1552.