What is Tamaulipasaurus?

Tamaulipasaurus morenoi (Clark and Hernandez 1994, Fig. 1) Early Jurassic ~165mya, was a very early burrowing lizard originally considered “similar to living amphisbaenian and dibamid squamates but represents an entirely new lineage related to squamates but outside the group.” That’s because it has a robust quadratojugal, a bone otherwise unknown in squamates (see figure 2).

Evidently that was confusing back then.
Despite it’s strong resemblance to Bipes (Figs. 2, 3), Clark and Hernandez did not know what Tamaulipasaurus was back in 1994, and they still don’t know what it is, based on Clark’s current website (which also has other issues covered here and here). They put too much importance on the presence of the quadratojugal.

It’s not that important. 
As was demonstrated earlier, the quadratojugal has a way of disappearing and reappearing in various clades. So it’s not a big deal if it’s there or if it is not in a large phylogenetic analysis that includes hundreds of traits. While we’re on the subject, temporal fenestra also appear and disappear on occasion, so don’t apply hard and fast ‘rules’ to their appearance. Just run the analysis. Let parsimony prevail.

Figure 1. Tamaulipasaurus, a burrowing reptile with an autapomorphic quadratojugal.

Figure 1. Tamaulipasaurus, a burrowing reptile with an autapomorphic quadratojugal. The big question is not the novel quadratojugal, but that tiny little fenestra in the rostrum. Is it the orbit, as in Spathorhynchus and as Clark and Herenandez identify it? Or is it simply a rostral feenstra with the orbit confluent with the temporal fenestra, as in Bipes?

Phylogenetic analysis
Clark and Hernandez ran an analysis based on Gauthier (1988) as modified by Laurin (1990). They found 108 MPTs (that’s low resolution). They nested Tamaulipasaurus either between kuehneosaurs and lepidosaurs or between rhynchocephalia and squamata. Pretty broad. No indicated sister taxa.

With more taxa
in the large reptile tree that novel quaratojugal does not affect the nesting of Tamaulipasaurus as a sister to Spathorhynchus. Both are derived from a sister to Crythiosaurus, given the Clark and Hernandez data (i.e. with the labeled orbit considered the actual orbit). I find that problematic given the many other morphological differences (Fig. 2).

Earliest known burrowing lizard
The presence of such a derived lizard as early as the Early Jurassic indicates that predecessors to all these taxa must have first appeared even earlier, likely in the Permian with radiation and diversification throughout the early Mesozoic.

Figure 2. Spathorhynchus, Tamaulipasaurus and Bipes to scale.

Figure 2. Spathorhynchus, Tamaulipasaurus and Bipes to scale. Bones colorized in Tampaulpasaurus as Clark and Hernandez identify them. Note the different ways that the jugal is oriented in Spathorhynchus.

Convergence?
As noted by Clark and Hernandez, Tamaulipasaurus shared several traits and bears a strong general resemblance to the living burrowing lizard with forelimbs, Bipes (Figs. 2,3)

The big question is
not the novel quadratojugal. I’m more interested in that tiny little fenestra in the rostrum. Is it the orbit, as in Spathorhynchus (Fig. 2) and as Clark and Herenandez identify it? Or is it simply a rostral feenstra with the orbit confluent with the temporal fenestra, as in Bipes? In Bipes it appears that the prefrontal and jugal are fused to the maxilla, colorized here (Fig. 3). The only bone missing is the quadratojugal. Even the mandibles look very similar.

Figure 3. Tamaulipasaurus compared to Bipes. There is that tiny foramen in the rostrum in Bipes, exactly where the orbit was identified in Tamaulipasaurus. So, here the eyeballs are added to show where the orbits is and perhaps was in Bipes and Tamaulipasaurus.

Figure 3. Tamaulipasaurus compared to Bipes. There is that tiny foramen in the rostrum in Bipes, exactly where the orbit was identified in Tamaulipasaurus. So, here the eyeballs are added to show where the orbits is and perhaps was in Bipes and Tamaulipasaurus. This is DGS used on a drawing of a 3D specimen, useful here just to readily compare like colored bones.

So which is it? 
In phylogenetic analysis, surprisingly it makes little difference whether the foramen is an orbit or not. All the other traits trump the identification either way. No other of the 592 tested taxa are closer in morphological traits. My money is on the confluent orbit hypothesis. After seeing the photo (Fig. 1) from the Clark website,the opening  looks more like a foramen than an orbit, and it’s right where a foramen should be in a sister. Until higher rez photos become available, I’m working from the drawings of Clark and Hernandez (1994) for ‘circumorbital sutures’, which may include other errors.

References
Clark JM and Hernandez RR 1994. A new burrowing diapsid from the Jurassic La Boca formation of Tamaulipas, Mexico, Journal of Vertebrate Paleontoogy 14: 180-195.

The other Slavoia and the holotype

Earlier we looked at the basal amphisbaenid, Slavoia darevskii (Fig. 3 below, Talanda 2015).

I just read about the holotype (Sulminski 1984) and at least 45 other specimens attributed to Slavoia, like this one (Fig. 1, ZPAL MgR-III/77, Campanian, Late Cretaceous). Six of the 46 skulls are associated with postcranial skeletons, like the holotype, Fig. 2, ZPAL MgR-I/8). If you think this skull looks like Macrocephalosaurus, you’re not the only one.

Slavoia specimen ZPAL MgR III/77 nests not with amphisbaenids, but with Macrocephalosaurus, a contemporary from the same horizon.

Slavoia specimen ZPAL MgR III/77, one of 46 skulls,  nests not with amphisbaenids, but with Macrocephalosaurus, a contemporary from the same horizon. Talanda reports, “The specimen has only half of the elements visible in this drawing. The skull roof and the middle part are not preserved.”

Sulminski nested Slavoia with scincomorphan lizards, but he reported, “It is interesting that described here lizard displays some characters similar to macrocephalosaurid and polyglyphanodontid  species discovered in the same localities of Mongolia. This concerns also particularly the structure of the temporal region, palatal construction and in number of teeth.”

The #77 and #8 specimens nested with macrocephalosaurs in the large reptile tree.

On the other hand,
the #112 specimen nested at the base of the amphisbaenids, as we learned earlier. So the #112 specimen needs a new generic name, or there are other issues that need be dealt with.

Dragging
the amphisbaenid #112 specimen over to the macrocephalosaur specimens adds 17 steps to the most parsimonious tree score. That’s a very low number considering that there are only 17 taxa separating the macrocephalosaurs from the amphisbaenids in the large reptile tree. So, there is a bit of convergence going on here between the macrocephalosaurids and amphisbaenids. The authors note all the skulls vary in size and shape, which they attribute to ontogeny and intraspecific variation. And, of course, none are perfectly preserved. Talanda reports, “The [#77] specimen has only a half of the elements visible in this drawing. The skull roof and the middle part are not preserved.”

Figure 2. The holotype of Slavoia (#8) compared to the lateral view skull (#77). While larger, the #77 skull is relatively shorter. These two nest together in the large reptile tree along with macrocephalosaurids.

Figure 2. The holotype of Slavoia (#8) compared to the lateral view skull (#77). While larger, the #77 skull is relatively shorter. These two nest together in the large reptile tree along with macrocephalosaurids. Note the large size of the limbs.

Does this represent a solution?
Sulimski (1984) recognized the similarity between his skinks and macrocephalosaurids. Talanda (2015) considered his specimen a basal amphisbaenid, a clade derived from skinks in the large reptile tree, but Talanda nested his amphisbaenids between Cryptolacerta and Dibamus + snakes. So there is disagreement here.

Figure 1. basal amphisbaenid Slavoia from Talanda 2015, showing in situ fossil, tracing by Talanda and colorizing added here. Several bones, like the lacrimal and prefrontal, are missing in the Talanda tracing, which evidently was not traced from this photograph.

Figure 3. The #112 specimen from Talanda 2015 which both he and I nested as a basal amphisbaenid. Note the similarity to macrocephalosaurids (above). The teeth appear to be more robust here, as they are in the palate view specimens that have more of an amphisbaenid palate. I don’t see large limbs here, but limb size varies in the amphisbaenids.

Phylogeny is sometimes simple and straightforward.
Sometimes it is not.

This case shows the importance
of using specimen-based taxa in analyses, not specific, generic or suprageneric taxa. It would not be okay to take the best traits from several Slavoia specimens because some may not be Slavoia specimens! This case also highlights a need to determine where every one of these varied Slavoia specimens do nest. And it will be okay if some are lumped while others are split.

The limbs are large in the #8 specimen, but are not visible in the #112 specimen. In amphisbaenids limbs, even in basal taxa, can be vestiges, but not vestiges in the very derived Bipes.

We all have a lot to learn here. It’s not all set in stone.

References
Sulimski A 1984. A new Cretaceous scincomorph lizard from Mongolia. Palaeontologia Polonica, 46, 143–155.
Talanda M 2015.
 Cretaceous roots of the amphisbaenian lizards. Zoologica Scripta. doi:10.1111/zsc.12138

New basal amphisbaenid: Slavoia

An update here, September 28, 2015, looks at the holotype of Slavoia, which does not nest with the specimen described below. 

The amphisbaenids
are typically small burrowing skinks (according to the large reptile tree) with roots deeply preceding the very derived Tamaulipasaurus (Clark and Hernandez 1994, Figs. 1, 4) in the Early Jurassic. Because Tamaulipasaurus reacquired a quadratojugal it was considered a diapsid incerta sedis and is not included in any amphiisbaenid phylogenetic studies. This is a mistake rectified here.

Figure 1. Amphisbaenids recovered by the large reptile tree.

Figure 1. Amphisbaenids recovered by the large reptile tree. Click to enlarge.

With the erroneous deletion
of Tamaulipasaurus, the fossil record of amphisbaneids does not go deeper than the Cretaceous. Many taxa are extant. That is why Talanda (2015) titled his recent paper, “Cretaceous roots of the amphisbaenian lizards.”

Talanda reports on
Slavoia darevskii (ZPAL McR-I.112, from the Late Cretaceous of Mongolia, Fig. 2). Slavoia does indeed nest as a basal amphisbaenid, but it is clear that it must be a late-surviving taxon of an earlier radiation with roots that must go back to the Triassic or Late Permian based on the presence of Tamaulipasaurus and other lepidosaurs.

Unfortunately
Talanda used the squamate cladogram of Gauthier et al. (2012) which nested amphisbaenids between a clade that included the burrowing helodermatid, Cryptolacerta, and the basal scleroglossan, Tupinambis, and a clade that included the amphisbaenid, Dibamus (Fig. 1) and snakes with highly derived burrowing snakes, like Leptotyphlops, nesting with the very basal snake Dinilysia.

Missing from the Gauthier et al./Talanda cladogram
are the large reptile tree sisters to Slavoia, the extant Sirenoscincus and the extinct and odd, Sineoamphisbaena.

Furthermore
in the Gauthier et al./Talanda cladogram the basal gekko, Tchingisaurus nests as a sister to the aquatic pre-snake, Pontosaurus, which nests as a sister to the basal mosasaur, Aigialosaurus. Unfortunately, these taxa are all separated by several other taxa, often in widely separate clades, in the large reptile tree.

There is also an odd mix In the Gauthier et al./Talanda cladogram of proto-squamates mixed in with squamates. For instance, Carusi wrongly nests with the scerloglossan, Shinisaurus. Unfortunately Gauthier et al.and Talanda tree do not yet recognize or distinguish tritosaurs or protosquamates. Nor is there a recognition of the relationship between skinks and amphisbaenids or of geckos and snakes, all as recovered in the large reptile tree.

DGS
found a bone pattern distinct from that interpreted by Talanda who did not identify several bones found using the colorizing technique (Fig. 1).

Figure 1. basal amphisbaenid Slavoia from Talanda 2015, showing in situ fossil, tracing by Talanda and colorizing added here. Several bones, like the lacrimal and prefrontal, are missing in the Talanda tracing, which evidently was not traced from this photograph.

Figure 2. Click to enlarge. Basal amphisbaenid Slavoia from Talanda 2015, showing in situ fossil, tracing by Talanda and colorizing added here. Several bones, like the lacrimal and prefrontal, are missing in the Talanda tracing, which evidently was not traced from this photograph. Every attempt was made to line it up, but only certain elements actually do line up with the Talanda tracing. Can you see the new quadratojgual there?

Given all these problems,
Slavoia is correctly nested as a basal amphisbaenid in the Talanda study. Slavoia provides good clues to the the evolution and morphology of its strange sister, Sineoamphisbaenia (Fig. 3), which it greatly resembles.

Figure 6. Sineoamphisbaena is a sister to Sirenoscincus in which the prefrontal contacts the postfrontal.

Figure 3. Sineoamphisbaena is a sister to Slavoia in the large reptile tree and shares a short rostrum and upper temporal bar with this taxon. The quadrate is prone in this taxon.

Getting back to Tamaulipasaurus…
Traditional paleontologists are loathe to consider Tamaulipasaurus an amphisbaenid, a scincoid, a scleroglossan or even a squamate because it has a complete lower temporal bar created in the usual way with a quadratojugal between a jugal and quadrate. However in this taxon the jugal lacks a postorbital process. A quadratojugal is typically not seen in amphisbaenids, scincoids, scleroglossans and squamates. Clark and Hernandez (1994) write: “The skull is superficially similar to that of burrowing squamates, especially amphisbaenians and dibamids, but the presence of plesiomorphic characters, such as a complete lower temporal bar, contradict a phylogenetic relationship within Squamata.”

The simple solution, of course, 
is to toss Tamaulipasaurus (Figs. 1, 4) into a large gamut cladogram to see where it nests most parsimoniously. And, to no surprise, it nests with derived amphisbaenids. No other of the the 580 tested taxa are closer (more similar). Despite the autapomorphy of the long lost reappearance of the quadratojugal in this one isolated taxon (and also perhaps in Slavoia (Fig. 2), all the rest of the traits of Tamaulipasaurus are amphisbaenid, very similar to Bipes (Fig. 1).

Figure 3. Tamaulipasaurus, distinct from nearly all squamates, has a quadratojugal and the jugal lacks a postorbital process. It is still an amphisbaenid.

Figure 4. Tamaulipasaurus, distinct from nearly all squamates, has a quadratojugal and the jugal lacks a postorbital process. It is still an amphisbaenid.

Upon seeing the quadratojugal in Tamaulipasaurus,
Clark and Hernandez froze in their tracks and didn’t want to venture a solution more specific than “Diapsida”. That QJ bone wasn’t supposed to be there. And yet it was. Clark and Herenandez followed their textbooks instead of testing for parsimony in a large gamut cladogram.

It’s no big deal
We looked at the reappearance of the quadratojugal in other taxa here. So it happens every so often, and it happened again with Tamaulipasaurus.

Along the same lines,
we looked at the reappearance of digit zero in Limusaurus, the bird-like theropod, here. Extra phalanges and extra digits appear in certain plesiosaurs and ichthyosaurs. An extra skull bone appears anterior to the pineal foramen in dicynodonts. Extra vertebrae appear in a amphisbaenids and snakes. So an unexpected quadratojugal is nothing to freak out about.

References
Clark JM and Hernandez RR 1994. A new burrowing diapsid from the Jurassic La Boca formation of Tamaulipas, Mexico, Journal of Vertebrate Paleontoogy 14: 180-195.
Talanda M 2015.
Cretaceous roots of the amphisbaenian lizards. Zoologica Scripta. doi:10.1111/zsc.12138

Worm lizards (Amphisbaena) rafting the oceans???

A new paper by Longrich et al. (2015) discusses the worldwide distribution of burrowing skinks versus their fossil record, which, in their study, extends no deeper than the Cretaceous extinction event. With this data they imagine that burrowing skinks must have rafted over the oceans between the continents to aid in their dispersal.
Figure 1. From Longrich et al. 2015, hypothetical rafting paths of burrowing skinks.

Figure 1. From Longrich et al. 2015, hypothetical rafting paths of burrowing skinks.

From their abstract
“Worm lizards (Amphisbaenia) are burrowing squamates that live as subterranean predators. Their underground existence should limit dispersal, yet they are widespread throughout the Americas, Europe and Africa. This pattern was traditionally explained by continental drift, but molecular clocks suggest a Cenozoic diversification, long after the break-up of Pangaea, implying dispersal. Here, we describe primitive amphisbaenians from the North American Palaeocene, including the oldest known amphisbaenian, and provide new and older molecular divergence estimates for the clade, showing that worm lizards originated in North America, then radiated and dispersed in the Palaeogene following the Cretaceous-Palaeogene (K-Pg) extinction. This scenario implies at least three trans-oceanic dispersals: from North America to Europe, from North America to Africa and from Africa to South America. Amphisbaenians provide a striking case study in biogeography, suggesting that the role of continental drift in biogeography may be overstated. Instead, these patterns support Darwin and Wallace’s hypothesis that the geographical ranges of modern clades result from dispersal, including oceanic rafting. Mass extinctions may facilitate dispersal events by eliminating competitors and predators that would otherwise hinder establishment of dispersing populations, removing biotic barriers to dispersal.”
Unfortunately
Longrich et al. did not include the derived (i.e. not primitive) Early Jurassic burrowing skink, Tamaulipasaurus (Clark and Hernandez 1994, Fig. 2), in their data. Tamaulipasaurus nests as a sister to Bipes and Amphisbaena the most derived burrowing skink. That means burrowing skinks had just about ceased producing novel morphologies by the Early Jurassic, 165 mya. That means burrowing skinks could have dispersed throughout the supercontinent of Pangaea prior to its breakup around 130 mya and no burrowing skinks would have to raft the oceans.
Figure 1. Tamaulipasaurus, a burrowing skink from the Early Jurassic, long before the breakup of Pangaea.

Figure 2. Tamaulipasaurus, a burrowing skink from the Early Jurassic, long before the breakup of Pangaea. Clark and Hermandzz identify that foramen as an orbit. It may be misidentified with a confluent orbit and temporal fenestra as in Bipes.

To make matters worse,
Ascendonanus (Rößler et al. 2012, Fig. 3) is an Early Permian iguanid, one of the oldest lepidosaurs known, and varanids are not basal taxa, but are as derived as skinks on the large reptile tree.
Figure 1. The skull of Ascendonanus has a diapsid temporal configuration with clearly visible upper temporal fenestra and a typical iguanid skull morphology.

Figure 3. The skull of Ascendonanus has a diapsid temporal configuration with clearly visible upper temporal fenestra and a typical iguanid skull morphology.

And then there’s Cosesaurus
a derived tritosaur, a clade of lepidosaurs that developed in parallel with squamates but had their heyday (widest radiation) in the Triassic.
Remember,
when you find a fossil, it probably represents one of millions at the height of that species radiation, rather than at the origin or the demise, when very few of that species are alive. So given the present phylogenetic and chronological bracketing the fossil record for burrowing skinks probably extends much further back in time than Longrich et al. surmise, evidently back to the Early Permian or Late Pennsylvanian.
References
Clark JM and Hernandez RR 1994. A new burrowing diapsid from the Jurassic La Boca formation of Tamaulipas, Mexico, Journal of Vertebrate Paleontoogy 14: 180-195.
Longrich NR, Vinther J, Pyron RA, Pisani D and Gauthier JA 2015. Biogeography of worm lizards (Amphisbaenia) driven by end-Cretaceous mass extinction.
Proceedings of the Royal Society B: 2015 282 20143034 DOI: 10.1098/rspb.2014.3034. http://rspb.royalsocietypublishing.org/content/282/1806/20143034
Rößler R, Zierold T, Feng Z, Kretzschmar R, Merbitz M, Annacker V and Schneider JW 2012. A snapshot of an early Permian ecosystem preserved by explosive volcanism:
New results from the Chemnitz Petrified Forest, Germany. PALAIOS, 2012, v. 27, p. 814–834

Assembling the Squamate Tree of Life – part 3 – the Tritosauria and the Krypteia

Gauthier (2012) is the largest phylogenetic analysis of the Squamata. Earlier here and here we looked at various aspects of this powerful paper. Today we’ll finish up.

Unfortunately, Gauthier et al. (2012) ignored the descendants of a sister to the stem squamate Huehuecuetzpalli. The large reptile tree found the odd drepanosaurs, tanystropheids and pterosaurs were members of this previously ignored lizard clade, here called the Tritosauria. Having a large and encompassing reptile tree as a guide might have alerted Gauthier et al. (2012) to include tritosaurs, but alas, this clade was not on their radar.

Maybe someday it will be…

The Fossorial Taxa
Fossorial animals dig through dirt and are adapted to living underground. Among squamates, these include certain snakes and amphisbaenians. Gauthier et al. (2012) found that amphisbaenians and all snakes formed a natural clade, which they called the Krypteia (hidden ones).

On the other hand, the large reptile tree found amphisbaenians and dibamids nested within skinks while snakes were diphyletic, arising from two distinct varanid clades, one clade out of Heloderma and Lanthanotus and another clade of snakes out of Ardeosaurus and Adriosaurus.

As in other prior lizard/snake trees the very derived, very tiny snake, Leptotyphlops, nested at the base of all snakes in the Gauthier (2012) tree. I never understood this. Even the jaws don’t even move up and down like all other tetrapod jaws!! It’s hard to tell what’s what in Leptotyphlops with so many bones gone or fused. In the large reptile tree it’s basically the very last taxon in the new Lepidosauromorpha and more derived than the other burrowing snakes.

According to Gauthier et al. (2012) this most basal of snakes was related to a basal amphisbaenian, Spathorhynchus, despite the many basic differences. The large reptile tree recovered Spathorhynchus as a fossorial skink, distinct from all snakes.

The large reptile tree concentrated on taxa at the bases of reptilian clades and subclades in order to recover relationships. It cannot compete with the Gauthier et al. (2012) tree once one gets into the various squamate clades, but at the bases the Gauthier et al. (2012) tree lacks several key taxa that could prove to be important. From the Scleroglossa, the Gauthier et al. (2012) tree lacks Liushusaurus, Eolacerta, Yabeinosaurus, Tamaulipasaurus, Bahndwivici and Cryptolacerta.

What would their inclusion do to the Gauthier et al. (2012) tree?
It’s puzzling how such a large and carefully scored tree as the Gauthier et al. (2012) tree could arrive at so many key oddball (mis-matching) sisters. Perhaps more fossil taxa could have brought the two large trees to a closer accord.

One Last Hoohah!
Like the large reptile tree, Gauthier et al. (2012) found Estesia to nest closer to Varanus than Heloderma, confirming that the Monstersauria may be polyphyletic.

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
Gauthier, JA, Kearney M, Maisano JA, Rieppel O and Behkke 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. online here.

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

The Origin of the Amphisbaenia

Updated August 12, 2014. Moving Cryptolacerta to a closer relationship to Heloderma, elevating Sineoamphisbaena to its place between skinks and amphisbaenids.

Amphisbaena literally means, “goes both ways.” The name is that of the mythological “Mother of Ants,” an ant-eating serpent with a head on both ends. Amphisbaena is also a genus within the Amphisbaenia. Like its mythological namesake, Amphisbaena can back up as easily as it moves forward, despite having no legs.

Amphisbaenia are the worm lizards, typically (with one exception, Figure 1) legless squamates that burrow and have a superficial resemblance to earth worms, including having their scales arranged in rings (annuli). Their right lung is reduced to make more room for the left lung. (In snakes the left lung is reduced.) The eyes are reduced and deeply recessed and the tail resembles the head. Amphisbaenians are so different from other squamates that they have been considered a third suborder, after lizards and snakes.

The primitive Amphisbaenian, Bipes.

Figure 1. The primitive amphisbaenian, Bipes.

Bipes, a Primitive Extant Amphisbaenian
Bipes (Figure 1) is a living amphisbaenian with strong front legs. The hand is stout, like that of a mole, with digits 2 and 3 the longest, digit 1 absent and digit 5 vestigial. The vestigial hind limbs do extend beyond the body wall. By contrast, in typical lizards digit 4 is the longest.

Extinct Burrowers
Several fossil taxa have been linked to amphisbaenians. Tamaulipasaurus lived during the Early Jurassic. Sineoamphisbaena and Crythiosaurus lived during the Late Cretaceous.  Spathorhynchus lived during the early Oligocene. Most of these are known from skulls and partial skulls. No hands yet known in any of these taxa.

Amphisbaenian Origins – part 1 – Sineoamphisbaena
Wu et al. (1993), Wu et al. (1996) and Gao (1997) proposed and argued that a round-skulled Late Cretaceous squamate, Sineoamphisbaenea (Figure 2), was the oldest known amphisbaenian. Unfortunately, it didn’t look very much like most amphisbaenians (Figure 2) which made accurate nesting something of a problem in the eyes of many.

Amphisbaenian Origins – part 2 – Not Sineoamphisbaena
Kearney (2003) argued that Sineoamphisbaena nested closer to Macrocephalosaurus and that Amphisbaena nested with Dibamus and snakes, not far from Gekko and the legless geckos, the Pygopodidiae.

 

Figure 2. Cryptolacerta and kin, including Heloderma and the Amphisbaenia.

Figure 2. Cryptolacerta and kin, including Heloderma and the Amphisbaenia.

Amphisbaenian Origins – part 3 – Cryptolacerta
Müller et al. (2011) argued that a new Eocene lizard, Cryptolacerta  (Figure 2), was the sister to the Amphisbaenia and both were sisters to Sineoamphisbaena and the Teiioidea, a lizard taxon that includes the skinks, Gymnophthalmus and Chalcides. 

Where Do Amphisbaenians Nest in the Large Study?
Here Cryptolacerta does indeed nest close to skinks and amphisbaenians, but it nests closer to Heloderma, another burrowing lizard. Müller et al. (2011) reported that Cryptolacerta had sealed up its upper temporal fenestrae with expansion of the very large postfrontal bone. I was unable to duplicate that reconstruction. Instead I found upper temporal fenestrae in the specimen. A GIF movie and comparative reconstructions can be found here. In any case, amphisbaenians do not add bone to their skulls, they lose bone.

Amphisbaenians nest close to skinks with Sineoamphisbaena nesting close to the base of the other amphisbaenians. In consideration of Kearney (2003), I deleted all amphisbaenians, then all skinks and amphisbaenians from the large study, but those tests failed to dislodge Sineoamphisabaenia form its node, which kept it far from Macrocephalosaurus.

Summary
While amphisbaenians are distinct from most other lizards, they are closer to skinks and legless skinks than to any other lizard taxa. More legless taxa will be added to the large tree as time goes by and I will report on each one in turn.

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:
Cope ED 1894. On the genera and species of Euchirotidae. American Naturalist 28: 436-437.
Gao K 1997.
 
Sineoamphisbaena phylogenetic relationships discussed. Canadian Journal of Earth Sciences. 34: 886-889. online article
Kearney M 2003. The Phylogenetic Position of Sineoamphibaena hextabularis reexamined. Journal of Vertebrate Paleontology 23 (2), 394-403.
Müller J, Hipsley CA, Head JJ, Kardjilov N, Hilger A, Wuttke M and Reisz RR 2011. Eocene lizard from Germany reveals amphisbaenian origins. Nature 473 (7347): 364–367. doi:10.1038/nature09919
Wu XC., Brinkman DB, Russell AP, Dong Z, Currie PJ, Hou L, and Cui G 1993. Oldest known amphisbaenian from the Upper Cretaceous of Chinese Inner Mongolia. Nature (London), 366: 57 – 59.
Wu X-C Brinkman DB and Russell AP 1996. Sineoamphisbaena hexatabularis, an amphisbaenian (Diapsida: Squamata) from the Upper Cretaceous redbeds at Bayan Mandahu (Inner Mongolia, People’s Republic of China), and comments on the phylogenetic relationships of the Amphisbaenia. Canadian Journal of Earth Sciences, 33: 541-577.
Papenfuss TJ 1982. The Ecology and Systematics of the Amphisbaenian Genus Bipes. Occasional papers of the California Academy of Science 136: 1-42.

wiki/Cryptolacerta
wiki/Amphisbaenia
wiki/Bipes
wiki/Sineoamphisbaena