SVP 2018: Dual origin for traditional mosasaurs?

Mekarski MC 2018
reports, “The discovery of a new species of ‘aigialosaur’ with an exquisitely preserved
forelimb provides new, solid evidence in support of the polyphyletic mosasaur hypothesis. This model, combined with stratigraphic data, evidence from other skeletal regions, and corroborated by newly produced phylogenetic studies, lead to the conclusion that ‘mosasaurs’ do not exist in the biological sense, that the term ‘mosasaur’ must be redefined, and our understanding of this group’s evolutionary history reimagined.”

Unfortunately
Mekarski only lists several mosasaur genera, but does not split them into the two convergent clades she proposes in her abstract. The large reptile tree includes just three mosasaurs and not the new aigialosaur, and… so far… the mosasaur clade is monophyletic. Should be interesting when this paper is published.

Figure 2. Plotosaurus from Camp 1951 with hypothetical body outline.

Figure 2. Plotosaurus from Camp 1951 with hypothetical body outline.

We’ve seen polphyly
in seals/sea lions, turtles, and whales. So, maybe mosasaurs?

References
Mekarski MC 2018. Limbs into fins: convergent evolution and the polyphyly of the Mosasauridae. SVP abstracts.

The origin of the Mosasauria in the LRT

Figure 1. Tylosaurus represented by three species. T. kansasensis, T. proriger and T. dyspelor. Note the differences in flipper size.

Figure 1. Tylosaurus represented by three species. T. kansasensis, T. proriger and T. dyspelor. Note the differences in flipper size.

Wikipedia reports,
Mosasauria: “The exact phylogenetic position of the clade containing mosasaurids and their closest relatives (aigialosaurids and dolichosaurs) within Squamata remains uncertain. Some cladistic analyses recovered them as the closest relatives of snakes, taking into account similarities in jaw and skull anatomies; however, this has been disputed[ and the morphological analysis conducted by Conrad (2008) recovered them as varanoids closely related to terrestrial monitor lizards instead. Longrich, Bhullar and Gauthier (2012) conducted a morphological analysis of squamate relationships using a modified version of the matrix from the analysis of Gauthier et al. (2012); they found the phylogenetic position of the clade containing mosasaurs and their closest relatives within Squamata to be highly unstable, with the clade “variously being recovered outside Scleroglossa (as in Gauthier et al., 2012) or alongside the limbless forms”.

By contrast
the large reptile tree (LRT. 1006 taxa) nests the mosasaurs Tethysaurus and Tylosaurus with Aigialosaurus and this clade is a sister to the clade Saniwa + (Estesia + Varanus). All have a common ancestor that is a sister to Bahndwivici and Yabeinosaurus + Sakurasaurus. In other words, not close to snakes, earless monitors, Gila monsters or amphisbaenids.

Figure 2. Tylosaurus and other mosasaurs. Boxed: The shoulder girdle, left paddle and cartilaginous sternal cartilages of Tylosaurus in dorsal view. These broad ribs and sternum anchored powerful pectoral muscles to the front paddles.

Figure 2. Tylosaurus and other mosasaurs. Boxed: The shoulder girdle, left paddle and cartilaginous sternal cartilages of Tylosaurus in dorsal view. These broad ribs and sternum anchored powerful pectoral muscles to the front paddles.

Tylosaurus proriger (Marsh 1872, Late Cretaceous) was a giant mosasaur, a clade that traditionally and currently nests with small Aigialosaurus. Mosasaurs were sea-going giant varanoid lizards that gave live birth and had extra phalanges on the medial digits as the hands and feet were transformed into paddles. Large teeth appear on the pterygoids, but these are convergent with those found on basal marine snakes like Pachyrhachis. The nasals were fused together and fused to the premaxilla ascending process.

Figure 3. Aigialosaurus, a small mosasauroid, compared to Coniasaurus, an even smaller mosasauroid, not related to Dolichosaurus and snakes.

Figure 3. Aigialosaurus, a small mosasauroid, compared to Coniasaurus, unrelated to mosasaurs, but related to  Dolichosaurus and snakes.

Other much more distantly related aquatic squamates include
dolichosaurs like Dolichosaurus, Adriosaurus and Pontosaurus. Those are in the lineage of pre-snakes, like Tetrapodophis in the LRT.

On a side note:
Caldwell 2012 asked, “What, if anything is a mosasaur?”

From the Caldwell abstract:
“This treatise critically assesses Camp’s [1923] diagnostic characters for Anguimorpha, Platynota, Varanoidea, and Mosasauroidea, concluding that Camp’s data permit mosasaurs to be viewed only as anguimorphans, not platynotans nor varanoids. A similar critical assessment is given for the characters used to diagnose anguimorphans and varanoids in Estes et al. [1988], concluding here that not a single character out of twenty-two is shared between varanoids and mosasaurs… It is concluded here that there is no character-based evidence to support phylogenetic hypotheses that mosasaurs are derived aquatic varanoid lizards. It is recognized that the concept and term “mosasaur” has ceased to exist in any biologically meaningful way, and that the future requires the construction of a new suite of terms and concepts to convey what we now think we know about these animals.”

I could not locate any Mesozoic varanids, though they were undoubtedly present.

Estesia is not considered a varanid, but it nests with them in the LRT. Rather, Wikipedia reports that Estesia is close to the living Gila monster, Heloderma, a desert lizard.

On an another note
I just learned about this website: http://homepages.vodafone.co.nz/~jollyroger_wave/DinoNew/links2.htm
listing blogs and other web pages related to prehistoric topics. Both PterosaurHeresies and ReptileEvolution are listed. Thank you Vodphone/JollyRoger/DinoNews!

References
Caldwell M 2012. A challenge to categories: “What, if anything, is a mosasaur?” Bulletin de la Société Géologique de France 183(1): DOI: 10.2113/gssgfbull.183.1.7
Marsh OC 1872. Note on Rhinosaurus. American Journal of Science 4 (20):147.
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

wiki/Mosasaur
wiki/Tylosaurus
wiki/Tethysaurus
wiki/Saniwa

Magnuviator, another basal scleroglossan.

A recent paper brings us
a Late Cretaceous “iguanomorph,” Magnuviator ovimonsensis (DeMar et al. 2017). It nested with Saichangurvel originally and here in the LRT, but both nest in the LRT with Acanthodactylus at the base of the Scleroglossa, not within the Iguania. The authors provided illustrations of the in situ fossils which I have restored to the in vivo configuration (Fig. 1) more or less.

Figure 1. Magnuviator ovimonsensis in situ from DeMar et al. 2017) and in vivo.

Figure 1. Magnuviator ovimonsensis in situ from DeMar et al. 2017) and in vivo.

DeMar et al.
added Magnuviator to the cladogram provided by Conrad 2008. Earlier we looked at the problems therein and in other earlier studies. As in the earlier Saichangurvel study, Magnuviator nests close enough to the clade Iguania that there are no intervening taxa.

References
DeMar Jr DG, Conrad JL, Head JJ, Varricchio DJ and Wilson GP 2017. A new Late Cretaceous iguanomorph from North America and the origin of New World
Pleurodonta (Squamata, Iguania). Proc. R. Soc. B 284: 20161902.

Saichangurvel: not an iguanid, but very close…

This appears to be yet another case of a priori taxon exclusion.
Saichangurvel davidsoni (Conrad and Norell 2007; (IGM 3/858; Late Cretaceous) was originally considered a member of the Iguania, but here nests with Acanthodactylus, a lacertid taxon not mentioned in the original text, but nesting as a sister to the Iguania and is a basalmost scleroglossan.

Conrad and Norell report
“Iguania, like Squamata as a whole, has a rich, but patchy fossil record. Although many Cretaceous species have been identified, Saichangurvel davidsoni is the first known from a complete skeleton. Indeed, the recent revelation that none of the Euposaurus remains may be diagnosed as iguanians (Evans, 1993) renders Saichangurvel davidsoni the earliest iguanian known from complete remains.”

Contra Evans 1993
The LRT nests tiny Euposaurus with the much larger Iguana (Fig. 2) as yet one more example of phylogenetic miniaturization at the genesis of major clades. In this case the major clades are Iguania and Squamata. BTW the ResearchGate.net link for Euposaurus takes you to another SE Evans paper.

Distinct from Acanthodactylus,
the teeth of Saichangurvel have three cusps, convergent with Iguana and that may be why the specimen was originally nested with iguanids. The upper temporal fenestrae are not reduced by a posterior extension of the postfrontal. Acanthodactylus has simple cone-shaped teeth.

Figure 1. Saichangurvel in situ, a complete squamate originally considered a member of Iguania but here nesting with Acanthodactylus.

Figure 1. Saichangurvel in situ, a complete squamate originally considered a member of Iguania but here nesting with Acanthodactylus.

The large reptile tree
(LRT) nests Saichangurvel very close to the Iguania (Fig. 2 in pink), but not in that clade. Unfortunately two of the top lizard experts in the world, Conrad and Norell, excluded taxa pertinent to the analysis, like Acanthodactylus and other basal scleroglossans (Fig 2 in green), That’s my only trump card here.

Figure 2. Subset of the LRT focusing on the Iguania and basal Scleroglossa, including Acanthodactylus and Saichangurvel

Figure 2. Subset of the LRT focusing on the Iguania and basal Scleroglossa, including Acanthodactylus and Saichangurvel

References
Conrad JL and Norell MA 2007. A complete late Cretaceous Iguanian (Squamata, Reptilia) from the Gobi and Identification of a new iguanian clade. American Novitates 3584:1-47.
Daza JD, Abdala V, Arias JS, Garcia-Lopez D and Ortiz P 2012. Cladistic Analysis of Iguania and a Fossil Lizard from the Late Pliocene of Northwestern Argentina”. Journal of Herpetology. 46(1):104-119.
Evans SE 1993. A re-evaluation of the Late Jurassic (Kimmeridgian) reptile Euposaurus (Reptilia: Lepidosauria) from Cerin, France. Geobios 27: 621–631.

Modifying characters in phylogenetic studies: Simoes et al. 2016

This blog post will hold a special interest
for those who do not like the character list of the large reptile tree. Simoes et al. 2016 attempt to show that large studies, even those created by universally respected and dedicated PhDs (Gauthier et al. 2012 and Conrad 2008), may not be “of the highest quality.” They report, “Our results urge caution against certain types of character choices and constructions.”

Nice to know someone else out there
is also testing cladograms with critical insights. But, as you’ll see, the Simoes corrections, no matter how praise-worthy, well-intentioned and insightful, do not solve several problems.

At least one of the two tested analyses HAS to be of poor quality,
because the prior two analyses (Gauthier et al. 2012 and Conrad 2008) do not agree with one another (see below) in major and minor ways. When the LRT is introduced as a third candidate, now at least two are of poor quality, because the LRT provides yet a third topology. Which one best reflects actual evolutionary events? Or are all three ‘poor’?

Simoes et al. 2016
modified two competing scleroglossan studies (Gauthier et al. 2012, Conrad 2008) by culling ‘poor’ characters while keeping the original ordering of remaining character states and then by making all character states unordered. They report, “the concern for size is usually not followed by an equivalent, if any, concern for character construction/selection criteria. Problematic character constructions inhibit the capacity of phylogenetic analyses to recover meaningful homology hypotheses and thus accurate clade structures.” 

This has been a frequent criticism
of the large cladogram at ReptileEvolution.com, despite the fact that it continues to grow organically (with no cuts and grafts over the past several years) with additional taxa that all continue to resemble one another. And that it is developed by someone who is learning as he goes, with no a priori expertise or even knowledge of every new clade added to the LRT.

Simoes et al. 2016 found in the Gauthier et al. and the Conrad studies
“more than one-third of the almost 1000 characters analysed were classified within at least one of our categories of “types” of characters that should be avoided in cladistic investigations.These characters were removed or recoded, and the data matrices re-analysed, resulting in substantial changes in the sister group relationships for squamates, as compared to the original studies.”

Note the Simoes team did not,
apparently, attempt to reexamine problematic taxa and re-score any errors they might have found. While constructing the LRT, scoring errors are corrected constantly.

Simoes et al. 2016 conclude:
“The modified versions of Conrad’s (2008) and Gauthier et al.’s (2012) matrices do not provide revised phylogenetic hypotheses that we claim to be “fixed” or “superior” versions of the same—that would also require a re-analysis of the scorings performed for all terminal taxa that are well beyond the goals of this study. In addition, these results still reflect the original authors’ notions of primary homologies for many characters. Our main goal was to identify general problems with character conceptualizations and constructions for morphological characters for all morphological data sets, and then to identify these problematic characters within our area of expertise, specifically studies of squamate phylogeny. The results of this study provide a different perspective of squamate relationships and indicate how specific issues with character construction may deeply affect our current notion of the squamate tree of life.”

No word yet on what Gauthier et al. and Conrad have to say
about the criticism and changes to their matrices and tree topologies.

Four basic rules from Simoes et al. 
“We have identified four basic operational rules for the construction of characters, and accurate coding and scoring, but note there may well be more:

  1. utilization of as many similarity sub-criteria as possible in order to create characters that are more likely to reflect similarity due to recency of common ancestry;
  2. avoidance of logically inconsistent character construction, such as logically dependent characters, exemplified by our character type series I A;
  3. take into consideration previous studies suggesting possible biological dependency/independency among distinct morphological attributes used as characters; 
  4. acknowledge that continuous variation is widespread in nature and that such data must be treated as such. In the case of phylogenetic analyses, measurement characters must not be treated as discrete when there is a continuous range of variation.

When there is evidence for a disjoint distribution of data, and authors wish to treat them as discrete, a clear statement must be made supporting the disjoint nature of that data.”

These are good ideals to strive for.
The problem with related traits such as, longer vertebral column and short underdeveloped limbs, will always be with us. On the other hand, continuous variation sometimes leads to personal choice when judging those that are on the margins of one and another. Character construction is not perfect and never will be. Neither will scoring. But we can still strive for those — to a point. At some stage, all thinking has to stop and the SEND button must be pressed to upload the data and results to an editor or to the public.

Thankfully
the tree figures provided by Simoes et al 2016 were color coded for simplicity.  Unfortunately neither study includes taxa published after 2012. For their time, both the 2008 and 2012 studies were laudable efforts, but with the LRT, things have changed. Neither study recognized the Tritosauria and Protosquamata, although both correctly nest tritosaurs outside the crown group Squamates. Some protosquamates, like Dalinghosaurus, nested within derived clades by default.

Result: Gauthier et al. 2012
Both revisions retain snakes and amphisbaenids as sister taxa and highly derived burrowing snakes that open the jaws laterally as basal taxa. The modified and unordered tree correctly nest pro-snakes closer to snakes, but both fail to separate them from mosasaurs, which should arise from varanids. The unordered tree correctly moves geckos closer to snakes, but not close enough. Eicthstaettisaurus incorrectly moves further from geckos. Legless pygopodid geckos move to the base of legless amphibaenids + snakes and legged pro snakes + mosasaurs. This is where reconstructions would help workers see the red flags.

Results: Conrad 2008
Gekkos did not shift when this dataset was modified and unordered. All versions of the Conrad study retain the amphisbaenid – snake relationship, which was not repeated in the LRT. The clades Scincomorpha and Anguimorpha disappeared. The clade Diploglossa appeared in the modified version. Anguimorpha reappeared in the unordered version.

Conrad 2008 vs. Gauthier et al. 2012
These two studies did not agree with one another, despite having first hand access to most of the taxa, having extensive character and taxon lists and both had PhDs as authors.

  1. Conrad nested Eicstattisaurus at the base of the Squamata. Gauthier did not.
  2. Conrad nested gekkos as basal squamates. Gauthier did not.
  3. Conrad nested skinks and snakes next. Gauthier did not. 
  4. Conrad nested mosasaurs as highly derived. Gauthier did not.
  5. And there are a dozen+ other differences.

So, which one of these is valid?
That means the other is not valid (does not echo evolutionary events). The LRT indicates that both have problems because it presents a third topology based on traits that apply not only to lizards, but to all reptiles in general. Similarities appear within all major clades. Differences appear between all major clades. Since all three studies are based on genera, one wonders how such differences arise.

And what happens when ALL the changes are made by Simoes et al. 2016?

  1. The Conrad and Gauthier studies do not look more like each other after the changes
  2. Gauthier nests geckos as more derived, with Sineoamphisbaena, apart from other amphisbaenids but closer to the pro-snakes (still not allied with Eichstaettisaurus or snakes) and mosasaurs (still not allied with varanids).
  3. Conrad major squamate clades don’t change much, but genera change sisters quite a bit. At all stages Conrad allies varanids with mosasaurs, but it is not clear if that includes Aigialosaurus, Pontosaurus and Adriosaurus, which all nest with mosasaurs in the Gauthier studies, but the last two nest apart and with snakes in the LRT.

Concluding remarks

Even with the best minds, the best characters and firsthand access to data, Conrad 2008 and Gauthier 2012 could not come to one accord, even with the help of Simoes et al. 2016. And the LRT provides yet a third tree topology for squamates that takes into account the nesting of prosquamates and tritosaurs, something prior workers were unaware of based on their limited gamuts and paradigms. Simoes et al. were correct in unordering character traits, but that did not improve their trees. The LRT is unordered because ordering makes a priori assumptions that may not be valid

It is apparent that Conrad, the Gauthier team and the Simoes team trusted their numbers because they followed a ‘plug and go’ philosophy, lacking the critical reinspection of every relationship to make sure all sister taxa looked alike, did not quickly redevelop lost bones, or reverse the order of evolution (going from exotic and highly derived to simple and plesiomorphic). All taxa were reconstructed in the LRT and that makes for great ease in re-inspecting scores and traits. In the last four years several squamates unavailable to prior workers, like Tetrapodophis, have clarified relationships in the LRT.

Large studies that load lots of taxa and characters together and then push the start button don’t have the benefit of making sure every additional taxon fits and continues to make sense. Neither the Conrad nor the Gauthier originals nor their Simoes modifications were able to become fully resolved like the LRT is. In large studies, such as these, partial taxa should be included only if parsimony informative traits are preserved. Otherwise you blur the big picture.

One of the strengths of the LRT is that it grew slowly from a few taxa to many. Just like an imperfect child, it had and continues to have imperfections, yet it also continues to deliver new insights into reptile interrelationships that can be read, appreciated, confirmed and/or refuted by others. At present it is the only voice raised in heresy to all the traditional paradigms that cannot be validated, are poorly resolved and can be readily modified by others.

I don’t expect ANYONE to use my character list. No PhD in his/her right mind will ever use it. And we all know that. It would be like adopting an older child. It’s not yours, you didn’t raise it and you have to adapt your thinking to understand it. Better to grow your own analysis, like I did.

On the other hand, I DO hope and encourage others to use various subsets of the taxon list that the LRT recovers. It’s just a list of genera and specimens. No controversy there. Add my sisters to your trees and see where they take you. So far, several PhDs have done so with success and that’s great. Hopefully others will follow.

The taxa are flawless. The characters and scoring will always be flawed to some degree. That’s the world we all live in and paleontology will always have to deal with sometimes crumby (literally crumby) data.

References
Conrad JL 2008. Phylogeny and systematics of Squamata (Reptilia) based on morphology. Bulletin of the American Museum of Natural History 310: 1–182.
Gauthier JA, Kearney M, Maisano JA., Rieppel O and  Behlke ADB 2012. Assembling the squamate tree of life: Perspectives from the phenotype and the fossil record. Bull. Peabody Mus. Nat. Hist. 53, 3–308.
Simoes TR , Caldwell MW, Palci A and Nydam RL 2016. Giant taxon-character matrices: quality of character constructions remains critical regardless of size. Cladistics (2016) 1–22. doi: 10.1111/cla.12163. Online here.

Thanks to Dr. Neil Brocklehurst
for bringing this paper to my attention. I’m sure his intention in doing so was not satisfied.

Mid-Cretaceous lizards in amber from Myanmar

A new paper
from Daza et al. (2016) brings us several lizards in amber from the Mid Cretaceous (Fig. 1).

Figure 1. Mid-Cretaceous lizards in amber from Daza et al. 2016. Highlighted specimens are examined here.

Figure 1. Mid-Cretaceous lizards in amber from Daza et al. 2016. Highlighted specimens are examined here.

I was chiefly interested in
the unidentified ones, JZC Bu267 (Fig. 2) and JZC Bu1803 (Fig. 4).

Figure 2. JZC Bu 267 nests with the pre-snake, Jucarseps in the large reptile tree.

Figure 2. JZC Bu 267 nests with the pre-snake, Jucarseps in the large reptile tree.

JZC Bu 267
is a tiny, slender, short-legged, long-toed lizard that nests with the Early Cretaceous pre-snake, Jucarseps, (Bolet and Evans 2012, Fig. 3) in the large reptile tree. This nesting is based on relatively few traits as the skull is largely missing while dermis covers large portions of the post-crania. The two are about the same size and overall proportions.

The authors report, “The preservation of  JZC Bu267 is exceptional; it includes the epidermis and soft tissues and even a unique extended tongue tip with a narrow medial projection that does not resemble the form of any described squamate tongues.” According to Wikipedia, reptiles developed forked tongues in several clades independently.

Figure 1. Jucaraseps in situ. This tiny long lizard is in the lineage of terrestrial snakes.

Figure 3. Jucaraseps in situ. This tiny long lizard is in the lineage of terrestrial snakes and nests as a sister to JZC Bu 267,

So this find
extends the range of the Jucarseps clade from SW Europe to SE Asia.

Figure 4 JZC-Bu1803 has a relatively large skull. This and other traits nest it with the basal scleroglossan, Calanguban in the large reptile tree.

Figure 4 JZC-Bu1803 has a relatively large skull. This and other traits nest it with the basal scleroglossan, Calanguban in the large reptile tree.

JZC Bu1803
(3.2cm snout vent length) Is more thoroughly covered in fine scales. Nevertheless, a large enough list of traits was gleaned from the photo to nest JZC Bu 1803 with the basal scleroglossan, Calanguban (Simoes, Caldwell and Kellner 2014, Early Cretaceous), which is also the same size.

According to Daza et al. “The ventral scales are large, quadrangular, and arranged in regular transverse and longitudinal rows as in most living teiids and lacertids. Remarkable features of this specimen are the extremely long digits and claws.

“A digital endocast of the leftmaxilla exposed the entire tooth row section, a dentition including about 14 functional teeth, and an estimated 19 tooth loci. Tooth attachment is pleurodont and morphology is heterodont, with an abrupt transition from conical and recurved teeth (first 12) to tricuspid (with divided crowns, last 7). Tricuspid (or triconodonot) dentition is widespread among squamates. Among extant groups, the combination of anterior fang-like and posterior tricuspid teeth with parallel margins, where mesial and distal cusps are shorter than the main apex,most closely resembles that of lacertids and teiids.”

Figure 4. Calanguban nests as a sister to JZC Bu 1803 in the large reptile tree.

Figure 5. Calanguban nests as a sister to JZC Bu 1803 in the large reptile tree.

So this find
extends the range of the Calanguban clade from SW Europe across the then narrow Atlantic to NE Brazil.

Figure 6. The two new and unidentified amber embedded specimens nest as squamates that already have names here.

Figure 6. The two new and unidentified amber embedded specimens nest as squamates that already have names here.

The authors indicate
that more data will be forthcoming on these specimens. More can be seen on YouTube here.

References
Bolet A and Evans SE 2012. A tiny lizard (Lepidosauria, Squamata) from the lower Cretaceous of Spain. Palaeontology 55:491-500.
Daza J, Sanley EL, Wagner P, Bauer A and Grimaldi DA 2016. Mid-Cretaceous amber fossils illuminate the past diversity of tropical lizards. Science Advances 2(3): e1501080. DOI: 10.1126/sciadv.1501080
Simoes TR, Caldwell MW and Kellner AWA 2014.
 A new Early Cretaceous lizard species from Brazil, and the phylogenetic postion of the oldest known South American squamates. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2014.947342

YouTube with rotating scans

 

 

 

 

Gilmoreteius (=Macrocephalosaurus) revisions

Figure 1. Macrocephalosaurus (=Gilmoreteis) in several views. Data from Sulimski 1975.

Figure 1. Macrocephalosaurus (= Gilmoreteis, ZPAL MgR-I jI4) in several views. Data from Sulimski 1975. Note the subtle and not so subtle differences between the detailed tracing and the simplified drawing.

Recent work
here and here on the scleroglossan squamate, Slavoia also introduced new data on its sister,  Macrocephalosaurus (recently renamed Gilmoreteius, Fig. 1, holotype: MCN 1867, referred specimen ZPAL MgR-I jI4, Sulminski 1975) and resulted in a slight revision of scoring on Macrocephalosaurus (Fig. 2).

Figure 2. Subset of the large reptile tree. Gillmoreteius nests within a clade of basal Scleroglossa within the Squamata and Lepidosauria. Two of the tested Slavoia specimens nest as sisters while a third (112) nests with pre-amphisbaenids.

Figure 2. Subset of the large reptile tree. Gillmoreteius nests within a clade of basal Scleroglossa within the Squamata and Lepidosauria. Two of the tested Slavoia specimens nest as sisters while a third (112) nests with pre-amphisbaenids.

According to Sulminski (1975)
‘Macrocephalosauridae differ from all known Sauria (lizards) in having a vorner/pterygoid contact. In many respects the Macrocephalosauridae show more resemblances to the Scincomorpha than to the Iguania, and are tentatively referred to the former. However, the morphology of the dentition and the manner of tooth replacement in the Macrocephalosauridae is of the iguanid type, whereas the heterodont dentition and elongate frontal proportions are scincomorph characters. The supratemporal is fused to the squamosal. The tail is relatively long, probably longer than the body.’

These earlier workers did not access the large reptile tree  (subset in Fig. 2). Sulminski did not note that among squamates, both Sineoamphisbaena and Amphisbaena also develop a vomer/pterygoid contact, but these contacts are not found in closely related sister taxa. Thus, all appear to be by convergence and are not that important. Other lepidosaurs, like SphenodonHomoeosaurus and Macrocnemus also have this contact by convergence.

As others have noted earlier,
Gilmoreteius was a likely plant-eater based on those multi-cusped tiny teeth and large torso.

Note:
In figure 1 all images are from the Sulminski (1975) paper. Sulminski illustrated the skull slightly different in each case, one detailed and one simplified. Of course, sometimes such changes affects scoring. In this case, not so much. Have not run into a paper showing two different illustrations of the same specimen. Which one should we gather data from? Probably the more detailed one in this case.

References
Gimore CW 1943. Fossil lizards of Mongolia. Bulletin of the American Museum of Natural History 81(4):361-384.
Langer MC 1998. Gilmoreteiidae new family and Gilmoreteius new genus (Squamata Scincomorpha): replacement names for Macrocephalosauridae Sulimski, 1975 and Macrocephalosaurus Gilmore, 1943. Comunicacoes do Museu de Ciencias e Tecnologia 11: 13-18.
Mo J-Y, Xu X and Evans SE 2009.
 The evolution of the lepidosaurian lower temporal bar: new perspectives from the Late Cretaceous of South China. Proceedings of the Royal Society doi: 10.1098/rspb.2009.0030 online paper
Sulimski A 1975. Macrocephalosauridae and Polyglyphanoodontidae (Sauria) from the Late Cretaceous of Mongolia. Palaeontolgia Polonica 33:25-102. online here.

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

Norellius nyctisaurops – a -very- basal pre-snake, -very- close to geckos

A new paper
by Conrad and Daza (2015) rediagnoses and names AMNH FR 21444 (Fig. 1, Early Cretaceous, ), “an important early and relatively basal lizard: (Conrad and Norell 2006).” Conrad and Daza describe the specimen as “a gecko-like basal squamate as identified by its braincase morphology.” it is tiny with a skull length of 1.5 cm. Postcrania is unknown.

Figure 1. Norellius from Conrad and Daza 2015. At upper right I highlight the 'missing' lacrimal and provide an alternate imagined rostrum based on that of sister taxa.

Figure 1. Norellius from Conrad and Daza 2015. At upper right I highlight the ‘missing’ lacrimal in red and provide an alternate imagined rostrum based on that of sister taxa. Look closely at the pterygoid. There are tiny teeth there, the origin of pterygoid teeth in snakes!

Added to 
the large reptile tree, Norelliius nests next to the Gekko clade that has Tchingisaurus at its base. Norelliius nests at the base of the clade that produced Eichstaettisaurus, Tetrapodophis and snakes, further cementing these two clades together. And it’s the fiirst good lock at the palate around this node.

Daza et al. 2013
was not able to resolve the position of AMNH FR 21444. According to Conrad and Daza, “It has large orbits, a complete postorbital bar and supratemporal arch, and a broad pyriform recess (Fig. 1). The skull is broadest at the level of the orbits and, apparently, tapered anteriorly. The lacrimal is absent; the maxilla and prefrontal form the margins of the lacrimal foramen.” 

Funny thing,
they say the lacrimal is absent, and it is absent on the left with a space left over to receive it, but it appears to be present on the right (Fig. 1). Sister taxa all have a lacrimal.

Norellius is difficult to nest
as it lacks important bones at the front and back of the skull. And it nests very close the the origin of several major scleroglossan clades. In other words, it is very plesiomorphic. Nevertheless a few traits do ally it with Ardeosaurus, Eichstaettisaurus and other pre-snakes to the exclusion of other clades.

Conrad and Daza
consider Gekkonomorpha as basal within Squamata. The large reptile tree does not support this, but recovers Iguania and several other taxa as more basal (splitting off earlier).  It should be noted that Conrad and Daza do not yet recognize the Protosquamata or the Tritosauria, two lepidosaur clades/grades basal to the Squamata. They haven’t added pertinent taxa to their studies, including the lepidosaur Macrocnemus and its kin.

Ironically
Conrad and Daza note: “Norellius nyctisaurops shows no gekkotan characteristics in its dermatocranium.” Only the braincase identifies it as a gekknomorph according to their study.

Conrad and Daza consider Norellius close to the base of Squamata (which it is not) and note, “Even so, the elongate postorbital skull, curved and elongate jugal, long postdentary part of the jaw, and very gecko-like braincase differ strikingly from the morphology seen in basal rhynchocephalians [Gephyrosaurus]. Clearly, more Jurassic and Triassic squamates are needed to help bridge the morphological gap between basal lepidosaurs and modern Squamata.” The large reptile tree provides several taxa to fill this purported gap. Again, the conclusions of Conrad and Daza appear to be based on taxon exclusion. The large number of pertinent taxa in the large reptile tree provide a gradual accumulation of derived characters.

Pterygoid teeth!
Look closely at the pterygoid of Norellius. There are tiny teeth there, the origin of large pterygoid teeth in snakes! Mosasaurs grew those pterygoid teeth convergently, hence the confusion with Pythonomorpha, another invalid clade (snakes + mosasaurs, Cope 1869).

References
Conrad JL and Daza JD 2015. Naming and rediagnosing the Cretaceous gekkonomorph (Reptilia, Squamata) from Öösh (Övörkhangai, Mongolia). Journal of Vertebrate Paleontology 35:5, e980891
Conrad JL and Norell MA 2006. High-resolution x-ray computed tomography of an Early Cretaceous gekkonomorph (Squamata) from Öosh ( €Ov€orkhangai; Mongolia). Historical Biology 18:405–431.
Daza JD, Bauer AM and Snively E 2013. Gobekko cretacicus (Reptilia: Squamata) and its bearing on the interpretation of gekkotan affinities. Zoological Journal of the Linnean Society 167:430–448.

Reconstruction from jumbled scraps: the squamate, Kuroyuriella

Figure 1. The skull of Kuroyuriella reconstructed from bone scraps (above), most of which are layered on top of one another. Not all elements are identified, but enough are to nest this taxon with Ophisaurus.

Figure 1. The skull of Kuroyuriella (represented by two specimens of different size) reconstructed from bone scraps (above), most of which are layered on top of one another. Not all elements are identified, but enough are known to score and nest this taxon with Ophisaurus.

When provided disarticulated scraps,
start with the easy bones, then fill in the gaps in the puzzle. Sometimes, as in Kuroyuriella mikikoi (Evans and Matsumoto 2015, Early Cretaceous), there are enough parts to more or less recreate the skull most similar (among tested taxa in the large reptile tree) to that of Ophisaurus and basal to Myrmecodaptria and CryptolacertaEvans and Matsumoto nested Kuroyuriella  between Huehuecuetzpalli and the suprageneric clade Rhynchocephalia, both well outside the Squamata.

From the online paper:
“Together, SBEI 1510 and SBEI 1608, as type and referred specimen, characterize Kuroyuriella mikikoi as a small lizard having paired frontals with deep subolfactory processes; a median parietal without a parietal foramen, with sculpture of low relief, and with lateral shelves that restricted the adductor muscle origins to the ventral surface; upper temporal fenestrae that were at least partially closed by expanded postorbitofrontals; an unsculptured maxilla with a strongly concave narial margin; a large flared prefrontal; and a slender, relatively small pterygoid. In the shallow lower jaw, the teeth are closely packed, cylindrical, and pleurodont with lingual replacement; a subdental ridge is present; the dentary bears a tapering coronoid process that braces the coronoid, and has a posterior extension with a curved free margin; the surangular, angular, and splenial are all present and the surangular is shallow; the adductor fossa is open but not expanded; and the articular surface is asymmetrical.

In order to explore the affinities of Kuroyuriella mikikoi, it was coded into the matrix of Gauthier et al. (2012), as extended by Longrich et al. (2012) (184 characters coded out of 622, 70.4% missing data),

The consistent placement of Kuroyuriella on the squamate stem is problematic and probably artifactual, but whether the weighted analysis is giving a more accurate placement is uncertain. Of the derived character states possessed by Kuroyuriella, 76 [1] (postorbital partly occludes upper temporal fenestra), 364 [1] (dentary coronoid process extends beyond level of coronoid apex), 367 [2] (coronoid process of dentary overlaps most of anterolateral surface of coronoid), and 369 [2] (dentary terminates well posterior to coronoid apex) provide some support for placement of Kuroyuriella on the stem of scincids, and 129 [1] (prefrontal extends to mid-orbit), 104 [1] (absence of parietal foramen) and 385 [1] (posterior mylohyoid foramen posterior to coronoid apex) would be consistent with that placement. However, given the considerable difference between the results using equal weighting and Implied Weighting, Kuroyuriella remains incertae sedis pending recovery of more complete material.”

Figure 2. Ophisaurus, the extant glass snake or legless lizard is close to Kuroyuriella in the large reptile tree.

Figure 2. Ophisaurus, the extant glass snake or legless lizard is close to Kuroyuriella in the large reptile tree.

Here
Ophisaurus (Fig. 2) and Kuroyuriella both nest will within the Squamata, not ouside. of it in the large reptile tree. Reconstruction of the skull helps to ‘see’ this lizard as it was. I can’t imagine how difficult it would be to do try to establish traits  with a jumble of disarticulated bones.

As you’ll see, I think the parietal foramen was present. The parietal may have had longer posterior processes, now broken off.

References
Evans SE and Matsumoto R 2015. An assemblage of lizards from the Early Cretaceous of Japan. Palaeontologia Electronica 18.2.36A: 1-36
palaeo-electronica.org/content/2015/1271-japanese-fossil-lizards
http://palaeo-electronica.org/content/2015/1271-japanese-fossil-lizards