Dorsetisaurus: a Mesozoic tegu, not an anguimorph

Known from the Early Cretaceous of Mongolia
and the Late Jurassic of Portugal, Dorsetisaurus purbeckensis (BMNH R.8129, skull width: 1.4cm; Hoffstetter 1967; Fig. 1) was attributed to the clade of glass lizards (Anguimorpha) originally and in two later papers. Evans 2006 nested it between the highly derived legless skink, Amphisbaenia, and the basal gecko (in the LRT), Chometokadmon (which Evans considered an anguimorph).

FIgure 1. Dorsetisaurus bits and pieces restored here and scored nests in the LRT with Tupinambis, the extant tegu.

By contrast
in the large reptile tree (LRT, 1318 taxa) Dorsetisaurus nests with the basal scerloglossan, lacertoid, teiid, Tupinambis (Fig. 2), the extant tegu lizard. Even the slight notch in the ventral maxilla is retained over 120 million years of evolution.

Figure 2. Tupinambis is the extant tegu lizard, a sister to Dorseitsaurus in the LRT.

On a side note:

Gauthier et al. 2012 put together two squamate trees of life, one based on traits, another based on genes. Neither matches the LRT, which includes more fossil taxa.

References
Evans SE, Raia P, Barbera C 2006. The Lower Cretaceous lizard genus Chometokadmon from Italy. Cretaceous Research 27:673-683.
Gauthier, JA, et al. 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 (2012): 3-308.
Hoffstetter  R 1967. Coup d’oeil sur les Sauriens (lacertiliens) des couches de Purbeck (Jurassique supérieur d’Angleterre Résumé d’un Mémoire). Colloques Internationaux du Centre National de la Recherche Scientifique 163:349-371.

wiki/Dorsetisaurus
http://fossilworks.org/bridge.pl?a=taxonInfo&taxon_no=38022

Bipedal Cretaceous lizard tracks

These are the oldest lizard tracks in the world…

(if you don’t consider Rotodactylus (Early Triassic) strictly a ‘lizard’ (= squamate). One rotodactylid trackmaker, Cosesaurus, is a tiny lepidosaur).

Figure 1. Bipedal lizard tracks from South Korea in situ. They are tiny.

From the abstract

“Four heteropod lizard trackways discovered in the Hasandong Formation (Aptian-early Albian), South Korea assigned to Sauripes hadongensis, n. ichnogen., n. ichnosp., which represents the oldest lizard tracks in the world. Most tracks are pes tracks that are very small. The pes tracks show “typical” lizard morphology as having curved digit imprints that progressively increase in length from digits I to IV, a smaller digit V that is separated from the other digits by a large interdigital angle. The manus track shows a different morphology from the pes. The predominant pes tracks, the long stride length of pes, narrow trackway width, digitigrade manus and pes prints, and anteriorly oriented long axis of the fourth pedal digit indicate that these trackways were made by lizards running bipedally, suggesting that bipedality was possible early in lizard evolution.”

Actually, the lizard was not running.
Typically in running tracks the prints are very far apart and these tracks are sometimes left toe to right heel.

Figure 2. Original and new tracings of the bipedal lizard tracks from South Korea. PILs are added. Manual digit 4 and 5 appear to have shifted.

 The authors did not venture who made the tracks.
They reported, “based on the palaeobiogeographic distribution of facultative extant families, the lizard that produced S. hadongensis tracks could well have been a member of an extinct family or stem members of Iguania, which was present in the Early Cretaceous.”

Actually the closest match among tested taxa
is with Eichstaettisaurus (Fig. 1), a basal member in the lineage of snakes. And this clade is close to the origin of geckos. ReptileEvolutiion.com and the large reptile tree would have been good resources for the authors to use. Lots of lizard pedes were illustrated and scored there.

Figure 3. Originally imagined  as a generic lizard (below), here Eichstattsaurus matched and scaled to the track size walks upright.

 Based on a phylogenetic analysis of the tracks

the closest match in the LRT is with Eichstaettisaurus, so a slightly larger relative made them. Distinct from the skeletal taxon, the trackmaker had a longer p2.1 than 2.1 and pedal digit 1 was quite short. Otherwise a good match in all other regards.

So why walk bipedally?

It was walking, not running, so escape from predation can be ruled out. Elevating the upper torso and head, like a cobra, can be intimidating to rivals, or just offer a better view over local plant life. This sort of flexibility could have helped them get into the trees and then to move to higher branches.

References

Lee H-J, Lee Y-N, Fiorillo AR &  LÃ J-C 2018. Lizards ran bipedally 110 million years ago. Scientific Reports 8: 2617. doi:10.1038/s41598-018-20809-z

https://www.nature.com/articles/s41598-018-20809-z

The water-walker, the rib-glider and the frill-neck are all cousins!

Update March 5, 2016 with the addition of the cladogram from the large reptile tree.

Some reptile oddballs
>do< nest together. In this case, the extant “Jesus” lizard, Basiliscus, the rib-glider, Draco, and the frill-neck, Chlamydosaurus now nest together in the large reptile tree.

Figure 1. Draco volans. Note the anterior maxillary fangs, and the antorbital fenestra between the lacrimal and prefrontal, traits shared with Chlamydosaurus (Fig 2).

Draco (Fig. 1) and Chlamydosaurus (Fig. 2) are particularly interesting
as both share anterior maxillary fangs and an antorbital fenestra between the prefrontal and jugal (rather than between the lacrimal and maxilla as in other taxa with an antorbital fenestra). A long list of shared character traits unites these two still quite different lizards.

Figure 2. Chlamydosaurus also has anterior maxillary fangs and an antorbital fenestra between the prefrontal and lacrimal, as in Draco (Fig.1).

Basiliscus
is (at this point in the proceedings) a sister to the last common ancestor. But with that parietal crest, it has definitely evolved apart from the above two taxa for a long time.

Figure 3. Basiliscus, the “Jesus” lizard, does not share as many traits as Draco and Chlamydosaurus do, but is related, given the short list of Iguanids currently employed.

We’ve seen this before, 
where and when some odd little reptiles shared more traits with each other than with any other tested reptiles. Members of the Fenestrasauria (Cosesaurus, Kyrgyzsaurus, Sharovipteryx, Longisquama, and pterosaurs) also include bipeds with dorsal frills. One of them also glided with outstretched ribs and legs, although distinct from Draco. In Sharovipteryx, the hind legs were much longer than the ribs.

Figure addendum 1. Cladogram of the Iguania, the sister taxa of the Scleroglossa, both members of the clade Squamata, a subset of the clade Protosquamata, the sister taxon to the Tritosauria. Many more scleroglossans are shown in the large reptile tree at ReptileEvolution.com.

We don’t have 
close prehistoric relatives for Draco or Chlamydosaurus yet. So at this point the evolution of rib-gliding or frill-spreading is not yet a gradual demonstration. But the other shared traits are, to my knowledge, unique synapomorphies.

I will update the cladogram this weekend.

 

DGS: pulling more data out of Eichstaettisaurus gouldi

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

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

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

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

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

References
Evans SE, Raia P and Barbera C 2004. New lizards and rhynchocephalians from the Lower Cretaceous of southern Italy. Acta Palaeontologica Polonica 49:393-408.

The LH 20523 specimen of Scandensia is really Tijubina

Two lizards were described in 2011.
Bolet and Evans (2011) described what they thought was ‘new material’ of Scandensia (LH 20523), but it had a very long stiff tail and tiny rib osteoderms. This specimen is only known from the posterior half (Fig. 1). Simões (2011) redescribed the complete Tijubina, which also had a very long stiff tail and tiny rib osteoderms. Both are from the Early Cretaceous, the former from Spain, the latter from Brazil.

The large reptile tree nested the LH 20523 specimen with Tijubina, in the middle of the Tritosauria, several nodes away from Scandensia. The holotype of Scandensia nests between basal rhynchocelphalians and basal squamates + tritosaurs. It doesn’t have a long stiff tail or dorsal osteoderms. Distinct from the LH 20523 specimen, Scandensia has a lumbar region of very short ribs.

Figure 1. Tijubina and Scandensia holotypes. Scandensia is a much larger genus. The tail is not well preserved and could be longer in Scandensia. Note the lumbar area in Scandensia not present in Tijubina. Also note the great size of metatarsal 4 in Tijubina, not present in Scandensia.

The LH 20523 specimen has a regenerated tail with cartilaginous growth. The authors estimate the tail was 3x the the snout vent length, which they note contrasts with the holotype of Scandensia, which has subequal tail and snout-vent lengths. This is the first clue that these two are not the same taxon. But then, they reasoned, the Scandensia tail may have been incompletely preserved or regenerating.

Figure 2 The LH 25023 specimen that Bolet and Evans (2011) referred to Scandensia, but nests here with Tijubina.

Bolet and Evans (2011) were surprised to see osteoderms around the rib cage because the holotype of Scandensia does not have these. This is the second clue.

The very robust fourth metatarsal is a trait shared with Tijubina, not with Scandensia, a third clue.

Figure 3. Ankles of the LH 20523 specimen. Here Bolet and Evans see a single astragalocalcaneum (in yellow on the drawing, and present in all squamates) but the photo does not support a single proximal ankle bone. Rather a split appears between the astragalus and calcaneum, as in all tritosaurs.

Bolet and Evans report a single astragalocalcaneum, as in Scandensia, but the photo of the LH 20523 specimen shows a split between the proximal ankle bones and the shape is different than shown. Was this wishful thinking? or more precise observation. No tritiosaurs have a fused proximal tarsus, so this would be an autapomorphy if true.

Were Bolet and Evans aware of Tijubina?
I don’t think so. It is not mentioned in their paper. A query to both authors goes unanswered at present.

References
Bolet A and Evans SE 2011. New material on the enigmatic Scandensia, an Early Cretaceous lizard from the Iberian Peninsula. Special Papers in Palaeontology 86:99-108.
Bonfim Júnior DC and Marques RB 1997. Um novo lagarto do Cretáceo do Brazil (Lepidosauria, Squamata, Lacertilia – Formação Santana, Aptiano da Bacia do Araripe. Anuário do Instituto do Geociencias 20:233-240
Bonfim-Júnior F de C and Rocha-Barbosa O 2006. A Paleoautoecologia de Tijubina pontei Bonfim-Júnior & Marques, 1997 (Lepidosauria, Squamata Basal da Formação Santana, Aptiano da Bacia do Araripe, Cretáceo Inferior do Nordeste do Brasil). Anuário do Instituto de Geociências – UFRJ ISSN 0101-9759 Vol. 29 – 2 / 2006 p. 54-65.
Evans SE and Barbadillo LJ 1998. An unusual lizard (Reptilia: Squamata) from the Early Cretaceous of Las Hoyas, Spain. Zoological Journal of the Linnean Society 124:235-265.
Simões TR 2012. Redescription of Tijubina pontei, an early cretaceous lizard (Reptilia; Squamata) from the crato formation of Brazil. An Acad Bras Cienc. Feb 2, 2012. pii: S0001-37652012005000001. [Epub ahead of print].

 

Phylogenetic bracketing and pterosaurs – part 1

Since pterosaurs (and other tritosaurs) nest between rhynchocephalians and squamates, there are a few traits they likely shared based on phylogenetic bracketing (unless specifically excepted based on fossil evidence). According to Evans (2003) these include:

(1) A derived skin structure with a specialized shedding mechanism involving distinct epidermal generations that are periodically lost and replaced, linked to
a cyclic alternation between a and b keratogenesis. — Ttritosaurs had scales. Pterosaurs also had pycnofibers, hair-like structures that first appear in Sharovipteryx. Unfortunately there is no evidence of skin shedding in any fossil lepidosaur.

(1A) The possession of a crest of projecting scales along the dorsal midline of the body and tail may also be unique to members of this group. — this reaches its acme with the tritosaur fenestrasaur, Longisquama.

(2) Paired male hemipenes housed in eversible pouches at the posterior corners of a transverse cloacal slit. These hemipenes are well developed in squamates and rudimentary in Sphenodon. — the fossil record does not include such structures.

(3) Notching of the tongue tip, possibly in relation to the development of the vomero-nasal system. — Barely notched in Iguana. I don’t see this in known rhynchochephalians or tritosaurs based on the division of the choanae into anterior and posterior fenestra, which appears in basal scleroglossans only.

(4) Separate centres of ossification in the epiphyses of the limb bones (a condition acquired independently in mammals and some birds). — This has never been noted in tritosaurs.

(5) Specialized mid-vertebral fracture planes in tail vertebrae to permit caudal autotomy facilitated by the organisation of associated soft tissue. — This has never been confirmed in any tritosaur, but then again, they are rare as fossils.

(6) A unique knee joint in which the fibula meets a lateral recess on the femur (not end to end as in many tetrapods) — This must be a very subtle trait. I see this trait in Tupinambis, Varanus and Bahndwivici, but not in very many other lepidosaurs.

(7) Specialized foot and ankle characters including a (a) hooked fifth metatarsal, (b) a specialized mesotarsal joint with a fused astragalocalcaneum and (c) an enlarged fourth distal tarsal. —  (a) The hook comes and goes. In basal rhynchocephalians, not present. It is present in Sphenodon through Mesosuchus, starts to fade with Rhynchosaurus and is gone in Hyperodapedon. Something of twisted fifth metatarsal present in most tritosaurs. Minor hook in basal squamata, becomes larger in Varanus, absent in snakes and other limbless lizards, of course. (b) In tritosaurs no ankles are fused except in drepanosaurs. (c) Also large in tritosaurs.

(8) Other soft tissue features include a sexual segment on the kidney; reduction or absence of the ciliary process in the eye; presence of a tenon (cartilaginous
disc) in the nictitating membrane and its attachment to the orbital wall. — These have never been observed in any lepidosaur fossil. But that doesn’t mean they weren’t there.

(9) In addition to these characters, all lepidosaurs show one of two kinds of tooth implantation, pleurodonty and acrodonty. — Basal tritosaurs have pleurodont teeth. Macrocnemus and later tritosaurs have thecodont teeth that happen to be much larger.

Part 2 is posted here.

References
Evans SE 2003. At the feet of the dinosaurs: the origin, evolution and early diversification of squamate reptiles (Lepidosauria: Diapsida). Biological Reviews, Cambridge 78: 513–551.

 

Some thoughts on Sineoamphisbaena

One of the strangest (= most unlike its sister taxa) reptiles is Sineoamphisbaena, which nests in the large reptile tree at the base of the burrowing skinks that ultimately gave rise to amphisbaenids like Amphisbaena and Bipes.

Wikipedia reports: “Sineoamphisbaena is an extinct genus of squamate of uncertain phylogenetic placement. Wu et al. (1993), Wu et al. (1996) and Gao (1997) proposed and argued that it was the oldest known amphisbaenian; this, however, was challenged by other authors, such as Kearney (2003) and Conrad (2008), who instead assignedSineoamphisbaena to the group of squamates variously known as Macrocephalosauridae, Polyglyphanodontidae or Polyglyphanodontia. A large-scale study of fossil and living squamates published in 2012 by Gauthier et al. did not find evidence for a particularly close relationship between amphisbaenians and Sineoamphisbaena; in their primary analysis Sineoamphisbaena was found to be the sister taxon of the clade containing snakes, amphisbaenians, the family Dibamidae and the American legless lizard. The primary analysis of Gauthier et al. did not support a close relationship between Sineoamphisbaena and polyglyphanodontians either; however, the authors noted that when all snake-like squamates and mosasaurs were removed from the analysis, and burrowing squamates were then added individually to it, Sineoamphisbaenagrouped with polyglyphanodontians. Gauthier et al. (2012) considered it possible that Sineoamphisbaena was a burrowing polyglyphanodontian.”

The large reptile tree agrees with the original Wu et al. (1993) nesting, at the base of a clade of burrowing prehistoric lizards, some of which included amphisbaenids. Their analysis, unfortunately used suprageneric taxa and they recovered all legless taxa (including snakes) in one clade.

Figure 1. The lineage of Sineoamphisbaena with Chalcides as more primitive and Crythiosaurus + Spathorhynchus as more derived. The quadrate is orange.

The temporal region of Sineoamphisbaena has been difficult to interpret because of its unique character and bone fusion patterns not quite like any other. Unlike most burrowing lizards, Sineoamphisbaena did not lose any temporal bones. It rearranged them, fusing some. Here (Fig. 2) is the original interpretation and some suggested reinterpretations.

Figure 2. The skull of Sineoamphisbaena as originally interpreted and as reinterpreted here with color coding matched to that of a more “normal” sister, Chalcides guentheri. Note the squamosal forms the posterior border of the upper temporal fenestra of both taxa. And the long jugal is really composed of the jugal + postorbital. It was not a stretch for the squamosal to contact the postfrontal. If it did fuse, then a crack in the specimen has put a question to that.

Distinct from the original interpretation,
the old postorbital is the new squamosal, continuing to border the posterior upper temporal fenestra. The old jugal is the new jugal + postorbital, matching Chalcides. The old squamosal is the new supratemporal, a bone considered missing originally. The old lacrimal is fused to the prefrontal from what I can tell by comparison to Crythiosaurus. The prefrontal and lacrimal fuses to the maxilla in Bipes.

Burrowing lizards,
evolved in a wide variety of ways and all, except Sineoamphisbaena, lose skull (temporal) bones. All appear to have evolved from a variety of the genus Chalcides because some retain a long low rostrum. Others, like Bipes, have a short blocky snout, but Bipes does not rotate its upper teeth medially as Sineoamphisbaena does. So that split likely preceded tooth rotation. It’s a little confusing with lots of convergence in a little clade due to their burrowing niche.

Figure 3. Chalcides, Crythiosaurus and Bipes with bones colored. Note, only the quadrate remains in Bipes. Other bones are lost or fused. Sineoamphisbaena lost the epipterygoid. Crythiosaurus nests basal to Bipes in the large reptile tree, but the extreme reduction of the quadrate is an autapomorphy.

There may be another skink closer to Sineoamphisbaena, but I haven’t found it yet.

References
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.

wiki/Sineoamphisbaena

Viviparity in lizards

A new paper by Pyron and Burbrink (2013) combines lizard viviparity and lizard phylogeny and finds multiple origins for viviparity…and, multiple reversals to oviparity. The paper also suggests that the basal condition in lizards was oviparity. Only living taxa were tested.

Figure 1. From Wang and Evans 2011, a gravid Cretaceous lizard with 2 embryos. Odd that they are located as high as the forelimb, but when you have 15, allowances have to be made.

Earlier, Wang and Evans (2011) produced fossils of a Cretaceous lizard and her embryos (Fig. 1), all 15 of them!

From the Wang and Evans abstract:
“Although viviparity is most often associated with mammals, roughly one fifth of extant squamate reptiles give birth to live young. Phylogenetic analyses indicate that the trait evolved more than 100 times within Squamata, a frequency greater than that of all other vertebrate clades combined. However, there is debate as to the antiquity of the trait and, until now, the only direct fossil evidence of squamate viviparity was in Late Cretaceous mosasauroids, specialised marine lizards without modern equivalents. Here, we document viviparity in a specimen of a more generalised lizard, Yabeinosaurus, from the Early Cretaceous of China. The gravid female contains more than 15 young at a level of skeletal development corresponding to that of late embryos of living viviparous lizards. This specimen documents the first occurrence of viviparity in a fossil reptile that was largely terrestrial in life, and extends the temporal distribution of the trait in squamates by at least 30 Ma. As Yabeinosaurus occupies a relatively basal position within crown-group squamates, it suggests that the anatomical and physiological preconditions for viviparity arose early within Squamata.”

I would hasten add: perhaps not early in pylogeny, but often. Note these yabeinosaurs (Fig. 1) are beneath the rib cage close to the humerus. Moreover, the orientation is not head first toward the cloaca. Evidently it all works out.

We’ve seen fossils of reptiles huddling together in Decuriasuchus, Heleosaurus and others.

We’ve also looked a possible viviparity in mesosaurs. Ichthyosaurs and plesiosaurs are also notable live-bearers. Pterosaurs maintained embryos within the mother until shortly before hatching took place, based on the extreme thinness of the leathery eggshells and the degree of development of known embryos.

References
Pyron RA and Burbrink FT 2013. Early origin of viviparity and multiple reversions to oviparity in squamate reptiles. Ecology letters. doi: 10.1111/ele.12168.
Wang Y and Evans SE 2011. A gravid lizard from the Cretaceous of China and the early history of squamate viviparity. Naturwissenschaften Sept 98(9):739-43.

New Middle Jurassic lizard – svp abstracts 2013

From the abstract
Conrad et al. (2013) wrote: “The last three decades has seen a dramatic increase in our knowledge regarding the earliest evolution of the major squamate clades, but most known fossils are Cretaceous or younger. The earliest known squamates are the incompletely known Parviraptor, Eichstaettisauridae, Ardeosaurus, and the Paramacellodidae with their osteodermal armor. We report on a new late Middle Jurassic lizard from the Shishugou Formation of China representing the oldest complete squamate skeleton. The animal possesses vomerine teeth, a rectangular frontal, and incipient cusps on its marginal teeth. The preserved hind limb is very elongate. The entire body was encased in osteoderms.

The resultant phylogenetic hypothesis finds a “gecko-morphotype” (unarmored, relatively large-eyed, morphs with limbs of intermediate length and simple, insectivore-style teeth) to be ancestral for squamates. Our new lizard is recovered as a basal episquamate, related to lateratans, anguimorphs, and iguanomorphs.

The Late Jurassic saw the rise of therian mammals and coelurosaurian dinosaurs. At the same time, squamates enter the fossil record in both the gecko-morphotype and armored forms (e.g., Paramacellodus and our new taxon). We suggest that the selective pressure from this changing fauna may have helped “push” squamates into new morphotypes. Many known Late Jurassic and Cretaceous episquamates possess long legs (e.g., Bavarisaurus, Saichangurvel) and/or extensive osteodermal armor (e.g. Paramacellodus). These pressures may have contributed to the marginalization of the previously diverse and widespread rhynchocephalians.”

Notes
Conrad et al. are following Hedges (2005), a DNA study, in nesting geckos at the base of the squamata, iguania nesting higher. Hedges found legless Dibamus as the most basal squamate. Of the remaining taxa (Bifurcata), the gekkonids form a basal lineage. The Unidentata, squamates that are neither dibamids nor gekkonids, are divided into the Scinciformata (scincids, xantusiids, and cordylids) and the Episquamata. These include Laterata (Teiformata, Lacertiformata, and Amphisbaenia, with the latter two joined in Lacertibaenia) and Toxicofera (iguanians, anguimorphs and snakes). So, distinct from the large reptile tree, Hedges (2005) links Iguana and snakes on the basis of DNA.

It is unfortunate that Conrad et al. used a DNA tree that differs so much from a morphological tree because fossils cannot be tested for DNA.

Figure 1. Lacertulus, a basal tritosaur lepidosaur, also at the base of the Squamata.

It is also unfortunate that Conrad et al. do not recognize the third squamate clade, the Tritosauria, that reached their origin in the Permian (Lacertulus, Fig. 1) and reached their acme in the Triassic. Tritosaurs dwindled in diversity into the Cretaceous when only Huehuecuetzpalli and pterosaurs survived. These too became extinct by the end of the Cretaceous.

Figure 2. Click to enlarge. Reconstruction of TA1045, an unnamed Early Permian pre-lizard from Germany. Close to Dalinghosaurus, this genus had shorter legs and a longer torso. In grey above are the transverse belly scales.

TA 1045 (Fig. 2) is an unnamed tritosaur lepidosaur from the Early Permian. Considering the antiquity of TA 1045 and Lacertulus (both Permian) and the diversity of Triassic tritosaurs and Middle Jurassic squamates, there are certainly many more basal squamates  out there to be found in Triassic strata. Odd that they have not been discovered as yet.

I’m looking forward to seeing the new armored lizard to nest it morphologically.

References
Conrad J, Wang Y, Xu X, Pyron A and Clark JG. 2013. Skeleton of a heavily armored and long legged middle Jurassic lizard (Squamata, Reptilia). Journal of Vertebrate Paleontology  abstracts.
Hedges VN 2005. The phylogeny of squamate reptiles (lizards, snakes, and amphisbaenians) inferred from nine nuclear protein-coding genes. CR Biology 328(10-11):1000-1008. Epub 2005 Oct 27.

Another lizard with an antorbital fenestra!

Earlier we looked at the nesting of pterosaurs within a third clade of lepidosaurs (lizards), the Tritosauria, outside of the Squamata (Iguania + Scleroglossa). Pterosaurs, as everyone knows, have an antorbital fenestra. That’s the principal reason why most pterosaur workers try to force fit them into the Archosauria.

The frilled lizard, Chlamydosaurus kingii, is famous for many things: bipedal walking, frilled neck skin and that cantankerous attitude. Now let’s add: antorbital fenestra (Fig.1). This is the only living lizard that I know of (there may be more!) that has an antorbital fenestra. That makes six non-homologous appearances in the Reptilia. Here and here are the other five.

Figure 1. Frilled lizard skeleton. Click to enlarge. Note the small skull opening between the naris and orbit. That’s an antorbital fenestra. And this one raises the total of distinct non-homologous antorbital fenestra to six and the second among lepidosaurs. Fenestrasaurs were the first. Drepanosaurs may be homologous with Jesairosaurus at the base.

With its bowed hind limbs
The frilled lizard presents a good analog for how bowlegged pterosaurs (chiefly derived forms) would have run bipedally, perhaps prior to flight. This is the first time I’ve seen a skeleton of Chlamydosaurus, having featured this lizard in an early paper (Peters 2000) as an example of a reptile capable of bipedal locomotion, convergent with fenestrasaurs. I am pleased to note the ilium of Chlamydosaurus has a small anterior process (a hallmark of bipedal reptiles, exaggerated in fenestrasaurs, including pterosaurs). The tail, with those deep chevrons and wide transverse processes, would have been more robust than in any fenestrasaur. The closely apprssed tibia and fibula are also cursor traits. The asymmetric foot is no impediment to bipedal locomotion, contra the opinion of many pterosaur workers.

That antorbital fenestra has an unknown (to me) function. If anyone has that data, please let me know.

Added note: Darren Naish was kind enough to refer me to other lizards with this sort of antorbital fenestra, Pogona vitticeps, the bearded lizard is one, and here is a Digimorph link to it. A quick Googling revealed that the Harderian gland is located at the medial corner of the orbit. The lacrimal gland is smaller and appears at the posterior eyelids. According to Wikipedia, “The Harderian gland is a gland found within the eye’s orbit which occurs in tetrapods (reptiles, amphibians, birds and mammals) that possess a nictitating membrane and the fluid it secretes (mucous, serous or lipid) varies between different groups of animals.”

And how about that retroarticular process~! Perhaps related to the neck frill. I understand not all of the bones of the frill are included here.

The frilled lizard can be seen in action here on YouTube.

More on bipedal pterosaur tracks here.

References
This image (Fig. 1) comes from taxidermy.net. There are several more images of Chlamydosaurus from other angles there.

Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.