4 nostrils in Chamaeleo?

The skull of the smooth chameleon,
Chamaeleo laevigatus (Figs. 1, 2), has two extra holes in the anterodorsal plane of its rostrum (Fig. 1). Despite appearances, the holes visible in top view are not nostrils.

Figure 1. The chameleon Trioceros jacksonii colored using DGS. The sutures are difficult to see in the original skull, much easier in the colorized tracing.

Figure 1. The chameleons Chamaeleo and Trioceros. Note the lateral nostrils on both taxa. Chamaeleo has two more openings in dorsal view.  Not sure if Trioceros was the same. Note the giant pterygoids on Chamaeleo. The prefrontal and postfrontal are in contact. The premaxilla is tiny in ventral view.

The Chamaeleo rostrum
is angled at about 50º from the jawline. Given just the skull, you might think those openings in dorsal view are nostrils. With skin and scales on (Fig. 2), the nostrils are located on the lateral plane, as in other chameleons, like Trioceros (Fig. 1), surrounded by traditional circumnarial bones.

Figure 2. Chamaeleo laevigatus invivo. Red arrow points to external naris.

Figure 2. Chamaeleo laevigatus invivo. Red arrow points to external naris.

Diaz and Trainer 2015 published
some nice images of chameleon hands and feet, colorized here (Fig. 3) for additional clarity. The metacarpals and metatarsals are the bones that radiate. The phalanges are all vertical here.

Figure 3. The manus and pes skeleton of a chameleon from Diaz et al. 2016 with colors added and the second from left image relabels the fingers, correcting a typo.

Figure 3. The manus and pes skeleton of a chameleon from Diaz et al. 2015 with colors added and the second from left image relabels the fingers, correcting a typo. Manual 1 has only two phalanges. The metacarpals and metatarsals open horizontally in these images. Note the ankle elements are not co-ossified.

References
Diaz RE Jr. and Trainor PA 2015. Hand/foot splitting and the ‘re-evolution’ of mesopodial skeletal elements during the evolution and radiation of chameleons. BMC Evolutionary Biology201513:184.

wiki/Smooth_chameleon
digimorph.org/Chamaeleo_laevigatus/
Chamaeleo laevigatus GRAY, 1863″. The Reptile Database

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Early Cretaceous stem chameleon/horned lizard

Unnamed stem chameleon (Daza et al. 2016; Early Cretaceous, 1.2cm in length; JZC Bu154; Fig. 1) is a tiny neonate preserved in amber. It also nests basal to horned lizards like Phrynosoma, in the large reptile tree (LRT, 1089 taxa). Note the long, straight hyoid forming the base of the shooting tongue. The split fingers and toes of extant chameleons had not yet developed in this taxon. Found in amber, this newborn lived in a coniferous forest.

Figure 1. The Early Cretaceous stem chameleon/horned lizard found amber. Snout to vent length is less than 11 mm. Much smaller than a human thumbnail.

Figure 1. The Early Cretaceous stem chameleon/horned lizard found amber. Snout to vent length is less than 11 mm. Much smaller than a human thumbnail. Insitu fossil from Daza et al. 2016,  colorized and reconstructed here. At a standard 72 dpi screen resolution, this specimen is shown 10x actual size.

This specimen further cements
the interrelationship of arboreal chameleons and their terrestrial sisters, the horned lizard we looked at earlier with Trioceros and Phyrnosoma in blue of this cladogram (Fig. 2) subset of the LRT.

Figure 3. Subset of the LRT focusing on the neonate stem chameleon/horned lizard.

Figure 2. Subset of the LRT focusing on the neonate stem chameleon/horned lizard.

Figure 6. Phyronosoma, the horned lizard of North America.

Figure 3. Phyronosoma, the horned lizard of North America.

Figure 2. Trioceros jacksonii overall. Size is 12 inches (30 cm) from tip to tip.

Figure 4. Trioceros jacksonii overall. Size is 12 inches (30 cm) from tip to tip.

References
Daza JD et al. 2016. Mid-Cretaceous amber fossils illuminate the past diversity of tropical lizards. Sci. Adv. 2016; 2 : e1501080 4 March 2016

A deeper extension for the Lepidosauria

By definition
the Lepidosauria includes Rhynchocelphalia (Sphenodon), Squamata (Iguana), their last common ancestor and all descendants. By this definition pterosaurs and kin are lepidosaurs because they nest between rhychocephalians and iguanids in a traditionally unrecognized clade the Tritosauria (Fig. 1).

Figure 1. Subset of the LRT focusing on the Lepidosauria. Now the drepanosaur clade lumps with the rhynchocephalians in the crown group. Extant lepidosaurs are in gray.

Figure 1. Subset of the LRT focusing on the Lepidosauria. Now the drepanosaur clade lumps with the rhynchocephalians in the crown group. Extant lepidosaurs are in gray.

While reviewing
the large reptile tree (LRT, 1087 taxa, subset Fig. 1) following the addition of Avicranium, the base of the Rhynchocephalia  shifted back to include Jesairosaurus, and the drepanosaursSaurosternon and Palaegama, which formerly nested as outgroup Lepidosauriformes now nest basal to the tritosaurs, pro-squamates and squamates within the Lepidosauria, based on the traditional definition.

With this change
the non-lepidosaur Lepidosauriformes are reduced to just the glider clade, Coletta, Paliguana, and Sophineta, taxa with a diapsid skull architecture. These remain stem lepidosaurs. The membership of the clade Lepidosauriformes do not change.

Remember,
despite their diapsid temporal morphology, these are not members of the clade Diapsida, which is restricted to Archosauromorph ‘diapsids’ only. Petrolacosaurus is a basal member of the monophyletic Diapsida. The clade name ‘Lepidosauriformes’ includes all lepidosauromorphs with upper and lateral temporal fenestrae. If you know any traditional paleontologists who still think lepidosaurs are related to archosaurs, please show them the LRT.

Once a definition for a clade is made
then the next step is to see which taxa fall under than definition… and then to see if that definition is a junior synonym for a previously published definition based on clade membership. Remember, traditional traits may not give you monophyly, but phylogenetic analysis always will.

And
yes, I do review all the scores in the LRT and announce updates when they are made.

 

Shringasaurus: new rhynchocephalian lepidosaur with horns

Sengupta, Ezcurra and Bandyopadhyay 2017 bring us
a new, very large, horned rhynchocephalian lepidosaur, Shringasaurus (Fig. 1). Unfortunately, that’s not how the Sengupta team nested it (due to the sin of taxon exclusion, see below). Even so, there is consensus that the new taxon is closely related to the much smaller Azendohsaurus (Fig. 1).

Figure 1. Shringasaurus to scale with Azendohsaurus. Line art modified from Sengupta et al. Color added here. Note the anterior lappet of the maxilla over the premaxilla. The supratemporal  (dark green) remains.

Figure 1. Shringasaurus to scale with Azendohsaurus. Line art modified from Sengupta et al. Color added here. Note the anterior lappet of the maxilla over the premaxilla. The supratemporal  (dark green) remains.

From the abstract:
“The early evolution of archosauromorphs (bird- and crocodile-line archosaurs and stem-archosaurs) represents an important case of adaptive radiation that occurred in the aftermath of the Permo-Triassic mass extinction. Here we enrich the early archosauromorph record with the description of a moderately large (3–4 m in total length), herbivorous new allokotosaurian, Shringasaurus indicus, from the early Middle Triassic of India. The most striking feature of Shringasaurus indicus is the presence of a pair of large supraorbital horns that resemble those of some ceratopsid dinosaurs. The presence of horns in the new species is dimorphic and, as occurs in horned extant bovid mammals, these structures were probably sexually selected and used as weapons in intraspecific combats. The relatively large size and unusual anatomy of Shringasaurus indicus broadens the morphological diversity of Early–Middle Triassic tetrapods and complements the understanding of the evolutionary mechanisms involved in the early archosauromorph diversification.”

Allokotosauria
Shringasaurus was nested in the clade, Allokotosauria, According to Wikipedia, “Nesbitt et al. (2015) defined the group as a  containing Azendohsaurus madagaskarensis and Trilophosaurus buettneri and all taxa more closely related to them than to Tanystropheus longobardicus, Proterosuchus fergusi, Protorosaurus speneri or Rhynchosaurus articeps.” This definition was based on the invalidated hypothesis that rhynchosaurs and allokotosaurs were close to the base of the Archosauriformes as the addition of more taxa will demonstrate. Basically this clade equals Trilophosaurus, Azendohsaurus and now Shringasaurus. In the large reptile tree (LRT, 1049 taxa) this clade nests between Sapheosaurus + Notesuchus and Mesosuchus + Rhynchosauria all nesting within Sphenodontia (=  Rhynchocephalia), so they are all lepidosaurs. All you have to do is add pertinent taxa to make this happen in your own phylogenetic analysis.

Figure 2. Scene from the 1960 film, The Lost World, featuring a giant iguana with horns added presaging the appearance of Shringasaurus.

Figure 2. Scene from the 1960 film, The Lost World, featuring a giant iguana with horns added presaging the appearance of Shringasaurus.

Coincidentally the 1960 film,
The Lost World featured an iguana made up with horns similar to those of Shringasaurus.

References
Sengupta S, Ezcurra MD and Bandyopadhyay S 2017. A new horned and long-necked herbivorous stem-archosaur from the Middle Triassic of India. Nature, Scientific Reports 7: 8366 | DOI:10.1038/s41598-017-08658-8 online here.

No Wiki page yet.

What is the enigmatic Otter Sandstone (Middle Triassic) diapsid?

Coram, Radley and Benton 2017
presented a “small diapsid reptile [BRSUG 29950-12], possibly, pending systematic study, a basal lepidosaur or a protorosaurian.” According to Coram et al. “The Middle Triassic (Anisian) Otter Sandstone was laid down mostly by braided rivers in a desert environment.”

Figure 1. The Middle Triassic Otter Sandstone diapsid BRSUG 29950-12 under DGS nested with basalmost lepidosaurs like Megachirella.

Figure 1. The Middle Triassic Otter Sandstone diapsid BRSUG 29950-12 under DGS nested with basalmost lepidosaurs like Megachirella. Skeleton is exposed in ventral (palatal) view.

The LRT is here to nest and identify published enigmas
The large reptile tree (LRT 1041 taxa) nests BRSUG 29950-12 with the basalmost lepidosaur Megachirella. They are a close match and preserve nearly identical portions of their skeletons (Fig. 2). Megachirella was originally considered a sister to Marmoretta, another basal sphenodontian from the much later Middle/Late Jurassic.

FIgure 2. Megachirella (Renesto and Posenato 2003) is a sister to the BSRUG diapsid.

FIgure 2. Megachirella (Renesto and Posenato 2003), also from Middle Triassic desposits, is a sister to the BSRUG diapsid and provides a good guide for its eventual reconstruction.

At the base of the Lepidosauria
in the LRT nests Megachirella, derived from a sister to Sophineta (Early Triassic) and Saurosternon + Palaegama (Latest Permian) and kin. Sisters to Megachirella within the Lepidosauria include the tritosaurs Tijubina + Huehuecuetzpalli (Early Cretaceous), Macrocnemus (Middle Triassic) and the prosquamate Lacertulus (Late Permian). Also similar and related to Palaegama is Jesairosaurus (Middle Triassic). So the genesis of the Lepidosauria is Late Permian. The initial radiation produced taxa that continued into the Early Cretaceous. The radiation of derived taxa continued with three major clades, only one of which, the Tritosauria, is now completely extinct.

Note
It is important to remember that lepdiosaurs and protorosaurs are not closely related, but arrived at similar bauplans by convergence, according to the LRT. The former is a member of the new Lepidosauromorpha. The latter is a member of the new Archosauromorpha. Last common ancestor: Gephyrostegus and kin.

Nesting at the base of the Lepidosauria
in the Sphenodontia clade makes the BSRUG specimen an important taxon. Let’s see if and when this taxon is nested by academic workers that they include all of the pertinent taxa and confirm or re-discover the Tritosauria. The LRT provides a good list of nearly all of the pertinent taxa that should be included in that future study, many of which are listed above. Based on that list, the BSRUG specimen is a late-survivor of a perhaps Middle Permian radiation of basal lepidosaurs.

References
Coram RA, Radley JD and Benton MJ 2017. The Middle Triassic (Anisian) Otter Sandstone biota (Devon, UK): review, recent discoveries and ways ahead. Proceedings of the Geologists’ Association in press. http://dx.doi.org/10.1016/j.pgeola.2017.06.007

Do gliding lizards (genus: Draco) actually grab their extended ribs?

Figure 1. Extant Draco flying with hands either grabbing the leading edge of the membrane or streamlining their hands on top of it.

Figure 1. Extant Draco flying with hands either grabbing the leading edge of the membrane or streamlining their hands on top of it. Images from Dehling 2016.

Gliding lizards
of the genus Draco (Figs. 1, 2) come in a wide variety of species. Similar but extinct gliding basal lepidosauriformes, like Icarosaurus (Fig. 2), form a clade that arose in the Late Permian and continued to the Early Cretaceous.

Figure 2. Two Draco species fully extending their rib membranes without the use of the hands.

Figure 2. Two Draco species fully extending their rib membranes without the use of the hands.

A recent paper
(Dehling 2016) reported, “the patagium is deliberately grasped and controlled by the forelimbs while airborne.” Evidently this ‘membrane-grab’ behavior has not been noted before. I wondered if the rib skin is indeed grasped, or does the forelimb merely fold back against the leading edge of the patagium in a streamlined fashion? Photographs of climbing Draco specimens (Fig. 2) show that the patagium  can fully extend without the aid of the forelimbs to stretch them further forward.

Figure 3. Icarosaurus. Note the tiny ribs near the shoulders. The bases for the strut-like dermal bones are the ribs themselves flattened and transformed by fusion to act like transverse processes, which sister taxa do not have. Note the length of the hands corresponds to the base of the anterior wing strut.

Figure 3. Icarosaurus. Note the tiny ribs near the shoulders. The bases for the strut-like dermal bones are the ribs themselves flattened and transformed by fusion to act like transverse processes, which sister taxa do not have. Note the length of the hands corresponds to the base of the anterior wing strut, a great place to rest the manus or grab the membrane.

A quick review of prehistoric gliding keuhneosaurs
(Fig. 3) show that the manus unguals are not quite as large and sharp as those of the pes and that the manus in gliding mode extends just beyond the shorter two anterior dermal struts so that the glider -may- have grasped the anterior struts in flight. Or may have rested the manus there. Remember, these are taxa unrelated to the extant Draco, which uses actual ribs to stretch its gliding membrane. The same holds true for the more primitive Coelurosauravus and Mecistotrachelos, which have not been traditionally recognized as basal kuehneosaurs.

* As everyone should know by now…
the so-called transverse processes in kuehneosaurs are the true ribs, only fused to the vertebrae. The ribs remain unfused to the vertebrae in the older and more primitive coelurosauravids. No sister taxa have transverse processes elongate or not.

References
Dehling M 2016. How lizards fly: A novel type of wing in animals.

Earliest(?) stem squamate – SVP abstracts 2016

Klugman and Pritchard 2016
believe they have found the earliest lepidosaur stem squamate (see below). The large reptile tree finds earlier stem squamates (Fig. 1, click here to enlarge).
Earlier we looked at the wider and narrower definitions of the term ‘stem’.
Figure 1. CLICK TO ENLARGE. Stem taxa are closest ancestors to living taxa. Here basal diapsids and marine enaliosaurs are stem archosaurs. Triceratops is a stem bird. Captorhinids are stem turtles. Pterosaurs are stem squamates.

Figure 1. CLICK TO ENLARGE. Stem taxa are closest ancestors to living taxa. Here basal diapsids and marine enaliosaurs are stem archosaurs. Triceratops is a stem bird. Captorhinids are stem turtles. Pterosaurs are stem squamates. The colors here indicate the wider definition of ‘stem’.

From the Klugman and Pritchard abstract (abridged)
“Crown group lepidosaurs are highly diverse: they comprise more than 7,000 globally distributed extant species of lizards and snakes (Squamata), plus the single rhynchocephalian genus Sphenodon. The earliest known lepidosaurs are rhynchocephalians from the Late Triassic of Europe, (1) and this group quickly diversified and achieved a global distribution by the end of the Triassic. In contrast, early squamates have a sparse fossil record; their first representatives are found in the Early-Middle Jurassic of Laurasia (2). Although Rhynchocephalia and Squamata diverged in the Middle Triassic, a 40-50 million years ghost lineage exists for Squamata. Jurassic squamates are already considerably derived, and have already diversified into their extant groups, which testifies to a substantial gap in the known fossil record. Here we report on a new lepidosaur from a Norian microvertebrate site in Petrified Forest National Park, Arizona. This fossiliferous locality is from the Upper Blue Mesa Member of the Chinle Formation, and is dated to 221 mya. The depositional environment is a shallow anoxic lake, where skeletal elements preserved are disarticulated and often fragmentary. The site has yielded a diverse small vertebrate fauna, including the new lepidosaurs and several undescribed rhynchocephalians. Skeletal elements are represented by numerous small, delicate pleurodont maxilla and dentaries. We integrated the material of the new lepidosaurs into phylogenetic analyses of Permo-Triassic Diapsida and Mesozoic Lepidosauromorpha, using maximum parsimony, maximum likelihood, and Bayesian analysis. All analyses support the new taxon as the sister taxon to all other Squamata, (3) substantially reducing the ghost lineage of Squamata. This discovery indicates that the absence of squamate fossils in their early evolutionary history could be caused in part by collection bias towards larger, more robust specimens. This taxon provides a look into the early evolutionary history of squamates. It also adds direct evidence of yet another major lineage of extant terrestrial vertebrates to originate in the Triassic.”
Notes
  1. In the LRT Megachirella (Middle Triassic) is an earlier basal rhynchocephalian. Bavariasaurus (Late Jurassic) and
  2. Lacertulus (Late Permian; Fig. 2) are basal stem squamates. Ascendonanus (Rößler et al. 2012), an Early Permian lepidosaur in the iguanid clade is the earliest lepidosaur I have encountered yet, although this is based on low-rez data. Based on these nestings, the original radiation of lepidosaurs must have occurred in the Permian and then enjoyed very long period of stasis.  Lacertulus is the oldest known lepidosaur and older than any Late Triassic Petrified Forest taxa. It does not have pleurodont (fused to the jaw) teeth.
  3. The LRT is an analysis that includes a long list of pro or proto-squamates and tritosaurs that are sisters to the Squamata. Palaegama (Late Permian), Tridentinosaurus (Early Permian) and Saurosternon (Latest Permian) are sisters to the Lepidosauria and they are basal to the highly derived Late Permian taxon, Coelurosauravus. So the original radiation of lepidosaurs and their lepidosauriform sisters must have been in the Early Permian. If one deletes Sphenodon, then another stem squamate would be Macroleter (Middle Permian). Earlier than this and you get into stem turtles.
Figure 1. Lacertulus, a basal squamate from the Late Permian

Figure 2. Lacertulus, a basal squamate from the Late Permian

References
Klugman B and Pritchard AC 2016. Earliest stem-squamate (Lepidosauria) from the Late Triassic of Arizona. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
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