Megachirella: Not at the origin of squamates. Lacertulus is older.

We looked at Lacertulus and the origin of the Squamata in the Late Permian
here in October 2011.

We looked at the splitting of the Tritosauria from the Protosquamata
here in December 2014.

Siimòes et al. 2018
proposed to nest Megachirella watchtleri (Fig. 1) at the origin of squamates in the Middle Triassic, 75 million years earlier than the previously known oldest squamate fossils. They reported, “For the first time, to our knowledge, morphological and molecular data are in agreement regarding early squamate evolution, with geckoes—and not iguanians—as the earliest crown clade squamates. Divergence time estimates using relaxed combined morphological and molecular clocks show that lepidosaurs and most other diapsids originated before the Permian/Triassic extinction event, indicating that the Triassic was a period of radiation, not origin, for several diapsid lineages.”

Figure 1. New µCT scans of Megachirella from Simoes et al. 2018.

Figure 1. New µCT scans of Megachirella from Simoes et al. 2018.

Unfortunately
|they did not include relevant taxa. According to the large reptile tree (LRT, 1224 taxa, www.reptileevolution.com/reptile-tree.htm) Megachirella nests at the base of the Rhynchocephalia (= Sphenodontia) along with Pleurosaurus (excluded from the Simoes team study) when many more relevant taxa are included.

Figure 2. Megachirella nests in the middle of this cladogram, that also nests turtles between rib gliders and choristoderes.

Figure 2. Megachirella nests in the middle of this cladogram, that also nests turtles between rib gliders and choristoderes.

 

Lacertulus is older (Late Permian) and more directly related to squamates.

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

FIgure 3. Megachirella (Renesto and Posenato 2003) is a sister to the BSRUG diapsid and reconstructed here.

Nesting turtles with rib gliders
(Coelurosauravus) only hints at major flaws in the Simoes et al. cladogram topology. Nesting Sophineta and Palaegama close to and basal to Megachirella confirms findings made years earlier by the LRT. Marmoretta is also close, but nests within the Rhynchocephalia in the LRT.

Figure 2. Pleurosaurus and Palaeopleurosaurus skulls compared to those of sister taxa.

Figure 2. Pleurosaurus and Palaeopleurosaurus skulls compared to those of sister taxa.

Tijubina (which Simoes redescribed in 2012) is also missing from the Simoes et al. 2018 study.

Figure 1. Palaegama is basal to Coelurosauravus ('rib' gliders), Megachirella (rhynchocephalians), Lacertulus (protosquamates) and Tijubina (tritosaurs)

Figure 5. Palaegama is basal to Coelurosauravus (‘rib’ gliders), Megachirella (rhynchocephalians), Lacertulus (protosquamates) and Tijubina (tritosaurs)

 

 

References
Simòes T, and 8 co-authors 2018. The origin of squamates revealed by a Middle Triassic lizard from the Italian Alps. Nature 557: 706â709 (2018)

Publicity
https://www.livescience.com/62693-mother-of-lizards-fossil.html

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What is Fraxinisaura? And what does it look like?

Much missing data here
and incomplete sister taxa likewise missing many bones.

Schoch and Sues 2018
bring us a new Middle Triassic lepidosauromorph reptile with pleurodont tooth implantation. The bones are all disarticulated. They reported, “Phylogenetic analysis recovered Fraxinisaura rozynekae among Lepidosauromorpha and as the sister taxon of the Middle to Late Jurassic Marmoretta oxoniensis. Unfortunately, currently existing character-taxon matrices do not allow confident resolution of the interrelationships of these and other early Mesozoic lepidosauromorph reptiles.”

By contrast
the large reptile tree (LRT, 1200 taxa, Fig. 3) nests Fraxinisaura between Lacertlus and Schoenesmahl, two basal prosquamates not tested by Shoch and Sues. This is where the LRT really shines as it minimizes taxon exclusion problems.

Figure 1. Fraxinisaura as originally reconstructed (below) and as reconstructed here (above) using bone images.

Figure 1. Fraxinisaura as originally reconstructed (below) and as reconstructed here (above) using bone images. Surprisingly, both reconstructions nest Fraxinisaura in the same spot.

First I scored
the Schoch and Sues drawing in the LRT. Then I scored a new reconstruction based on assembling the bone photos in Schoch and Sues 2018.

Surprisingly,
both reconstructions (Fig. 1) nest Fraxinisaura in the same spot in the LRT.

Figure 2. Click to enlarge. Cleaned up reconstruction of the former Bavarisaurus (cololizard at present). Gray areas added based on sister taxa. This is a tritosaur.  Note the large naris bounded ventrally by the maxilla. The ventral pelvis is shallower. I don't understand the pterygoid morphology anteriorly. The upper and lower teeth don't match. That's a red flag, but it is the only data available.

Figure 2. Click to enlarge. Cleaned up reconstruction of the former Bavarisaurus (cololizard at present). Gray areas added based on sister taxa. This is a tritosaur.  Note the large naris bounded ventrally by the maxilla. The ventral pelvis is shallower. I don’t understand the pterygoid morphology anteriorly. The upper and lower teeth don’t match. That’s a red flag, but it is the only data available.

Unfortunately,
Schoch and Sues had too few, and no relevant (closely related) taxa in their taxon list. And the freehand sketch turned out to be not very accurate. They added a darker gray area to the nasals (Fig. 1) because they weren’t ready to accept that the naris might be quite large in Fraxinisaura. I was ready to accept that possibility because Schoenesmahl (Fig. 2) also has a giant naris. Once again, taxon exclusion tends to affect our decisions and sometimes makes us fudge the data.

Figure 2. Subset of the LRT focusing on Fraxinisaura and kin among the prosquamata.

Figure 4. Subset of the LRT focusing on Fraxinisaura and kin among the prosquamata.

Lacertulus is late Permian.
So, it’s no surprise to see Fraxinisaura in the Middle Triassic. Most basal tritosaurs are also Middle Triassic, so it’s no surprise to see prosquamates there, too.

Figure 1. Lacertulus, a basal squamate from the Late Permian

Figure 3. Lacertulus, a basal pro-squamate from the Late Permian.

Fraxinisaura rozynekae (Schoch and Sues 2018, Middle Triassic, SMNS 91547) was originally considered a basal lepidosaurmorph close to Marmoretta. Here it nests between the basal pro-squamates, Lacertulus and Schoenesmahl. The naris is very large. The premaxillary teeth are procumbent and tiny. The humerus and femur are very large and narrow. The original parietal appears to be a clavicle and the parietal is not figured. Scale bars do not produce an identical reconstruction when bones are used instead of freehand drawing.

References
Schoch R and Sues H-D 2018. A new lepidosauromorph reptile from the Middle
Triassic (Ladinian) of Germany and its phylogenetic relationships. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1444619

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

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.

 

SVP abstracts 2017: The earliest lepidosaurs

Simöes 2017 brings us
new insights into the origin and early radiation of lepidosaurs, but seems to focus on the squamate side of that equation. Earlier Simöes brought us new data on Ardeosaurus (late Jurassic proto-snake) and Calanguban (Early Cretaceous, late-surviving basal squamate).

From the abstract:
“The origins and early radiation of lepidosaurs remain largely enigmatic by several factors, including:

  1. the oldest unequivocal fossils currently attributed to the Squamata are from the Middle Jurassic;
  2. available studies of broad level/deep-time diapsid reptile relationships provide very limited sampling of either fossil or living lepidosaurs (often, Squamata being represented as a single terminal unit);
  3. morphological and molecular evidence of squamate relationships disagree on what is the earliest squamate clade (iguanians vs dibamids and geckoes);
  4. among others.”

“Here, I provide a new phylogenetic dataset with a deep sampling of the major diapsid and
lepidosaurian lineages (living and fossil) at the species level in order to identify the
composition and early evolution of lepidosaurs. All taxon scorings were based on
personal observation of specimens and/or 3D CT scans from 51 collections from around
the world, making it the largest species sample ever collected for investigating the origin
of lepidosaurs—over 150 species.”

“The results indicate novel relationships among diapsids and re-shape the lepidosaurian
tree of life. Previously proposed early lepidosaurs are found to belong to other lineages of
reptiles. Importantly, heretofore unrecognized squamate fossils are found as the earliest
squamates, dating back to the Early Triassic, thus filling what was thought to be a fossil
gap of at least 50 million years. In most results (morphology only and combined data)
geckoes are the earliest squamate crown clade, iguanians are always found as later
evolving squamates, and scincomorphs are polyphyletic, thus dramatically differing from
previous morphology based studies, but agreeing with the molecular data.”

Figure 1. Lacertulus, a basal squamate from the Late Permian

Figure 1. Lacertulus, a basal protosquamate from the Late Permian

How does this data compare
to the large reptile tree? The LRT has 140 lepidosaur taxa, but I don’t get the feeling that Simöes included tritosaurs and protosquamates, some of which extend back to the Late Permian (Lacertulus, Fig. 1). If Simöes does not include those clades, the hypothesis needs more taxa. The abstract is enigmatic with regard to which early lepidosaurs now belong to other lineages and which unrecognized squamates are now earliest squamates.

But I like that Simöes is looking at more taxa!!

Unfortunately,
Simöes does not provide outgroup taxa in the abstract. I’m guessing he did not test a wide gamut of taxa, like the LRT, to see if they were lepidosaurs or not. That’s how you recover protosquamates and tritosaurs. In the LRT geckoes are not the basalmost squamates and scincomorphs are not polyphyletic.

I look forward to this paper!!

References
Simöes TR 2017. The origin and early evolution of lepidosaurian reptiles. Abstracts from the Society of Vertebrate Paleontology 2017.

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.

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