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.

 

Ascendonanus nestleri: an early Permian iguanid, not a varanopid.

Please see:
https://pterosaurheresies.wordpress.com/2018/03/20/the-early-permian-ascendonanus-assemblage/ Which shows that of the five specimens assigned to Ascendonanus at least two are widely divergent. The other three have not yet been tested. One is an iguanid. Another is a basalmost diapsid.

Just out today by Spindler et al. 2018, but previewed earlier
“A new fossil amniote from the Fossil Forest of Chemnitz (Sakmarian-Artinskian transition, Germany) is described as Ascendonanus nestleri gen. et sp. nov., based on five articulated skeletons with integumentary preservation. The slender animals exhibit a generalistic, lizard-like morphology. However, their synapsid temporal fenestration, ventrally ridged centra and enlarged iliac blades indicate a pelycosaur-grade affiliation. Using a renewed data set for certain early amniotes with a similar typology found Ascendonanus to be a basal varanopid synapsid. This is the first evidence of a varanopid from Saxony and the third from Central Europe, as well as the smallest varanopid at all. Its greatly elongated trunk, enlarged autopodia and strongly curved unguals, along with taphonomical observations, imply an arboreal lifestyle in a dense forest habitat until the whole ecosystem was buried under volcanic deposits. Ascendonanus greatly increases the knowledge on rare basal varanopids; it also reveals a so far unexpected ecotype of early synapsids. Its integumentary structures present the first detailed and soft tissue skin preservation of any Paleozoic synapsid.”

Except
Ascendonanus is not a varanopid synapsid. It’s an arboreal lepidosaur, an iguanid squamate in the large reptile tree (LRT, 1176 taxa, subset Fig. 3) with a typical skull, skin, size and niche typical for this clade. Only the torso has more vertebrae than is typical, but the related Liushusaurus also has more than 25 presacral vertebrae.

The Early Permian
is not where we expect to see lizards. No others are known from this period. Perhaps that is why Spindler et al. 2018 chose to restrict their taxon list to synapsids and their outgroups…and to ignore those upper temporal fenestrae, so plainly visible (Fig. 1). And note those slender, vertical epipterygoids. You don’t see those on synapsids.

Figure 1. The skull of Ascendonanus has a diapsid temporal configuration with clearly visible upper temporal fenestra and a typical iguanid skull morphology.

Figure 1. The skull of Ascendonanus has a diapsid temporal configuration with clearly visible upper temporal fenestra and a typical iguanid skull morphology. Note manual digit 5 preserved beneath the palm of the hand and restored to a lateral position. Not also the two jugal ascending processes, due to the split leaving medial and lateral halves of this bone. Note the two slender epipterygoids inside the temporal openings. Only squamates have such bones.

Ascendonanus nestleri (Spindler 2017, TA1045) is a German iguanid squamate found in vulcanized early Permian (291mya) sediments. It is the oldest lepidosaur known and based on its phylogeny, suggests an earlier radiation of lepidosaurs that earlier presumed. Other early lepidosauriformes include Paliguana and Lacertulus from the Late Permian. Other basal iguanids and pre-iguanids, like Scandensia, Calanguban, Euposaurus and Liushusaurus are late-survivors in the Late Jurassic and Early Cretaceous. Iguana is a late-survivor of an early radiation living today.

Ascendonanus was originally described
as a tree-climbing varanopid synapsid by Spindler et al. (2018), but no lepidosauriformes were tested. The bones are difficult to see through the scaly skin (Fig. 1). Upper temporal fenestra and other lepidosaur traits were overlooked, perhaps because lizards are otherwise unknown from the Early Permian. No other basal synapsids were arboreal, but some Iguana species are also arboreal. No other varanopids are quite as small, but other iguanids are smaller.

By the way, like more paleo workers
Spindler et al. 2018 were unaware of the synapsid/prodiapsid split that removes many former varanopids from the clade Synapsida, despite their having typical synapsid temporal fenestration. One more reason NOT to label taxa based on traits, but to only label taxa after a wide gamut cladistic analysis, like the LRT.

Thus
we no longer call Ascendonanus a diapsid based on its diapsid temporal configuration. True diapsids, like Eudibamus and Petrolacosaurus, all nest within the Archosauromorpha. By convergence, all members of the clade Lepidosauriformes, including Ascendonanus, all have a diapsid temporal configuration or a modification based on that.

Figure 1. Ascendonanus nestler is an Early Permian lepidosaur nesting with Saniwa, a member of the Varanoidea.

Figure 2. Ascendonanus nestler is an Early Permian iguanid squamate lepidosaur, not a varanopid synapsid.

Sorry to say it,
taxon exclusion is once again the problem here. Spindler et al. 2018 were also following tradition when they included caseids and eothyrids in they analysis of synapsids. The Caseasauria nest elsewhere when given the opportunity to do so.

Figure 3. Ascendonanus cladogram, subset of the LRT. Here Ascendonanus nests with iguanids, not varanopids.

Figure 3. Ascendonanus cladogram, subset of the LRT. Here Ascendonanus nests with iguanids, not varanopids.

Figure 5. Ascendonanus pes.

Figure 5. Ascendonanus pes.

References
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.
Spindler F, Werneburg R, Schneider JW, Luthardt L, Annacker V and Räler R 2018. First arboreal ‘pelycosaurs’ (Synapsida: Varanopidae) from the early Permian Chemnitz Fossil Lagerstätte, SE Germany, with a review of varanopid phylogeny. DOI: https://doi.org/10.1007/s12542-018-0405-9

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.