The most basal lepidosauriforms and lepidosaurs to scale

Lepidosauriform fossils are extremely rare in the Mesozoic and Paleozoic.
In the Earliest Permian we find Tridentinosaurus (Fig. 1; Dal Piaz 1931,1932; Leonardi 1959), a taxon ancestral to the pseudo-rib-gliders of the Late Permian (Coelurosauravus) through the Early Cretaceous (Xianlong) and close to the origin of all other lepidosauriforms, including living snakes, lizards and the tuatara (genus: Sphenodon).

Figure 1. Basal lepidosauriformes to scale from Tridentinosaurus (Earliest Permian) to Huehuecuetzpalli (Early Cretaceous). Subtle differences lump and split these taxa into their various clades.

Figure 1. Basal lepidosauriformes to scale from Tridentinosaurus (Earliest Permian) to Huehuecuetzpalli (Early Cretaceous). Subtle differences lump and split these taxa into their various clades.

 

Sometime during the Early Permian
the Lepidosauria split between the Sphenodontia + Drepanosauria and the Tritosauria + Protosquamata in the large reptile tree (LRT, 1381 taxa).

Short-legged
Jesairosaurus, in the Early Triassic, nests basal to the clade of slow-moving, arboreal drepanosaurs. On another branch, Megachirella (Middle Triassic) and Gephyrosaurus (Early Jurassic) are basal members of the Sphenodontia.

Long-legged
and probably arboreal Saurosternon and Palaegama, (both Late Permian) are the earliest known Lepidosauria, but they are basal to the Tritosauria + Protosquamata clades.

Figure 5. Subset of the LRT focusing on the Tritosauria. Note the separation of one specimen attributed to Macrocnemus.

Figure 5. Subset of the LRT focusing on the Tritosauria. Note the separation of one specimen attributed to Macrocnemus.

Late-surviving, long-legged basal Tritosauria
include tiny Tijubina and Huehuecuetzpalli (both Early Cretaceous). This clade gave rise to giant Tanystropheus, exotic Longisquama and volant Pteranodon.

Tiny and long-legged Late Permian
Lacertulus is the basal taxon in the previously unrecognized clade Protosquamata, the parent clade to the extant Squamata. This taxon documents the antiquity of this clade.

Going back to the Early Permian
we have a long-torso, short-legged specimen, MNC TA-1045, that nests in the LRT just outside the extant Squamata (Iguana). MNC TA-1045 was found alongside the genus Ascendonanus (MNC-TA0924), a basal archosauromorph diapsid with a shorter torso you can see here. The MNC TA-1045 specimen pushes the genesis of the lepidosaurs back to the Early Permian, nearly coeval with the basalmost lepidosauriform shown in figure 1, Tridentinosaurus.

The Lepidosauromorph-Archosauromorph dichotomy
was already present in the Viséan (Early Carboniferous, 330 mya), so the new Lepidosauromorpha had 30 million years to diverge into captorhinomorphs, diadectomorphs, millerettids and lepidosauriforms by the time Tridentinosaurus first appears in the Earliest Permian (300 mya).

Late surviving,
but basalmost lepidosauromorphs include Sophineta , Paliguana and Coletta (all Early Triassic). These taxa have an upper temporal fenestra not seen in outgroup taxa.

Proximal outgroups for the Lepidosauriforms
include the late-surviving owenettids: Barasaurus (Late Permian) and kin, Owenetta (Late Permian) and kin, and the late-surviving macroleterids (Middle Permian) and nycteroleterids (Middle Permian) before them.

At least that’s what the data says so far.
With every new taxon the tree grows stronger and more precise, so the odds of changing the tree topology with additional taxa continue to drop. Looking forward to seeing more Paleozoic arboreal lepidosauromorph discoveries as they arrive.

References
Dal Piaz Gb. 1932 (1931). Scoperta degli avanzi di un rettile (lacertide) nei tufi compresi entro i porfidi quarziferi permiani del Trentino. Atti Soc. Ital. Progr. Scienze, XX Riunione, v. 2, pp. 280-281. [The discovery of the remains of a reptile (lacertide) in tuffs including within the Permian quartz porphyry of Trentino.]
Leonardi P 1959. Tridentinosaurus antiquus Gb. Dal Piaz, rettile protorosauro permiano del Trentino orientale. Memorie di Scienze Geologiche 21: 3–15.

www.reptileevolution.com/reptile-tree.htm

 

 

 

 

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Enigmatic Teraterpeton understood, at last, with better data

Finally
some photographic skull material has appeared online for Teraterpeton (Fig. 1). Not sure when these first appeared. Could have been years ago. I have not been searching until a day or two ago (see below).

First added
to the large reptile tree (LRT, 1371 taxa) on the basis of drawings by Sues 2003, the long rostrum and antorbital fenestra + the infilling of the lateral temporal fenestra of Teraterpeton  are traits that don’t go together anywhere else on anyone’s cladogram. Sues considered Teraterpeton an archosauromorph nesting with short-snouted Trilophosaurus (Figs. 1, 3).

In the LRT
Trilophosaurus is a rhynchocephalian lepidosaur nesting between derived sphenodontids, like short-snouted Sapheosaurus, and primitive rhynchosaurs, like short-snouted Mesosuchus. All related taxa have a diapsid-like temple architecture, even though the new clade Diapsida (Petrolacosaurus and kin) is restricted to members of the Archosauromorpha in the LRT. Lepidosaurs with a diapsid architecture have their own clade name: “Lepidosauriformes.” Details here and here.

The latest thinking identifies the large hole in the rostrum of Teraterpeton
that extends nearly to the orbit as a naris alone, not a combination of naris + antorbital fenestra. Here (Fig. 1) a broken strut-like bone lying atop the slender maxilla appears to have separated a naris from an antorbital fenestra in vivo. Even so, the present scoring for Teraterpeton with an antorbital fenestra without a fossa does not nest it with other taxa having an antorbital fenestra with or without a fossa.

Figure 1. Skulls of Teraterpeton and Trilophosaurus compared.

Figure 1. Skulls of Teraterpeton and Trilophosaurus compare well aft of the orbit, not so much below the orbit or in the rostrum.

This would not be the first time
an antorbital fenestra appeared in a lepidosaur. Pterosaurs and their ancestors, the fenestrasaurs, also have this trait by convergence with several other tetrapod taxa.

Comparing Trilophosaurus to Teraterpeton
(Fig. 1) is difficult until you get to the postorbital region of the skull. Then it’s a good match. Trilophosaurus has a reduced rostrum, a small naris, a robust maxilla and no hint of an antorbital fenestra. But like Teraterpeton alone, the lateral temporal fenestra found in all related taxa, is infilled with a large flange of the quadrate. Even so, the crappy character list for the LRT is able to nest these two taxa together.

Trilophosaurus and Teraterpeton nest with
the distinctively different Shringasaurus and Azendohsaurus in the LRT. The large variety in their morphologies hints at a huge variation yet to be found here. This is yet one more case where a list of traits may fail you, but a suite of several hundred traits will eliminate all other possibilities by a statistical process known as maximum parsimony. While the parsimony is minimal in this clade, it is still more than any other candidate taxa can offer from a list that has grown to over 1300.

A recent abstract on Teraterpeton
by Pritchard and Sues 2016 bears a review.

“Teraterpeton hrynewichorum, from the Upper Triassic (Carnian) Wolfville Formation of Nova Scotia, is one of the more unusual early archosauromorphs, with an elongate edentulous snout, transversely broadened and cusped teeth, and a closed lateral temporal fenestra. Initial phylogenetic analyses recovered this species as the sister taxon to Trilophosaurus spp. New material of Teraterpeton includes the first-known complete pelvic girdle and hind limbs and the proximal portion of the tail. These bones differ radically from those in Trilophosaurus, and present a striking mosaic of anatomical features for an early saurian.”

I agree completely, which makes solving this mystery so intriguing, and one perfectly suited to the wide gamut of the LRT.

The ilium has an elongate, dorsoventrally tall anterior process similar to that of hyperodapedontine rhynchosaurs

In all cladograms trilophosaurs are close to rhynchosaurs.

The pelvis has a well-developed thyroid fenestra, a feature shared by Tanystropheidae, Kuehneosauridae, and Lepidosauria. 

These taxa all nest within the Lepidosauriformes in the LRT. Mystery solved.

Figure 1. Azendohsaurus skull reconstructed with two premaxillary teeth, not four.

Figure 2. Azendohsaurus skull reconstructed with two premaxillary teeth, not four.

“The calcaneum is ventrally concave, as in Azendohsaurus”. 

Teteraterpeton and Trilophosaurus nest as sisters to Azendohsaurus (Fig. 2)  in the LRT.

The fifth metatarsal is proximodistally short, comparable to the condition in Tanystropheidae.” 

This condition is also found in lepidosaur tritosaur fenestrasaurs, including pterosaurs. Tanystropheidae nest as tritosaurs in the LRT. Mystery solved.

“Much as in the manus, the pedal unguals of Teraterpeton are transversely flattened and dorsoventrally deep.” 

The unguals of Trilophosaurus are also exceptionally deep and transversely flat.

“Phylogenetic analysis of 57 taxa of Permo-Triassic diapsids and 315 characters supports the placement of Teraterpeton as the sister-taxon of Trilophosaurus in a clade that also includes Azendohsauridae and, rather unexpectedly, Kuehneosauridae.”

Add taxa and the unexpected kuehneosaurs will drift to a more basal node.

“The mosaic condition in Teraterpeton underscores the importance of thorough taxon sampling for understanding the dynamics of character change in Triassic reptiles and the use of apomorphies in identifying fragmentary fossils.”

The term ‘mosaic’ is misleading. In the LRT there are no closer sisters to Teraterpeton than Trilophosaurus, and then, rather obviously, the similarities are immediately obvious only in the cheek region, distinct from all other taxa in the LRT.

Figure 2. Trilophosaurus has filled in the lateral temporal fenestra, reduced the orbit and increased the upper temporal fenestra, among other differences with Azendohsaurus.

Figure 3. Trilophosaurus has filled in the lateral temporal fenestra, reduced the orbit and increased the upper temporal fenestra, among other differences with Azendohsaurus.

Forcing Teraterpeton
back to long-snouted clades with an antorbital fenestra, like the Diandongosuchus clade, adds a minimum of 11 extra steps to the LRT.

Key to understanding
the lepidosaur nature of these taxa involves first understanding that the first dichotomy in the clade Reptilia separates the new Archosauromorpha from the new Lepidosauromorpha. Until someone else does this and it becomes consensus, we will continue to experience the confusion exhibited by Pritchard and Sues 2016 (above). This has been documented online for the last seven years.

References
Pritchard AC, Sues H-D 2016. Mosaic evolution of the early saurian post cranium revealed by the postcranial skeleton of Teraterpeton hrynewichorum (Archosauromorpha, Late Triassic). Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Sues H-D 2003. An unusual new archosauromorph reptile from the Upper Triassic Wolfville Formation of Nova Scotia. Canadian. Journal of Earth Science 40(4): 635-649.

Thanks to
reader NP for bringing this taxon back to my attention.

The first Langobardisaurus: MCSNB 2883

The day before yesterday
we looked at the latest (fourth) specimen attributed to the genus Langobardisaurus (Renesto 1994, Late Triassic). Today let’s look at the first specimen. This is really my first serious look at it because the second and third specimens were so much easier to study, both with good skulls.

The holotype of Langobardisaurus
(Renesto 1994, MCSNB 2883) has never (to my knowledge) been reconstructed, as it is here (Fig. 1), and not with to scale comparisons to the other three specimens. Saller et al. 2013 considered all four to be conspecific. However, as I found out, and as in so many putative pterosaur genera and Archaeopteryx genera, no two are alike.

Figure 1. Four Langobardisaurus specimens compared to scale. Contra Saller et al. 2013, these four specimens do not appear to be conspecific.

Figure 1. Four Langobardisaurus specimens compared to scale. Contra Saller et al. 2013, these four specimens do not appear to be conspecific.

Larger than the others (if the scale bars are correct),
the holotype of Langobardisaurus appears to have a smaller skull, smaller fingers and longer hind limbs. Distinct from two of the specimens, the tail remains long and robust. Powerful caudofemoral muscles were attached the elongate and numerous caudal ribs (fused transverse processes). The gastralia were more numerous with less space between sets. Such gastralia help hold up the anterior skeleton when standing bipedally. This specimen (MCSNB 2883) appears to be, by convergence, like Sharovipteryx, an obligate biped.

Figure 2. Langobardisaurus holotype in situ MCSNB 2883.

Figure 2. Langobardisaurus holotype in situ MCSNB 2883. Inserts show pectoral girdle elements and pes (x2).

Almost a worst case scenario for a roadkill fossil
the pectoral + skull region of MCSNB 2883 (Fig. 3) provides an excellent opportunity to try out the Digital Graphic Segregation (DGS) method. In the original photo you can see what a mess it is and how Renesto has labeled some of the bones and teeth, but ignores others and never outlines any of the bones. Colors just make things easier to understand in cases like this and it ensures that you are studying every millimeter of this fossil. Even tiny bone corners that peek out from beneath the rubble can be color coded. The reconstruction (Fig. 1) confirms or refutes your identifications as they fit or do not fit the assembled puzzle of bones without resorting to the danger of freehand illustration.

Figure 3. The pectoral region of Langobardisaurus (MCSNB 2883) with DGS color overlays. Compare to Figure 4 for identification of pectoral elements. Anterior skull elements are also present here.

Figure 3. The pectoral region of Langobardisaurus (MCSNB 2883) with DGS color overlays. Compare to Figure 4 for identification of pectoral elements. Anterior skull elements are also present here. Premaxillae and sternum are both yellow. Scapulae are blue. Coracoids are violet. Clavicles are green. Interclavicle is tan. Ribs are red. The tiny metacarpals are still attached to the end of the ulna and radius (amber and green).

The coincidence of the interclavicle, clavicle and sternum
in Langonbardisaurus (Fig. 4) and other fenestrasaurs like Cosesaurus and Longisquama is the precursor structure to the pterosaur sternal complex, seen only in this clade within the entire Tetrapoda.

Figure 5. Langobardisaurus (MCSNB 2883) pectoral girdle in left lateral and ventral views.

Figure 4. Langobardisaurus (MCSNB 2883) pectoral girdle in left lateral and ventral views.

References
Muscio G 1997. Preliminary note on a specimen of Prolacertiformes (Reptilia) from the Norian (Late Triassic) of Preone (Udine, north-eastern Italy). Gortania – Atti del Museo Friulano di Storia Naturale 18:33-40
Renesto S 1994. A new prolacertiform reptile from the Late Triassic of Northern Italy. Rivista di Paleontologia e Stratigrafia 100(2): 285-306.
Renesto S and Dalla Vecchia FM 2000. The unusual dentition and feeding habits of the Prolacertiform reptile Langobardisaurus (Late Triassic, Northern Italy). Journal of Vertebrate Paleontology 20: 3. 622-627.
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.
Saller F, Renesto S, Dalla Vecchia FM 2013. First record of Langobardisaurus (Diapsida, Protorosauria) from the Norian (Late Triassic) of Austria, and a revision of the genus. Neues Jahrbuch für Geologie und Paläontologie. 268 (1): 89–95. doi:10.1127/0077-7749/2013/0319
Wild R 1980. Tanystropheus (Reptilia: Squamata) and its importance for stratigraphy. Mémoires de la Société Géologique de France, N.S. 139:201–206.

uninisubria/Langobardisaurus
wiki/Langobardisaurus

Plotosaurus enters the LRT

Figure 1. Skull of Plotosaurus. Note the mislabeling of the right supratemporal as a squamosal.

Figure 1. Skull of Plotosaurus. Note the mislabeling of the right supratemporal as a squamosal. The posterior frontal processes are atypical for lizards.

Plotosaurus benisoni (originally Kolposaurus, preoccupied; Camp 1942, 1951; Late Cretaceous; 9m) is a large mosasaur (Lepidosauria, Squamata, Scleroglossa) with relatively small flippers and a large tail fin. It enters the LRT as a sister to Tylosaurus. The nasals, tiny in Tylosaurus, are absent in Plotosaurus.

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

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

References
Camp CL 1942. California Mosasaurs. Memoirs of the University of California 13:1-68.
Camp CL 1951. Plotosaurus, a new generic name for Kolposaurus Camp, preoccupied. Journal of Paleontology 25:822.

wiki/Plotosaurus

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.