Megachirellla and Marmoretta are basal to Pleurosaurs

Earlier we looked at pleurosaurs (Fig. 1, elongate, aquatic rhynchocephalians). Pleurosaurus goldfussi (Meyer 1831) was discovered first. Paleopleurosaurus is a more primitive taxon with a distinct premaxillary tooth. Note the retraction of the nares, common to many aquatic reptiles.

The present blogpost updates their origins with phylogenetic analysis, adding these two taxa to the large reptile tree.

Dupret (2004) nested pleurosaurs (Fig. 1) with Sapheosaurus. Adding pleurosaurs to the large reptile tree (not updated yet) nested them with Marmoretta and Megachirella (Figs. 2-5), helping to remove the ‘enigma’ status from the latter. Dupret (2004) did not include these two taxa in analysis.

The pleurosaurs

Figure 1. The pleurosaurs, Pachypleurosaurus and Pleurosaurus, known rhynchocephalians, now nesting with Marmoretta and Megachirella.

Pleurosaurs are yet one more clade of “return to the water” reptiles, and probably the last one anyone thinks of. They’re just not often reported on. Wiki reports, Pleurosaurus fossils were discovered in the Solnhofen limestone formation of BavariaGermany and CanjuersFrance.” The limbs were reduced. The torso and tail were elongated. Pleurosaurs probably swam in an eel-like or snake-like undulating pattern.

But where did they come from?

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs

Marmoretta oxoniensis (Evans 1991) Middle/Late Jurassic, ~2.5 cm skull length, orginally considered a sister of kuehneosaursdrepanosaurs and lepidosaurs. Here Marmoretta was derived from a sister to GephyrosaurusMarmoretta was a sister to Planocephalosaurus and Megachirella. 

Distinct from Gephyrosaurus, the skull of Marmoretta was flatter overall with a larger orbit. The parietals were longer. The naris was larger and more dorsal. The prefrontal was narrower. The lacrimal was still visible. The jugal was reduced.

A flat-headed rhynchocephalian, Marmoretta nests near the base of that clade, prior to the fusion of teeth together and to the jaws in many derived taxa, including pleurosaurs.

Figure 1. Megachirella, a flat-headed rhynchocephalian close to Marmoretta and basal to pleurosaurs.

Figure 3. Megachirella, a flat-headed rhynchocephalian close to Marmoretta and basal to pleurosaurs.

Megachirella wachtleri (Renesto and Posenato 2003, Renesto and Bernardi 2013) KUH-1501, 2 cm skull length, Middle Triassic, was a tiny lepidosauromorph with a moderately elongated neck and flattened skull. The teeth were short and stout. Megachirella was originally nested with Marmoretta and the large study confirms it, but it is also basal to the aquatic pleurosaurs.

Figure 4. Megachirella in situ with bones colorized. Some bones are represented by impressions of the lost bone.

Figure 4. Megachirella in situ with bones colorized using DGS techniques. Some bones are represented by impressions of the lost bone. The yellow premaxilla tooth is represented by a questionable impression/crack. The nasal may not be a bone, according to S. Renesto. Scale bar = 1 cm.

 

Shifting the pleurosaurs to Gephyrosaurus adds 13 steps. To Planocephalosaurus adds 23 steps. More steps are added with a shift to other rhynchocephalians.

Figure 5. Skull elements of Megachirellla traced in color (Fig. 4) then transferred to line art in three views.

Figure 5. Skull elements of Megachirellla traced in color (Fig. 4) then transferred to line art in three views. Reconstructions are important in such roadkill taxa. 

Megachirella is a Middle Triassic rhynchocephalian. That leaves plenty of time for a sister to evolve into a Late Jurassic pleurosaur. The retracted naris common to pleurosaurs is clear on both Marmoretta and Megachirella. All three had an open lateral temporal fenestra.

If you find any mistakes here, please let me know. Such specimens are at or a little beyond the edge of my experience.

References
Carroll RL 1985. A pleurosaur from the Lower Jurassic and the taxonomic position of the Sphenodontids.
Dupret V 2004. The pleurosaurs: anatomy and phylogeny. Revue de Paléobiologie, Geneve 9:61-80.
Evans SE 1991. A new lizard−like reptile (Diapsida: Lepidosauromorpha) from the Middle Jurassic of Oxfordshire. Zoological Journal of the Linnean Society 103:391-412.
Fraser NC and Sues H-D 1997. In the Shadows of the Dinosaurs: early Mesozoic tetrapods. Cambridge University Press, 445 pp. Online book.
Heckert AB 2004. Late Triassic microvertebrates from the lower Chinle Group (Otischalkian-Adamanian: Carnian), southwestern U.S.A. New Mexico Museum of Natural History and Science Bulletin 27:1-170.
Meyer H 1831. IV Neue Fossile Reptilien, aud der Ordnung der Saurier.
Renesto S and Posenato R 2003. A new lepidosauromorph reptile from the Middle Triassic of the Dolomites (northern Italy). Rivista Italiana di Paleontologia e Stratigrafia 109(3) 463-474.
Renesto S and Bernardi M 2013. Redescriptions and phylogenetic relationships of Megachirella wachtleri Renesto et Posenato, 2003 (Reptilia, Diapsida). Paläontologische Zeitschrift, DOI 10.1007/s12542-013-0194-0

Calanguban, another basalmost scleroglossan squamate

Calanguban alamoi (Simoes, Caldwell and Kellner 2014, Early Cretaceous) was originally considered the oldest scincomorph, but in the large reptile tree (not updated yet) it nests with Liushusaurus (Fig. 1) at the base of the Scleroglossa. Due to the large size of its skull and orbit, this was considered an immature specimen. But all sisters are likewise tiny with a large orbit and short rostrum. So what we appear to see hear is yet another case of miniaturization at the base of a major clade.

Earlier we looked at Euposaurus another basal squamate, but at the base of the Iguania.

Figure 1. Liushusaurus (above) and Calanguban (below) to scale. Both nest at the base of the Scleroglossa, which makes them sisters to the basalmost tested iguanid, Iguana.

Figure 1. Liushusaurus (above) and Calanguban (below) to scale. Both nest at the base of the Scleroglossa, which makes them sisters to the basalmost tested iguanid, Iguana. 

References
Evans SE and Wang Y 2010. A new lizard (Reptilia: Squamata) with exquisite preservation of soft tissue from the Lower Cretaceous of Inner Mongolia, China.
Simoes TR, Caldwell MW and Kellner AWA 2014. A new Early Cretaceous lizard species from Brazil, and the phylogenetic postion of the oldest known South American squamates. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2014.947342

wiki/Liushusaurus

Cartorhynchus compared to ichthyosaurs and sauropterygians

While phylogenetic analysis nests the new ichthyosaur-mimic, Cartorhynchus, with pachypleurosaurs, sometimes it helps to put the contenders side-by-side (Fig. 1). I’ve also updated the odd pectoral girdle and traced the visible palatal elements since Catorhynchus was first presented here (which has been updated).

Figure 1. Sauropterygian sisters to Cartorhynchus (green) compared to ichthyosaurian sister candidates. No ichthyosaurs have a short snout and flat belly. Cartorhynchus and sauropterygians swim with their flippers. All ichthyosaurs swim with their tails. Cartorhynchus nests between Pachypleurosaurus and Qianxisaurus in the large reptile tree.

Figure 1. Sauropterygian sisters to Cartorhynchus (green) compared to ichthyosaurian sister candidates. No ichthyosaurs have a short snout and flat belly. Cartorhynchus and sauropterygians swim with their flippers. All ichthyosaurs swim with their tails. Cartorhynchus nests between Pachypleurosaurus and Qianxisaurus in the large reptile tree. That’s where you find a small premaxilla and large clavicles.

Cartorhynchus certainly has a distinct morphology, even for a pachypleurosaur.  But then pachypleurosaurs are basal to a wide range of marine reptiles including placodonts, plesiosaurs, thalattosaurs (including Helveticosaurus and Vancleavea), ichthyosaurs and mesosaurs.

The large head, short neck and flippers instead of limbs set Catorhynchus apart from other basal sauropterygians. Placodonts also have a short neck and short rostrum, so it happens.

Like all pachypleurosaurs,
Cartorhynchus has both an anterior and posterior coracoid (Fig. 2) forming a chest shield like a plesiosaur. That makes it a flipper swimmer, not a tail swimmer, like ichthyosaurs, which evolved from long, mesosaur-like sauropterygians, like Wumengosaurus. No ichthyosaur has a flat robust gastralia basket, wide rib cage, and short rostrum like Cartorhynchus and the pachypleurosaurs have. Note the long premaxillary ascending process makes contact withe the frontals, as in Pachypleurosaurus. The palate is more pachypleurosaur-like than ichthyosaur-like.

The scapula-coracoid
In many pachypleurosaurs and their descendants, the anterior coracoid and scapula are fused together. Many illustrations of pachypleurosaurs don’t note this, but call the unit a scapula. You can discover this for yourself by looking at a wide variety of clade members. In Catorhynchus, the scapula is not fused to the coracoid (Figs. 2, 3).

Figure 2. Cartorhynchus lenticarpus in situ showing palatal and pectoral elements

Figure 2. Cartorhynchus lenticarpus in situ showing palatal and pectoral elements. What Motani et al. considered a displaced angular is here interpreted as the anterior coracoid. Yes, the scapulae are preserved upside down. That helps make more sense of the flipped up clavicles. In vivo they were appressed to the elongate interclavicle oriented laterally. The palate morphology is closer to pachypleurosaurs than to ichthyosaurs.

Cartorhynchus and basal ichthyosaurs share many traits.
But Cartorhynchus and basal sauropterygians share a few more. That tips the scales in favor on sauropterygians, based on the hypothesis of maximum parsimony. Ichthyosaurs can also trace their ancestry through basal pachypleurosaurs. So they’re not that far removed.

Figure 3. Cartorhynchus reconstruction with palate and pectoral elements in color.

Figure 3. Cartorhynchus reconstruction with palate and pectoral elements in color. This is a wide, flat specimen, like other basal sauropterygians, like Qianxisaurus. The palatal elements can be seen through the orbit and broken rostrum with line extensions completing their outlines. Even the twin tiny internal nares can be seen here. In ichthyosaurs the internal nares are set much further back in the skull. 

The new palatal data confirms the pachypleurosaur affinities of Catorhynchus. Note the presence of internal nares essentially below the external nares. In Wumengosaurus and ichthyosaurs the internal nares are set further back in the skull.

The new interpretation of the ultra-wide interclavicle makes the overall shape more fusiform, despite the presence of a small neck, and it locates the scapula as far laterally as the widest ribs, which makes more sense in the reconstruction based on the squared off proximal humerus giving it room to move dorso-ventrally, more like an underwater wing.

References
Motani R et al. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866

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.

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.

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.

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.

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.

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 7. Eichstaettisaurus gouldi palate in situ and colorized.

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 3. Eichstaettisaurus schroederi.

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 1. Eichstaettisaurus gouldi. A transitional taxon in the lineage of terrestrial snakes.

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, ArdeosaurusAdriosaurus (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 1. Various specimens of Adriosaurus documenting the reduction of large clawed hands to small clawless paddles, then ultimately disappearing completely.

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.

Not Bavarisaurus?

Conrad (2014) reports
The lizard ingested by Compsognathus  (Fig. 1) is a new species, not congeneric with the holotype of Bavarisaururus macrodactylus (= Homoeodactylus macrodactylus, Wagner 1852). That is verified here.

Figure 1. Click to enlarge. The little Jurassic lizard Bavariasaurus was found inside the belly of the little Jurassic dinosaur, Compsognathus. But it is not the same genus as the holotype.

Figure 1. Click to enlarge. The little Jurassic lizard Bavariasaurus was found inside the belly of the little Jurassic dinosaur, Compsognathus. But it is not the same genus as the holotype.

From the Conrad (2014) abstract:
“Bavarian limestone deposits represent some of the few areas preserving articulate Jurassic squamates. Bavarisaurus, two species of Eichstaettisaurus, and Ardeosaurus have been recognized from those deposits. Although usually identified as Bavarisaurus macrodactylus or Bavarisaurus cf. macrodactylus, a lizard preserved as a cololite in the theropod Compsognathus longipes shows important differences from the type specimen of Bavarisaurus macrodactylus. This cololite lizard specimen (hereafter, ‘cololizard’) is preserved as a combination of bone and bone-impressions, some of which are extremely clear. The skull preserves the premaxilla, maxilla, prefrontal, frontal, parietal, postfrontal, jugal, pterygoid, ectopterygoid, and mandible. The humerus and much of the thoracic skeleton, tail, pelvis, and hind limb are preserved. Comparative studies demonstrate that the ingested form is a new species. A cladistic analysis of 133 fossil and living lepidosaurs scored for 1318 morphological characters suggests that Eichstaettisaurus gouldi and Bavarisaurus macrodactylus are sister species.

“Eichstaettisaurus schroederi and the cololizard form a polytomy with that clade in an holophyletic Eichstaettisauridae with the unambiguous synapomorphies of paired premaxillae, angulated jugals, and presence of a hook-like postglenoid humeral process. Eichstaettisaurus gouldi and Bavarisaurus macrodactylus are united by the shared presence of a straight frontoparietal suture. The cololizard differs from Bavarisaurus macrodactylus in possessing an anteriorly arching (rather than a W-shaped) frontoparietal suture, a fused (unpaired) parietal, and anteroposteriorly-oriented parietal supratemporal processes. The cololizard differs from Eichstaettisaurus schroederi in possessing a weakly inclined maxillary nasal process, an anteroposteriorly elongate (rather than tall)prefrontal, a longer prefrontal orbital process, absence of cristae cranii, and an anteriorly arched (rather than transverse) frontoparietal suture. The cololizard will soon be named as a type specimen within the type specimen for Compsognathus, and further expands known Jurassic Bavarian lizard diversity.”

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.

Homoeosaurus? macrodactylus holotype
The holotype of Bavarisaurus/Homoeosaurus? macrodactylus (Wagner 1852, Fig. 3) is indeed different than the ingested lizard (Fig. 1, Nopcsa 1903, Hoffstetter 1964).

Figure 3. Homoesaurus/Bavarisaurus? macrodactylus actually nests with Huehuecuetzpalli, so the lizard inside Compsognathus is indeed different.

Figure 3. Homoesaurus/Bavarisaurus? macrodactylus actually nests with Huehuecuetzpalli, so the lizard inside Compsognathus is indeed different.

Figure 3. Eichstaettisaurus schroederi.

Figure 3. Eichstaettisaurus schroederi is considered by Conrad to be a sister to the ingested lizard, but it doesn’t appear to share many traits as far as I can tell, and phylogenetic analysis confirms this. Eichstaettisaurus actually nests basal to Adriosaurus and snakes.

No one should know lizards better than Conrad
whose 2008 paper tested 222 fossil and extant taxa with 363 character traits. Unfortunately that phylogeny: (1) failed to find a third lepidosaur clade; (2) nested snakes with amphisbaenians (legless traits must have swamped out other traits); (3) failed to find the diphyletic origin of snakes, but nested the highly derived Leptotyphlops at the base; (4) nested the pre-snake Adriosaurus with mosasaurs; and (5) failed to recover the Eichstaettisaurus / Ardeosaurus link with Adriosaurus and snakes. Otherwise, the tree looked pretty good.

The large reptile tree nests the ingested lizard in the middle of the Tritosauria. The tree nests the holotype of Homoeosaurus macrodactylus with Huehuecuetzpalli, not with Homoeosaurus solnhofensis. The tree nests Eichstaettisaurus with Ardeosaurus close to Adriosaurus, the ancestor of terrestrial snakes.

References
Conrad J 2008. Phylogeny and systematics of Squamata (Reptilia) based on morphology. Bulletin of the American Museum of Natural History 310:1-182.
Conrad J 2014. The lizard (Squamata) in Compsognathus (Theropoda) is a new species, not Bavarisaururus. Journal of Vertebrate Paleontology abstracts.
Hoffstetter R 1964. Les Sauria du Jurassique supérieur et specialement les Gekkota de Baviére et de Mandchourie. Senckenberger Biologische 45, 281–324.
Nopcsa F 1903. Neues ueber Compsognathus. Neues Jahrbuch fur Mineralogie, Geologie und Palaeontologie 16: 476-494.
Wagner A 1852. Neu-aufgefundene Saurier, Uberreste aus dem lithographischen Schiefern und dem obern Jurakalke: Abhandlungen der Bayerischen Akademieder Wissenschaften Mathematisch-naturwissenschafliche Kl, 3(6): 661-710.

 

Euposaurus: basal squamate/basal iguanid

Among the many lizards found in Late Jurassic  (155 mya) European lithographic limestones that have no living counterparts, there is one, Euposaurus (Fig. 1) that is basal to all members of the clade Iguania, which includes Iguana, the iguana; Phyronsoma, the horned lizard; Trioceros, the chameleon; and Draco, the rib-gliding lizard.

Euposaurus cirrensis, a basal squamate and basal  member of the clade Iguania.

Figure 1. Euposaurus cirrensis, (not the generic holotype) a basal squamate and basal member of the clade Iguania. The large orbit and less than fused ankles are primitive, not juvenile, traits.

Euposaurus cirinensis ( Lortet 1892, MHNL 15681, Late Jurassic, Kimmeridgian, 155 mya, 3.5cm snout vent length) nests as the basalmost member of the Iguania (Cocude-Michel 1963) and is a basal squamate. Evans (1994) assigned it to Squamata incerta sedis. The large skull and large orbit might seem to be juvenile traits, but all sister taxa share these traits. Liushusaurus and Calanguban are sister taxa at the base of the Scleroglossa.

Figure 2. Euposaurus insitu.

Figure 2. Euposaurus insitu.

Evans 1994 reexamined the three specimens attributed to Euposaurus and reported they “belong to different genera. Euposaurus thiolleri, the type species, is a juvenile pleurodont lepidosaur which is probably, but not certainly, a lizard. It has no characters which suggest that it is an iguanian and is here designated Lepidosauria incertae sedis. The remaining two specimens have an acrodont dentition and are juvenile rhynchocephalians. One is referable to Homoeosaurus; the other appears to belong to the group currently represented by Sapheosaurus, Kallimodon, Piocormus (aka Sapheosaurus) and Leptosaurus although the latter two may not be valid genera.”

Figure 2. Basal squamates. Here Euposaurus is a basal Iguania. Liushusaurus and Calanguban are basal Scleroglossa. Scandensia is presently their last common ancestor.

Figure 3. Basal squamates. Here Euposaurus is a basal Iguania. Liushusaurus and Calanguban are basal Scleroglossa. Scandensia is presently their last common ancestor.

Derived from ScandensiaEuposaurus is larger overall and has a larger skull with a robust palate. The tail is longer and more robust. The limbs are more robust. Scandensia is much smaller than its predecessor, the mis-named “Langobardisaurus” rossii, so the origin of lepidosaurs is one more case of miniaturization, as in mammals, birds and reptiles.

Figure 4. Langobardisaurus? rossii compared to tiny Scandensia.

Figure 4. Langobardisaurus? rossii compared to tiny Scandensia.

References
Cocude-Michel M 1963. Les rhynchocephaJes et les sauriens de calcaires
lithographiques (Jurassique supérieur) d’Europe occidentale. Nouvelles Archives
du Muséum d’Histoire Naturelle de Lyon 7: 1-187.
Evans SE 1994. A re-evaluation of the Late Jurassic (Kimmeridgian) reptile Euposaurus (Reptilia: Lepidosauria) from Cerin, France. Geobios 27(5):621-631.
Lortet M 1892. Les reptiles fossiles du Bassin du Rhone. Archives du Musee de
Histoire Naturelle, Lyon 5: 1-139.

image from planet-terre

Euposaurus corninesss 

Musée des confluences, Lyon / Pierre Thomas 

http://planet-terre.ens-lyon.fr/planetterre/objets/Images/Img307/307-rhynchocephales-Cerin-06.jpg

Drepanosaur skull: Pritchard and Nesbitt 2014 JVP abstracts

Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

Figure 1. Megalancosaurus including the palate, the only palate ever figured for a drepanosaur. This is not the specimen described by Pritchard and Nesbitt 2014.

Pritchard and Nesbitt (2014) present new skull data based on a 3D drepanosaur skull (posterior elements only) from the Triassic of Arizona. Comments follow.

From the abstract:
“Drepanosaurs are an enigmatic clade of Late Triassic diapsids from Europe and North
America with superficially chameleon-like bauplans. The phylogenetic position of the
group among diapsids is contentious. (1) Most hypotheses suggest that drepanosaurs are
basal archosauromorphs closely related to ‘protorosaurs’ (e.g., Protorosaurus,
Tanystropheus). (2) Other phylogenies place drepanosaurs as non-saurian diapsids,
suggesting a substantially older origin for the lineage. Clarifying the phylogenetic
position of drepanosaurs is important to understanding the degree of taxonomic
diversification among diapsids prior to the Permo-Triassic Extinction (PTE).
The poor quality of the drepanosaur fossil record has hampered an understanding of
their position. (3) Nearly all drepanosaur skeletal material is badly distorted (4), and all
described skulls are crushed such that phylogenetically important characters are
obscured. (5) A new drepanosaur specimen from the Late Triassic Coelophysis Quarry of
New Mexico includes a partial, three-dimensionally preserved skull. The postorbital
region of the skull, atlas-axis complex, and anterior cervical vertebrae are preserved in
near-articulation. (6) 3D reconstruction of micro computed tomography (CT) data allows the first detailed description of most drepanosaur skull bones. Many are surprisingly
plesiomorphic (e.g., squamosal with massive descending process, quadrate lacking
posterior concavity, occipital condyle with notochordal pit), sharing more in common
with non-saurian diapsids than early archosauromorphs. (7).

A phylogenetic analysis of 300 characters and 40 early diapsids supports the
hypothesis that drepanosaurs fall outside of Sauria. (8). This suggests a very long ghost
lineage (~35 million years), extending well into the Late Permian. The results of this
phylogeny suggest that both drepanosaurs and a number of early saurian lineages must 
have originated by the Late Permian. Although the fossil record suggests an enormous
morphological diversification among saurians following the PTE, a great deal of
taxonomic diversification among diapsids must also have occurred prior to the extinction.”

(1) not at all contentious. Drepanosaurs are derived from Jesairosaurus in the Tritosauria. This has been known for several years.

(2) Protorosaurus and Tanystropheus are not related to one another. This has been known for many years.

(3) Repeating a false allegation.

(4) crushed flat, but not otherwise distorted (see Fig. 2).

(5) Not so, IMHO.  Use DGS to retrieve data. Works every time.

(6) good news, but the key traits are found in the preorbital region. The big question is: did they have an antorbital fenestra? I see one on several specimens.

(7) These traits were first identified in Megalancosaurus. The occiput data is news. Non-saurian diapsids could include sauropterygians, ichthyosaurians, rib gliders and basal younginiforms according to traditional trees, which are outdated at best. Saurians include lepidosaurs and archosaurs. In this regard, drepanosaurs are saurians, tritosaur lepidosaurs.

(8) 40 is way too few taxa if you don’t know where drepanosaurs nest, especially if Jesairosaurus and Huehuecuetzpalli are excluded (I haven’t seen the inclusion set). Using 420 taxa drepanosaurs firmly nest within the Tritosauria and Lepidosauria, thus within the traditional definition of Sauria, which is a junior synonym of Amniota/Reptilia. Actually there is no long ghost lineage. Drepanosaurs originated in the Triassic following Jesairosaurus in the Early to Middle Triassic.

This is my take (Figs. 1, 2) on the skull of the drepanosaur Megalancosaurus. Note the occiput is not exposed in this 2D crushed specimen. It’s a fragile construction with a large naris, an antorbital fenestra, large orbit, diapsid temporal architecture (like that of a pterosaur) and a Y-shaped hyoid.

Interpretation of figure 6, the skull of Megalancosaurus.

Figure 7. Interpretation of figure 6, the skull of Megalancosaurus. Struts of bone surround antorbital fenestra here.

References
Pritchard A and Nesbiitt S 2014. The cranial morphology of drepanosaurs and the PermoTriassic diversification of diapsid reptiles. JVP abstracts 2014.