Another odd rhynchocephalian: Ankylosphenodon

You don’t find very much
about Ankylosphenodon pachyostosus (Reynoso 2000) online, even though it is odd and known by a complete skeleton. It’s a basal rhynchocephalian, nesting between Gephyrosaurus and Marmoretta in the large reptile tree. The long torso and tail, along with those small limbs gives credence to the possibility that Marmoretta and Megachirella were similarly equipped (they are known from a skull and anterior torso only) at the base of the Pleurosauridae, which we looked at earlier here.

Figure 1. Ankylosphenodon pachyostosus. Click to enlarge. This long-bodied taxon nests at the base of the pleurosaurs, Marmoretta and Megachirella.

Figure 1. Ankylosphenodon pachyostosus. Click to enlarge. This long-bodied taxon nests at the base of the pleurosaurs, Marmoretta and Megachirella.

Middle Cretaceous, Mexico, considered an herbivore. Martinez et al. 2013) nested Ankylosphenodon between Sphenodon and Clevosaurus and Sphenotitan, but Marmoretta, Megachirella, and Gephyrosaurus were not included in their taxon list and neither were a host of derived rhynchocephalians. `

From Wikipedia (translated from Italian, I think).
“This animal had a body rather robust, with short legs positioned at the sides of the body and a skull from the remarkable features. These included a set of teeth unusual: there were, in fact, long teeth roots open, deeply “embedded” in the jaw and placed in the vicinity of the channel Meckel . Another feature dell’anchilosfenodonte was given by significant thickening of the ribs and vertebrae ( pachiostosi ), a feature that normally is found in aquatic vertebrates.”

References
Reynoso VH 1996. Early Cretaceous Lepidosaurs (Reptilia: Diapsid) from Central Mexico and the Phylogeny of Lepidosauromorphs. 369 pp. Unpublished PhD Thesis, McGill University, Montreal, Canada.
Reynoso VH 2000. An unusual aquatic sphenodontian (Reptilia: Diapsida) from the Tlayua Formation (Albian), central Mexico. Journal of Paleontology 74:133-148.

Kallimodon(?) reconstructed

Figure 1. Kallimodon from WikiCommons.

Figure 1. Kallimodon from WikiCommons.

I found this purported Kallimodon specimen on WikiCommons and traced it out. The museum number is not available. If anyone knows it, please let me know. I can’t say if it is Kallimodon or not. I don’t have access to images of the holotype (1887-VI-I), or if I do (there are several specimens on Google), not one is identified as the holotype.

Figure 2. Kallimodon in situ after adjusting levels and a tracing.

Figure 2. Kallimodon? in situ after adjusting levels and a tracing. Possible eggs are in light blue on the in situ specimen. This specimen is small, only about 20 percent larger than pictured here.

Whatever the provence of this specimen, DGS enables details to be brought out, despite or because of crushing. There is a palate labeled Kallimodon, but it obvious comes from another specimen. And I can’t be sure it is the holotype without seeing the label.

Figure 3. Kallimodon reconstructed. This taxon, whether it is Kallimodon or not, nests with Sphenodon, but has distinct proportions.

Figure 3. Kallimodon? reconstructed. This taxon, whether it is Kallimodon or not, nests with Sphenodon, but has distinct proportions, with a small skull, long torso and long legs.

Though distinct from all other rhynchocephalians, this specimen nests with Sphenodon, the living rhynchocephalian. There is also some confusion regarding the naming and numbering of this taxon:

Etymology
Homoesaurus pulchellus Zittell, 1887
Kallimodon pulchellus (Zittell, 1887) Frickhinger 1994
Locality: Kelheim, Bayern (Bavaria) State, Germany.
Horizon: Solnhofen.
Age: Tithonian Stage, Upper Malm Epoch, Late Jurassic.

References
Cocude-Michel, M 1963.  Les rhynchocéphales et les sauriens des calcaires lithographiques (Jurassique supérieur) d’Europe occidentale.  Nouv. Arch. Mus. Hist. Nat. Lyon 7 187 pp.
Frickhinger, K A 1994. Die Fossilien von . The Fossils of Solnhofen: Goldschneck-Verlag, 336pp.
Zittell KA 1887. Rhynchocephalia – Handbuch der Palaeontologie 3:583-800. München and Leipzig.

Paleofile

 

Megachirellla and Marmoretta are basal to Pleurosaurs

Earlier we looked at pleurosaurs (Fig. 1, elongate, aquatic rhynchocephalians). Pleurosaurus goldfussi (Meyer 1831) was discovered first. Palaeopleurosaurus 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

Finally, some Priosphenodon post crania!

Earlier we looked at the skull of Priosphenodon (aka Kaikaifilusaurus) No dorsal or occipital views, but plenty of data to nest it at the base of the rhynchosaurs, despite its identification as a rhynchocephalian (sphenodontian).

Now (Fig. 1), courtesy of Dr. Sebastián Apesteguía (Argentina), who wrote his thesis on Priosphenodon, an image of the skeleton as a museum model is available. I understand that the carpals are among the few imagined parts here.

Figure 1. Priosphenodon model. This is the first data I've seen on the dorsal skull and postcrania. Photo courtesy of Dr. Apesteguía.

Figure 1. Priosphenodon model. This is the first data I’ve seen on the dorsal skull and postcrania. Photo courtesy of Dr. Apesteguía. Inset shows that the foot and manus of the model were switched based on comparisons to Hyperodapedon, a related rhynchosaur. The artist was unsupervised.

You’ll note
the wide, bulging cheeks and extremely narrow parietal (skull roof), as in rhynchosaurs. The nares had not become confluent. That comes in more highly derived forms. But look at those twin anterior dentary tips, as in rhynchosaurs. No anterior process on the ilium though. Stance probably not as sprawling as this, and not as erect as in rhyncosaurs.

References
Photo courtesy of Dr. Sebastian Apesteguía Specimen model at the new museum of Cipolletti (Rio Negro Province, Argentina), currently under construction. The sculptor is Jorge Antonio Gonzalez.

The Origin of Rhynchosaurs Revisited

Earlier we looked at the origin of rhynchosaurs. Today, another look.

Figure 1. The best data I have been able to found to document the origin of rhynchosaurs like Scaphonyx and Hyperodapedon. Despite their apparent (from the literature) commonality, there is precious little in the literature about rhynchosaurs.

Figure 1. The best data I have been able to found to document the origin of rhynchosaurs like Scaphonyx and Hyperodapedon, to scale. Despite their apparent (from the literature) commonality, there is precious little in the literature about rhynchosaurs. Lower images from Evans and Jones 2010. I’m a little unsure about the lacrimal on Scaphonyx. Help will be appreciated.

This post was inspired
by learning that Kaikaifilusaurus was conspecific with Priosphenodon (Fig. 1). I was also reviewing the Gauthier et al. (1988) of archosaur traits not shared by lepidosaurs, including the postnarial connection of the nasal and premaxilla. (BTW, Brachyrhinodon and Pleurosaurus (lower right, fig. 1) has this connection while pterosaurs do not.) Here bone colors help tell the story of rhynchosaur origins better than any 1000 words can. The reappearance of the lacrimal, quadratojugal  and socketed teeth are all part of the story. There may also have been a love child produced by the illicit mating of a Priosphenodon with a Mesosuchus. Well, maybe that mystery will be solved when a taxon is found that nests with them.

The reappearance of teeth
on the premaxilla of Mesosuchus documents some sort of legacy genetic code reappearing. So, if this is the case, there was evidently something in the water that permitted the reappearance of several other previously lost traits.

The infilling of the squamosal
on Priosphendon is also an autapomorphy not shared with other rhynchocephalians.

You can look from here to there,
but you won’t find a closer sister taxa among the archosauromorpha that nests more parsimoniously with rhynchosaurs than the rhynchocephalians. If you do, please let me know. In the meantime, the most comprehensive family tree on this subject can be found here.

References
Benton MJ 1983. The Triassic reptile Hyperodapedon from Elgin, functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B, 302, 605-717.
Benton MJ 1990. The Species of Rhynchosaurus, A Rhynchosaur (Reptilia, Diapsida) from the Middle Triassic of England. Philosophical transactions of the Royal Society, London B 328:213-306. online paper
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Carroll RL 1977. The origin of lizards. In Andrews, Miles and Walker [eds.] Problems of Vertebrate Evolution. Linnean Society Symposium Series 4: 359 -396.
Carroll RL 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company.
Cruickshank ARI 1972. The proterosuchian thecodonts. In Studies in Vertebrate Evolution (ed. Jenkins KA and Kemp TS) 89-119. Edinburgh: Oliver and Boyd.
Dilkes DW 1995. The rhynchosaur Howesia browni from the Lower Triassic of South Africa. Paleontology 38(3):665-685.
Evans S. E. & Jones M. E. H. 2010. The Origin, Early History and Diversification of Lepidosauromorph Reptiles. In Bandyopadhyay S (ed.) New Aspects of Mesozoic Biodiversity,  Lecture Notes in Earth Science 132, 27-44.
GauthierJ, Kluge, AG & Rowe T 1988. The early evolution of the Amniota. pp. 103–155 in Benton, M.J. (ed.), The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds. Oxford: Clarendon Press.
Huxley TH 1869. On Hyperodapedon. Quarterly Journal of the Geological Society, London, 25, 138-152.
Huxley TH 1887. Further observations upon Hyperodapedon gordoni. Quarterly Journal of the Geological Society, London, 43, 675-694.

wiki/Hyperodapedon
wiki/Rhynchosaur

Sapheosaurus Bridges the Sphenodontid/Trilophosaur/Rhychosaur gap

Sapheosaurus (Meyer 1850, Kimmeridgian Late Jurassic, France) has been known and largely ignored for a long time. Two species of this large sphenodontian are identified, S. laticeps with 22 presacrals and S. thiollierei with 26.

Figure 1. Sapheosaurus, a complete and articulated sphenodontian (rhynchocephalian) preserved on its back.  Plus the related Kallimodon in palatal view.

Figure 1. Sapheosaurus, a complete and articulated sphenodontian (rhynchocephalian) preserved on its back. Plus the related Kallimodon in palatal view. Note the narrow upper temporal fenestrae and narrow parietal. Kallimodon was found to be a sister to Sapheosaurus by Rauhut et al. 2012. Note the parallel rows of dentition also seen in Sphendon and rhynchosaurs.

 

Sapheosaurus nests between rhynchocephalians and rhynchosaurs.

Sapheosaurus nests between rhynchocephalians and rhynchosaurs.

Adding Sapheosaurus to the large reptile tree nests it between Brachyrhinodon and the higher rhynchocephalians, Trilophosaurus, Mesosuchus and the rhynchosaur, Hyperodapedon. Conventinal thinking nests rhynchosaurs and trilophosaurs at the base of the archosauriformes, close to Prolacerta, but no series of archosauromorph taxa share so many traits.

Sapheosaurus tree from Rauhut  et al. 2012

Figure 3. Sapheosaurus tree from Rauhut et al. 2012

Of course, there’s a time problem.
Rhynchosaurs and trilophosaurs were Triassic and Sapheosaurus is Late Jurassic. Of course, sphenodontians are well know for their phylogenetic longevity, with New Zealand’s own Sphenodon outlasting all of its former contemporaries.

In the Rauhut et al. (2012) tree (Fig. 3) they include many more sphenodontians than in the large reptile tree. Unfortunately they used the archosauromorph, Youngina, as an outgroup. It’s not related. Using Squamata was also ill-advised. After tall, which traits from which taxa would you cherry-pick? As in the large reptile tree, Brachyrhinodon and Sapheosaurus are close to one another. No rhynchosaurs or trilophosaurs are included in the Rauhut et al. tree, so, unfortunately, we will never see how they would nest there.

The palate of Kallimodon is interesting
because it demonstrates the side-by-side teeth that make the higher (but earlier) taxa so interesting (see Fig. 3 caption). Brachyrhinodon has similar parallel palatine teeth.

Figure 1. Rhynchocephalian and Rhynchosaur palates. That's Priosphenodon in the middle leading to Mesosuchus and Howesia, to Trilophosaurus and Azendohsaurus and rhynchosaurs. That's where the palatine grows as large as and alongside the maxilla. In derived taxa these two bones fuse creating the illusion that the maxilla has the entire tooth pad. Look at those palatine stems on Priospbenodon, which really come out on rhynchosaurs.

Figure 1. Rhynchocephalian and Rhynchosaur palates. That’s Priosphenodon in the middle leading to Mesosuchus and Howesia, to Trilophosaurus and rhynchosaurs. That’s where the palatine grows as large as and alongside the maxilla. In derived taxa these two bones fuse creating the illusion that the maxilla has the entire tooth pad. Look at those palatine stems on Priospbenodon, which really come out on rhynchosaurs.

References
Apesteguía S and Novas FE 2003. Large Cretaceous sphenodontian from Patagonia provides insight into lepidosaur evolution in Gondwana. Nature 425:609-612
Apesteguia S,  Gomez  RO, and Rougier GW 2012. A basal sphenodontian (Lepidosauria) from the Jurassic of Patagonia: new insights on the phylogeny and biogeography of Gondwanan rhynchocephalians. Zoological Journal of the Linnean Society 166:342-360
Benton MJ 1985. Classification and phylogeny of the diapsid reptiles. Zoological Journal of the Linnean Society 84(2):97-164
Rauhut OWM, Heyng AM, López-Arbarello A and Hecker A. 2012. A new rhynchocephalian from the Late Jurassic of Germany with a dentition that is unique amongst tetrapods. PLoS ONE 7(10):e46839
Reynoso VH 2000. An unusual aquatic sphenodontian (Reptilia: Diapsida) from the Tlayua Formation (Albian), central Mexico. Journal of Paleontology 74:133-148
von Meyer H 1850. Mittheilungen an Professor Bronn gerichtet: Neües Jahrbuch fur Mineralogie, Geologie und Palaontologie, Bd 18, p. 195-204.

The Odd Swimming Sphenodontids

Updated November 11, 2014 with the Dnesting of pleurosaurs with Megachirella and Marmoretta. And updated December 3, 2014 with the division of the pleurosaurs into two convergent clades. 

Hard to believe that our favorite New Zealand “Living Fossil,” Tuatara (Sphenodon), had some aquatic sisters, but here they are.

Figure 1. Pleurosaurus and Palaeopleurosaurus to scale with sisters.

Figure 1. Pleurosaurus and Palaeopleurosaurus to scale with sisters.

Pleurosaurus goldfussi (Meyer 1831), Late Jurassic. 60 cm in length. The Triassic terrestrial sphenodontians produced a Late Jurassic marine lineage known as the pleurosaurs after the first of these to be discovered, Pleurosaurus and also one of the most derived. Palaeopleurosaurus appears to be a stretched out version of its terrestrial antecedent, Planocephalosaurus, and was a transitional form to later, longer, more streamlined pleurosaurs.

Added Dec 03, 2104: > That was the traditional nesting. New analyses indicate that Pleurosaurus nested between Palaegama, Megachirella and Marmoretta at the base of the Lepidosauria, which radiated in the Middle to Late Permian. Palaeopleurosaurus had a convergent return to an aquatic niche as it nested between Gephyrosaurus and Planocephalosaurus. The similar Ankylosphenodon was a sister taxon.

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

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

Pleurosaurs were Late Jurassic aquatic sphenodontids, characterized by a long, streamlined and elongated body (with a short neck), small limbs and (as in most aquatic reptiles) nares that were displaced from the snout tip to closer to the orbits. The premaxilla of Palaeopleurosaurus was ventrally elongated to form a sharp spike that would have snared prey. They swam with snake-like undulations of the entire body. Their neural spines grew to become large rectangles, as in snakes. Pleurosaurs produced no Cretaceous descendants.

There is not much that is controversial about these lepidosaurs. They are not often studied and they are rarely on anyone’s Top 10 list, so I thought I’d toss them out for a little publicity.

Added Dec. 03, 2014: > Well, perhaps I spoke too soon as the two traditional pleurosaurs are not that closely related to one another. That’s a little bit of news!

References
Carroll RL 1985. A pleurosaur from the Lower Jurassic and the taxonomic position of the Sphenodontids.
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.

wiki/Planocephalosaurus
wiki/Pleurosaurus

Lacertulus and the Origin of the Squamata in the Permian

This post was updated December 04, 2014 with a revision of the nesting of Lacertulus as a basalmost protosquamate, close to the origin of the Tritosauria and Rhynchocephalia. This was due to the inclusion of taxa to the large reptile tree. 

Updated July 7, 2020
the LRT moves Meyasaurus, Indrasaurus and Hoyalacerta to the base of the Yabeinosaurus + Sakurasaurus clade within the Scleroglossa and Squamata.

Traditional Hypotheses
The paradigm in paleontology holds that lepidosaurs (lizards and sphenodontians) and archosaurs (dinosaurs and crocs) both descended from a sister to Youngina. The present reptile family tree tested this traditional hypothesis with many more taxa and found a new tree that kept Youngina with protorosaurs and archosaurs, but moved lepidosaurs over to another major branch, the lepidosauromorpha.

Lacertulus

Figure 1. Lacertulus, a basal protosquamate.

Paliguana, at the base of the Lepidosauriformes
A skull-only taxon, Paliguana, nested at the base of the Lepidosauriformes. It lived 250 mya during the latest Permian or earliest Triassic. It gave rise to a clade of pre-lepidosaurs including Sophineta, Palaegama, Saurosternon and the Triassic gliders.

Paleagama gave rise to the Lepidosauria: including the Rhynchocephalia (Sphenodontia), the Tritosauria and the Protosquamata (including the Squamata).

Lacertulus at the base of the Protosquamata (basal Lepidosauria)
Lepidosauria is now restricted to the last common ancestor of Squamata (lizards, snakes and amphisbaenians) and Rhynchocephalia (or Sphenodontia, represented by Sphenodon), and all descendants of that ancestor (e.g., Gauthier et al., 1988). Unfortunately there are many lepidosaurs that nest in neither of these clades.

Lacertulus, at the base of the Squamata
The living and extinct lizards all descended from a sister to Lacertulus from the Late Permian. It was described as a potential biped, but the nonfusion of the astragalus and calcaneum removed it from the Squamata in the eyes of Carroll and Thompson (1978). Since then, a few more squamates without a fused astragalus and calcaneum have been discovered including Meyasaurus and Huehuecuetzpalli. Along with Lacertulus, some of these nested at the base of a third, previously unidentified, squamate clade, the Tritosauria, which included tanystropheids and pterosaurs. The others nested with the Protosquamata, which includes the Squamata.

The Longevity of Individual Squamate Taxa
Many of these tritosaurs and protosquamates survived into the Jurassic and Cretaceous, but not beyond. All are now extinct. Given the longevity of Sphenodon into the modern era and the long-lived examples of Huehuecuetzpalli and Homoeosaurus, perhaps other lizards known from more recent times will also be found closer to the Permo-Triassic origin of squamates.

Prior “Oldest Known Lizards”
When Protorosaurus was discovered, it was described as the “oldest known lizard.” Here it nested far from the lizards.  Paliguana was also described as the “oldest known lizard.” Currently the oldest known fossil lizard is Tikiguania from the Late Triassic, 220 mya. Most other old fossil lizards are known from the Jurassic and Cretaceous.

The most primitive squamate and the oldest squamate
The basal most squamate, Scandensia, lived in the Early Cretaceous, far from its origins in the Permian. A phylogenetic descendant, the TA1045 specimen is an anguimorph scleroglossan that lived in the Early Permian. It is the oldest known squamate.

References
Carroll and Thompson 1982. A bipedal lizardlike reptile from the Karroo. Journal of Palaeontology 56:1-10.

Moving Rhynchosaurs and Trilophosaurs Back into the Rhynchocephalia (Sphenodontia)

Rhynchosaurs are among the strangest reptiles that ever lived.
Characterized by a weird wide skull and protruding toothless, beak-like premaxillae, rhynchosaurs had rows of crushing teeth and giant jaw muscles for grinding food before swallowing to hasten digestion. Although the body was nothing special, no other reptile had such a skull. And evidently THAT is the cause of the current lack of a solid phylogenetic nesting.

Pre-rhynchosaurs, like Mesosuchus, appeared in the late Early Triassic to early Middle Triassic. All rhynchosaurs, including Hyperodapedon, disappeared in the Late Triassic.

Hyperodapedon in various views.

Figure 1. Hyperodapedon in various views. Note the extreme width of the skull and multiple rows of grinding teeth.

Where Did Rhynchosaurs Fit In?
Romer (1956) considered rhynchosaurs and sphenodontians to be related, but Cruickshank (1972), Benton (1983), Carroll (1988) and Dilkes (1998) split them apart, perhaps by placing too much emphasis on the lack of fusion in the tarsus and lack of acrodont teeth (see below). Caroll (1988) placed Trilophosaurus and rhynchosaurs with Prolacerta, Tanystropheus, Proterosuchus and Euparkeria. Unfortunately, no phylogenetic analysis has yet tested this nesting against a large gamut of reptiles, other than the large study.

rhynchosaurs588

Priosphenodon and its sphenodontid sisters, including Trilophosaurus and the rhynchosaur Hyperodapedo

Let’s Look at the Candidates
Above a selection of several rhynchocephalians is compared to three candidate diapsids. Overall Hyperodapedon, Mesosuchus and Trilophosaurus share more traits with Brachyrhinodon than with Youngina, Prolacerta or Proterosuchus. This is also demonstrated by several hundred characters and taxa in the large reptile tree. No other terrestrial reptile had such a wide skull, but Mesosuchus comes close. Brachyrhinodon and Priosphenodon come close to MesosuchusProlacerta and Proterosuchus were known for their narrow skulls filled with sharp teeth.

Here’s the Hump We Have to Get Over
According to the textbooks, lepidosaurs all have a fused astragalus and calcaneum and derived characters of bone growth with epiphyses. The problem is Trilophosaurus and rhynchosaurs don’t fuse those proximal ankle bones.

Benton (1983) reported, “Rhynchosaurs have no special relationship with the sphenodontids. The supposed shared characters are either primitive (e.g. complete lower temporal bar, quadratojugal, akinetic skull, inner ear structure, 25 presacral vertebrae, vertebral shape, certain character of limbs and girdles) or incorrect (e.g. rhynchosaurs do not have acrodont teeth, the ‘beak-like’ premaxilla of both groups is quite different in appearance, the ‘tooth plate’ is wholly on the maxilla in rhynchosaurs but on maxilla and palatine in sphenodontids).”

These nits and picks are important, but taken as a whole (which is what we must do) currently there are no taxa more closely related to rhynchosaurs than rhynchocephalians (sphenodontians) and the trilophosaurs. Granted, all other rhynchocephalians had fused ankle bones, but having an unfused ankle is simply a matter of not fusing those bones, which develop separately in embryos. Acrodont teeth also form with fusion. Again, this would be a simple matter of switching off a gene.

Some of the Strangest Teeth You’ll Ever See
Benton (1983) discussed the placement of teeth wholly on the maxilla in rhynchosaurs. Let’s see what that looks like. The palatine (in orange) is the key bone in this controversy. In Mesosuchus the palatine is reduced and has lost its teeth. In Hyperodapedon the palatine retains teeth and extends lateral to the choanae to contact the premaxilla. In Howesia the palatine fuses to the maxillary tooth plate. In Trilophosaurus the palatine likewise fused to the maxillary tooth plate and the palatine teeth fused to the maxillary teeth, creating laterally elongated teeth with three lateral cusps. Click here for enlargement.

The palates of several rhynchocephalians, including rhynchosaurs

Figure 3. The palates of several rhynchocephalians, including rhynchosaurs. Click to enlarge.

Summary
Romer was right. Rhynchosaurs are closer to rhynchocephalians (sphenodontians). The differences noted by Benton (1983) are insufficient to outweigh a larger suite of characters that nest these taxa together.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Benton MJ 1983. The Triassic reptile Hyperodapedon from Elgin, functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B, 302, 605-717.
Benton MJ 1990. The Species of Rhynchosaurus, A Rhynchosaur (Reptilia, Diapsida) from the Middle Triassic of England. Philosophical transactions of the Royal Society, London B 328:213-306. online paper
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Carroll RL 1977. The origin of lizards. In Andrews, Miles and Walker [eds.] Problems of Vertebrate Evolution. Linnean Society Symposium Series 4: 359 -396.
Carroll RL 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company.
Case EC 1928. A cotylosaur from the Upper Triassic of western Texas: Journal of Washington Academy of Science 18:177-178.
Cruickshank ARI 1972. 
The proterosuchian thecodonts. In Studies in Vertebrate Evolution (ed. Jenkins KA and Kemp TS) 89-119. Edinburgh: Oliver and Boyd.
Dutuit J-M 1972. Découverte d’un Dinosaure ornithischien dans le Trias supérieur de l’Atlas occidental marocain. Comptes Rendus de l’Académie des Sciences à Paris, Série D 275:2841-2844. 
Flynn JJ, Nesbitt, SJ, Parrish JM, Ranivoharimanana L and Wyss AR 2010. 
A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible”. Palaeontology 53 (3): 669–688. doi:10.1111/j.1475-4983.2010.00954.x
Fraser NC and Benton MJ 1989.
 
The Triassic reptiles Brachyrhinodon and  Polysphenodon and the relationships of the sphenodontids. Zoological Journal of the Linnean Society 96:413-445.
Gregory JT 1945. Osteology and relationships of Trilophosaurus: University of Texas, Publication 4401:273-359.
Heckert AB et al. 2006. Revision of the archosauromorph reptile Trilophosaurus, with a description of the first skull of Trilophosaurus jacobsi, from the upper Triassic Chinle Group, West Texas, USA: Palaeontology 4(3):1-20.
Huxley TH 1859.
 Postscript to, R. I. Murchinson. On the sandstones of Morayshire (Elgin & c.) containing reptile remains; and their relations to the Old Red Sandstone of that country. Quarterly Journal of the Geological Society, London, 15, 138-152.
Huxley TH 1869. On Hyperodapedon. Quarterly Journal of the Geological Society, London, 25, 138-152.
Huxley TH 1887. Further observations upon Hyperodapedon gordoni. Quarterly Journal of the Geological Society, London, 43, 675-694. Parks P 1969. Cranial anatomy and mastication of the Triassic reptile,  Trilophosaurus [M.S. thesis]: University of Texas, 100 pp.
Romer AS 1956. Osteology of the Reptiles. University of Chicago Press, Chicago.

wiki/Hyperodapedon
wiki/Rhynchosaur
wiki/Brachyrhinodon
wiki/Trilophosaurus
wiki/Azendohsaurus