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

Tree topology change separates protosquamates from tritosaurs

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

New data
added to the large reptile tree has changed the topology of the Lepidosauria. This is the biggest change I’ve seen in the last four years, yet it occurred in a fairly dark alley of the Amniota where very few researchers lurk.

Now the Tritosauria has been halved,
extending only from Tijubina to pterosaursPalaegama is still the outgroup.

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

Figure 1. Palaegama is basal to Coelurosauravus (‘rib’ gliders), Megachirella (rhynchocephalians), Lacertulus (protosquamates) and Tijubina (tritosaurs). Taxa to scale. Note the miniaturization at the base of the Lepidosauria and the similarity of all these sister taxa.

Palaegama is still basal to the so-called ‘rib’ gliders (not ribs, but dermal extensions as we discovered here). It is also basal to all Lepidosaurs.

Among the Lepidosaurs…
Former tritosaurs now form a grade of protosquamates extending from Lacertulus and Bavarisaurus to the primal division of Iguania and Scleroglossa.

Figure 2. Protosquamates to scale. Click to enlarge. Colors indicate clades.

Figure 2. Protosquamates to scale. Click to enlarge. Colors indicate clades.

Tiny Scandensia remains as the last common ancestor of the Lepidosauria and the MFSN 19235 specimen is its larger predecessor.

Other protosquamates include the Daohugou lizard, Carusia, Meyasaurus, Homoeosaurus, Dalinghosaurus and Hoyalacerta.

This change followed the addition of several basal rhynchocephalians, like Megachirella, that shed new light on the origin of the Lepidosauria and the radiations that succeeded them. We looked at those additions here.

Nomenclature
The Tritosauria remains a clade distinct from Squamates. We’ll need a new name for the clade that includes Lacertulus and Iguana, their last common ancestor and all of its descendants. That clade does not include the Tritosauria. A clade that includes the new clade and the Tritosauria is also needed. The Rhynchocephalia is a sister taxon and Palaegama is the current outgroup.

The interesting thing, and we’ve seen this before…
The order of the protosquamates is exactly the opposite as I originally thought. The logic behind this is like folding a piece of paper. The sister taxa at the fold are the same. The beauty of the new topology places the Permian Lacertulus at the base of its clade, where it belongs chronologically and nests the most derived taxon, Scandensia from the Early Cretaceous where it belongs. We’ve seen this before when M. Mortimer nested beaked dinosaurs basal to theropods and I pointed out the hypothesis that the tree was upside-down. See. It can happen to anybody.

The problem with Scandensia is, it looks a lot like the basal rhynchocephalian, Gephyrosaurus and it has long digits like Palaegama. So, I was readily fooled by what appeared to be the real deal — but it was not the real deal. When you look at the protosquamates (Fig. 2), there is no obvious direction to this clade or grade of lepidosaurs. The details of the skeleton reveal their relationships.