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

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