Ozimek volans: homology and analogy

Earlier we looked at the new protorosaur
Ozimek volans (Fig. 1) here and determined by phylogenetic analysis that it was a sister to Prolacerta, not Sharovipteryx.

Today, just a short note
about its homology with Prolacerta and its purported and invalid analogy with the unrelated membrane gliders Sharovipteryx and Cynocephalus.

Figure 1. Ozimek volans compared to its homolog sister, Prolacerta, and to two putative analogs, Sharovipteryx and Cynocephalus, all to scale. Note the lack of climbing claws and the weakness of the limbs and girdles in Ozimek.

Figure 1. Ozimek volans compared to its homolog sister, Prolacerta, and to two putative analogs, Sharovipteryx and Cynocephalus, all to scale. Note the lack of climbing claws and the weakness of the limbs and girdles in Ozimek, adorned here with hypothetical membranes.

Floating is just one niche possibility
based on the weakness of the muscle anchors in Ozimek. I have never seen such skinny arms and legs, so I am at a loss for a suitable niche for it.
I don’t see large climbing claws,
long manual digits, large muscles and their anchors on Ozimek that one finds on Cynocephalus. If it were it otherwise, I might support the gliding hypothesis.
Gliding animals need strong limbs
and muscle anchors not only for supporting their total weight in the air, but also for climbing trees and the momentum shock of both take-off and landing. In this regard, Ozimek appears to be quite a bit weaker than either Cynocephalus or Sharovipteryx. If it was like Sharovipteryx the diameter of the limb bones should have been scaled up to deal with the magnitude greater mass.
Sharovipteryx has elongate ilia and pectoral elements with short arms, plus seven sacrals, all lacking in Ozimek, its putative sister.
Sharovipteryx does not have a lateral membrane
Old and bad reconstructions of Sharovipteryx used to add a membrane between imagined long forelimbs with short fingers and the longer hind limbs. No one has ever seen such a membrane in the fossil. No sisters have such a membrane. Rather a uropatagium trails each hind limb, as in pterosaurs and Cosesaurus. Phylogenetic bracketing adds a pterosaur-like brachiopatagium behind each tiny Sharovipteryx forelimb, but it is likewise not visible in the fossil. The Dzik and Sulej team counts on the validity of the fantasy lateral membrane between the limbs to make their Ozimek a glider. But it was never there in any case.
Figure 1. Dzik and Sulej are so sure that their Ozimek was a spectacular big sister to Sharovipteryx that they gave a model gliding membranes and used the largest disassociated humerus for scale. More likely it was an aquatic animal that did not move around much underwater.

Figure 2. Dzik and Sulej are so sure that their Ozimek was a spectacular big sister to Sharovipteryx that they gave a model gliding membranes and used the largest disassociated humerus for scale. No membranes are present lateral to the pancaked ribs in Sharovipteryx and so this patagium on Ozimek, lacking such ribs, is also based on fantasy.

Prolacerta is also hollow-boned,
and is the sister of Ozimek in the LRT. No tested taxon, including Sharovipteryx, is phylogenetically closer.
Langobardisaurus analogy
Overall, Ozimek looks like a big, skinny Langobardisaurus (Fig. 3).
Figure 2. Langobardisaurus compared to Ozimek and its sister, Prolacerta.

Figure 3. Langobardisaurus compared to Ozimek and its sister, Prolacerta to scale. Structurally, Ozimek was similar to Langobardisaurus, but had much longer, weaker limbs and girdles and despite a long list of similarities, still nested with Prolacerta.

Langobardisaurus had the same long neck
and big skull as seen in Ozimek, but is not related, The girdles are larger and the limbs are more robust in the smaller Langobardisaurus than in the larger Ozimek. So, whatever Langobardisaurus was doing, Ozimek might have been doing, but more slowly, cautiously and secretly, perhaps like a spider.

Protorosaurs and Tritosaurs
appear on opposite sides of the LRT, but closely resemble one another such that macrocnemids and langobardisaurs were both considered protorosaurs (even by me) before the LRT showed macorcnemids and langobardisaurs actually nested with tritosaur lepidosaurs. The convergence is amazing and potentially confusing unless a rigorous analysis is performed. The LRT has been successful in separating such convergent taxa and continues to do so.

References
Dzik J and Sulej T 2016. An early Late Triassic long-necked reptile with a bony pectoral shield and gracile appendages. Acta Palaeontologica Polonica 61 (4): 805–823.
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2 thoughts on “Ozimek volans: homology and analogy

  1. ? Perhaps a bittern-like reed [horsetail] mimic and ambush predator? — that is, if articulation would allow erect bipedal pose. Or similarly, perhaps taking a stick-insect pose in water like the Ranatra water bugs.. BTW, in addition to your issues of lack of shock absorbing in limbs and pectoral girdle, the neck looks to be easily broken on a bad landing!

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