A closer look at Jesairosaurus

Updated November 29, 2015 with a new reconstruction and nesting for Jesairosaurus.

Earlier we looked at Jesairosaurus (Jalil 1991) and the origin of the Drepanosauridae. Today we’ll take a closer look at Jesairosaurus.

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Jesairosaurus was originally considered a procolophonid, then a prolacertiform
Sure it has a long neck, but in phylogenetic analysis, it doesn’t nest with Prolacerta or Marlerisaurus, but after the basal lepidosauriform Palaegama and prior to drepanosaurs and kuehneosaurs. Note the dorsal nares and large orbit. There’s a very tall scapula here, a precursor to the tall stem in drepanosaurs.

Distinct from most lepidosauriforms,
Jesairosaurus has fairly large thecodont teeth. Gastralia appear here for the first and last time in this lineage. The ventral pelvis isn’t fused, but the thyroid fenestra is gone.

Like most lepidosauriforms,
the scapulocoracoid was not fenestrated. And there’s a nice ossified sternum there.

On a side note…
As you know, I’m always attempting to improve the data here. Several months ago I mentioned to a detractor that most prior workers reported  forelimbs present in Sharovipteryx. Only Unwin et al. (2000) thought they were buried in the matrix. My detractor claimed the opposite, that I was the only one to see forelimbs. No word yet on this issue. Still waiting.

Another detractor claimed I had seen soft tissue on a Bavarian museum fossil pterosaur. When I asked which specimen, he refused to provide the number.

In a third case I asked to see a closeup of a pterosaur mandible tip that had been published. I wondered if the sharp tip might be a tooth, as it is in other sharp mandible pterosaurs. The offer was refused with the phrase, “trust us, it’s not there.” I replied “trust” is antithetical to Science. No reply and no closeup yet.

So, is it so hard to provide a museum number? A closeup of a photograph? Or a reply to a note on forelimbs? Should we trust other scientists? Or should we test and confirm or refute? There may be cooperation among other paleontologists. Or maybe they’re all very protective of their data. Evidently I also have a very bad reputation, and that may be the reason for the lack of cooperation. These things happen when paradigms are broken.

Jalil N-E 1997. A new prolacertiform diapsid from the Triassic of North Africa and the interrelationships of the Prolacertiformes. Journal of Vertebrate Paleontology 17(3), 506-525.
Unwin DM, Alifanov VR and Benton MJ 2000. Enigmatic small reptiles from the Middle-Late Triassic of Kyrgyzstan. In: Benton M.J., Shishkin M.A. & Unwin D.M. (Eds) The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge U. Press: 177-186.




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