Where the heck is the sternal complex in Shenzhoupterus?

Shenzhoupterus in situ.

Figure 1. Shenzhoupterus in situ. The tip of the long parietal crest is noted.

Shenzhoupterus (Figs. 1-6, Lü et al. 2008) is a wonderfully bizarre derived pterosaur with an outsized skull and long, heron-like limbs, a deep prepubis and a tubby torso. The skeleton is complete and – mostly – articulated.

The big problems are the skull and the sternum. The bones of the cheek region of the skull are all there, they’re just jumbled beyond recognition. The sternum is apparently gone (but wait, there’s more!! ~ and these two problems are interrelated!!)

This is a job for DGS (digital graphic segregation)!
But first the easy stuff. See the tip of the parietal crest (Fig. 1)? It was overlooked by the original authors and illustrators. This long crest is homologous with that of its close relatives Germanodactylus cristatus (Fig. 6) and Sinopterus.

Shenzhoupterus skull in situ

Figure 2. Shenzhoupterus skull in situ

We’ll take this a step at a time. Here (Fig. 2) is a close look at the skull in all its chaos.

Shenzhoupterus skull in situ with sternum in blue.

Figure 3. Shenzhoupterus skull in situ with sternal complex in blue. It is below the skull elements yet the outline betrays its presence.

Here (Fig. 3) the sternal complex (sternum + clavicles + interclavicle) is illustrated in blue. Yes, it is difficult to see. But it is there, exposed and identified by DGS.

Shenzhoupterus skull in situ with elements identified.

Figure 4. Shenzhoupterus skull in situ with only one side of cheek elements + sternal complex identified.

Here (Fig. 4) only one side of the cheek elements and the entire occiput are identified. Even without the other side elements the bones are chaotic. They only make sense when you put them back together, and even then there’s a derived and distinct morphology present (Fig. 5). DGS was able to identify the elements using a photograph and a computer better than the naked eye. Moreover, the elements of the rostrum are better delineated.

Shenzhoupterus reconstructed alongside original interpretation of skull.

Figure 5. Shenzhoupterus reconstructed alongside original interpretation of skull. The real test to see if identifications are correct is to put the pieces back together again and see if they fit together and fall into established patterns set by related pterosaurs.

Comparisons to related taxa complete the analysis (Fig. 6). Note the original interpretation looks nothing like the related pterosaurs and fails to identify skull elements.

Figure 6. Germanodactylus cristatus and the Shenzhoupteridae, Shenzhoupterus and Nemicolopterus. The Tapejaridae were close relatives.

Figure 6. Germanodactylus cristatus and the Shenzhoupteridae, Shenzhoupterus and Nemicolopterus. The Tapejaridae were close relatives.

And then there’s the wing ungual.
A closeup photo of the Shenzhoupterus wingtip (Fig. 7) reveals the ungual, hyper-flexed but still articulated. No wonder it was originally overlooked.

Shenzhoupterus wingtip and ungual.

Figure 7. Shenzhoupterus wingtip and ungual. Curled back like this, it is easy to overlook.

Overall a closer examination using every available tool is warranted here. A simple examination using the eyeball alone is not sufficient to segregate the elements of the Shenzhoupterus cheek region. It takes a graphic tool to do so. Identifying one element after another until all elements are accounted for. That’s how the sternal complex beneath the skull was discovered. It wasn’t immediately apparent until all the other skull elements were delineated and identified.

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
Lü J, Unwin DM, Xu L and Zhang X 2008. A new azhdarchoid pterosaur from the Lower Cretaceous of China and its implications for pterosaur phylogeny and evolution. Naturwissenschaften 95 (9): online (preprint). doi:10.1007/s00114-008-0397-5. PMID 18509616.

wiki/Shenzhoupterus

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4 thoughts on “Where the heck is the sternal complex in Shenzhoupterus?

  1. “The real test to see if identifications are correct is to put the pieces back together again and see if they fit together and fall into established patterns set by related pterosaurs.”

    Then shouldn’t your reconstruction with the orbit oddly divided into three fenestrae fail the test?

    Besides part of what you identify as the jugal, I see nothing in that mass of bone. I think you have to come to grips with the fact that fossilization doesn’t always leave elements neatly lying there to be picked apart by DGS. In this case, the granular texture would make me guess the skull was split when the other slab was removed, leaving us with a crushed mess of bone in section like Protarchaeopteryx or NGMC 91.

  2. Just a suggestion here: It is perfectly, perfectly okay as a scientist to say, “I don’t know.” I encounter this all the time in studying ceratopsian skulls (which are much bigger and much less prone to crushing!). I know that every one of them had a squamosal and parietal. Every one of them had a squamosal and parietal suture. Sometimes it just ain’t visible, due to preservation, preparation, or fusion. More than once, I’ve looked at a photo, said “Aha! There it is!”, and gone back to the specimen to find that my (very reasonable) interpretation of the photo was incorrect. Based on sister taxa, I could draw in very reasonable reconstructions of where the sutures are, and I’d probably be 99.9% correct, but I would still be working outside the bounds of what the specimens really say. In other words, I would be making up data – albeit in an informed manner (but still making up data). It is tough to admit when I don’t know something and can’t find it out even from the fossil. But that’s just science! (and part of what makes finding new specimens so exciting)

    So. . .Shenzhouopterus is fairly complete but badly crushed and probably damaged during the splitting procedure. Some bones very well may be missing. Some might be there, but we just can’t recognize them. And we may never be able to tell. That’s OK! It is okay (if frustrating) to not know the answer.

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