A Skull For Rhamphorhynchus, Part Two

Rhamphorhynchus muensteri in the flesh, in a "perching" mode. This illustration is a little dated.

Rhamphorhynchus muensteri in the flesh, in a “perching” mode. This illustration is a little dated, lacking a cruropatagium or uropatagium, instead having little “rackets” at the end of the legs to account for the long fifth toe.

My last post on Rhamphorhynchus muensteri‘s skull elicited some dialogue on the dietary preferences one might infer from looking at Rhamphorhynchus‘s skull. This was done regardless of the preservation of gut remains or implied habitus. In preparation of a larger thesis on dietary inference, I made some comments that seemed to cast doubt on whether Rhamphorhynchus was a piscivore. For now, my operating argument for “piscivore” is a morphofunctional one: There is an explicit morphology related to the eating of — specifically — fish. This has no relation to eating any other prey found at sea. Rhamphorhynchus, in my formulation, would be an occasional, perhaps opportunistic, fish-eater, but it doesn’t match the “piscivore” morphology. I will come back to this.

The skull of Rhamphorhynchus muensteri (or at least, of Rhamphorhynchus in general, segregated into about 3-4 “morphotypes” that seem to represent semaphoronts (see Bennett, 1995, for more details) that had been relegated to various species over the last century and more) is well known. And thanks to some providential preservation, science can recover most of the skull in most major views, even rear. There are issues with the last, as the skull that best shows this (CM 11434, Witmer et al., 2003; Hone et al., 2013) is crushed dorsoventrally and obscures the skull’s aspect somewhat.

The skull and mandible of Rhamphorhynchus muensteri (Goldfuss, 1841) in dorsal (top), side (middle), and bottom (bottom) views. The views are not perfect, as the source material for each view differs somewhat to accommodate some attempt at accuracy.

The skull and mandible of Rhamphorhynchus muensteri in dorsal (top), side (middle), and bottom (bottom) views. The views are not perfect, as the source material for each view differs somewhat to accommodate some attempt at accuracy.

The best thing to notice about (implied) undeformed skulls like this is that, with really long teeth, you get an idea how the arrangement of teeth affect the shape of the jaw. The bony jaw is narrow and triangular, lacks teeth at the tip. But the teeth form a margin of sorts around the bone, which makes the jaw seem less triangular and more spade-like in aspect, a feature it shares with a few animals, among them caimans (crocs) and spoonbills (birds). What can be made of this shape? Is it even relevant? What is with the enormous gular space the jaws make between them, and why does the mandible have such a large anterior brace but not much of a rear one? Questions, questions…

One of the things I like doing with these skull drawings, though they aren’t rigorous attempts to capture all variation, is to use them to get a general idea (with reference to the originals) of where muscles should go and make a casual, back-of-hand attempt to quanlify some of their jaw mechanics. But why do this in a vacuum? I did this for Anurognathus ammoni a while back, with some general observations, and now can do this with another small, coeval pterosaur. As these pterosaurs both occurred in the Solnhofen, though perhaps not necessarily at the same time or over the same explicit territory (in life), they were contemporaries, and this allows us to look at potential variation in morphospace.

Thus, I can do this:

Anuro vs RhamphoNote: This is based on some very general observations. There isn’t enough data to qualify some of this, especially explicit muscle positions. Many assumptions are being made, as discussed here. But this is back-of-hand stuff. An additional element of interest in this was to show how strikingly different two groups could be. I could use Pterodactylus antiquus (or Ardeadactylus longicollum) and make of them a more radical distinction, but those species share more dental features with Anurognathus ammoni than Rhamphorhynchus muensteri does, and there are other important issues to deal with. Rhamphorhynchus and Anurognathus, at least, retain the “pre-pterodactyloid” morphology, and are the two best known non-pterodactyloid pterosaurs from Solnhofen.

How these two animals interacted with their food differed substantially. The problem is determining if there was a difference between their diet that can be inferred from this jaw morphology, a question that cannot be simply answered without a broader sample (of living taxa) which constrains error. This is part of that broader project which I will come back to some time later.

Bennett, S. C. 1995. A statistical study of Rhamphorhynchus from the Solnhofen Limestone of Germany: Year-classes of a single large species. Journal of Paleontology 69: 569-580.
Hone, D. W. E., Habib, M. B. & Lamanna, M. C. 2013. An annotated and illustrated catalogue of Solnhofen (Upper Jurassic, Germany) pterosaur specimens at Carnegie Museum of Natural History. Annals of the Carnegie Museum 82 (2): 165-191. (link to paper here, via Hone at Pterosaur.net)
Witmer, L. M., Chatterjee, S., Franzosa, & Rowe, T. 2003. Rhamphorhynchus muensteri†. Digimorph, https://digimorph.org/specimens/Rhamphorhynchus_muensteri/ (accessed 5 Jan, 2014).

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