What’s With That Deep Prepubis?

The “dark wing” specimen of Rhamphorhynchus muensteri JME SOS 4785 (Tischlinger and Frey 2002) has one overlooked oddity worth mentioning. It had an incredibly deep prepubis (Figure 1.)

The darkwing Rhamphorhynchus JME SOS 4785

Figure 1. The darkwing Rhamphorhynchus JME SOS 4785. Note the incredible depth of the prepubis, deeper than in any other pterosaur.

Prepubis
The prepubis of pterosaurs is a pelvic bone not found in the vast majority of tetrapods. It is not homologous with the prepubis of monotremes and marsupials. Nor is it homologous with the so-called “prepubic” bones of crocodilians, which are homologous with the pubic bones of other amniotes (Seeley 1901). The prepubis of ornithischian dinosaurs is a process of the pubis and not a separate ossification.The prepubis is new bone found in all fenestrasaurs (Cosesaurus, Sharovipteryx, Longisquama and pterosaurs).

Radiating from the ventral pubis, the pterosaur prepubis typically has a narrow elongated proximal stem and a thin, plate-like distal expansion. This expansion is often perforated, at times to such an extent that the perforation expands beyond the anterior margin of the prepubis resulting in a forked appearance with anterior and ventral processes. That’s the case in our Rhamphorhynchus. In derived taxa a suture may form at the union (Wellnhofer, 1974). In Pteranodon the prepubes may fuse medially (Bennett, 1991, 2001). The anterior rims of the prepubes contact the posterior rims of the posterior set of gastralia (Bennett 1991, 2000).

Rhamphorhynchus prepubis rotated into the correct position

Figure 2. Prepubis fron Claessens et al. (2009) rotated into the correct position

The Claessens, O’Connor and Unwin (2009) Error
Claessens et al. (2009, Fig. 2) sought to demonstrate the ventral expansion of the pterosaur abdomen to facilitate respiration via “caudoventral rotation of the prepubis.” They described a Rhamphorhynchus prepubis articulated to the pubis with a moveable joint and with its major axis in line with the gastralia. The prepubis was correctly identified, but unfortunately Claessens et al. (2009) failed to notice it had been flipped during taphonomy. The anterior process of the distal prepubis is visible ventral to the pubis. The ventral process is hidden beneath the pelvis. Flipped back and properly configured the prepubis greatly deepens the torso without a moveable joint at the pubis, as in other Rhamphorhynchus specimens, like the “dark wing” example.

So, Why the Deep Prepubis in Rhamphorhynchus muensteri?
Several examples of other Rhamphorhynchus specimens are here, here and here. In certain respects, in none of these does the prepubis reach the depth seen in R. muensteri, somewhat deeper than the pelvis itself and hanging below the knees. The elongated prepubis in R. muensteri ventrally elongates the already wide torso but it doesn’t really create a more voluminous torso because the two prepubes seen in anterior or posterior view form a narrow V shape. I note that in all Campylognathoides (and Nesodactylus) specimens up to but not including the Pittsburgh specimen, the prepubes don’t reach the knees. They don’t even get close. In the Pittsburgh specimen of Campylognathoides, the giant prepubes do extend to the knees. In the tiny basal Rhamphs that follow the prepubes also extend to the knees (in lateral view), but in every case, the femur is relatively short, so the prepubes are not noticeably elongated. That also pertains to the giant, R. longiceps. However, the femur in R. muensteri is relatively longer, and so is the prepubis. Subsequent R. gemmingi specimens either return to the short femur/short(er) prepubis morphology, or the part(s) are missing so comparisons cannot be made so well in the employed specimens. Future reconstructions of more specimens are the next steps in this study.

Other ideas are always welcome.

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
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I and II]. Ph.D. thesis, University of Kansas [Published by University Microfilms International/ProQuest].
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. – Palaeontographica, Abteilung A, 260: 1-112. Part II. Functional morphology. – Palaeontographica, Abteilung A, 260: 113-153.
Claessens, LPAM, O’Connor PM and Unwin DM 2009. Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism. PLoS ONE 4(2):e4497. http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004497
Seeley HG 1901. Dragons of the air. An account of extinct flying reptiles. London, Methuen: 1-240.
Tischlinger H and Frey E 2002. Ein Rhamphorhynchus (Pterosauria, Reptilia) mit ungewöhnlicher Flughauterhaltung aus dem Solnhofener Plattenkalk. Archaeopteryx, 20, 1-20.
Wellnhofer P 1974. Campylognathoides liasicus (Quenstedt), an upper Liassic pterosaur from Holzmaden – the Pittsburgh specimen. Annals of the Carnegie Museum, Pittsburgh, 45:5–34.

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