Abstract

Multiple pterosaur specimens have revealed details of their soft tissue anatomy, including wing membranes supported internally by strengthening fibres (aktinofibrils), a hair-like integument across their bodies, necks and heads (pycnofibres), elaborate soft-tissue head crests, tail vanes and other structures. These have enabled a more comprehensive picture of them as living animals than skeletal remains alone could, though many aspects of the structure and composition of these soft tissues remain controversial.

The histology of pterosaur wing membranes has been a particularly contentious issue, with much debate focused on an alleged portion of wing membrane (DGM 1475-R) from the Lower Cretaceous Santana Formation of northeast Brazil. Initially described as a portion of wing membrane from the proximal wing region by Martill and Unwin (1989), after re-examination of the same specimen Kellner (1996) argued that it represented a piece of body wall. With DGM 1475-R showing features not seen in other specimens of pterosaur wing membrane and being one of the few three-dimensionally preserved portions of pterosaur membrane known, resolving this controversy is key to understanding this important component of pterosaur flight anatomy.

In this study, DGM 1475-R was re-examined in an attempt to clarify the identity of its soft-tissues. Interpretation of the humerus and several ribs associated with the soft-tissue tentatively suggests that the specimen represents a thalassodromid pterosaur. A new section was taken through the soft-tissues and acid etched to highlight histological features. Multiple layers were identified within the soft tissue, including an external epidermis and a layer of muscle. The structures between these layers - numerous objects that appear to be fibres larger than the undoubted muscle fibres - are more ambiguous. These were previously identified as aktinofibrils (Martill et al., 1990), but this is considered unlikely due to differences in the shape, density and distribution of the structures when compared to aktinofibrils in other pterosaur wings. Instead, it is tentatively suggested that they represent a further layer of muscle fibres, but this cannot be conclusively proven. Further comparisons were made between GM 1475-R and a dissected bat wing to find additional diagnostic wing tissues, but they were found to have such fundamental histological differences that such comparisons were of little use.

Aktinofibrils are the only known diagnostic features of pterosaur wings, suggesting that their absence in DGM 1475-R argues against the specimen stemming from the wing tissues. Interpretations of pterosaur wing membrane and flight based on DGM 1475-R being wing membrane are therefore suspect.

Additional Notes

Supervisor: David Martill

Course: Master of Philosophy - MPhil

Date Deposited: 2017-05-09

URI/permalink: https://library.port.ac.uk/dissert/dis12874.html