Publication Date
7-29-1983
Series Number
189
Abstract
Two incompfete skeletons and other isolated bones of Dimorphodon macronyx (Buckland), an early rhamphorhynchoid pterosaur from the Lower Lias (Hettangian) of England, have remained undescribed in the collections of the Peabody Museum of Natural History since their acquisition by O. C. Marsh over a century ago. Some of this material comes from Aust Cliff near Bristol, and therefore constitutes the first record of Dimorphodon outside the Lyme Regis area of Dorset. The two individuals are smaller than those in the British Museum (Natural History) described by Owen, and juvenile proportions characterize both cranial and postcranial remains. Much of the material is three-dimensional and has been prepared from its matrix; it provides some of the fullest structural and functional information available for any pterosaur. A particularly well-preserved humerus gives insight into the articulations and folding of the wing, and two sets of distal tarsals demonstrate the mesotarsal flexion of the ankle. Comparison with more extensive but less fully prepared material in the British Museum (Natural History) allows some osteological identifications to be established or corrected; it also provides the basis for a new assessment of structure and function in pterosaurs. The forelimbs could not have moved parasagittally but were well suited for an active flight stroke. The hindlimbs were positioned and moved like those of bipedal dinosaurs and birds. The feet were digitigrade and were not adapted to hang fromtreesorcliffs.Comparativeosteology indicates that these features and abilities conform very well to an "advanced archosaurian" Bauplan seen in dinosaurs and birds.