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The Anatomy of the Thecodont Reptile Euparkeria capensis Broom

Rosalie F. Ewer

Abstract

The South African Museum specimens of Euparkeria originally described by Broom (1913 a, b) and later studied by Haughton (1922) have been further prepared using the dental mallet. In addition, material in Professor D. M. S. Watson's collection has been prepared and studied. As a result of inquiries made at Aliwal North, it is suggested that all the material may represent a single find and a small exposure of Cynognathus zone shale close to the town is considered to be the most probable location of the site. On the basis of the specimens already mentioned a detailed description of most of the skeleton is given, the only parts remaining unknown, or incompletely known, being the carpus and manus, the braincase and the caudal vertebrae. The following features are discussed in functional terms: skull architecture; the limbs and their girdles; the vertebral column and ribs. The skull, although showing some adaptation to predacious habits, is relatively unspecialized and a subsequent reversal of trend towards a more omnivorous or even vegetarian diet is not impossible. A consideration of the probable arrangement of the jaw muscles suggests that the antorbital fenestra of the archosaurs was not originally evolved in relation to the development of the pterygoideus D musculature. A study of the limbs and their girdles indicates that Euparkeria was facultatively bipedal and that when this gait was adopted the femora were brought into a vertical position, although they must have been held horizontally while at rest or moving slowly. It is suggested that the alteration in position of the rib articulations along the length of the vertebral column is related to efficiency of pulmonary ventilation. Expansion of the tips of the neural spines is shown to be related not to the development of dermal armour but to the arrangement of the muscles of the transversospinalis system. The term `scute tables' used to designate these expansions is therefore abandoned and they are referred to simply as spine tables. The relationships of Euparkeria to other groups is briefly discussed. Euparkeria shows a number of progressive features related to a highly carnivorous habit and increased locomotor efficiency combined with retention of several primitive characters. Previous authors have tended to lay emphasis on one or other of these types of characteristic and accordingly classify Euparkeria either as an advanced form or as a very primitive one: the consequent variation in proposed systematic position ranges from inclusion in the Sphenosuchidae (v. Huene 1962) to the Erythrosuchidae (Hughes 1963). It is concluded that Euparkeria, although a progressive form, is closely related to the latter family with which it may be convenient, for the time being, to classify it. It could well have been directly ancestral to advanced pseudosuchians such as Ornithosuchus and Hesperosuchus and possibly to the prosauropods and sauropods but not to the ornithischians or the birds and was a trifle too advanced to have been directly ancestral to the Aetosauridae, to which it is, however, closely related.

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