On the origin of the sauropods and the classification of the Saurischia

Abstract

SUMMARY. Existing classifications of the Saurischia are briefly reviewed. The sauropods of the later Mesozoic are generally considered to have originated from the prosauropods of the Upper Trias–the Thecodontosauridae, Plateosauridae and Melanorosauridae. The Melanoro‐sauridae have been rightly recognized as the family which is most like the sauropods, and have therefore been considered transitional between the better known Thecodontosauridae and Plateosauridae on the one hand and the sauropods on the other. Re‐examination of melanorosaurid material in South Africa shows that none is properly associated and that the proportions cannot be determined. Information is given on undes‐cribed skeletons and trackways, all from the lower part of the Stormberg Series; the most interesting are the quadrupedal ‘Soebeng trackways’, just like those of Jurassic sauropods. The Stormberg sauropodomorphs are listed. Present concepts of sauropodomorph phylogeny, embodying the evolutionary series pseudosuchian → thecodontosaurid → plateosaurid → melanorosaurid → sauropod, are incompatible with the stratigraphical position of the Melanorosauridae below the Thecodontosauridae (in South Africa). There is no evidence to suggest that the sauropod line of evolution was other than purely quadrupedal, i.e. the sauropods were not quadrupedal reversions from bipedal forbears. The various prosauropods were partly bipedal offshoots from this main quadrupedal line, undergoing adaptive radiation and extinction in the Trias. The similarity of their teeth to those of sauropods is only partial and superficial, and probably has no phylogenetic significance. Triassic carnosaurs, hitherto placed in the Palaeosauridae and Teratosauridae, differ considerably from the later carnosaurs; it is only the nature of their teeth (where known) which has led to their classification as carnosaurs, the post‐cranial skeletons of palaeo‐saurids and teratosaurids being virtually indistinguishable from those of the contemporary thecodontosaurids and plateosaurids respectively. Only because these Triassic forms were so like the prosauropods was it thought that all Carnosauria and the Sauropodomorpha were of common origin. But in the Teratosauridae there is no proven association of teeth with post‐cranial skeleton, and in the Palaeosauridae (here called Gryponychidae) the teeth are unknown; further, even if these prosauropod‐like skeletons are correctly associated with carnosaur‐like teeth, it could mean no more than that the prosauropods included both carnivores and herbivores. Some post‐cranial ‘teratosaurid’ material from China and England is referred to the Melanorosauridae, greatly extending the geographical and strati‐graphical ranges of that family. The Gryponychidae and all other supposedly teratosaurid post‐cranial remains are also transferred from the Carnosauria to the Prosauropoda. The respective stratigraphical‐geographical ranges confirm that it is not easy to separate either the Gryponychidae from the Thecodontosauridae or the post‐cranial remains of ‘Terat...

The origin and early radiation of dinosaurs

“…These groups are still recognized as the two major subdivisions of dinosaurs. However, for much of the 19th and 20th centuries paleontologists considered saurischians and ornithischians to represent separate lineages, which independently diverged long ago from separate "thecodont" (a term applied to an illdefined assemblage of primitive archosaurs) ancestors and thus were not particularly closely related (e.g., Colbert, 1964;Charig et al, 1965;Romer, 1966). Thus, in a cladistic sense, dinosaurs were seen as a polyphyletic (non-natural) group.…”

III: Mesozoic Mammals

“…The upper Red Bed vertebrate fauna is dominated by small and large prosauropods (Charig, Attridge, and Crompton 1965). Less numerous elements are the advanced mammallike reptiles, tritylodonts (Ginsberg 1962), ictidosaurs (Crompton 1958), primitive crocodiles (Nash 1975), and a few thecodonts (Walker 1972).…”

Fossil plants from Allan and Carapace Nunataks, and from the upper Mill and Shackleton Glaciers, Antarctica

“…1, 2 only;Townrow, 1957), or Voltzio'Psis Potonie (e.g., Carpentier, 1935 as Voltzia). (ii) The species that are present are those found in the Molteno, probably upper Middle Triassic (Charig, Attridge, and Crompton, 1965), or the Ipswich Coal Measures, usually dated Middle and Upper Triassic (Jones and de Jersey, 1947;de Jersey, 1962). (iii) Species found so far only in the Rhaetic, such as Pa'chypteris crassa and Dicroidium obtusifolium are absent, though some species found along with them are present, for example D. feistmanteli (in its larger leaved form).…”