Skull material of the prosauropod dinosaur Massospondylus, previously known only from Africa, has been found in the Kayenta Formation (Glen Canyon Group) of northeastem Arizona.A reconstruction of the skull, corrected for distortion, is compared with that of Plateosaurus. The dentition provides evidence for an herbivorous diet in pro sauropods; the presence of small palatal teeth is reported for the first time in any dinosaur. The associated fauna is related to faunas from the Elliot and Clarens sandstone formations in southern Africa, and an Early Jurassic (rather than Late Triassic) age is accepted for these formations as well as for the Kayenta Formation.

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...

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SynopsisA description is given of a new genus of mammal-like reptile, Mirotenthes, of which a remarkably complete and well-preserved skeleton was collected in 1936 by Professor Camp of the University of California, from the late Permian deposits of the South African Karroo.Unlike the majority of Permian mammal-like reptiles, Mirotenthes was an agile form of small dimensions. Many of the skeletal characters exhibit a significant approach towards the mammalian threshold. The limb structure is very advanced and the digital formula is mammalian. The differentiation of ribs to form a definite rib-cage of mammalian type is particularly noteworthy and may indicate the presence in this genus of a mammalian respiratory mechanism.The systematic study of this complete skeleton does much to bridge the gap between the primitive basal groups of mammal-like reptiles and the advanced Triassic groups from which the mammals derive. It has been known for many years that small, fast-moving carnivorous forms were present in the late Permian fauna, but the evidence has been fragmentary. The complete skeleton described in this paper throws new light on these hitherto poorly known genera.

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