The anatomy of the internal nares indicates that an arrangement of Jacobson’s organ and associated nerves, blood vessels and glands comparable to that of monotremes was present and an attempt is made to interpret its anatomy in functional terms.
An incomplete skull and postcranial skeleton of the traversodontid cynodont Luangwa drysdalli Brink, from the Middle Triassic Ntawere Formation of Zambia, shows that the region of the orbit, and the braincase show certain tendencies towards mammalian structure.
It is proposed that the carnivorous therapsids should be classified into two equal ranks, the Gorgonopsia and the Theriodonta and that they were probably derived separately from the sphenacodont pelycosaurs.
Procynosuchus indicates that the dual-gait mechanism of the hindlimb was functionally intermediate between a primitive sprawling gait and the obligatory erect gait of the later cynodonts.
ABSTRACT The braincase and endocranial cavity of a specimen of a nonmammalian eucynodont Chiniquodon is described and illustrated, and a tentative reconstruction of the gross anatomy of the brain…
The fossil record of the Mesozoic Mammals is dominated by two groups of animals, the Mammal like Reptiles and the Living and Fossil Marsupials, which are related to each other and have different evolutionary histories.
The correlated progression model is tested by the nature of the integration between the parts as seen in living mammals, by computer simulations of the evolution of complex, multifunctional, multifactorial biological systems, and by reference to the synapsid fossil record, which is fully compatible with the model.
It is argued that the organization of the cynodont skull can be seen as a logical functional development from the more primitive condition, and in particular, the streptostylic nature of the jaw articulation, the enlargement of the dentary and reduction of the postdentary bones, may all be correlated with the development of a masseter muscle.
It is argued that the current views are variously based on an overemphasis of superficial dental similarities, misinterpretation of the structure of the mammalian braincase, and too ready acceptance of parallel evolution amongst the groups concerned.
An hypothesis is presented in which the origin of the therapsids resulted from a correlated progression of character evolution leading to higher levels of metabolic activity and homeostatic regulation of the body.