The importance of Karoo fossils in the search for mammal origins.

Gow, Chris E.
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Bernard Price Institute for Palaeontological Research
It has long been known that mammals belong to the group Synapsida (more familiar to most in South Africa by the now discredited term Mammal-like Reptiles), a group with a long fossil history, much of which was first established from the Karoo. In palaeontology mammals are traditionally defmed by the possession of a squamosal/dentary jaw joint, as opposed to the quadrate/articular jaw joint of non-mammalian tetrapods. This paper recounts some of the advances in our knowledge of the therapsids (advanced synapsids) over the past 50 years, including the discovery of a sequence offorms leading to those which possess both premammalian and mammalianjaw hinges, transitional forms which thus by defInition qualify as mammals. Briefmention is made of some historical aspects of phylogenetic interpretation, pointing out that some early workers following Darwin, were as aware of the central role of species in phylogenetics as are the disciples of Hennig and Eldredge and Gould. Briefreference is made to the crown group defmition of mammals proposed by Rowe (1988), as it contrasts with the traditional character-based definition. Finally, it is encouraging that modem workers are not only as aware of the problems of distinguishing homology and homoplasy as were earlier workers, but are starting to acknowledge the importance of missing information. In this way, just as the double jaw joint was first predicted and then found, we can actively seek to fill some of the many remaining gaps in our knowledge.
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