BCB311

Thursday, March 16, 2006

PRIMITIVE MAMMALS IN AN EGG OR A POUCH?

The topic of my presentation is primitive mammals. According to Solomon,
Villee and Davis (1985) mammals are thought to have evolved from a group
of reptiles called therapsids. These were dog-like carnivores with legs
adapted for running and differentiated teeth (considered a mammalian
trait). Furthermore the fossil record shows that early mammals were
quite small or similar in size to a mouse or shrew.

Solomon, Villee and Davis (1985) states that by the end of the
Cretaceous period there were three main groups of mammals. These are
currently divided into three subclasses:
Prototheria. egg-laying mammals, also called monotremes.
Metatheria.pouched mammals, also known as marsupials.
Eutheria. placental mammals.
I will limit my presentation to the Prototherians and Metatherians
because they are considered primitive in comparison with the placental
mammals. The latter form of reproduction was last to evolve.

My main aim is to discuss as well as to compare the reproductive
strategies of the above mentioned groups.

Dane McDonald
Department of Biodiversity and Conservation Biology
University of the Western Cape
Private Bag X17
Bellville 7535

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