6.2: From the Beginning - Evolution of Mammals
- Page ID
- 62158
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In this course we will focus on the Anthropoidea, a suborder of primates that includes monkeys, apes and humans. We will concentrate our attention here primarily on monkeys. Colour vision, a large brain and intelligence are of great importance in the lives of anthropoids, enabling them to eat foods inaccessible to many other animals and to exploit social situations. In this course, we will be looking at characteristics of primates that differ, or are enhanced, in anthropoids and discussing these attributes in relation to the evolution of the large anthropoid brain and the evolution of humans.
Mammals come in a bewildering variety of shapes and sizes and yet all of the 4700 or so species have some characteristics in common. Indeed, it's the existence of these common features that justifies the inclusion of all such diverse types within the single taxonomic group (or class) called the Mammalia.
Mammals have also been around for a long time; for example, take the shrew-like 200-million-year-old fossil named Megazostrodon. Rather than shuffling along, with splayed-out limbs in the manner of many reptiles, this animal had limbs that were more erect and aligned under the body. Fossil evidence shows that the skulls of very early mammals have a distinctive lower jaw structure and sites on the skull for the attachment of chewing muscles. We can be confident that between 225 and 195 million years ago, mammal-like reptiles evolved into true mammals, though for the next 100 million years or so these unobtrusive animals, none larger than a pet cat, continued to 'scuttle around the feet of the dinosaurs'. Their diversity did not appear until more than 100 million years later, during a period of geological time that witnessed the demise of the dinosaurs and their close relatives.