Back to Basics - The Importance of Basal Taxa

Look at this cladogram (copy of 'Cladogram 2 - Cichlidae' from last exercise). You'll notice that group of fish from Madagascar come right off the base of the tree. This is called a basal taxon. These fish are especially important for conservationists because they retain many of the characteristics believed to be present in the ancestral species. This can help biologists identify the factors responsible for variations in groups that have appeared more recently. For its small size, Madagascar is home to many basal taxa (forms of organisms that have retained many of their primitive characteristics).

What is a primitive characteristic?

In groups of organisms, primitive characteristics appear in a large number of diverse animals that separated a long time in the past. The five fingers of a human hand (for example) are a primitive characteristic shared with a wide variety of different mammal groups, including various rodents (e.g. squirrels), insectivores (e.g. shrews), carnivores (e.g. raccoons) and marsupials (e.g. possums).

What is a derived characteristic?

The hoof of a horse is a derived characteristic that evolved from hand-like feet.

The fossil record shows how the multiple 'fingers' of a horse slowly became reduced until horses ran on a single digit with a giant fingernail, the hoof.

© 2007 Wildlife Conservation Society