BIOL 1101 Lecture Notes - Lecture 81: Protist, Archaea, Coenocyte
27 Jun 2016
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Document Summary
The bacteria and archaea are well-accepted taxa and are relatively easy to define. They used to be a kingdom called the protista, but now have been demoted to an informal grouping of eukaryotes that are single- celled or are related to those that are single-celled. This creates a group ranging from single-celled protozoans to giant seaweeds. The protist group causes disagreement because it is not monophyletic. It is a catchall group for what are probably many eukaryotic, unicellular lineages. Molecular studies (especially using ribosomal rna) have revolutionized our ideas about protistan relationships since the mid-1990s. Ideally, molecular data would identify monophyletic groups that have distinctive, obvious characteristics (e. g. , mammals, birds, and fish). These three animals all underwent convergent evolution and they all look alike, even though they have different evolutionary ancestry. In order to classify them correctly, we have to ignore their superficial similarities and look at more obscure characteristics, such as whether they have feathers or mammary glands.
