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Cladistics: The Tree(s) of Life A cladogram is a diagram that shows how organisms are related in terms of their evolutionary development. A cladogram can be thought of as a family tree for a group of related organisms. Cladistics is a rapidly evolving science. As scientists learn more about the DNA and proteins of living organisms, they reorganize cladograms such that related organisms are grouped together based on molecular similarity. Bracketed organisms are most closely related and share the most recent common ancestor. For example, in the Cladogram of Eukaryotes, animals and fungi share a more recent common ancestor with each other than they do with plants and other eukaryotes. Protolife Cladogram of All Living Things Archaea (halophiles, methanogens, extremophiles) Eubacteria (true bacteria) Eukaryotes (plants, animals, fungi, protista) More Ancient Cladogram of Metazoa (Animals) Bilateria (most animals) Cladogram of Eukaryotes Cnidaria (jellies, anemones, Metazoa (animalia) corals) Fungi (mushrooms, Ctenophora (comb jellies) molds) Porifera (sponges) Stramenopiles (diatoms, brown algae) Alveolates (dinoflagellates, ciliates) Rhodophyta (red algae) Plantae (green plants) More recent Cladogram of Bilateria Deuterostomia (echinoderms and vertebrates) Arthropoda (insects, spiders, crabs) Onychophora (velvet worms) Nematoda (roundworms, C. elegans) Nematomorpha (horsehair worms) Priapulida (penis worms) ? Rotifera (rotifers) ? Platyhelminthes (flatworms, tapeworms) Annelida (segmented worms, earthworms, leeches) Sipuncula (peanut worms) Mollusca (clams, snails, octopi, mussels, squid) Notice that Bilateria include several different phyla of animals called worms. C. elegans and other nematodes are worms, but they are different (genetically and physiologically) from other worms such as the annelids or platyhelminthes. “Worm” tends to be used generically to refer to animals sharing a “worm-like” shape. The cladogram for Bilateria is abbreviated (some phyla were not included to save space). Cladistics: The Tree(s) of Life BABEC 6/6/10 Page 2-11 Cladistics: The Tree(s) of Life This page intentionally left blank Cladistics: The Tree(s) of Life BABEC 6/6/10 Page 2-12
