Adaptive Radiation Cambrian Explosion Cambrian Explosion Early Paleozoic
Adaptive Radiation
Cambrian Explosion
Cambrian Explosion
Early Paleozoic era (Cambrian period) Late Proterozoic eon 542 Cnidarians Sponges 500 Arthropods Molluscs Annelids Brachiopods Chordates Echinoderms Millions of years ago Fig. 25 -10
Fig. 25 -18 Close North American relative, the tarweed Carlquistia muirii Dubautia laxa KAUAI 5. 1 million years MOLOKAI OAHU 3. 7 LANAI million years 1. 3 MAUI million years Argyroxiphium sandwicense HAWAII 0. 4 million years Dubautia waialealae Dubautia scabra Dubautia linearis
Studying Hawaiian Drosophila Dawkins on Hawaiian Drosophila
Melawi eye biter Scale-eating cichlid
Placental and marsupial mammals radiated soon after dinosaur extinction, AND after many other mammal lineages also went extinct (see next slide)
Radiation due to key character evolution?
Russell 1968
4 genera appeared over a 2 my period Pappogeomys, Cratogeomys, and Orthogeomys diverged over 800, 000 years Molecular data also support a relatively rapid radiation…
From Korth 1994 Tertiary Record of Rodents of North America • The fossil record indicates rapid radiation leading to modern pocket gopher genera in the Blancan • Radiation corresponds with increase in hypsodonty and expansion of grassland
Maybe expansion of Blancan grasslands was responsible for pocket gopher radiation?
Replicated sister-group comparisons: allow a more refined approach to assessing “key characters” as causes of adaptive radiations Both clades of herbivorous insects are more taxonomically diverse than their sister groups This pattern was seen in 11 of 13 sister group comparisons of herbivorous vs. other
Example radiation: Land plants are a monophyletic group that has evolved fit many ecological niches
Waxy cuticle prevents water loss Stomata allow gas exchange through the waxy cuticle
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