The Three Heavily Skeletonized Evolutionary Faunas Of Phanerozoic Marine Taxa
Redrawn from Sepkoski, J.J. Jr, 1984, A kinetic model of Phanerozoic taxonomic diversity, III.
Post Paleozoic families and mass extinctions: Paleobiology 10:246-267.
This graph shows the distribution through the past 600 million years of the three main faunas (all the animals living at some time or place) of skeletonized (and easily fossilized) animals. These include; 1) an ancient Cambrian fauna (yellow, with only a few survivors today), 2) the Paleozoic fauna (green, now relatively rare), and the 3) Modern fauna (blue, and still rapidly expanding). The purple field is the record of soft bodied organisms.
Observe at the end of the Cambrian the Cambrian fauna (yellow) begins to decline, while the Paleozoic fauna (green) explodes in abundance and diversity in the Ordovician. The transition was not accompanied by a significant extinction (the 5 numbered arrows) and the exact causes of the changes are still strongly debated.
The change in the fossil record resulted in a significant change in the rock record, especially in carbonate rocks.
Contributed by Lynn Fichter