PCB-4674 Lecture Notes - Lecture 5: Cladogenesis, Anagenesis, Punctuated Equilibrium
Document Summary
Lecture 5- a brief history of life / fossil evidence. The first fossils of multicellular organisms, jellyfish, appear at about 580 million years ago. The ediacaran fauna (early assemblage of fossils), lived in the years prior to the. All organisms fossilized in this period were radially symmetric. Between this time and about 520 million years ago, most of the major phyla of multicellular organisms we know today first appeared in the fossil record. This period is known as the cambrian explosion due to the sudden appearance of organisms. One of the possible causes of the explosion was the oxygen levels increased due to the abundance of photosynthetic bacteria. The most famous example of cambrian fossils, dated to 520 mya. The last one did in most of the dinosaurs probably due to asteroid impact. Perhaps the largest was the permian one where 90% of all life went extinct: end- permian: 250 mya, k-t: 65 mya.
