Boston University Biologist Lynn Margulis in the 1960's and officially in her 1981 book " Symbiosis in Cell Evolution ". • Although now accepted as a plausible theory, both she and her theory were ridiculed by mainstream biologists for a number of years. Thanks to her persistance, biology can now offer a plausible explanation for the evolution of eukaryotes Mitochondria were descendents of Mitochondria were descendents of free-living, oxygen-using bacteria free-living, oxygen-using bacteria that invaded eukaryotic cells 1.4 that invaded eukaryotic cells 1.4 billion years ago. billion years ago. Evidence Evidence Mitochondria have their own DNA and Mitochondria have their own DNA and ribosomes. ribosomes. Mitochondria reproduce through Mitochondria reproduce through division, like bacteria.
60 Proterozoic Eon • Multicellular eukaryotes arise 1.5 bya • 2 possible origins – Individuals form a colony – Single cell divides and stays stuck together • Volvocine green algae display variations in the degree of multicellularity • Multicellular animals emerge toward the end of the eon • First animals were invertebrates – Bilateral symmetry facilitates locomotion
62 Phanerozoic Eon • Proliferation of multicellular eukaryotic life extensive during Phanerzoic Eon (543 mya to today) – Paleozoic Era – Mesozoic Era – Cenozoic Era
Life forms in the Paleozoic were affected by a combination of geologic and biologic events, principally plate tectonics and evolution – spans range from the appearance of marine skeletonized animals to complex reptile and plant development on land Paleozoic Biota
64 Phanerozoic Eon, Paleozoic Era 543-248 mya • Cambrian period • Ordovician period • Silurian period • Devonian period • Carboniferous period • Permian period
65 Phanerozoic Eon, Paleozoic Era, Cambrian Period • 543-490 mya • Warm and wet with no ice at poles • Cambrian explosion – abrupt increase in diversity of animal species – Cause unknown – shell evolution, atmospheric oxygen? • All existing major types of marine invertebrates plus many other that no longer exist • Although new species have arisen since, no major reorganizations of body plans • First vertebrates 520 mya
66 The Cambrian Explosion & the Burgess Shale
The Burgess Shale Biota one of most important fossil finds Consists of a rare preservation of soft- bodied organisms – these phyla represent the basic stock from which all present-day invertebrates have evolved & even primitive chordates The Burgess Shale located in the Rocky Mountains, British Columbia, Canada.
The Burgess Shale Biota Fossil of Ottoia , a carnivorous worm, Phylum Pripulida Worm Arthropod Trilobite Velvetworm-like arthropod Earliest known primitive chordate Sponge predator Homalozoa
69 Phanerzoic Eon, Paleozoic Era, Ordovician Period • 490-443 mya • Warm temperatures and atmosphere very moist • Diverse group of marine invertebrates including trilobites and brachiopods • Primitive land plants and arthropods first invade land •
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- Summer '19
- On the Origin of Species, Extinction event, Cretaceous–Tertiary extinction event, Geological history of Earth