To: All Msg #27, Apr0393 12:58PM Subject: a brief history of life I got the information fo

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From: Chris Colby To: All Msg #27, Apr-03-93 12:58PM Subject: a brief history of life Organization: animal -- coelomate -- deuterostome From: (Chris Colby) Message-ID: <> Newsgroups: -------------------------------------------------------------- I got the information for this post from "History of Life" by Richard Cowen (1990, Blackwell Scientific) and a few other sources (ex. "Biology of Plants" Raven, by Evert and Eichhorn). I plan to expand/revise this and insert it into my FAQ. This isn't my field, so any corrections/clarifications are welcome. For now, this is in response to Bird's "abrupt appearance" statement. ------------------------------------------------------------------ One of the postulates of Bird's 'theory' is that life appears suddenly in the fossil record. If by this Bird means that the flora and fauna of today appear long ago and survive until present, he is sadly mistaken. If his theory is supposed to mesh with a single event creation scenario -- the fossil record lends him no support. Rocks as old as 3.5 Billion years old have yielded prokaryotic fossils. Specifically, some rocks from Australia called the Warrawoona series give evidence of bacterial communities organized into stromatolites; these mats of bacteria still form today in a few locales (for example, Shark Bay Australia). Bacteria are the only life forms found in the rocks for long, long time. Fungi-like things appear about 900 MYA (0.9 Billion years ago). Prior to the Cambrian (~600 MYA), animals start appearing; the Ediacarian animals dating from just before the Cambrian are found in rocks near Adelaide, Australia. It is unclear if these forms have any surviving descendents. Some look a bit like Cnidarians (jellyfish, sea anemones and the like). The Cambrian 'explosion' produced a wide variety of animals. Probably all the phyla (the second highest taxonomic category) of animals appeared around the Cambrian. Some paleontologists think more animal phyla were present then than now. The animals of the Burgess shale are an example of Cambrian animal fossils. These fossils, from Canada, show a bizarre array of creatures. Although creationists are fond of pointing to the Cambrian explosion as evidence of their views -- they ignore four things 1.) Evidence of life (including animals) prior to the Cambrian 2.) Although quick, the Cambrian explosion is not instantaneous in geologic time 3.) Although all the phyla of animals came into being, these were _not_ the modern, derived forms we see today. Our own phylum (which we share with other mammals, reptiles, birds, amphibians and fish) was represented by a small, sliver-like thing called _Pikia_. 4.) Plants were not yet present. The Cambrian explosion is not evidence of a single creation event producing the current biota. Following the Cambrian, the number of marine families leveled off at a little less than 200. The Ordovician explosion (~500MYA) followed. This 'explosion', larger then the Cambrian, introduced numerous families of the Paleozoic fauna (including crinoids, articulate brachipods, cephalopods and corals). The Cambrian fauna, (trilobites, inarticulate brachiopods, etc.) declined slowly during this time. By the end of the Ordovician, the Cambrian fauna had mostly given way to the Paleozoic fauna and the number of marine families was just over 400. It stayed at this level until the end of the Permian period. Somewhere in between these two points, plants and fungi (in symbiosis) invaded the land (~400 MYA). At the same time, or shortly thereafter, arthropods (ex. myriapods) followed. By the Devonian period (~380 MYA) vertebrates had moved onto the land, _Ichthyostega_ is the among the first known land vertebrates (an amphibian). It was found in Greenland and was derived from lobe-finned fishes called Rhipidistians. The Permian extinction (~250MYA) was the largest extinction in history. The last of the Cambrian Fauna went extinct. The Paleozoic fauna took a nose dive from about 300 families to about 50. It is estimated that 96% of all species in existence met their end. Some estimate that as many as 50% of all families went extinct (you have to kill of 100% of the species in a family before it goes extinct, hence the difference between the two numbers.) Following this event, the Modern fauna, which had been slowly expanding since the Ordovician, took over. The Modern fauna (including fish, bivalves, gastropods and crabs) was barely affected by the Permian extinction and increased to over 600 marine families at present. (The Paleozoic fauna held steady at about 100 families.) A second extinction event shortly following the Permian kept animal diversity low for awhile. Amphibians gave rise to reptiles, animals with scales to decrease water loss and a shelled egg permitting young to be hatched on land. Among the earliest well preserved reptiles is _Hylonomus_, from rocks is Nova Scotia. During the Jurassic (~200 MYA) and Cretaceous (~150MYA) periods the dinosaurs ruled and flowering plants (angiosperms), together with insects, diversified. The end of the Cretaceous (~65 MYA) is marked by a minor mass extinction that was the demise of all the lineages of dinosaurs save the birds. Once the dinosaurs were out of the picture, mammals -- previously confined to nocturnal, insectivor- ous niches -- diversified. One eventual outcome of this diversification was the evolution of primates including one species with diminished fur growth, the ability to brew beer and have pizza delivered to their domicile. A lot has been written about humans, primarily because humans have been the only ones doing the writing. Some, filled with vanity but devoid of knowledge, see the need to postulate miraculous mechanisms for their existence. Others see the need to drink more beer and order more pizza. You make the call. Chris Colby --- email: --- "'My boy,' he said, 'you are descended from a long line of determined, resourceful, microscopic tadpoles--champions every one.'" --Kurt Vonnegut from "Galapagos"


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