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Essay / Research Paper Abstract
This 4 page paper addresses the evolutionary pathway of the jawed and jawless fish. Bibliography lists 3 sources.
Page Count:
4 pages (~225 words per page)
File: AM2_PP674787.doc
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Unformatted sample text from the term paper:
during embryonic development in the blastopore phase Deuterostomes develop an opening that ultimately becomes the anus. In protostomes, in contrast, this first opening becomes the mouth. For Deuterostomes,
however, the mouth develops from the second embryonic opening. Within the Superphylum Deuterostomia there are four, possibly five, Phyla still in
existence. These are the Chordata, the Echinodermata, the Hemichordata (acorn worms), and the Xenoturbellida. The fifth Phylum that might be classified here is the Chaetognatha, the arrow worms
(Thuesen, 2009). Our understanding of the worlds seas and oceans and the organisms that live there has
evolved considerably over the years. There have been many significant events that added to our knowledge of marine biology. One of the more notable of these events was
the discovery of fossil remains that proved vertebrates originated in salt water as opposed to freshwater as was originally thought. Fossils of the earliest known vertebrates were those of
the ostracoderms which existed during the Ordovician period about four hundred and sixty million years ago (Thuesen, 2009). By this time in the evolutionary line the gnathostomata had separated
and developed a different line (Holland, 1998). Scientists contend that these early vertebrates evolved from an echinoderm-like ancestor from the Ehchinodermata Phylum, a Phylum that includes such animals
as sea urchins, starfish, and sea cucumbers. The Chordata Phylum, of course, encompasses vertebrate animals. Within the Chordata Phylum there are urochordates, cephalochordates, and agnathans (jawless fish).
Part of the evidence supporting the evolution of Chordates from an Echinoderm like ancestor is the fact that both chordates and hemichordates
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