Lab 7 - Fish and Amphibians

Lab 7 - Fish and Amphibians - LAB # 7 FISH, AMPHIBIANS AND...

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A number of animals, both invertebrate and vertebrate, seem to be closely related in terms of their biochemistry and basic structure. These animals, which are believed to have originated from free-swimming echinoderm larva, may be divided into several phyla. The most important fossil forms include the Phyla Conodonta (conodonts), Hemichordata (acorn worms and the extinct graptolites) and the Chordata (the most important of which are vertebrates). Phylum Conodonta Conodonts are tiny tooth-, comb- or blade-like fossils made of carbonate apatite; material similar in composition to vertebrate teeth. Due to their distinctive form and abundance in certain marine sediments, conodonts have been widely utilized as index fossils. Their range extends from the Cambrian through the Upper Triassic. Three types of conodont fossils can be distinguished. These include simple, tooth-like forms (Cambrian-Ordovician); row types with a bar- or blade-shaped base, a larger main cusp and numerous denticles; and platform types with a plate-like base. The latter two morphological groups range from the Ordovician through the Triassic. Although often forming tooth-like structures, the peculiar growth of the conodont elements and lack of wear indicates that they are not teeth. The conodont structures may have acted as supports for soft tissues. Until recently, the relationships of the conodonts were unknown. However, the discovery of a 40 millimeter long eel-like fossil with conodont-like structures imbedded in it's soft tissues has apparently settled the question of conodont affinities. The recovery of this unusual Mississippian-age fossil indicates that conodonts are closely related to the Phylum Chordata. Phylum Hemichordata The hemichordates include the modern acorn worms and their extinct relatives, the graptolites. Graptolites (Class Graptolithina ; Lower Cambrian- Mississippian) are the only hemichordates with a substantial fossil record. They consist of extinct colonial organisms with chitin-like skeletons. A portion of their life was spent as sessile benthonic organisms and at other times they were planktonic. They were most abundant in the Ordovician and Silurian, where they serve as index fossils. Graptolites are usually preserved as carbonized "pencil mark"- like structures on the bedding surfaces of shales. Phylum Chordata The Chordata differ from the groups previously studied in lab by the presence of a dorsal nerve cord, gills and notochord at some stage during the life history of the animal. The notochord is a flexible, rod-like structure which generally extends from the base of the skull to the back of the tail and serves as an anti-telescoping device during muscle contraction and for tissue support. Subphylum Vertebrata
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This note was uploaded on 01/16/2012 for the course GEOL 106 taught by Professor Dr.phillipmurphy during the Fall '10 term at Tarleton.

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Lab 7 - Fish and Amphibians - LAB # 7 FISH, AMPHIBIANS AND...

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