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Lab 9 - Fish and Amphibians

Lab 9 - Fish and Amphibians - PALEO LABORATORY 9 PAGE 1...

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PALEO LABORATORY # 9, PAGE 1 PALEO LAB IX - FISH AND AMPHIBIANS 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. The notochord is found in some lower vertebrates and in the embryonic stages of the "higher" vertebrates. However, it is lost during the ontogeny of "higher" vertebrate taxa and is almost never preserved in the fossil record. EXERCISE # 1 - Observe the specimens of primitive chordates provided [TSU VP 234, VP 235, VP 600 (preserved specimen)]. What feature(s) are diagnostic of the Phylum Chordata? Subphylum Vertebrata The vertebrates are advanced chordates in which there is an increased organization of the muscular and nervous systems. They are active, mobile creatures and have evolved systems that reflect this. Vertebrates are bilaterally symmetrical with the long axis of the body usually in a horizontal position. There is a tendency to concentrate sensory organs on the anterior end, the direction which vertebrates move. One of the evolutionarily significant morphological features of the Vertebrata is the vertebral column, which strengthens the body and provides a firm foundation for the muscles used in undulatory movement. The vertebral column may be composed of cartilage or bone. Cartilage is soft, translucent material that is confined to deeper layers of the body and is capable of expansional growth. Bone is much stronger than cartilage, it is not capable of "expansional" growth (bone "grows" by replacing a cartilaginous precursor) and bone has many irregular, branching cell spaces not present in cartilage. As cartilage is soft material, it is typically not preserved in the fossil record except where strengthened by calcification. The ancestry of vertebrates has been much debated. Most paleontologists now believe that the echinoderms are at or near the ancestry of vertebrates due to similarities in embryology, biochemistry and the similarity of echinoderm larva to those of primitive chordates. R.P.S. Jefferies, a British paleontologist, believed that the vertebrates came from carpoid "echinoderms", coined the term Calcichordata for that group, and placed them within the Chordata. His interpretation is not accepted by the majority of paleontologists but it certainly shows the similarities between the phyla. The vertebrates may be divided into two morphological groups, the Pisces (fish-like forms, constituting five classes) and the Tetrapods ("four-footed", largely land-dwelling vertebrates, divided into four classes).
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