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Unformatted text preview: 1 Vertebrates occur within the Phylum Chordata, a deuterostome (anus forms from the blastopore) group within the clade Bilateria, known for its amazing series of homologous structures. Analysis of homologies is fundamental to evolutionary biology because it is instrumental in learning how structures evolve. This is apparent in the field of systematics, where homologous structures are used as evidence of common descent. For instance, the existence of homologous forelimbs in land vertebrates indicates their phylogenetic affinities, as does the existence of ctenidia in molluscs and strobili in higher plants. Similarly, lack of homology between the mandibles of insects and crustaceans argues against their inclusion in the same clade (a monophyletic group). All organisms within the Phylum Chordata share four basic homologous structures. These structures are known as the four hallmark characteristics of chordates and include: 1) pharyngeal gill slits, 2) post-anal tail, 3) dorsal, hollow nerve tube, and 4) notochord. Although all chordates share these four characteristics, many species have reduced some of these traits or only possess them during embryonic development. In today’s lab we will compare the anatomies of five vertebrate species, focusing on the similarities and differences in homologous structures between species. Objectives Know the four hallmark characteristics of chordates Understand the concept of homologous structures Understand the vertebrate body plan Materials Dissecting tools Demo specimens to observe & compare: Lamprey, Dogfish shark, Bony fish, Mudpuppy, Turtle Specimen to dissect : Rat BSC2011 Lab 9 Vertebrate Comparative Anatomy BSC 2011 Lab 9 – Comparative Vertebrate Anatomy 2 Rat Rat Anatomy Dissection Procedure to open the body cavity : 1. Make a small incision with a pair of scissors just above the end of the sternum (see diagram). Do not cut too deeply (not more than 4-5mm) into the body cavity or you will damage the underlying tissues/organs (tip: keep the tip of your scissors pointed upwards while you cut to prevent cutting too deeply). 2. With your scissors, cut through the abdominal wall of the rat following the A line on the drawing below. Do not cut the diaphragm (the thin layer of muscle that separates the thoracic cavity from the abdominal cavity). Instead cut along a line laterally (B line) just slightly above the diaphragm (in the thoracic cavity). Also cut laterally for lines C and D to allow you to open up the cavities and observe the underlying structures....
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- Fall '11
- Comparative Anatomy, Gill, Testicle, comparative vertebrate anatomy, Vertebrate Comparative Anatomy