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SILURAN PERIOD

430 -418 million years ago

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Many of the changes of the nervous and endocrine systems in ancestral sarcopterygians are shared by tetrapods. These changes included a modified cerebrum, a cochlea homolog involved in sound perception, and novel neuropeptides and hormones.

A number of changes evolved in the nervous systems of the sarcopterygian ancestors of tetrapods. The hippocampus modified its position to be located along the medial and dorsomedial wall of the evaginated cerebral hemisphere (Hassler, p. 117). The fornix connected hippocampus and septal region (Hassler, p. 122). The olfactory tubercle possessed the same subdivisions as observed in mammals (Hassler, p. 122). These fish also evolved paleostriatal and nestriatal areas homologous to those in tetrapods (Hassler, p. 127). The lagena from the vestibule functioned in the perception of sound. Autonomic fibers traveled only through the ventral roots of spinal nerves.

Some of the modifications of sarcopterygian hormones and neuropeptides were conserved in tetrapods such as changes in neurohypophysial hormone sequences (Shinohara-Ohtani, 1998), the -MSH sequence in the POMC gene (Lee, 1999), and structural changes of ultimobranchial body (Shinohara-Ohtani, 1998). The distribution of neuropeptide Y, -MSH, and ANF recognition sites in the brains of lungfish is similar to that observed in amphibians. The distribution of FMRF-amide in lungfish brains is more similar to amphibians than other fish (Vallarino, 1998). A duplication of the proenkalphin gene produced prodynorphin in the lineage which produced sarcopterygians and tetrapods (Danielson, 1999). The distribution of -MSH recognition sites in the brains of lungfish is similar to that observed in amphibians (Vallarino, 1998).