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TETRAPODS

TETRAPODS

Modern tetrapods have not always existed in the fossil record, nor have they existed since the first appearance of fossil tetrapods. The first tetrapods were preceded by fish that resemble them more than do any modern tetrapods. Modern tetrapods form a clade which share a number of features of the skeletal system (modified skull bones, stronger vertebral column, a sacrum, three hip bones, shared bones of the hands and feet), nervous system (a number of new axonal tracts and nuclei, gene duplications of olfactory receptors and the development of a vomeronasal organ), cardiovascular system (an interatrial septum, reorganized blood vessels), muscular system (many muscle groups which are retained throughout tetrapods today), digestive system (salivary glands, a modified esophagus, a glandular cardiac region in the stomach, an ileocecal valve, a duodenum, lacteals, and villi), and respiratory system (lungs with simple squamous epithelia, collagen, and smooth muscle, a short trachea, cartilage around nostrils, conchae, and cartilage of the larynx).

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