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| Description: (a) Ancestral fish and extant jawless fish, such as lampreys, have nine cartilaginous gill arches that support eight gill slits. (b) In early jawed fish, such as the placoderms, the first two pairs of gill arches were lost, and the third pair became modified to form a hinged jaw. This left six gill arches to support the remaining five gill slits, which were still used in breathing. (c) In modern jawed fish, the fourth gill arch is also incorporated into the jaw, allowing stronger, more powerful bites to be delivered.
Picture Stats: Views: 6677 Filesize: 121.07kB Height: 1153 Width: 850 Source: https://biology-forums.com/index.php?action=gallery;sa=view;id=101 Keywords: The evolution of the vertebrate jaw |