BIOL1002 Lecture Notes - Lecture 7: Actinopterygii, Pharyngeal Jaw, Amniote
6 Nov 2018
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Document Summary
The first vertebrates appear in the fossil record about 540 million years ago, during the. These early vertebrates lived in the ocean and had craniums made of cartilage. Several key innovations have occurred since in the diversification of vertebrates: The first vertebrates had a skeleton made of cartilage. The first vertebrates with bone evolved about 480 million years ago. These jawless fish had an exoskeleton made of bony plates (not an endoskeleton). They were likely to have swum with a notochord and breathed and fed using pharyngeal gill slits. The first jawed fish are seen in the fossil record about 440 million years ago. Jaw evolution was significant because of the additional feeding opportunities it allowed. Teeth followed soon after, making vertebrates more formidable predators. Jawed vertebrates are collectively known as the gnathostomes. Hypothesis: mutation and natural selection led to the modification of gill arches (flattened regions of bony or cartilaginous tissue between gills) into a jaw.
