Earth Sciences 2266F/G Lecture Notes - Lecture 6: Heterostraci, Pine Nut, Sawfish
26 Jul 2016
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Document Summary
By devonian time, all of the armoured plates started to diversify, and heterostracans come into play. Diverse shapes of armoured plates in the body. Instead of bumps they started to have ridges and concentric rings. Tail side is covered with smaller plates for more flexibility. This is a jawless fish, and similar to a modern sawfish, have a long structure at the front for sensing things, full of nerve endings and sensory cells similar to the lateral line. They can plow through the bottom of the water and sense where the food is. These 2 orgs are not related but have similar way of life so develop same type of structure. Some started to become better swimmers as they developed a more streamlined body and less of a large flat head. Another group related to this are anaspids and thelodonts. They can move very fast; entire bodies don"t have big armours anymore, now only small scales.
