出典:Wikipedia
出典:『Wikipedia』 (2011/06/17 23:37 UTC 版)
The Anaspida ("without shield") are stem gnathostomes, and are classically regarded as the ancestors of lampreys. Anaspids were small marine agnathans that lacked scales and paired fins, but have a striking highly hypocercal tail. They first appeared in the early Silurian, and flourished until the Late Devonian Extinction Event, during the late Devonian, where most species, save for lampreys, went extinct due to the environmental upheaval during that time.