may 22, 530000000 BC - Jawless fishes arise

Description:

The very first vertebrates evolve. The eel-like <i>Pikaia</i>, along with the somewhat shorter, flatter <i>Haikouichthys</i> and others, are transitional fossils and hypothesized to be the first fish (and therefore also the first vertebrates). Both have primitive notochords, gills or gill-like structures, and are similar to the present-day hagfish. <i>Pikaia</i> is much more primitive in all of these features, possibly representing an early ancestor, while <i>Haikouichthys</i> is a further derived craniate (having a distinctive head and skull).

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