Acanthostega (Greek for "spiky roof"); pronounced ah-CAN-tho-STAY-gah
Rivers and swamps of the northern latitudes
Late Devonian (365 million years ago)
Size and Weight:
About 2 feet long and 5-10 pounds
Stubby legs; long tail; eight digits on front and back flippers
One of the best-known of all the Devonian tetrapods--the first fish that climbed up out of the water and onto dry land--Acanthostega nevertheless seems to have represented a dead end in the evolution of early vertebrates, the giveaway being that this creature had eight primitive digits on each of its stubby flippers, compared to the modern standard of five. Despite its classification as an early tetrapod, it's possible to oversell the extent to which Acanthostega was a land animal. Based on certain anatomical features--such as its fish-like teeth and the "lateral line" sensory apparatus running along the length of its slender body--this tetrapod probably spent most of its time in shallow water, using its rudimentary legs only to crawl from puddle to puddle.