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About 375 million years ago (found in 2004)Reputable source · 2 sourcesWell documented

Tiktaalik: the fish that was becoming something else

On the timeline · around About 375 million years ago (found in 2004) · The Devonian: Age of FishesThe Devonian: Age of FishesTiktaalik: the fish that was becoming something else385 Ma382.5 Ma380 Ma377.5 Ma375 Ma372.5 Ma370 Ma367.5 Ma365 Ma

What happened

In 1998, paleontologist Neil Shubin was flipping through an undergraduate geology textbook when he noticed a map of Devonian-age rock outcrops, one of them in the Canadian Arctic, largely unexplored. After finding an old paper comparing that site's geology to formations he already knew, Shubin's team spent several difficult field seasons searching Ellesmere Island for fossils of exactly the age they needed, at the edge of their funding, before finally finding what they were looking for in 2004: Tiktaalik roseae, a nine-foot fish with a flat, crocodile-like skull, gills, and, on top of its head, air-breathing nostrils called spiracles. Its fins carried fish-like rays for paddling, but inside them sat sturdy bones corresponding to an upper arm, forearm, and even a wrist, along with a hip and pelvis built sturdier than a fish preparing to swim should need.

Why it matters

Tiktaalik shows evolution's transitions caught in the act: a fish already carrying the load-bearing joints a limb would need before it ever had to bear weight on land. Finding it exactly where geological reasoning said fossils of the right age should be, rather than by chance, remains one of paleontology's clearest demonstrations that the fossil record can be predicted, not just stumbled upon.

How we know

The claim rests on the fossil's own skeleton: wrist and forearm-like bones embedded inside what is otherwise a fish's fin, described from multiple specimens recovered on Ellesmere Island and published in Nature in 2006. Its pelvic anatomy, described from later specimens, showed hindlimb-supporting structures more developed than researchers initially expected from a still-finned animal.

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Part of a timelineLife Conquers the Land7 events · The 160 million years between the Cambrian explosion and the dinosaurs, when plants, jaws, limbs, and the amniotic egg turned a planet of water into one of forests and dry land.View all →
Tiktaalik: the fish that was becoming something else · Life Conquers the Land · SourcedStory