Tiktaalik Temporal range: Upper Devonian
Tiktaalik
Scientific classification
Kingdom:	Animalia
Class:	Sarcopterygii
Subclass:	Tetrapodomorpha
Genus:	Tiktaalik

Tiktaalik is a genus of extinct fish. This sarcopterygian (lobe-finned) fish from the later Devonian has many features similar to those of tetrapods (four-legged animals).

Tiktaalik lived about 375 million years ago. It is part of the transition between fish such as Panderichthys, known from fossils 380 million years old, and early tetrapods such as Acanthostega and Ichthyostega, known from fossils about 365 million years old. Its mixture of basal fish and derived tetrapod characteristics led one of its discoverers, Neil Shubin, to call Tiktaalik a 'fishapod'.

This, and other species like it, prove that legs started to develop before these animals were land-based. They were shallow-water carnivorous fish, or fishapods.Tiktaalik was therefore a transitional fossil, and an example of mosaic evolution.

Neil Shubin, co-discoverer of Tiktaalik, holding a cast of its skull

In the late Devonian, descendants of pelagic lobe-finned fish – like Eusthenopteron – showed a sequence of adaptations:

• Panderichthys, suited to muddy shallows;
• Tiktaalik with limb-like fins that could take it onto land;
• Early tetrapods in weed-filled swamps, such as:
  • Acanthostega which had feet with eight digits,
  • Ichthyostega with limbs.

Descendants also included pelagic lobe-finned coelacanth species.

Discovery site of Tiktaalik fossils, Ellesmere Island