Before the discovery of Tiktaalik we knew that limbed animals (tetrapods) were well along their way to invading land by the Late Devonian (around 360 million years ago). We also knew that some fish in the Middle Devonian (375 million years ago) were experimenting with the internal structure of their fins in ways that would ultimately allow for the evolution of the weight bearing structure of tetrapod limbs. The thought was that as the habitat in the Devonian changed and became drier, fish with limb-like fins were able to survive and propagate because they were able to move from pond to pond over land in search of food and new habitats.

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