Tiktaalik lived during the period when freshwater fishes were evolving the adaptations that enabled four-legged animals to live out of water. Tiktaalik may have lived somewhat before or somewhat after the ancestral species that gave rise to all of today’s limbed animals, including humans. The evolutionary lineage that contained Tiktaalik may have gone extinct, as shown in this diagram by the short line branching from the main evolutionary lineage, or it may have been part of the evolutionary line leading to all modern tetrapods (animals with four legs). The last common ancestor of humans and all modern fishes also gave rise to evolutionary lineages that led to modern lobe-finned fishes (represented today by the coelacanth). In this and succeeding figures, time is represented by the lengths of the lines; modern groups of organisms are listed at the top of the figure.

of the features of fish, but it also had traits characteristic of early tetrapods. Most important, its fins contained bones that formed a limb-like appendage that the animal could use to move and prop itself up.

A prediction from more than a century of findings from evolutionary biology suggests that one of the early species that emerged from the Earth’s oceans about 375 million years ago was the ancestor of amphibians, reptiles, dinosaurs, birds, and mammals. The discovery of Tiktaalik strongly supports that prediction. Indeed, the major bones in our own arms and legs are similar in overall configuration to those of Tiktaalik.

The discovery of Tiktaalik, while critically important for confirming predictions of evolution theory, is just one example of the many findings made every year that add depth and breadth to the scientific understanding of biological evolution. These discoveries come not just from paleontology but also from physics, chemistry, astronomy, and fields within biology. The theory of evolution is supported by so many observations and experiments that the overwhelming majority of scientists no longer question whether evolution has occurred and continues to occur and instead investigate the processes of evolution. Scientists are confident that the basic components of evolution will continue to be supported by new evidence, as they have been for the past 150 years.



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