Geologic period: Devonian
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The lobe-finned Eusthenopteron is another of an important group of animals that developed and thrived in the Devonian: Like Ichthyostega and Acanthostega, Eusthenopteron has a number of physical developments that presage land-dwelling animals. The skeleton of Eusthenopteron includes a distinct humerus, ulna, and radius in the pectoral fins, and a femur, tibia, and fibula in the pelvic fin.
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Some illustrations of Eusthenopteron show the animal crawling from the water onto land. Scientists discount this possibility, however, and believe Eusthenopteron was in fact a deep-water dweller.