About 375 million years ago, the amount of dry land available for habitation across the globe was increasing. One of the first creatures to take advantage of that terrestrial change is called Tiktaalik roseae by scientists. This crocodilelike predator provided an evolutionary bridge between land and sea; it had fins, scales and a jaw like a fish, but it also a neck, head, ribs and portions of other limbs found in land animals. Tiktaalik (tic-TAH-lick) displayed the characteristics necessary for evolutionary adaptation.
When a living creature is introduced to a new environment, it can evolve as a species over time. Its descendants develop characteristics that allow them to cope with the new surroundings and support their survival. This evolution can include adaptations in both body and behavior. Snow leopards, for example, developed spots on their coats through time; spots provided them natural camouflage. They could better conceal themselves from predators as well as from potential prey. Large cats also developed certain behavioral habits, such as crouching in grass to remain hidden from prey and possible predators, to adapt to their environments and ensure their survival.
In its evolutionary movement from sea to land, Tiktaalik developed physical changes in and around his cranium for land adaptation. Moving through water, fish are able to direct their entire bodies in any direction to point their head and mouth toward food sources. In shallow water or on land, survival requires a different anatomy. A neck is necessary because the body is fixed on legs and stationed in one position on the ground. The development of a neck allowed Tiktaalik to move his head in the direction of a food source without turning his whole body, as a fish would underwater.
A bone in the cranium of fish, called a hyomandibula, plays roles in feeding and in the respiration of the body. It contributes to the breathing process of fish as they move through their environment and water passes through their gills. Tiktaalik's hyomandibula was smaller than that of a fish; this suggests that this animal was relying less on its gills to breathe as it adapted to the open air on land. In humans, the hyomandibula evolved into a small bone, called the stapes, in the middle ear.
Scientists suggest that some fish began breathing air in shallow water 400 million years ago during the Devonian Era. The movement onto land included adapting their fins and other body parts to their new environment. Gills gave way to lungs so animals could breathe on land. The development of backbones in vertebrates was complemented by the transformation of fins to appendages to allow walking and stalking of prey. Some species developed claws to catch and tear at their food, and others eventually adapted to life in the air, with feathers and wings to carry them away from predators and toward food.
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