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They may have spent most of their lives in the water, leaving it only to escape the attentions of predatory fish. The first amphibians breathed through simple lungs and their skin. The fish showed other characteristics of terrestrial animals, including ribs, a neck, and nostrils on its snout for breathing air. Found in the Canadian Arctic in 2004, Tiktaalik had a crocodile-like head and strong, bony fins that scientists think it used like legs to move in shallow waters or even on land. Some lobefins are still around today, such as the famous "living fossil" fish, the coelacanth.Ī fossil creature from the Devonian discovered more recently has been hailed as a vital link between fish and the first vertebrates to walk on land. The fossils of these remarkable animals come from the red rocks of Devon. Named after the thick, fleshy base to their fins, lobefins are credited with the giant evolutionary stride that led to the amphibians, making lobefins the ancestors of all four-limbed land vertebrates, including dinosaurs and mammals. The second group, the bony fish, were covered in scales and had maneuverable fins and gas-filled swim bladders for controlling their buoyancy. They had small, rough scales, fixed fins, and sharp, replaceable teeth.
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The cartilaginous fish, so-called because cartilage formed their skeletons, later gave rise to sharks and rays. The Devonian ancestors of fishes living today belonged to two main nonarmored groups. Shark Ancestorsĭespite their heavy protection, these primitive fishes weren't built to last. Fossil specimens include species with horseshoe-shaped heads and others that looked like rounded shields. Other types of bone-plated fish that lacked jaws developed a range of bizarre forms. Early placoderms fed on mollusks and other invertebrates, but later species developed into ferocious, fish-slicing monsters measuring up to 33 feet (10 meters) long. The most formidable of them were the armored placoderms, a group that first appeared during the Silurian with powerful jaws lined with bladelike plates that acted as teeth. The Devonian, part of the Paleozoic era, is otherwise known as the Age of Fishes, as it spawned a remarkable variety of fish. Red-colored sediments, generated when North America collided with Europe, give the Devonian its name, as these distinguishing rocks were first studied in Devon, England. Known as Euramerica, or Laurussia, it was created by the coming together of parts of North America, northern Europe, Russia, and Greenland. The great supercontinent of Gondwana was headed steadily northward, away from the South Pole, and a second supercontinent began to form that straddled the Equator. When the Devonian period dawned about 416 million years ago the planet was changing its appearance.