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An approximately 300 million-year-old fossil skeleton discovered at Canyonlands National Park in Utah could be the first of its kind, researchers say. © Adam Marsh/National Park Service The fossil discovery at Canyonlands National Park was a rare intact skeleton. The exact species and classification have yet to be determined, but the fossil is a tetrapod -- meaning animal with four legs -- and could be an early ancestor of either reptiles or mammals. Paleontologists have determined the fossil could be anywhere from 295 million to 305 million years old, between the Pennsylvanian and the Permian geologic time periods.

ScienceDaily (Apr. 19, 2009) — New evidence gleaned from CT scans of fossils locked inside rocks may flip the order in which two kinds of four-limbed animals with backbones were known to have moved from fish to landlubber. Both extinct species, known as Ichthyostega and Acanthostega, lived an estimated 360-370 million years ago in what is now Greenland. Acanthostega was thought to have been the most primitive tetrapod, that is, the first vertebrate animal to possess limbs with digits rather than fish fins. But the latest evidence from a Duke graduate student's research indicates that Ichthyostega may have been closer...