Using evidence from the fossil record, scientists conclude that life began in the oceans. Early fish-like organisms gave rise to fish, which gave rise to the ancestor common to amphibians. To determine how changes like these occur in nature, scientists look for transitional fossils. These are fossils of organisms that have body structures that are found both in an ancestral species and in its descendants. For example, when scientists investigated the origins of amphibians, they hypothesized that there might have been an organism that had traits of both fish and amphibians. This hypothesis was supported with the discovery of a fossil, called Tiktaalik. Tiktaalik lived in the water. It had bones in its fins that were very similar to the wrist and feet bones of amphibians.