Transitional Fossils (Tiktaalik)
by Joe Marquez
| 3 Questions

Transitional FossilsĀ 

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.
At some point in the past, the bones in the fins of a population of fish became larger and longer. The bones became able to support the weight of the organisms when they were out of water. This happened over many generations. What other changes over time would be needed for fish to live out of the water?
Biological structures often have shapes (form) that enable organisms to perform particular tasks (function). How do transitional fossils, such as Tiktaalik, show that form is connected to function in living things?
It took more than 3 billion years for life to spread from the oceans onto land. All organisms that lived on land evolved during the 550 million years that followed. How might this relatively rapid diversification of land species be explained?
The move to land environments led to more changes in species over time.
The move to land environments led to fewer changes in species over time.
Spreading to land did not affect the amount of change in species over time.
The change in environments resulted in lower biodiversity.
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