Evolutionary relay

In evolutionary biology, evolutionary relay describes how independent species acquire similar characteristics as a result of their evolution in similar ecosystems, but not at the same time.

A classic example is the dorsal fin of the extinct ichthyosaurs and the shark. Another example is the streamlined, fish-like shape of the ichthyosaurs and the shape of extant dolphins and small whales. Except for the tail fins, cetaceans greatly resemble fish in outline, but are instead descended from four-legged land mammals. Their closest land relative today is thought to be the hippopotamus. Their modern shape is due to their water-based life cycle, as is the shape of the fish.

Evolutionary relay is a different phenomenon than convergent evolution and parallel evolution. In convergent evolution, independent organisms acquire similar characteristics while evolving in different habitats (e.g. bird and fly wings). Parallel evolution occurs when two independent species evolve together at the same time in the same ecospace and acquire similar characteristics (e.g. extinct browsing-horses and extinct paleotheres ).

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Convergent evolution
Parallel evolution
Mimicry