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The statocyst is a balance sensory receptor independently found in different organisms like: some aquatic invertebrates, including bivalves, [206] cnidarians, [207] echinoderms, [208] cephalopods, [209] and crustaceans. [210] Also found in single-cell ciliate. A similar structure is also found in Xenoturbella. [211]
Analogous structures - structures similar in different organisms because, in convergent evolution, they evolved in a similar environment, rather than were inherited from a recent common ancestor. They usually serve the same or similar purposes. An example is the streamlined torpedo body shape of porpoises and sharks. So even though they evolved ...
The recurrent evolution of flight is a classic example, as flying insects, birds, pterosaurs, and bats have independently evolved the useful capacity of flight. Functionally similar features that have arisen through convergent evolution are analogous, whereas homologous structures or traits have a common origin but can have dissimilar functions.
A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats and birds, the arms of primates, the front flippers of whales, and the forelegs of four-legged vertebrates like horses and crocodilians are all derived from the same ancestral tetrapod structure.
In the horizontal direction, the structures are homologous in their morphology, or anatomy, but different in their function due to differences in habitat. In the vertical direction, the structures are analogous in function due to similar lifestyles of organisms but anatomically different since they are part of different groups.
analogous structures A set of morphological structures in different organisms which have similar form or function but were not present in the organisms' last common ancestor. The cladistic term for the same phenomenon is homoplasy. ancestor ancestral trait. Also called an ancestral character, primitive character, or primitive trait.
When two species share a trait, evolution is defined as parallel if the ancestors are known to have shared that similarity; if not, it is defined as convergent. However, the stated conditions are a matter of degree; all organisms share common ancestors. Scientists differ on whether the distinction is useful. [3] [4]
By studying the number and complexity of different fossils at different stratigraphic levels, it has been shown that older fossil-bearing rocks contain fewer types of fossilized organisms, and they all have a simpler structure, whereas younger rocks contain a greater variety of fossils, often with increasingly complex structures.