Scientists Say: Vestigial
Vestigial (adjective, “Vehs-TIH-gee-uhl”)
This is a small, leftover form of something such as a body part or behavior that doesn’t have any function. If it’s a body part or organ, it might be much smaller than a functioning version in another species. Or it might only be partially developed.
For example, many mammals can swivel their ears, pointing them toward certain sounds. Humans can’t do that. Instead, we turn out heads. But we still have some tiny vestigial muscles around our ears. Those muscles are the leftovers of muscles our ancestors used to turn their ears. The only function those muscles serve now is as a party trick — when someone shows off by wiggling their ears.
In a sentence
Tiny pumpkin toadlets have a vestigial call that they can’t hear.
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mammal A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.
muscle A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.
organ (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
vestigial An adjective for some existing structure (such as body part or organ) that over many, many generations seems to have lost any useful function. It may be much smaller than a functional organ in another species, or may be only partially developed.