All mammals feed their young with milk, have hair, have a neocortex region of the brain, and have three middle ear bones. There are other characteristics shared by all mammals, but the above four are (for the most part) that only ones unique to mammals.
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Mammals are warm blooded animals that give live birth to their babies (as opposed to laying eggs) and nurse their babies with milk. Whales meet all 3 criteria.
All mammals have hair and nourish their young with milk.
The distinguishing feature of a spider with a black back is its dark-colored dorsal side.
All birds have feathers - a beak - no teeth - lay hard shelled eggs
A spider with a brown stripe on its back has a distinguishing feature that sets it apart from other spiders.
The distinguishing feature of a plant with an unlobed leaf is that the leaf does not have any divisions or indentations along its edges.
A sparrow with a white eye stripe has a distinguishing feature of a white stripe above its eye.
volcanoes
Black beetles with a brown stripe have a distinguishing feature of a noticeable stripe running across their bodies.
A brown spider with a black line on its back has a distinguishing feature that helps identify it from other spiders.
The distinguishing feature of a brown spider with a black head is the contrast between the brown body and the black head.