Odocoileus virginianus (Zimmerman, 1780) - white-tailed deer in Ohio, USA.

Mammals are the dominant group of terrestrial vertebrates on Earth today. The group is defined based on a combination of features: endothermic (= warm-blooded), air-breathing, body hair, mother's milk, four-chambered heart, large brain-to-body mass ratio, two teeth generations, differentiated dentition, and a single lower jawbone. Almost all modern mammals have live birth - exceptions are the duck-billed platypus and the echidna, both of which lay eggs.

Mammals first appear in the Triassic fossil record - they evolved from the therapsids (mammal-like reptiles). Mammals were mostly small and a minor component of terrestrial ecosystems during the Mesozoic. After the Cretaceous-Tertiary mass extinction at 65 million years ago, the mammals underwent a significant adaptive radiation - most modern mammal groups first appeared during this radiation in the early Cenozoic (Paleocene and Eocene).

Three groups of mammals exist in the Holocene - placentals, marsupials, and monotremes. Other groups, now extinct, were present during the Mesozoic.

Shown above is a male white-tailed deer, Odocoileus virginianus. The developing antlers are covered with a thin layer of furry tissue known as "velvet".

Classification: Animalia, Chordata, Vertebrata, Mammalia, Artiodactyla, Cervidae

Locality: western side of Newark, Licking County, Ohio, USA

More info. at: <a href="https://en.wikipedia.org/wiki/White-tailed_deer" rel="nofollow">en.wikipedia.org/wiki/White-tailed_deer</a> and