Summary[
edit] Description: Ursus arctos horribilis Ord, 1815 - grizzly bears in Wyoming, USA. (1 July 2016) 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. The grizzly bear is the second-largest predatory species in modern North America (the polar bear is slightly larger). Grizzly bears are omnivorous but are famous for being powerful predators. They were formerly abundant in Yellowstone until the government removed most of them decades ago. They are uncommon today - I've only encountered them four times, despite having done 17 Yellowstone visits from 1977 to 2016. Classification: Animalia, Chordata, Vertebrata, Mammalia, Carnivora, Ursidae Locality: East Entrance Road, Yellowstone, Wyoming, USA See info. at:
en.wikipedia.org/wiki/Grizzly_bear. Date: 1 July 2016, 15:11. Source:
Ursus arctos horribilis (grizzly bears) (Yellowstone, Wyoming, USA). Author:
James St. John.