Horse
The horse adapted to survive in areas of wide-open terrain with sparse vegetation, surviving in an ecosystem where other large grazing animals, especially ruminants, could not. Horses and other equids are odd-toed ungulates of the order Perissodactyla, a group of mammals that was dominant during the Tertiary period. In the past, this order contained 14 families, but only three—Equidae (the horse and related species), Tapiridae (the tapir), and Rhinocerotidae (the rhinoceroses)—have survived to the present day.
Echinoderm
There are a total of about 7,000 extant species of echinoderm as well as about 13,000 extinct species. They are found in habitats ranging from shallow intertidal areas to abyssal depths. Two main subdivisions are traditionally recognised: the more familiar motile Eleutherozoa, which encompasses the Asteroidea (starfish, 1,745 recent species), Ophiuroidea (brittle stars, 2,300 species), Echinoidea (sea urchins and sand dollars, 900 species) and Holothuroidea (sea cucumbers, 1,430 species); and the Pelmatozoa, some of which are sessile while others move around. These consist of the Crinoidea (feather stars and sea lilies, 580 species) and the extinct blastoids and Paracrinoids. A fifth class of Eleutherozoa consisting of just three species, the Concentricycloidea (sea daisies), were recently merged into the Asteroidea. The fossil record includes a large number of other classes which do not appear to fall into any extant crown group.