evolution of life
The history of the Earth is divided into geological eras characterized by the formation of minerals and the appearance of animal and plant species, and humans.

origin and evolution of species

simple organisms and echinoderms
Living beings formed of one or more cells, some of which possess a skeleton formed of calcareous spicules.

unicellulars , echinoderms , animal cell , sponge

insects and arachnids
Highly diversified grouping of all animal invertebrates, (over 1 million species of insects and 50,000 species of arachnids); they are more numerous than all other animal or plant species.

butterfly , honeybee , spider , examples of insects , examples of arachnids

mollusks
Land and aquatic invertebrates (more than 100,000 species) with soft nonsegmented bodies; they usually secrete a calcareous shell.

snail , bivalve shell , octopus , univalve shell

crustaceans
Usually aquatic invertebrates (over 40,000 species) whose segmented bodies have articulated appendages and often carapaces.

lobster

fishes
Cold-blooded aquatic vertebrates (about 30,000 species) having motor fins and bodies that are usually covered in scales.

bony fish , cartilaginous fish

amphibians
Four-limbed vertebrates with soft smooth moist skin, usually found in water in the larval stage and on land in the adult stage.

frog , examples of amphibians

reptiles
Cold-blooded vertebrates covered with scales (about 6,000 species) found mainly in warm countries; their four limbs are sometimes atrophied or absent.

snake , turtle , examples of reptiles

birds
Vertebrates (about 9,000 species) with feather-covered bodies, a bill, two legs and two wings that are usually adapted for flight.

bird , examples of birds

insectivorous mammals
Vertebrates (about 370 species) with four limbs and a body almost entirely covered with hairs and sometimes barbs; they feed on insects.

mole , examples of insectivorous mammals

rodents and lagomorphs
Rodents have one pair of constantly growing sharp incisors used for feeding; lagomorphs have two pairs.

rodent , rodent’s and lagomorph’s jaws , examples of rodents , examples of lagomorphs

ungulate mammals
Herbivorous vertebrates covered with hair, having four limbs bearing a varying number of digits ending in a corneous sheath (nail or hoof).

horse , examples of hoofs , examples of ungulate mammals

carnivorous mammals
Vertebrates with four limbs, covered with hair and having carnassial teeth to tear meat apart; they feed mainly on the flesh of animals.

dog , cat , dog breeds , cat breeds , examples of carnivorous mammals

marine mammals
Carnivorous aquatic vertebrates (about 116 species) with limbs evolved into fins, skin that is smooth or covered in short hairs, and sometimes a dorsal fin.

dolphin , examples of marine mammals

primate mammals
Vertebrates (about 200 species) with prehensile hands and feet, with five digits ending in a nail; they live mainly in trees and can stand erect.

gorilla , examples of primates

flying mammal
Vertebrate covered with hair, with forelimbs converted into wings by means of a membrane connecting the fingers, allowing it to fly.

bat , examples of bats

marsupial mammals
Four-legged vertebrates covered with hair; the female usually has a ventral pouch in which the embryo develops after birth.

kangaroo , examples of marsupials

evolution of lifeThe history of the Earth is divided into geological eras characterized by the formation of minerals and the appearance of animal and plant species, and humans.

simple organisms and echinodermsLiving beings formed of one or more cells, some of which possess a skeleton formed of calcareous spicules.

insects and arachnidsHighly diversified grouping of all animal invertebrates, (over 1 million species of insects and 50,000 species of arachnids); they are more numerous than all other animal or plant species.

mollusksLand and aquatic invertebrates (more than 100,000 species) with soft nonsegmented bodies; they usually secrete a calcareous shell.

crustaceansUsually aquatic invertebrates (over 40,000 species) whose segmented bodies have articulated appendages and often carapaces.

fishesCold-blooded aquatic vertebrates (about 30,000 species) having motor fins and bodies that are usually covered in scales.

amphibiansFour-limbed vertebrates with soft smooth moist skin, usually found in water in the larval stage and on land in the adult stage.

reptilesCold-blooded vertebrates covered with scales (about 6,000 species) found mainly in warm countries; their four limbs are sometimes atrophied or absent.

birdsVertebrates (about 9,000 species) with feather-covered bodies, a bill, two legs and two wings that are usually adapted for flight.

insectivorous mammalsVertebrates (about 370 species) with four limbs and a body almost entirely covered with hairs and sometimes barbs; they feed on insects.

rodents and lagomorphsRodents have one pair of constantly growing sharp incisors used for feeding; lagomorphs have two pairs.

ungulate mammalsHerbivorous vertebrates covered with hair, having four limbs bearing a varying number of digits ending in a corneous sheath (nail or hoof).

carnivorous mammalsVertebrates with four limbs, covered with hair and having carnassial teeth to tear meat apart; they feed mainly on the flesh of animals.

marine mammalsCarnivorous aquatic vertebrates (about 116 species) with limbs evolved into fins, skin that is smooth or covered in short hairs, and sometimes a dorsal fin.

primate mammalsVertebrates (about 200 species) with prehensile hands and feet, with five digits ending in a nail; they live mainly in trees and can stand erect.

flying mammalVertebrate covered with hair, with forelimbs converted into wings by means of a membrane connecting the fingers, allowing it to fly.

marsupial mammalsFour-legged vertebrates covered with hair; the female usually has a ventral pouch in which the embryo develops after birth.