the white of an egg, composed primarily of the protein albumin.
a membranous sac that acts as an organ of respiration and nutrition for the embryo, in humans, its blood vessels become the blood vessels of the umbilical cord.
in mammals, birds, and reptiles, the membrane that contains a developing embryo and its surrounding fluid.
a type of egg that is produced by reptiles, birds, and egg - laying mammals and that contains a large amount of yolk; usually surrounded by a leathery or hardshell within which the embryo and its embryonic membranes develop.
one of a subgroup of primates that includes monkeys, apes, and humans.
asteroid impact hypothesis
an explanation for the mass extinction of most dinosaurs; holds that a giant asteroid struck Earth and caused castastrophic climate change about 66 million years ago.
one of a subfamily of early hominids that lived between 4.2 million and 1 million years ago; includes the genus Australopithecus and possibly the genus Paranthropus.
in hominids, the conditions of being adapted to walk primarily upright on two legs.
a flexible and strong connective tissue.
the outer membrane that surrounds an embryo.
the skeleton of the head, epecially the portion of the skull where the brain is enclosed.
one of a varied group of mostly extinct reptiles that lived from about 235 million years ago to about 66 million years ago.
in animals, the characteristic of maintaining a high, constant body temperature through regulation of metabolism and heat loss.
in birds, a modified scale that provides lift for flight and conserves body heat.
an ape whose face has little hair and whose hands have nails and complex fingerprints, such as an orangutan, gorilla, or chimpanzee.
a member of the family Hominidae of the order Primates; characterized by bipedalism, relatively long lower limbs, and lack of a tail; examples include humans and their ancestors.
a member of the genus Homo of the family Hominidae; includes modern humans and closely related extinct species.
a hard protein that forms hair, bird feathers, nails, and horns.
a kind of fish that has fleshy fins that are supported by a series of bones; living species include lung-fishes and the coelocanth.
a gland that is located in the chest of a female mammal and that secretes milk.
a mammal that lacks a true placenta and gives birth to relatively underveloped young, and then carries and nourishes the young in a pouch.
a mammal that lays eggs
in primates, a thumb that can touch and move in opposition to the other fingers of the hand.
a mammal that nourishes it unborn offspring through a placenta inside its uterus.
one of the hard scales that resemble vertebrate teeth and cover skin of sharks and rays.
an adaptation in an ancestral group that evolves through natural selection to allow
an appendage that can grasp objects, as in a primate's hand, foots, or tail.
a kind of fish whose fins are supported by long, segmented, and flexible bony elements called rays.
a lineage of amniotes that gave rise to mammals; characterized by skulls that have a single opening in a bone behind the eye socket.
the aquatic, fishlike larva of a frog or toad.
a lineage of synapsids that were abundant during the late Permian period and gave rise to mammals; characterized by limbs positioned directly beneath the body; some may have been endothermic.
one of the 33 bones in the spinal column (backbone).
the membrane that is attached to a vertebrate embryo and that encloses the yolk and thus stores energy reserves for the developing embryo.