Amniotic Egg Structure, Mammalian Adaptations, and Amniote Evolution

Vocabulary flashcards covering the structure and membranes of the amniotic egg, derived terrestrial traits, mammalian embryonic adaptations, and the evolutionary classification of amniote skulls.

Amniotic egg

A novel adaptation evolved for terrestrial reproduction that encloses the embryo in a protective shell, provides an internal aquatic environment, and contains albumen along with four extraembryonic membranes.

Albumen

Fluid located between the shell and the chorion that provides the embryo with water, protein, and cushioning protection.

Amnion

A fluid-filled sac developing from folds in the embryo's body wall that surrounds just the embryo, providing hydration, shock cushioning, and an internal aquatic environment.

Chorion

A flexible extraembryonic membrane developing from folds in the embryo's body wall that surrounds the embryo, yolk sac, and allantois to facilitate gas exchange with the external environment.

Yolk sac

An extraembryonic membrane formed as an extension of the embryo's midgut that surrounds the yolk and utilizes blood vessels to transport nutrients to the embryonic circulatory system.

Yolk

Nutritional substance enclosed by the yolk sac that provides the embryo with nourishment in the form of lipids and protein.

Allantois

An extraembryonic membrane extending from the hindgut that stores nitrogenous waste produced by the embryo and fuses with the chorion as the embryo grows to facilitate gas exchange.

Reptile eggshell

The outermost water-tight, protective layer of a reptile's egg, characterized by a leathery texture.

Bird eggshell

The outermost water-tight, protective layer of a bird's egg, characterized by being hardened and composed of calcium carbonate.

Monotremes

A group of mammals that retain the ancestral egg-laying trait rather than undergoing gestational pregnancy.

Umbilical cord

A mammalian structure derived from the yolk sac and allantois that functions in nutrient transport and gas exchange.

Placenta

A structure in gestational mammals formed mostly by the fetal chorion and completed by the mother's uterine lining.

Costal respiration

A derived amniote trait where inhalation and exhalation are produced by the movement of ribs and rib musculature.

Temporal fenestrae

Holes located behind each eye in amniote skulls that serve as attachment sites for jaw muscles.

Anapsid

An amniote skull condition possessing no temporal holes; found in extinct early amniote groups and modern turtles (the latter due to secondary loss).

Diapsid

An amniote skull condition characterized by two temporal holes behind each eye; present in reptiles and birds.

Synapsid

An amniote skull condition characterized by one temporal hole behind each eye; present in mammals and extinct therapsids.