Concept 34.5: Amniotes are tetrapods that have a terrestrially adapted egg

Flashcards from Concept 34.5 of Pearson's Campbell Biology, Twelfth Edition.

Amniotes

Tetrapods whose living members are the reptiles (including birds) and mammals

• Named for their amniotic egg, containing four embryo-protecting membranes and reducing dependence on water for reproduction

Amniotic egg

An egg type in amniotes reducing water dependence for reproduction and has four membranes of the amnion, chorion, yolk sac, and allantois

• These often have shells when produced by reptiles to slow dehydration

• Many mammals have lost the eggshell, developing within the mother’s body instead

Amnion

A fluid-filled sac that surrounds, bathes, and cushions the embryo as the other membranes function in gas exchange, nutrient transfer, and waste storage

Rib cage

A body part in amniotes that improved breathing efficiency through the ventilation of the lungs

• This allowed for less dependency on gas exchange through the skin, causing lower permeability and enabling better water conservation

Reptiles

A group a member of the amniotes including tuataras, lizards, snakes, turtles, crocodilians, and birds; many share some characteristics:

• Scales containing keratin to prevent desiccation and abrasion

• Shelled eggs to prevent drying out

• Internal fertilization before the secretion of the shell

• Being ectothermic, except for birds which are endothermic

Ectothermism

Being able to absorb external heat as the main source of body heat; seen in most reptiles except birds

• Temperature is regulated through behavioral adaptations, like basking in the sun or shade

Endothermism

Being able to maintain body temperature through metabolic activity

• Seen in birds as reptiles that do not exhibit ectothermism

Pterosaurs

The first tetrapods to exhibit flapping flight, originating in the late Triassic

• Filled ecological roles that would later be played by birds after their extinction, about 66 mya

Dinosaurs

Land-based tetrapods that diversified into a vast range of shapes and sizes

• Herbivorous members evolved diverse adaptations for defense

• Theropods were bipedal carnivores including Tyrannosaurus rex

• Many were agile and fast moving; and some lived in groups, protected eggs, or were endothermic

• Went extinct about 66 mya potentially from an asteroid or comet impact

Theropods

Bipedal carnivorous dinosaurs including Tyrannosaurus rex and the ancestors of birds

Turtles

Group of tetrapods containing 351 species, most closely related to crocodilians and birds

• Their boxlike shell was acquired in stages over millions of years, made of upper and lower shields fused to the vertebrae, clavicles and ribs

• The earliest could not retract their head into their shell

• They have adapted to a variety of environments, like deserts, ponds, rivers, or the sea, but can be threatened by human development

Lepidosaurs

Tetrapod group represented by a single lizard-like species called the tuatara, restricted to 30 islands off the coast of New Zeealand and threatened by rats which consume their eggs

Squamates

Group of amniotes that includes all ~10,425 species of lizards and snakes, ranging in size from 16 mm to 3 m long

Snakes

Descended from lizards with legs; these move on land by producing waves of lateral bending from head to toe or via belly scales to grip and pull from the ground

• These are carnivorous and have adaptations to aid in preying, such as chemical sensors, vibration sensitivity, heat-detecting organs, tongue flicking, toxic venom, and loosely articulated jawbones and skin for swallowing

Crocodilians

Tetrapod group that includes all alligators and crocodiles; early species were small terrestrial quadrupeds before becoming larger and aquatic

• The 24 species of these are restricted to warm regions of the globe

Birds

Archosaurs with extensive modifications in their adaptation to flight; this group has about 10,000 species

• Adaptations include having no urinary bladder, only one ovary, small gonads, toothless mouths, and air-filled bones with honeycombed internal structures

• They also have color vision, acute eyesight, and fine muscle control to support flight for hunting, escape, and migration

• Large amounts of energy are dedicated to flight; feathers and some fat can insulate against heat loss while efficient respiratory and circulatory systems supply oxygen to tissues

Ratites

An order of flightless birds including the ostrich, rhea, kiwi, cassowary, and emu