Amniotes

What are amniotes?

Amniotes are vertebrates and include birds, reptiles, and mammals

What are the major adaptations of amniotes for life on land?

• Amniotic egg

• Rib ventilation of lungs

• Keratinized skin (less water loss)

• Internal fertilization

• Stronger limbs and muscles

What is an amniotic egg?

An egg with a protective shell and membranes that support the embryo’s development on land.

What are the parts of an amniotic egg?

amnion, chorion, allantois, yolk sac

What does the amnion do in the amniotic egg?

It surrounds the embryo in fluid, protecting it from dessication

How do amniotes ventilate their lungs?

they use rib ventilation (negative pressure breathing)—ribs and diaphragm expand the chest to draw air in.

What does “negative pressure breathing” mean?

Air is pulled into the lungs because expanding the chest cavity lowers internal pressure.

How is frog respiration different from that of amniotes?

Frogs use positive pressure breathing and also rely heavily on their skin for CO₂ excretion, unlike amniotes, which use only their lungs.

What evolutionary change allowed ribs to be used for breathing?

As limb muscles improved and reduced the need for wiggling, rib muscles were coopted for expanding the thoracic cavity.

What is one function of the allantois in the amniotic egg?

It stores waste and helps with gas exchange.

What animals are included in the amniote group?

Reptiles (including birds) and mammals.

What are the 4 extraembryonic membranes in the amniotic egg and their functions?

• Amnion: Cushions the embryo in fluid

• Chorion: Gas exchange

• Allantois: Waste storage + gas exchange

• Yolk sac: Nutrient supply

What advantage does the amniotic egg provide on land?

It resists desiccation, supports larger embryos, and reduces dependence on water for reproduction.

How is reptile skin adapted for terrestrial life?

It's thick, waterproof, and keratinized (beta-keratin) to reduce water loss.

What are osteoderms and where are they found?

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Bony plates in the dermis, found in crocodilians and some lizards.

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How is the circulatory system of amniotes adapted for land?

It’s high-pressure, often with separated circuits, reducing oxygen-deoxygenated blood mixing.

How many heart chambers do reptiles have?

Most reptiles have 3-chambered hearts, but crocodiles and birds have 4-chambered hearts.

What type of nitrogen waste do reptiles excrete?

Uric acid — low solubility, conserves water, ideal for dry environments.

Why is uric acid advantageous for reptiles?

It uses less water for excretion, allowing survival in arid conditions.

What parts of the reptilian brain are expanded?

The cerebrum (sensory integration) and cerebellum (motor control).

What is the Jacobson’s organ used for?

Chemosensation — detecting airborne molecules (especially in snakes and lizards).

What is the pit organ used for in some reptiles?

Detects infrared radiation (heat) — helps locate warm-blooded prey.

Are reptiles endothermic or ectothermic?

Ectothermic — their body temperature changes with the environment.

How do reptiles regulate their body temperature?

Through behavioral thermoregulation: basking, hiding in shade, and timing activity.

What are the two types of sex determination in reptiles?

Genetic Sex Determination (GSD) and Temperature-Dependent Sex Determination (TDSD)

What is TSD and which reptiles have it?

Sex determined by incubation temperature — seen in crocodiles, turtles, tuataras.

How do snakes use Jacobson’s organ?

They flick their tongue to collect scent particles and deliver them to the Jacobson’s organ inside their mouth.

What is the pit organ and what does it detect?

The pit organ detects radiant heat (infrared energy) from warm objects, like prey.

Why do snakes have advanced sensory organs like the Jacobson’s and pit organ?