Amniotes

amniote

synapomorphies:

• amniotic egg (or homologous membranes)

• axis is specialized for rotation

• two or more sacral vertebrae

• skin elaborations derived from epidermal placodes

• waterproof skin

  • highly keratinized epidermis

• metanephric kidney

• costal rib ventilation

metanephric kidney

kidneys that drain into ureters

shell

porous protection for the developing organism

albumen

a proteinous liquid that provides protection and water to the developing organism

yolk

the part of the egg which provides energy to the developing organism

chorion

the part of the egg that provides protection and allows for respiratory exchange

allantois

the part of the egg that allows for storage of waste and respiratory exchange

amnion

a membrane that envelops the embryo in a protective aquatic environment

benefits of amniotic egg

• less reliant on water

• supports large embryos

  • mechanical support

  • efficient gas exchange

  • storage of wastes without diffusion to external environment

cost of amniotic egg

must be laid on land!

epidermis

• derived from ectoderm

• mucous producing cells

• stratum corneum (keratinized)

dermis

• derived from mesoderm and neural crest

• connective tissue

• melanocytes

• secretory glands

• smooth muscle fibers

• blood vessels

• sensory structures and associated nerve tissue

jaw muscle diversification

What has allowed amniotes to no longer need to use buccal pumping?

inspiration

intercostals pull ribs anterior, diaphragmatic pulls liver posterior, ischiopubic rotates pubis

expiration

rectus and transversus abdominis rotate pubic bones dorsally

cuirassal breathing

it involves the use of gastralia, which are bones in the abdominal wall that connect the rib cage to the pelvis, to help with ventilation

gastralia

ventral set of ribs used for ventilation

which ribs expand body cavity

What is the difference between cuirassal breathing and modern rib ventilation in lizards?

bird inspiration

longissimus dorsi pulls ilium and lifts pelvis, while sternum rotates ventrally

bird expiration

other muscles pull tail and pubis downward, while sternum returns to resting position

tidal flow

the organism breathes in and out through the same trachea and bronchi, less efficient

unidirectional flow

birds and crocodiles breathe in air that passes through a one-way circuit and exits the respiratory system in one direction, more efficient