Chordates and Tetrapod Evolution Lecture Notes

This set covers the classification and evolutionary transitions of chordates, tetrapods, amphibians, and various amniote groups (reptiles and mammals) as discussed in the lecture.

Chordates

A group within the deuterosomes named for the fact that they possess a nodal chord.

Actinopterygii

The scientific name for ray-finned fish, which constitutes the majority of fish species today.

Sarcopterygian

A synonym for lobe-finned fish, the ancestral group from which tetrapods are descended.

Dipnoi

The scientific name for lungfish, which provided a pre-adaptation for tetrapods by evolving air-breathing structures.

Tetrapod

A group of bony fish and vertebrates that share the characteristic of having four limbs with digits.

Tiktaalik

A transitional fossil from the Devonian period known as a 'fishapod' that fills the gap between fish and semi-terrestrial tetrapods.

Amphibians

Extant tetrapods tied to aquatic environments for their life cycle, including salamanders, frogs, and caecilians.

Apoda

A group of amphibians, also known as caecilians, that have secondarily lost their limbs and typically burrow in mud.

Amniotes

A group of tetrapods comprising reptiles and mammals that share the presence of an amniotic egg.

Rib ventilation

An adaptation in amniotes where ribs contract and expand to help consume larger amounts of air to meet high oxygen demands.

Amnion

The membrane in an amniotic egg that directly protects the embryo within a cavity of amniotic fluid.

Chorion

An embryonic structure that protects the embryo, the amniotic sac, the yolk sac, and the allantois within the egg.

Allantois

A structure in the amniotic egg responsible for respiratory gas exchange and serving as a waste storage site.

Yolk sac

An internal structure of the amniotic egg that is full of nutrients to supply energy for the developing embryo.

Squamates

A major group of reptiles that includes lizards and snakes.

Serpentes

A monophyletic group of squamates that evolved from lizards and lost their limbs for advantages like burrowing.

Mammary glands

Milk-producing glands that are the namesake characteristic of mammals, facilitating high parental investment.

Keratin

The protein used by mammalian cells to produce hair and fur.

Middle ear

A unique mammalian structure containing the tiniest bones in the body that amplify sound waves for processing by the brain.

Differentiated teeth

A mammalian trait involving various tooth types (incisors, canines, molars) used for specialized tasks like eating, signaling, or fighting.

Monotremes

A group of egg-laying mammals, such as the duck-billed platypus and echidna, that lactate through modified sweat glands rather than nipples.

Marsupials

Mammals that possess a rudimentary placenta and give birth to premature young that finish developing inside a pouch called a marsupium.

Eutherians

Known as 'true placental mammals,' this group has highly developed placentas and long gestation periods.