Origin and Evolution of Vertebrates

Vocabulary and key evolutionary concepts regarding the origin and evolution of vertebrates, focusing on tetrapods, amniotes, mammals, and the lineage of the genus Homo.

Sarcopterygii

Also known as lobe-fins, this group originated in the Silurian period and is characterized by muscular pelvic and pectoral fins used for swimming and "walking" underwater across the substrate.

Coelacanths

A lineage of Sarcopterygii thought to be extinct $75$ million years ago until a living specimen was caught off the coast of South Africa in $1938$.

Tetrapods

Gnathostomes that have limbs; they evolved from lobe-fins and possess specific adaptations such as four limbs with digits, a neck, and fusion of the pelvic girdle to the backbone.

Tiktaalik

A transitional fossil nicknamed a "fishapod" that exhibited fish characters (scales, fins, gills, and lungs) and tetrapod characters (neck, ribs, fin skeleton, flat skull, and eyes on top of skull).

Amniotes

A group of tetrapods whose living members include reptiles, birds, and mammals, named for the amniotic egg which contains specialized membranes to protect the embryo.

Amniotic Egg

A key adaptation for terrestrial life containing four extraembryonic membranes: the amnion, chorion, yolk sac, and allantois.

Mammalia

A class of amniotes characterized by mammary glands that produce milk, hair, endothermy, a large brain, and differentiated teeth.

Monotremes

A small group of egg-laying mammals that includes echidnas and the platypus.

Marsupials

Mammals such as opossums, kangaroos, and koalas whose embryos develop within a placenta but are born early, completing development while nursing in a maternal pouch.

Marsupium

The maternal pouch in marsupials where embryonic development is completed during nursing.

Eutherians

Also called placental mammals, they have a more complex placenta than marsupials and complete embryonic development within a uterus joined to the mother.

Paleoanthropology

The scientific study of human origins.

Hominins

Species formerly called hominids that are more closely related to humans than to chimpanzees; the oldest fossil evidence dates back to $6.5$ million years ago.

Homo habilis

The earliest fossils placed in the genus Homo, dating from $2.4$ to $1.6$ million years ago; the name means "handy man" due to the association with stone tools.

Homo ergaster

The first fully bipedal, large-brained hominid that existed between $1.9$ and $1.5$ million years ago, showing a significant decrease in sexual dimorphism compared to ancestors.

Homo erectus

The first hominin species to leave Africa, originating by $1.8$ million years ago.

Homo neanderthalensis

Thick-boned hominins with large brains who lived in Europe and the Near East from $350,000$ to $28,000$ years ago and buried their dead.

Homo floresiensis

A new small hominin species identified from $18,000$-year-old fossils discovered in Indonesia in $2004$.

Homo sapiens

The species of all living humans, which appeared in Africa by $195,000$ years ago.