BIO 104_CH.32

RACHEL DUNKERLY - CALHOUN COMMUNITY COLLEGE

Chordata

Phylum that includes animals with a notochord, dorsal tubular nerve cord, pharyngeal pouches, and a postanal tail at some point in life.

Notochord

Dorsal supporting rod present in chordates; replaced by the vertebral column in vertebrates.

Dorsal tubular nerve cord

Chordate nerve cord lying above the digestive tract and containing a fluid-filled canal.

Pharyngeal pouches

Outpocketings of the pharynx; in many vertebrates only present in embryos and give rise to structures like gills or parts of the ear.

Postanal tail

Chordate tail that extends beyond the anus at some stage of development.

Nonvertebrate chordates

Chordates in which the notochord never becomes a vertebral column, such as lancelets and tunicates.

Vertebrate chordates

Chordates with a vertebral column; include fishes, amphibians, reptiles, birds, and mammals.

Lobe-finned fishes

Devonian fishes with fleshy, bone-supported fins homologous to tetrapod limbs; ancestors of amphibians.

Amnion

Extraembryonic membrane that encloses a fluid-filled sac around the embryo in reptiles, birds, and mammals.

Lancelets

Small, knife-shaped nonvertebrate chordates that retain all four chordate traits as adults and show segmentation.

Tunicates

Marine filter-feeding chordates (sea squirts) whose larvae have all chordate traits but adults retain only a pharynx with gill slits.

Vertebral column

Series of vertebrae that replace the notochord in vertebrates and form part of a strong, jointed endoskeleton.

Cephalization in vertebrates

High degree of head development with complex sense organs (eyes, ears, etc.).

Amniotic egg

Land-adapted egg with extraembryonic membranes and usually a shell; supports and protects the embryo on land.

Agnathans

Modern jawless fishes; cylindrical, smooth, scaleless, with no jaws or paired fins.

Cartilaginous fishes

Sharks, skates, rays, and chimaeras; skeleton of cartilage and multiple gill slits without a gill cover.

Lateral line system

Row of pressure-sensitive cells along sides of fishes that detect water movement and vibrations.

Swim bladder

Gas-filled sac in many bony fishes that regulates buoyancy.

Amphibian

Name means “living a double life,” reflecting aquatic larvae and terrestrial adults.

Cutaneous respiration

Gas exchange across the moist skin of amphibians.

Ectothermic

Lacking internal temperature regulation; body temperature matches the environment; includes most reptiles, fish, and amphibians.

Endothermic

Maintaining a constant internal body temperature via metabolic heat; characteristic of birds and most mammals.

Bird air sacs

Anterior and posterior air sacs that increase efficiency of gas exchange and lighten the body.

Monotremes

Egg-laying mammals that have a cloaca and secrete milk onto body surface; found only in Australia and New Guinea.

Marsupials

Mammals whose young complete development in a pouch and nurse from nipples inside the pouch.

Placenta

Organ formed from chorion and uterine wall that exchanges materials between maternal and fetal blood.

Primates

Order of mammals adapted to life in trees (arboreal) with mobile limbs and grasping hands and feet.

Opposable thumb

Thumb that can touch the other fingers, allowing for precise grip.

Hominids

Group including humans and their closest primate relatives (chimpanzees, gorillas, orangutans).

Bipedalism

Ability to walk on two feet; key feature used to identify hominins.

Hominins

Lineage that includes humans and their bipedal ancestors.

Sahelanthropus tchadensis

Early hominin-like fossil (~$7\,MYA$) from west central Africa with smaller canines and thicker enamel.

Ardi

Nickname for Ardipithecus ramidus; $4.4\,MYA$ female fossil that could walk erect but also climb in trees.

Australopithecines

Early hominins in Africa; included gracile Australopithecus and robust Paranthropus forms.

Mosaic evolution

Concept that human traits (e.g., bipedalism, brain size) did not evolve simultaneously but at different times.

Homo genus

Fossils assigned to Homo if brain size $\ge 600\,cc$, jaw and teeth resemble humans, and tool use is evident.

Homo habilis

Early Homo species (~$2.0-1.9\,MYA$) with larger brain (~$775\,cc$), omnivorous diet, and stone tools for processing meat.

Homo erectus

Widely distributed species (Africa, Asia, Europe; $1.9-0.3\,MYA$) with larger brain (~$1000\,cc$), flatter face, and striding gait.

Out-of-Africa migration

Homo erectus shows earliest extensive human migration out of Africa into Asia and Europe.

Replacement model

Out-of-Africa hypothesis; proposes modern humans evolved in Africa and then dispersed, replacing other Homo populations.

Multiregional continuity hypothesis

Proposes modern humans arose from earlier Homo in Africa, Asia, and Europe with regional continuity.

Neanderthals

Archaic humans (Homo neanderthalensis) living $>400,000$ to ~$30,000$ years ago with large brains and robust bodies.

Cro-Magnons

Earliest European Homo sapiens fossils; entered Asia and Europe from Africa ~$100,000$ years ago.