Fossilization, Dating Methods, and Early Hominin Evolution

Vocabulary flashcards reviewing concepts, dating techniques, anatomical traits, and hominin taxa covered in the lecture notes.

Fossil

Any preserved evidence of past life, including bones, teeth, footprints, burrows, and plant remains.

Taphonomy

The study of what happens to organisms after death until they are discovered as fossils.

Sedimentary Rock

The rock type where fossils are usually found, as sediments can bury remains gently without destroying them through extreme heat or pressure.

Relative Dating

The process of determining whether an object or fossil is older or younger than something else without determining an exact numerical age.

Stratigraphy

The study of rock layers, or strata.

Steno's Law of Superposition

A geologic principle stating that in undisturbed rock layers, the oldest layers are on the bottom and the youngest layers are on the top.

Cultural Dating

A relative dating technique that dates artifacts based on their association with known cultural traditions.

Absolute Dating

A dating method that provides a specific numerical age or date range for an object or event.

Dendrochronology

An absolute dating method that counts tree rings in wood and wooden artifacts, where one ring typically represents one year; also used to calibrate radiocarbon dates.

Half-Life

The time required for half of a radioactive substance to decay into a stable isotope.

Radiocarbon (Carbon-14) Dating

An absolute radiometric dating method with a half-life of $5{,}730\text{ years}$ used to date organic materials up to roughly $50{,}000\text{--}60{,}000\text{ years}$ old.

Potassium-Argon (K-Ar) Dating

A radiometric absolute dating method ("clock in a rock") based on the decay of Potassium-40 into Argon-40 (half-life of approximately $1.25\text{ billion years}$) that dates volcanic material from roughly $100{,}000\text{ years}$ to billions of years old.

Hominin

Humans and all species more closely related to humans than to chimpanzees following their evolutionary split; taxonomic family Hominidae, tribe Hominini.

Habitual Bipedalism

Walking on two legs as the primary form of locomotion; recognized as the most critical defining feature of hominins.

Foramen Magnum

The large opening underneath the skull through which the spinal cord passes; located anteriorly (centered underneath) in bipeds to support upright posture.

S-Shaped Spine

The spinal curvature characteristic of bipeds that serves to balance body weight directly over the hips and absorb shock during locomotion.

Basin-Shaped Pelvis

The short, broad pelvic structure typical of bipeds that supports internal abdominal organs and provides muscle attachments necessary for upright walking.

Valgus Angle

The inward angling of the femur from the hip to the knee, which centers the knees directly below the body for stable, efficient walking.

Abductor Muscles

Pelvic muscles that stabilize the pelvis and prevent the body from tilting or falling sideways while swinging the opposite leg during bipedal walking.

Lovejoy's Provisioning Hypothesis

An evolutionary hypothesis suggesting bipedalism originated because bipedal males could carry food back to females and offspring, enhancing reproductive success and pair bonding.

Holotype

The official physical specimen designated to formally represent and define the characteristics of a named species.

Taung Child

The juvenile Australopithecus africanus fossil discovered by Raymond Dart in South Africa that provided crucial initial evidence that human evolution began in Africa.

Sahelanthropus tchadensis

An early hominin species recovered in Chad, Central Africa, dating to approximately $7\text{ million years ago}$, with the most famous specimen known as Toumaï.

Orrorin tugenensis

An early hominin discovered in Kenya dating to about $6\text{ million years ago}$, exhibiting distinctive femoral features indicative of bipedal posture.

Ardipithecus ramidus

A woodland-dwelling hominin dating to roughly $4.4\text{ million years ago}$, exemplified by the specimen Ardi, showing adaptations for both arboreal climbing and terrestrial bipedalism.

Australopithecus afarensis

An East African hominin dating from roughly $3.9\text{--}3.0\text{ million years ago}$, famously represented by Lucy, demonstrating habitual bipedalism alongside retained ape-like cranial and upper-body traits.

Australopithecus sediba

A South African hominin dated to roughly $2\text{ million years ago}$ that exhibits a transitional mosaic of primitive Australopithecus and derived Homo-like anatomical traits.

Paranthropus boisei

A robust australopithecine nicknamed Nutcracker Man, characterized by massive molars, heavily built jaws, and prominent sagittal crests adapted for heavy mastication.

Robust Australopithecines

A hominin group characterized by megadontia (large molars), heavily built mandibles, and sagittal crests reflecting dietary adaptations for processing tough, fibrous, or hard foods.

Prognathism

The forward projection of the lower face and jaw relative to the upper cranium, which decreased progressively over the course of human evolution.