Hominid Evolution

How long ago did the australopithecines live?

4 mya to 1 mya

The pre-australopithecines lived around how many years ago?

7-6 mya.

What is bipedalism?

A form of two footed locomotion where movement occurs primarily through the use of the legs.

What is the law of superposition?

A principle that argues material from lower geological layers must be older than material from higher geological layers.

Radiocarbon dating

A radiometric dating method that relies on carbon-14, an isotope with a half life of 5,730 years.

Potassium-argon dating

A radiometric dating method that relies on radioactive potassium isotopes with a half-life of about 1.3 billion years.

Argon-Argon dating

A radiometric dating method that relies on the ratio of two argon isotopes used for material from similar time periods as in potassium argon dating.

What is comparative stratigraphy?

A relative dating method based on the assumption that things found in the same strata will be from the same time period because they were deposited together.

Isotope

A variation of a chemical element based on the number of neutrons in its nucleus.

What is the savanna hypothesis?

An explanation for the development of bipedalism that agues that bipedalism was selectively favored as open grassland environments expanded throughout Africa.

Non radiometric dating

Any chronometric dating method that is not based on the principles of radioactive isotope decay.

What is chronometric dating?

Any dating method that provides a numerical age estimate for the dated material

What is relative dating?

Any dating method that provides the age of something relative to do something else, rather than as a numerical age.

What is radiometric dating?

Any dating method that uses the principles of radioactive isotope decay to determine numerical age.

What are the last two pre-australopithecines?

Ardipithecus kadabba and Ardipithecus ramidus.

What is the two earliest australopithecine species?

Australopithecus Anamensis and Australopithecus Afarensis

Why did hominins evolve from an apelike primate?

Because of bipedal locomotion. This form of movement may have provided hominins with a more efficient means of exploiting patchy forests, freeing the hands for feeing in trees and on the ground.

What is obligate bipedalism?

Bipedal locomotion that is practiced all the time.

What is habitual bipedalism?

Bipedal locomotion that is practiced regularly.

What is occasional bipedalism?

Bipedal locomotion that is practiced sometimes.

What is the size of the mastoid process in bipeds in comparison to quadrupeds?

Bipeds have larger mastoid processes than quadrupeds.

What is the earliest known platyrrhine?

Branisella. It had three premolars in each mouth quadrant and low rounded molar cusps that indicate a possibly frugivorous diet.

What is a hominin?

Hominins are defined by two obligate behaviors: bipedal locomotion and nonhoning chewing.

How is the human pelvis different from the pelvis of a non-bipedal primate?

Human pelvises are bowl shaped to accommodate the unusual gluteal muscles present in bipeds. The ilia in a biped are smaller than a quadruped and positioned more laterally in the pelvis.

Why is the foramen magnum positioned like that on a biped?

It helps center the head over the upright vertebral column.

Paleomagnetic dating

Nonradiometric dating based on changes in Earth's magnetic polarity.

The kind of bipedalism practiced by a living chimpanzee .

Occasional bipedalism

What are adapiforms?

One of a group of early primates that lived between 56 and 34 mya.

What are omomyoids?

One of the group of early primates that lived between 56 and 34 mya.

Who is Lucy?

One of the most significant fossils: the 40% complete skeleton of an adult female.

What is the second pre-australopithecine?

Orrorin tugenensis.

What are the primate like mammals that lived in North America, Europe, and Asia during the Paleocene epoch?

Plesiadapiforms.

What does post-cranial mean?

Relating to the bones below or behind the head.

What are the two types of dating?

Relative dating and chronometric dating.

Hominins have a number of anatomical characteristics that reflect two fundamental behaviors: bipedal locomotion and non honing chewing. What are they?

S shaped spine, short pelvis from front to back, long legs, knees angled toward midline of the body, double arched food, non opposable big toe, blunt non projecting canines.

What is the first of the pre-australopithecine species?

Sahelanthropus tchadensis.

What are some characteristics of adapiforms?

The adapiforms have forward facing feet, nails instead of claws, and larger brains than other mammals.

What is cranial capacity?

The amount of space available in the cranium for the brain.

What is the mastoid process?

The bony projection located posterior to the ear that allows for the attachment of neck muscles.

Where are the two curves in the human vertebral column?

The curves are located in the thoracic and lumbar areas.

What were the first hominins?

The earliest hominins were the pre-australopithecines. They lived in forests.

Euprimates

The first true primates from the eocene: the tarsierlike omomyids and the lemurlike adapids.

How is the foramen magnum positioned in a biped?

The foramen magnum is positioned more anteriorly and inferiorly.

What is taphonomy?

The history of death assemblages.

What is the foramen magnum?

The large hole at the base of the cranium that allows the brain to connect to the spinal cord.

What is the ilium?

The large, blade like area of each os coxa.

Half life

The length of time it takes for one half of an amount of a radioactive isotope to decay.

Who are the australopithecines?

The members of the australopithecus genus were a group of our ancestors that lived between 3 and 1 mya.

What is the vertebral column?

The row of bones that form the backbone.

What is continental drift?

The shifting of the continents that is caused by the movement of Earth's continental plates.

What is stratigraphy?

The study of the deposition of geological and cultural layers.

How many species of australopithicines are there?

There are as many as 9 australopithicine species.

What are some physical characteristics of australopithicines?

They are habitual bipeds. They generally have smaller cranial capacities and body sizes than normal humans. They also have small canines, large premolars, and large molars.

What are some of the characteristics of omomyoids?

They have forward facing eyes, postorbital bars, grasping hands and feet, nails instead of claws, and large brains.

What is the most important characteristic in hominid evolution?

Walking habitually on two legs.