Paleoanthropology: Reconstructing Early Hominid Behavior and Ecology Chapter 10 Paleoanthropology: Reconstructing Early Hominid Behavior and Ecology

The Bipedal Adaptation Efficient bipedalism- only hominids. Advantages of bipedalism: Freed the hands for carrying objects and for making and using tools. In the bipedal stance, animals have a wider view of the surrounding countryside. Bipedal walking is an efficient means of covering long distances.

Obligate Bipedalism Bipedalism as the only form of hominid terrestrial locomotion. Requires major anatomical changes Other forms of locomotion on the ground became impossible.

Major Features of Hominid Bipedalism The foramen magnum (shown in red) is repositioned farther underneath the skull, so that the head is more or less balanced on the spine (and thus requires less robust neck muscles to hold the head upright).

Major Features of Hominid Bipedalism The spine has two distinctive curves—a backward (thoracic) one and a forward (lumbar) one—that keep the trunk (and weight) centered above the pelvis.

Major Features of Hominid Bipedalism The pelvis is shaped more in the form of a basin to support internal organs; moreover, the ossa coxae are shorter and broader, thus stabilizing weight transmission.

Major Features of Hominid Bipedalism Lower limbs are elongated, as shown by the proportional lengths of various body segments.

Major Features of Hominid Bipedalism The femur is angled inward, keeping the legs more directly under the body; modified knee anatomy also permits full extension of this joint.

Major Features of Hominid Bipedalism The big toe is enlarged and brought in line with the other toes; in addition, a distinctive longitudinal arch forms, helping absorb shock and adding propulsive spring.

Position of the Foramen Magnum (a) a human and (b) a chimpanzee. Note the more forward position in the human cranium.

Paleoanthropology The study of early humans. Reconstruct the anatomy, behavior, and ecology of our ancestors: A diverse multidisciplinary pursuit. Physical Sciences Biological Sciences Social Sciences Geology Physical anthropology Archaeology Geomorphology Ecology Ethnoarchaeology Geophysics Primatology Cultural anthropology Chemistry Psychology Taphonomy

Dating Methods Paleoanthropologists use two types of dating methods to tell us the age of sites and fossils: Relative dating determines only whether an object is older or younger than other objects. Chronometric (absolute) dating provides an estimate of age in years based on radioactive decay.

Relative and Chronometric Dating Relative Dating Chronometric Dating Examples Stratigraphy Fluorine Dating K/Ar Radiocarbon (14 C) Fission-track Methodological basis Provides a sequence only; i.e., no estimates in actual number of years Most techniques* are radiometric; i.e., steady decay of radioactive isotope provides estimate in actual number of years

Relative Dating Techniques Stratigrapy - based on the law of superposition, that a lower stratum (layer) is older than a higher stratum. Fluorine analysis applies to buried bones and groundwater seepage. Bones incorporate fluorine during fossilization. Biostratigraphy - related to changes in the dentition of animals. Paleomagnetism - based on the shifting of the geomagnetic pole.

Chronometric Dating Techniques Measure the rate of disintegration: Potassium/argon (k/Ar) 1-5 million-year range Half-life of 1.25 billion years. Dates rocks

Chronometric Dating Techniques Carbon-14 Less than 1,000 -75,000 years Half-life of 5,730 years

Steps in Interpreting Homind Evolutionary Events Selecting and surveying sites. Excavating sites and recovering fossil hominids. Designating individual finds with specimen numbers for clear reference. Cleaning, preparing, studying, and describing fossils. Comparing with other fossil material. Comparing fossil variation with known ranges of variation in closely related groups of living primates and analyzing ancestral and derived characteristics. Assigning taxonomic names to fossil material.