PALEONTOLOGY: KEY QUESTIONS

• How do we locate, recover, and date fossil remains?

• What are the features of the primate skeleton, and how can our knowledge of them help us identify fossil remains?

THE FOSSIL RECORD: PRESERVATION

–Not a representative sample of all of the species that have lived on earth

–Some species and body parts preserve better than others

–TAPHONOMY = study of the processes that affect the remains of dead animals

THE FOSSIL RECORD: FINDING FOSSILS

* More likely to be found in areas with little vegetation and lots of erosion (i.e. lake bottoms)

* Due to issues regarding the preservation and discovery of fossils, the fossil record of early primates is “limited and spotty”

DATING CONCEPTS• PALEONTOLOGY = study of ancient

life through the fossil record

• Anthropology & Paleontology --interested in establishing a chronology for primate and human evolution

• Much dating depends on STRATIGRAPHY = study of the sequence of geographical layers

RELATIVE DATING

• Uses natural layers or strata to establish a relative chronology—material from this layer is older than the material from that layer

• Association with known fossils, biostratigraphy = most common method of fossil dating

ABSOLUTE DATING (p.202!)

• Produce dates in years, so differences in age can be quantified

• Radiometric techniques = based on known rates of radioactive decay in elements found in or around fossils

• Radiocarbon (Half-life of 14C is 5,730 yrs.), dates organic remains from 100s to 40,000 ya (half life = time needed for ½ amount of 14C to decay)

• Potassium Argon (K/A) dates volcanic rock from 100,000 to billions ya

ABSOLUTE DATING

• Electron Spin Resonance (ESR) = Measures # of electrons excited to higher energy levels by natural radiation & trapped at those levels, dates teeth & cave deposits from 100s to 10 mya

• Luminescence = Same as ESR, but trapped energy is released using heat or light, dates pottery, bricks, burned rock up to 800,000 ya

•IF Humanlike remains were found between two layers of volcanic rock, how could we date the remains?

• K/Ar (potassium/argon) dating

• Remains are younger than the volcanic deposit below and older than the one above

Hypothetical Stratigraphic Sequence

Absolute Dating Techniques

Technique Abbrev-iation

Materials Dated

Effective Time Range

Carbon 14 14C organic materials

up to 40,000 years

Potassium-Argon

K/A and 40K

volcanic rock

older than 500,000 years

Uranium Series

238U minerals between 1,000 and 1,000,000

Thermo-luminescence

TL rocks and minerals

between 5,000 and 1,000,000 years

Electron Spin Resonance

ESR rocks and minerals

between 1,000 and 1,000,000 years

Continents At End of the Mesozoic

Placement of the continents at the end of the Mesozoic and beginning of the Cenozoic, about 65 mya

Tethys Seaway

Cenozoic Timescale

Taphonomy• Leopard + remains of early hominid in tree above entrance to cave

• Accumulation of bones, including hominid bones, in South African caves

• Bones, antlers, teeth found in the caves once thought to be early tools used by bipedal “killer apes” to hunt and forage

• Taphonomic research now shows that they are a natural accumulation & the “killer apes” were prey not predator!

Skeletons of:

• Modern Human

• Gorilla

• Domestic Cat

Skeletal Anatomy

Comparative Primate AnatomyDifferences in

stance:

Indri: Vertical clinging and leaping

Macaque: Generalized quadrupedalism

Gorilla: Semi-erect knuckle walking

Chimp: Knuckle-walking and tree climbing

Human: Fully erect bipedalism

Cranial Anatomy• Hominoid primates share same overall construction of the skull

• Proportions of the various bones of the skull, however, vary, as do the expression of various ridge-like features on surface of the bone

• What do you think are some of the reasons for these differences?

Sagittal crestFrontal

Brow ridge

Axial Skeleton (Trunk) of OW Primates

Changes in the anatomy of the trunk

Hominoid Comparative Anatomy

Changes in Human Skeleton

1. Skull more balanced on spine

2. Smaller neck muscles

3. Spine articulates under skull

4. Multiple curves of spine

5. Narrower rib cage

Changes in Human Skeleton (cont.)

6. Shorter wider pelvis

7. Proportionately longer legs

8. Upper leg angled inward so knees closer to midline

9. Big toe in line with other toes

10.Center of gravity in pelvic basin