Lecture on Chapter 3 Objective • Understanding the nature and the antiquity of hominin fossil record and having an appreciation of various disciplines that contribute to the field of paleoanthropology What do Paleoanthropologists do? • Collecting and interpreting fossil hominins • Establishing how and where fossils are found • Establishing the antiquities of the fossil record • Reconstructing fossil hominin paleobiology • Classifying the hominin fossil record • Establishing the tempo and mode of human evolution How do remains become incorporated into the geologic record? Fossilization process and recovery Organism dies or sheds body parts NECROLOGY Organic (soft tissue) parts decay Processes that occur between the Sedimentary process death of an organism and its BIOSTRATINOMY interact with subsequent burial in the sediment remaining (inorganic) parts are termed biostratinomy. Burial process Chemical alteration and lithification DIAGENESIS The physical and/or chemical effects after burial are called diagenesis. Recovery/collection process What types of environments are Ideal for fossilization process? A C B D What is paleoecology? A study of past ecological settings using proxy data • Ecology • Paleoecology • Source: currently living • Source: Fossil assemblages organisms in an intact ecosystem • Mostly characterization of a former milieu: making • Precise and comprehensive inferences on environmental description of environments and organismic fact and organism in an ecosystem • Fossils are the only data • Potentially all faunal and floral available (nature of the fossil components are available in the record) observed biocenosis Paleoecological research • Aims • at analyzing long-term past ecological trends (development of communities in certain environments) • Understanding • Antemortem events: all processes that affected a fossil organism • Postmortem events: taphonomic approach studying diagenesis Linking the past & present After Foley (1987) Things to consider in paleoecological studies after Hardt et al. 2007 Terms • Biocoenosis: • group of co-occurring live organisms • Thanatocoenosis: • group of co-occurring dead organisms Bone assemblage analyses • Characterizing the vertebrate accumulations • How did the assemblage form • Taphonomic characteristics of the assemblage • Identifications • counts of taxa and body parts • Number of specimens • Number of individuals • Number of species • Relative abundance of species • Body size, age spectra • mapping of spatial arrays of bones in situ • Skeletal articulation • Representation of skeletal parts • Size of bone accumulation, spatial density, pattern of arrangement • description of bone modification Locating paleoanthropological sites How are sites found/established? . Systematic surface surveys and reconnaissance . Remote sensing: satellite imaging and ground penetrating radar How do we recover paleoanthropological remains? . Excavations . Surface collections: 100% surface collection Some fossil faunal remains from Localities 8 and 9, Upper Laetolil Beds. Locality 9 Locality Locality 8 Locality Fossil bone Fossil distribution and orientation orientation and distribution Laetolil Beds Laetolil pattern at Localities 8 and 9 Upper 8 and Localities at pattern 25.0 20.0 15.0 % MNE 10.0 5.0 0.0 Tali Ribs Skull Teeth Pelvis Tibiae Radius Humeri Femora Calcanei Scapulae Vertebrae Phalanges Mandibles Horncores Metapodials Skeletal parts Importance of Stratigraphy in Paleoanthropology • A study of how strata (sediment layers) form and become deposited • Charles Lyell: Principles of Stratigraphy • Steno’s Principle of original horizontality • Steno’s Principle of superposition • Hutton’s Principle of cross-cutting relationships • Smith’s Principle of faunal succession • Index fossils • First appearance • Last appearance • Hutton and the Concept of Uniformitarianism How do we know the age of archaeological or paleoanthropological remains? Anthropologists rely on geochronologists for dating process of sediments and artifacts . An accurate time scale in paleoanthropology is very crucial for the understanding the evolutionary history of our species. The appreciation of reliable methods of dating has the potentials to radically alter interpretations of evolutionary relationships. Example of a stratigraphic correlation placing fossils in relative and absolute age Stratigraphic profile at Olduvai Gorge, Tanzania The Caves of Malapa, South Africa The Caves of Malapa, South Africa Establishing the Antiquity of the finds There are two ways in which paleoanthropologists may choose to determine the age of any finds 1. Relative Dating Methods • Lithostratigraphy – correlation of rocks characteristics over a large region • Tephrostratigraphy – correlation on the basis of tephra (volcanic ash) • Biostratigraphy – correlation based on fauna succession and their evolutionary history 2. Calibrated Relative Dating Methods (correlated to absolute chronology) • Obsidian hydration • Amino acid racemization • Paleomagnetism (use of geomagnetic polarity time scale) 1. Chemical techniques • F-U-N trio (Fluorine, Uranium, and Nitrogen) in bone remains Chronometric or Absolute Dating Method • A technique that utilizes radioisotopic calibration of different elements such as Carbon (C), Potassium (K), and Argon (Ar) • The method exploits some aspects of radioactive decay of K and Ar, where initially an action sets the clock to zero • Such as heating of a rock containing Ar during volcanic eruption, then radioactive decay steadily accumulates, thus recording the passage of time. Methods used in chronometric dating • Potassium-Argon (K40/Ar40) • Argon-Argon (Ar39/Ar40 ) • Fission-Track on volcanic glass particularly in Uranium series (Ur238/Ur239) • Thermoluminescence (TL) such as in quartz and feldspar minerals • Electron Spin Resonance (ESR) – e.g. on tooth enamels • Radiocarbon (C14) decay: ratio of C12 to C14 • Amino acid racemization (L-amino D-amino acids ratios over time) Advancement in dating methods SCLF techniques Geomagnetic polarity • Paleomagnetic dating of earth’s geomagnetic polarity time scale (GPTS) • Measures changes in periodicity and intensity of earth’s magnetic field • Changes usually take place about 5,000 years to occur • They are measured as either normal or reversed polarity events.