Relative dating methods. Paleoanthropology. Chronometric dating methods. Dating as probability statement

Transcription

1 Relative dating methods Paleoanthropology Fossil Man and Fossil Men Stratigraphy: based on superposition of geologic and cultural deposition More recent deposits lie on top of older deposits Biostratigraphy: based on evolutionary changes of fossils (e.g., pigs) The appearance of certain animals can be used as a key to the age of the deposit Chronometric dating methods Potassium-Argon (K/Ar): 1.3 billion year half-life. Dates volcanic deposits Carbon 14 (14C): 14C decays to 14N with a half-life of 5,730 years Dates carbonized organic materials Dating as probability statement Dates are imprecise because of errors that can occur during the collection and measurement of samples. Therefore, they are given with a range of values. E.g., million years means that there is a 67% chance that the date falls into the range of million years, and a 33% chance that the true date is outside that range. 1

2 Humans versus Apes In searching for fossil relatives of man, we need to be aware of the differences between men and apes. These fall into three functional categories that have evolved separately from one another: Cranial differences Dental differences Locomoter differences Modern African Apes Common Ancestor Modern Man 5-8 million years Cranial differences Larger brains (1200 cc vs. 500 cc) The larger brain creates a number of differences in other cranial features: flatter face smaller brow ridges no post-orbital constriction no sagittal crest Dental differences smaller canines no gap between upper canine and premolar no sectorial (modified) first lower premolar relatively small incisors and large molars very thick molar enamel a parabolic rather than U-shaped dental arch 2

3 Locomotor differences a foramen magnum that points down a curved lumbar spine a short, flared (versus long and thin) ilium (the upper most section of the hip bone or pelvis) a strong, robust talus (ankle bone) a strong, non-opposable big toe a complex two-way arch system in the foot Knee Comparisons Secondary Sexual Characteristics Much larger breasts Much larger penises But much smaller testicles than chimpanzees Gorillas have same size testicles as humans 3

4 Hominid Taxonomy Subfamily: Australopithecines Australopithecinae Family: Hominidae Sahelanthropus Ardipithecus Subfamily: Australopithecinae "Australopithecines" Subfamily Homininae "Hominines" Orrorin Kenyapithecus Sahelanthropus Orrorin Sahelanthropus Orrorin S. tchadensis O. tugenensis Ardipithecus Ardipithecus A. ramidus A. anamensis A. afarensis A. bahrelghazali A. africanus sub ramidus sub kadabba A. garhi A. aethiopicus A. boisei Robust Australopithecines Paranthropus A. robustus 4

5 Kenyapithecus Kenyapithecus Hominines Subfamily: Homininae playtops Homo Homo H. habilis H. erectus H. rudolfensis H. ergaster The Fossil Hunters H. antecessor H. sapiens H. heidelbergensis H. neanderthalensis Dutch physician Eugene Dubois First to have an explicit plan to search for fossil man Searched for early man in Java (1890s) Discovered and named Pithecanthropus (Homo) erectus Scorned, he hid the fossils for nearly 30 years British lawyer and amateur archaeologist Played a key role in the early unearthing of Piltdown Man Jaw of orang matched with modern skull Perpetrator or dupe? Charles Dawson 5

6 Marcelin Boule Raymond Dart French paleontologist Analyzed remains from La Chappelle-aux-Saints Declared Neanderthals as very primitive and apelike, not related to modern humans Brutish, bent-kneed, not fuly erect bipeds No--this isn t him! Anatomist in South Africa Received Taung skull in 1924 Coined name africanus Osteo-donto-keratic culture at Makapansgat Scottish physician, amateur paleontologist Went to South Africa to find fossil man following Dart Discovered australopithecines at Sterkfontein, Swartkrans, Kromdraai Robert Broom Canadian anatomist in charge of hominid fossils from Zhoukoudian Named Sinanthropus pekinensis (Homo erectus) on the basis of fragmentary remains Davidson Black British archaeologist Long term resident of East Africa Started work at Olduvai Gorge from s Always argued for very early human ancestors Homo habilis Louis Leakey Mary Leakey British archaeologist, wife of Louis Supervised archaeological work at Olduvai Discovered first australopithecine in East Africa (1959) Zinjanthropus () boisei Laetoli footprints and fossils 6

7 Amateur fossil hunter, son of Louis Instigated major Lake Turkana project Validated his father s Homo habilis with skull (KNM-ER 1470) found east of Lake Rudolf Richard Leakey American paleoanthropologist Worked at Hadar in Ethiopia in 1970s Famous for Lucy and First Family afarensis Donald Johanson 7