What is a Hominid? Hominid! Evolution: On The Origin of Humans The term hominid is also used in the more restricted sense as hominins Humans and relatives of humans closer than chimpanzees Bipedal Modern man is the only member of this group alive today Hominid Sites Earliest fossil hominid sites are in Africa They now span the latest Miocene to the early Pleistocene from about 6-7 mya to about 1.6 mya The major groups of sites are: 1. Ethiopia = Middle Awash valley & Hadar (Australopithecus afarensis) 2. Kenya = Lake Turkana 3. Tanzania = Olduvai Gorge 4. South Africa = various sites in limestone caverns centered around Sterkfontein What Makes A Hominid? - Bipedalism Primary feature distinguishing hominids from other hominoids is walking erect on two legs erect bipedalism Adaptations for bipedalism in the partial skeleton of Lucy, an australopithecine ( 3.2 mya) clearly seen in the hip, spine and leg bones 1
Why did bipedalism become the primary adaptation of hominids? Climate Change resulting in forest habitat being replaced by grasslands. Advantages of Bipedalism 1. Carrying behavior 2. Reduction of overall heat stress - facilitates heat loss through convection by exposing body to air currents, only humans have sweat glands that produce moisture to cool body 3. Most energy efficient way to travel long distances 4. Allows for better vision in open environments & defensive action against predators by freeing hands to throw objects Evidence for Early Bipedalism The record of bipedalism is most graphically preserved in the fossilized footprints at Laetoli, Tanzania, 3.6 mya Tracks of 2 individuals were uncovered in volcanic ash by Mary Leakey (1978-79) Footprints were left by 2 australopithecines in damp volcanic ash of Laetoli Notice how close the tracks are! Laetoli Footprints Laetoli footprints clearly show that the creatures who made them were fully bipedal Big toe hardly diverges from the rest of the foot, unlike in apes Gait = heel-strike followed by toeoff the way modern humans walk 2
2 early hominids walk bipedally across an open ash field produced by an erupting volcano. Rain wet the volcanic ash & footprints filled up with more ash, and were thus preserved. Footprints reveal that our ancestors walked upright with a gait very similar to our own. Laetoli Reconstruction First Adaptive Radiation 7-6 mya in the late Miocene, potential last common ancestors between humans and apes 1. Sahelanthropus tchadensis 7-6 mya in Chad (North Central Africa) 2. Orrorin tungenensis 6 mya in Kenya (East Africa) Note: These organisms were forest adapted. 1. Sahelanthropus tchadensis 2. Orrorin tungenensis Discovered in Chad (7-6 mya) Most complete cranium from this time period Mosaic of ape & human-like features, but at the ape grade of evolution: Cranial capacity (320-380 cc) U-shaped upper jaw Very wide distance between the orbits Large, thick continuous brow ridge Human-like flat face Human-like dentition Fossils from Tugen Hills in Kenya have been dated to about 6 mya Earliest Evidence for Walking on Two Legs? 3
Orrorin tungenensis (cont.) Fossils Include: upper portion of a femur, lower portion of the humerus, some lower jaw fragments, & teeth Arm bone: virtually identical to that of a chimpanzee Femur: more human-like, most important for showing adaptations for walking on 2 legs Was Orrorin a direct human ancestor, or a common ancestor of chimps and humans? Second Adaptive Radiation 5-4 mya in early Pliocene, first true hominids 1. Ardipithecus ramidus 5.5-4.5 mya in Ethiopia (East Africa) 2. Australopithecus anamensis 4.2-3.9 mya in Kenya (East Africa) Note: These organisms were forest adapted and fully bipedal. 1. Ardipithecus ramidus Ardipithecus ramidus (cont.) Between 4.5 and 5.5 mya from the Middle Awash valley site in Ethiopia Fossil Remains very fragmentary: limb bones, toe bones, jaws & teeth Earliest True Hominid or Last Common Ancestor? LAST COMMON ANCESTOR OF CHIMPS & HUMANS MOST LIKELY HAD A MIX OF FEATURES: SOME RETAINED IN CHIMPS, OTHERS RETAINED IN HUMANS! Straight toe bones suggest it may have been bipedal A mosaic of features seen in later hominids & modern chimpanzees 4
2. Australopithecus anamensis Lake Turkana Region of Kenya 4.2-3.9 mya Probably walked upright Teeth enamel thicker than Ardipithecus ramidus, so diet included hard foods Australopithecus anamensis (cont.) Fossil Remains very fragmentary Those shown here include: Jawbone part of the front of the face parts of an arm bone (radius) fragments of a lower leg bone (tibia) Third Adaptive Radiation 4-3 mya in middle Pliocene, many hominids 1. Australopithecus afarensis ( Lucy ) 4-3 mya in East Africa 2. Australopithecus africanus 4-2.5 mya in South Africa 3. Kenyanthropus platyops 3.5-3.2 mya in Kenya Note: These organisms lived in open woodlands & along wooded streams in the savannas, ate fruits and soft foods, maybe had a tool-culture like modern chimps 5
1. Australopithecus afarensis Australopithecus afarensis 4-3 mya in East Africa Pelvis & leg bones resemble modern humans Sexual dimorphism (males larger with sagittal crest) Tree climbers (curved fingers & toes) Ape-like Features: Small brain case (430 cc.) Prognathic (jutting out) face U-shaped palate (v. parabolic shape) A. afarensis Skeleton - Lucy 2. Australopithecus africanus 4-2.5 mya in Transvaal region of South Africa 1924: 1 st Australopithicine to be described by Raymond Dart! Globular cranium, slightly higher ratio of brain to body size than A. afarensis Face less prognathic than A. afarensis Proportions of arm to leg lengths may be more ape-like than A. afarensis 6
Australopithecus africanus A. afarensis verses A. africanus best known A. africanus cranium (front & lateral views) Most complete A. africanus skull Australopithecus afarensis Australopithecus africanus Taung Child 3. Kenyanthropus platyops Kenyanthropus platyops 3.5-3.2 mya: found in 2001 west of Lake Turkana in Kenya Ape-like features: small ear canal, small brain case Human-like features: flat face, small molars Importance: flat face appeared early in evolution, alongside the range of other facial forms. Evidence that evolution is not linear or progressive. 7
Fourth Adaptive Radiation 3-1 mya in late Pliocene, more robust hominids 1. Paranthropus boisei 2.2-1.2 mya in East Africa 2. Paranthropus robustus 2-1 mya in South Africa 3. Australopithecus garhi 3-2 mya in East Africa Note: Lived in open dry woodlands & savannas. The robust species are famous for eating hard-to- chew food, like seeds, nuts, and roots. May have used tools to dig for roots in dry seasons. 1. Paranthropus boisei 2.2-1.2 mya in East Africa: Ethiopia, Kenya, Tanzania Largest teeth found in any hominid! Referred to as hyper-robust due to massive molars and premolars Skull: broad, short face with flaring cheek bones, relatively small brain, pronounced sagittal crest in males Skull and dental features are adaptations for heavy chewing! Paranthropus boisei (KNM-ER 406) Paranthropus boisei (KNM-ER 406) 8
2. Paranthropus robustus Paranthropus robustus 2-1 mya in South Africa Short, broad face with deep zygomatic arches (cheek bones). Larger individuals have sagittal crests. Large molars covered with thick enamel Wear patterns on teeth: herbivorous diet of hard resistant foods such as seeds, nuts, roots Lived in grasslands near rivers and wetlands 3. Australopithecus garhi Australopithecus garhi 3-2 mya in East Africa: spotty fossil record, cranial & dental remains found in 1999 in Bouri, Ethiopia Bones of antelopes, horses, and other animals with cut marks made by stone tools: butchering animals & smashing bones for marrow. First meat eaters? Molars too large to be early Homo genus Ape-like long lower arm, human-like upper arm & leg Mixed traits: classified as a new species, maybe ancestor of early Homo genus 9
Australopithecus garhi Australopithecus garhi EARLIEST BUTCHERS: Signs that hominids scraped & smashed animal bones, like this antelope tibia, 2.5 mya One surprise in the A. garhi skull was enormous back teeth, instead of smaller ones seen in later Homo species Earliest documented percussion marks made by hominids, presumably extracting fatty marrow from these bones Rise of the Genus Homo Homo habilis Homo habilis Handy Man Homo erectus or Homo ergaster in Africa Homo heidelbergensis Archaic Homo sapiens Homo sapiens neanderthalensis - Neanderthal Homo sapiens sapiens Modern Man Slightly larger braincase and smaller face and teeth than Australopithecus Still retains ape-like features of long arms and moderately prognathic face 2.4 1.4 MYA Average height = 3 4 to 4 5 Average weight = 70 lbs. 10
Homo habilis Thick tooth enamel suggests they had an omnivorous diet, but were capable of eating fairly tough foods like leaves and woody plants By this time, the feet of early humans had a modern-type arch Homo erectus 1.89 MYA 143,000 years ago Modern human-like body proportions indicate adaptations for living exclusively on the ground Expanded braincase relative to the size of the face Left Africa and spread into Asia Longest lived early human relative (9 times longer than we have been around so far) Used fire (warmth, cooking) Evidence they cared for the sick and old (see skull to left) Average height = 4 9 to 6 1 Average weight = 88-150 lbs. Homo erectus Homo heidelbergensis Turkana boy fossil Hand axe first major innovation in stone tool technology Very large brow ridge Larger braincase and flatter face than earlier human ancestors Short, wide bodies adapted to living in colder climates Most likely candidate to have been common ancestor between Neanderthals and modern humans Average height = males 5 9, females 5 2 Average weight = males 136 lbs., females 112 lbs. 700,00 200,00 years ago 11
Homo heidelbergensis Homo sapiens neanderthalensis Used wooden spears to routinely hunt large animals Built shelters out of wood and rock 200,000 28,000 years ago Short, stocky bodies and huge noses were adaptations for living in cold environment Larger braincase than modern man Sophisticated tools, used shelters, wore clothing First human ancestor to bury their dead and mark the graves Modern humans led to their extinction but unclear as to exactly how Average height = males 5 5, females 5 1 Average weight = males 143 lbs., females 119 lbs. Homo sapiens neanderthalensis Homo sapiens sapiens La Ferrassie 1 Most complete Neanderthal skull ever found Ornamental jewlery Originated in Africa 200,000 years ago Highly vaulted, thin-walled skull led to more developed frontal lobe of brain Flat forehead and face Less heavily developed jaws and small teeth 12
Homo sapiens sapiens Homo sapiens sapiens Many advancements in art, culture and tool making technology Map of Hominid Evolution 13