Kevin Callahan's Lab Notebook
Fall Quarter 1997

Lab 7 Notes Fall 1997 Australopithecines Our Early Hominid Ancestors habitually bipedal change in dentition increase in brain size Hominid characteristics Three unique characteristics evolved independently. Bipedalism evolved first. Hominids are habitually bipedal apes. (Last weeks lab). Distinctive hominid teeth evolved second or at the same time. (This week’s lab.) Large brains evolved last. Purpose of the lab By reconstructing what the teeth and skull look like you can reconstruct what the diet, foraging, environment, territory range, and perhaps something about the social organization, group size, and mating strategy of the species. A written assignment is due next week. You only need to discuss FOUR (4) of the topics under "Be Sure To Discuss" list. Write about Australopithecus afarensis. Terms to know Masticatory system - the chewing system composed of the teeth, the muscles, and the bones of the cranium that anchor the chewing muscles. subsistence - what the animal lives on and how it gets it. Terms that describe gradients Describe the specimens features like they were on a general relative scale or gradient relative to each other e.g. the molars are big or small or the enamel is thick or thin. A few features you measure with calipers. Certain specific terms help describe what to look for (observe) with each species. Sometimes it is helpful to think of these features "morphing" through time. The Face prognathism - a protruding lower face. Chimps are prognathic orthognathic - flat faced. We are flat faced. Is the animal prognathic or orthognathic? Generally over time the faces become less prognathic. Temporalis muscle (Temple) Temporalis muscle - the muscle that moves the jaw for chewing on the side of the head. Sagittal crest - the ridge that the large chewing muscle attaches to on top of the head. If the cranium is large the sagittal crest is not needed to create an area to anchor the muscle to. Temple line Temple line - the line along the side of the cranium where the muscles attach to. Is it high and strongly marked or hard to see? temporal fossa - the slight hollow on the side of the skull behind the orbit or eye. You can feel the temporal muscle by touching your temple and moving your jaw. The Masseter muscle The muscle on the inside of the zygomatic arch (see pg. 10) You can feel it when you clench your teeth. The ascending ramus - The bone that is the vertical part of the mandible (lower jaw). A longer ascending ramus increases the power of the masseter muscle for chewing. Zygomatic arch zygomatic arch - the bone from the cheek area back to the ear. nuchal area - where the neck muscles attach to the cranium the nuchal muscles are the muscles at the back of the neck. gorillas need so much room to attach the nuchal muscle that they have a nuchal crest across the back of the cranium (occipital). Teeth Incisors - the front teeth What is the shape of the dental arcade - the shape of the jaw. Is it V shaped, U shaped, rectangularly shaped, parabolic? procumbent - are the incisors angled (vs. vertical)? Teeth and Diet mesial-distal length - How wide is the widest incisor from the mesial (middle) to the distal (distant) edge. Leaf eaters have narrow front teeth relative to the molars. Fruit eaters have wide incisors relative to the molars. Canines and Diastemas Canine - the longest tooth How big is it relative to the incisors? Canines may indicate male- male competition rather than meat eating. Canines need a space in the lower jaw in order to close the mouth. This gap for the canine to fit into is called the diastema. Some Australopithecines had it. Some did not. Canines and Premolars Some canines look like the incisors and are said to be incisiform. Others are large and dagger like. Incisor like canines indicate diet outweighed the sexual selection since the movements of chewing are more difficult with a large canine. Does the first premolar have a honing facet that sharpens up the canine? Premolars and Molars Premolars are large and cupsed if chewing is important. How big are the molars relative to other species? bucco-lingual width - How wide is the molar from the tongue to the cheek sides. Big molars are doing a lot of chewing and processing of tough food. Thick enamel is needed for tough food (seeds, roots) with mashing (not slicing). Cusps cusps - How high and sharp are the cusps? High cusps indicate thin enamel. Tall sharp cusps are for leaf eating or shearing/slicing a flat surfaced leaf, etc.. Short and blunt cusps are "mashers" like seed eaters and fruit eaters. Africa Darwin predicted that Africa would eventually yield remains of the earliest stages of human evolution Australo pithecine "Southern Ape" Australopithecines & Paranthropines Australopithecines gracile - "graceful"smaller Paranthropines robust - "larger" Paranthropines used to be called Australopithecines AUSTRALOPITHECINES ARDIPITHECUS RAMIDUS 4.4 MYA AUSTRALOPITHECUS ANAMENSIS 4.3-3.9 MYA AUSTRALOPITHECUS AFARENSIS 4-2.5 MYA AUSTRALOPITHECUS AFRICANUS 3.9-3.0 MYA Ardi pithecus ramidus "Ground Ape" "root" Ardipethecus ramidus 4.4 mya East African Rift Valley (Aramis, Ethiopia) Ardipithecus = "ground ape" Ramidus = "root" (the root species) Found 1994 Tim White, Berkeley Was A. ramidus bipedal? The arms do not seem to be those of a knucklewalker. The base of the cranium suggests erect posture.The humerus is too lightly constructed for knuckle walking. It is not clear if A. ramidus was bipedal. 90 ramidus fossils have been announced but not described. Thin tooth enamel. Thicker than a chimp. Small cranium. Ardipithecus ramidus A. ramidus lived in a woodland environment. The environment was more forested than than the environment of any later hominids. The species of Australopithecus There are two major groupings. The oldest 3 Australopithecines are gracile (thin or slight - smaller). The later 3 Paranthropines are robust (muscular strong, or healthy - larger) The change is towards heavy chewing with more powerful teeth, jaws, and attachments for chewing. Australopithecus anamensis 4.2 - 3.9 mya East African Rift Valley (Lake Turkana) Australopithecus = "southern ape" anamensis = "lake" Found 1995 Maeve Leakey Was A. anamensis bipedal? 21 specimens have been found Confirmed bipedalism Specimens blend primitive large ape-like canines and advanced bipedalism and thick tooth enamel. Cranium is small and chimp-like. AUSTRALOPITHECUS ANAMENSIS 4.3-3.9 MYA Sites: Kanapoi, Allia Teeth and jaws of a hominid Male 5’1" 112 lbs. Female 4’3 " 73 lbs Australopithecus afarensis 4 - 2.5 mya Rift Valley (Hadar, Ethiopia) No. Central Africa (Bahr el Ghazal, Chad). A. = "southern ape" "afar" = the people of Afar, Ethiopia Found 1974 Don Johanson & M. Taib Australopithecus afarensis Australopithecus afarensis hand (not Lucy’s) Note the shortness of the thumb (relative to your own hand). Australopithecus afarensis Dentition is more like ours (reduced canines, parabolic jaw shape). Slight diastema (lower jaw space for a canine) Omnivorous diet Small chimp-like cranium & as prognathic. Habitually bipedal femur & locking knee Upper body like a brachiator (possibly both) Highly sexually dimorphic (small females) Australopithecus afarensis Australopithecus afarensis females = less diastema AUSTRALOPITHECUS AFARENSIS 4-2.5 MYA "LUCY" A. afarensis A small female less than 4 feet tall Found in the Afar triangle area of Ethiopia The first solid evidence found of bipedalism The pelvis and femur were so bipedal that she could not be the earliest representative of bipedalism (the femur was angled towards a locking knee). She was not as efficient as us but she could run. LUCY Lucy had somewhat longer arms than us She had shorter thumbs THE LAETOLI FOOTPRINTS A. afarensis The Laetoli footprints, 1976 Tanzania, Mary Leakey (dateable) Volcanic ash preservation of footprints from 3.7 mya with Mostly inline big toes, arches, heel strike, bipedal stride. Pg. 201 Textbook afarensis social organization Laetoli suggests a possible pairing. afarensis was sexually dimorphic implying polyandry or an age graded dominant male, multi-male/ multifemale group like gorillas This has been questioned One afarensis site had 13 individuals who apparently died at the same time. Australopithecus africanus 3.5-2.5 mya South Africa (Taung, Sterkfontein "southern ape of africa" Raymond Dart 1924 The Taung child Australopithecus africanus The first Australopithecine to be identified by Raymond Dart in 1924 was The Taung Child (fossilized brain and small teeth). The Taung Quarry found and mailed to Raymond Dart a juvenile specimen with a face, baby teeth (except for the 1st molar -helps to give an age), and a fossilized brain called an endocast. The canine was not as developed as a chimp, but was not human. The Taung Child Estimated age 3 years old. Probably killed by an eagle (talon). Note the fossilized brain. Australopithecus africanus The dentition is more similar to ours with reduced canines, more parabolic jaw and no diastema (space in the lower jaw). Probably omnivorous. Small cranium=chimp-like. Habitually bipedal but may also have brachiated like A. afarensis The foramen magnum was centered like modern humans. Raymond Dart realized it was bipedal. AUSTRALOPITHECUS AFRICANUS 3.9-3.0 MYA Australopithecus africanus africanus A. africanus had a slightly larger brain than afarensis but not as large as the paranthropines or the Genus Homo. A. afarensis had a shorter thumb and neither a power grip or precision grip. A. africanus had a power grip but no precision grip. We have both a good power grip and precision grip. PARANTHROPINES "near man" PARANTHROPUS AETHIOPICUS 2.6-2.3 MYA PARANTHROPUS BOISEI 2.4 - 1.3 MYA PARANTHROPUS ROBUSTUS 2-1 MYA Paranthropines Paranthropines have a strong adaptation to chewing Large chewing teeth - molars and premolars (megadonts - large teeth). Robust jaws to hold the large teeth. Large zygomatic arches and sagittal crests to attach large chewing muscles to. Paranthropus aethiopicus Paranthropus = "near man" 2.6-2.3 mya "ethiopia" E. African Rift Valley Lake Turkana The "Black Skull" 1985 Richard Leakey Paranthropus aethiopicus Heavy chewing and hard foods; small cranium-chimp-like A transitional species between Australopithecus afarensis and the later robust forms (Paranthropines). In some ways more primitive than africanus, such as being as prognathic as afarensis. Paranthropus aethiopicus "The Black Skull" Paranthropus boisei 2.4 - 1.3 mya E.African Rift Valley (Olduvai Gorge) 1959 Louis & Mary Leakey 1st major find "near man" "boisei" Originally named "Zinjanthropus" Most robust of the paranthropines Paranthropus boisei Sagittal crest for heavy chewing muscles and flaring zygomatic arches, huge jaw and large molars for grinding hard vegetable foods. Not on our direct evolutionary line. Part of The Big Party Paranthropus boisei boisei and robustus are quite different from aethiopicus. boisei and robustus probably are descendants of africanus afarensis and aethiopicus had brains about the size of a chimp, about 400 cc africanus was bigger at about 450 cc boisei and robustus were larger 500-550 cc boisei and P. robustus boisei and robustus had both power grips and precision grips The molars were so big they crowded the incisors which became smaller. Boisei is (confusingly) more "robust" than robustus (Boisei was found later). Clifford Jolly’s Seed Eating Hypothesis Savannah baboons eat more fruits and leaves and thus have a smaller facial architecture for chewing (like the gracile australopithecines). Gelada baboons eat more seeds, roots, and small plants (smaller, harder things) and thus have larger teeth and a larger chewing apparatus (like the robust paranthropines). Paranthopus boisei from Koobi Fora, Kenya Note the prominent sagittal crest, enormous arching cheekbones for chewing, and flat face. Paranthropus boisei from Olduvai Gorge, Tanzania Note prominent sagittal crest to anchor huge temporalis muscles, flaring cheekbones, molars 4 x the size of ours, small incisors, flat dished face "Nutcracker man"aka Zinj. Paranthropus robustus 2-1 mya South Africa 1938 Robert Broom "robust near man" Heavy chewing and a diet of hard foods Sagittal crest, flaring zygomatic arches, huge grinding jaws, large molars, small cranium. Paranthropus robustus from Swartkrans, So. Africa Note the slight sagittal crest, broad, flat face, small canine, and enlarged rear teeth. Paranthropus boisei & robustus Note that boisei is larger and the sagittal crest is bigger than in robustus. Both have flat, almost dished, faces with large cheekbones Why Bipedalism? Disadvantages: slower than quadrupedalism at short distances e.g. dogs, horses and monkeys childbirth (narrow shape of the pelvis and the large head makes childbirth difficult) back problems Locomotion on the ground The ancestor of humans and african apes had given up quadrupedalism at least 15 my before. The problem was brachiators needed to move on the ground. Brachiators grasping fingers are too long to be placed palm down on the ground. Orangutans walk on the back of a fist. Gorillas and chimps walk on the back of the knuckles Part time brachiators needed their hands. Advantages of bipedalism Bipedalism was good for efficient long distance walking (useful in food gathering). Humans are much better at long distance running and walking than most quadrupeds. Over a distance of 300 to 400 yards a human can outrun a cat - even a cheetah. Over marathon-length distances (20 miles or more) a human can even outrun a dog or a horse. Long Distance Running Runners in the Southwest would run 125 miles at a stretch (messengers). e.g. Tarahumara (northern Mexico) North of the border had runners as well. Carried 200 lbs loads when moving a camp. Advantages of bipedalism Australopithecines were competing with predators. They were active during the day when many predators avoided the heat. They could see farther when upright and see scavenging birds and predators They exposed less body surface (the head) to the sun than quadrupeds (the whole back) The head was in the breeze for cooling. Advantages of bipedalism Hominids can carry things in their hands like food and children (who could not grasp the carriers hair to stay on). Hairlessness is cooler than fur. Evaporates. The environment may have been warmer, wetter, and more wooded in East Africa than now. Bipedalism may have been a way to reach higher. Chimps stand while forest feeding. Australopithecine life Habitat: Australopithecine fossils are typically found in open grassland habitats. This suggests an open country environment. This may actually have been a far ranging high country adaptation rather than adaptation to a savannah environment. Ardipithecus ramidus lived in forest. The Savannah Hypothesis Elisabeth Vrba of Yale studying antelope and bovid bones suggested two drying up periods in Africa (less trees, more grassland) occuring around 5 million years ago (bipedalism) and 2.5-2 mya (Genus Homo begins - larger brains and tool use). This "turnover pulse" of extinctions and adaptations has been criticized by soil scientists who find no increase in grass. Environment and change Over the past 5 my African climate has cycled between wet and dry. The most dramatic dryness occurred 2.8 mya. This could have played a role in the dawn of Homo habilis at 2.4 mya. Rick Potts suggests that adaptation to a wide range of environments caused the brain expansion in hominids. A.afarensis was found in dry & lush areas. Origins of bipedalism Upright threat displays of great apes and fighting? (But they are not bipedal). Owen Lovejoy’s gathering hypothesis is that freeing the hands to allow the male to bring food back to the female would allow more children to be born (it assumes a pair bond and serial monogamy - but afarensis was sexually dimorphic). Some think this hypothesis shows an androcentric bias. Carrying with the hands Most primates can walk bipedally occasionally, and usually do so to use the hands to carry something e.g. bananas. This may have confered an adaptive and reproductive advantage in a particular environment. Primates on a savanna would have to travel far to find edible vegetable food and the seasonal changes are more severe. Savannas Savannas have more predators (lions, leopards, cheetahs, wild dogs, hyenas). Many are primarily nocturnal hunters. Forests only have the leopard. More scavenged meat is available on the savanna-but not enough to live off of all the time(~one carcass every six days). Unlike vegetables it is available year round. Humans are cooperative (like baboons). Why bipedalism? One view notes that pongids and hominids were separated by the Great Rift Valley 8 mya. East of the valley was drier (savanna) and is where hominid fossils were found. West of the valley is moist and is forested and is where chimps and bonobos are found. Neoteny "holding youth" adult members of some species possess characteristics of young, even fetal members of related species. Adult humans "resemble" young chimps (large, round head, flat face, no prognathism,lack of body hair, centered foramen magnum that moves, mostly in-line big toe, retention of open cranial sutures. Neoteny & larger brains There is longer brain growth in humans. Brains of apes grow very rapidly around birth. Human brains retain the growth for a longer time. Neoteny may be the result of a mutation of one or more debvelopmental genes that retard the normal development of features. Is a larger brain the result of a mutation that retained the period of rapid brain growth? Summary Australopithecines probably lived in "small groups in forests and/or open areas;getting food by gathering, perhaps scavenging, and maybe even hunting small animals; organized around some sort of family unit and with interpersonal bonds supported by conscious sexuality, sharing of important resources, and defending the group members and territory" ( Feder and Park).

Lab 1 Notes Fall 1997
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