Australopiths Anthropology 201 Fall 2024 PDF

17. The Australopiths Anthropology 201 Fall 2024 Last Time… Covered everything > 4 Ma (in green) – Sahelanthropus – Orrorin – Ardipithecus First likely bipeds Rel...

17. The Australopiths Anthropology 201 Fall 2024 Last Time… Covered everything > 4 Ma (in green) – Sahelanthropus – Orrorin – Ardipithecus First likely bipeds Relationships to each other and to later hominins unclear 2 Today… Australopiths – Red – Purple – Orange The hominins diversify! 3  Objectives By the end of lecture, students should: Know the temporal and spatial distribution of the australopiths Pay special attention to our defining features of hominins Identify the features that show they were bipedal, and those that suggest they still used trees Distinguish dietary adaptations of Paranthropus Reading: Chapter 10, p. 243-258 4  What is an Australopith? The next group of fossil hominins as we move through time a.k.a Australopithecines (terms are interchangeable) Found from ~ 4 Ma to ~ 1 Ma Traditionally broken down into two genera: – Australopithecus – Paranthropus Two main geographic areas: – East Africa (older sites here) – South Africa (found here first!) Australopithecus afarensis is the best known species. Most of what we know about australopiths comes from this one 5  Hominins Diversify 4-1 Ma , major hominin groups emerge Australopithecus Paranthropus Kenyanthropus platyops – 3.5-3.2 Ma – Weird mixture of Australopithecus and K. platyops Paranthropus features 6  Where are australopiths found? Know: - countries - major fossil localities on this map 7  Australopithecus anamensis The oldest australopith Lower jaw Kenya/Ethiopia - 4.2-3.8 Ma Derived traits – Small(er) canines, thick enamel, large molars – Knee & ankle for bipedalism Chimp anamensis Primitive traits – box-shaped jaw like apes (parallel Tibia (shin bone) tooth rows), larger canines than later australopithecines – Upper limb features for arboreality Probably lived in mixed habitats (grasslands, woodlands) Upper Lower 8  Australopithecus afarensis Well-known from several sites in East Africa from 3.7 – 2.9 Ma Lived in mix of forest, woodland & savannah habitats Important specimens: – AL 288-1 (“Lucy”) found in Hadar, Ethiopia, 1974 by Don Johanson 40% complete skeleton revealed details of locomotion – AL 333 – “First Family” (n=13 individuals all found together) – Selam – Dikika Child - 3 year old female skeleton – Laetoli fossil footprint trackway 9  Why is A. afarensis so interesting? Best known, and largely representative Highly sexually in body size, of all australopiths Mixture of primitive and derived traits, moderate canine dimorphism many are intermediate – Diastema on mandible (for large Face prognathic, medium canines, honing canines) somewhat curved tooth rows, large Ape-like brain size (404 cc molars and premolars with thick enamel. cranial capacity in Lucy) Large neck and chewing muscles i.e. ape-like skull and teeth 10  A. afarensis body Major shift in adaptations related to locomotion Shows clear evidence of habitual bipedalism Changes in: – Pelvis – Femur/Knee – Foot Remember the “Walking with Lucy” video: https://www.youtube.com/watch?v=xT8Np0gI1dI 11  Bipedal Adaptations - Hip Pelvis – Ilium flared & rotated – allows hip abductors to Pan keep body over midline – Enlarged sacrum-ilium joint – more capacity for weight-bearing Aust. Homo 12  Bipedal Adaptations - Knee Femur & knee – Valgus knee – femur Homo angled medially (towards midline) - Aust. places body weight Pan closer to midline – Minimizes side-to- side motion when you walk – Puts support structure (knee) directly under trunk 13  Bipedal Adaptations - Foot – Enlarged heel (absorbs forces at heel strike) – Longitudinal arch (stiffens foot into propulsive lever and absorbs forces during stance) – Big toe in line with the other toes 4th Metatarsal Pan Gor. Aust. Homo Calcaneus = heel bone 14  But also some arboreal “retentions” Relatively long arms Mobile shoulder joint oriented superiorly Slender, curved fingers & toes May have spent time in the trees (safe from predators) 15  A. afarensis bipedalism From waist down, “Lucy” shows adaptations for bipedal walking, similar to modern humans: – Hip abductors, long femoral neck, carrying angle, large sacrum and femoral head (joints), plantar arches, large heel, etc… But was it as efficient as modern humans? – Compromised “bent-hip bent-knee” (BHBK) gait? – Short legs = more steps to move the same distance 16 Laetoli Footprints “Smoking gun” of habitual bipedalism in A. afarensis? Tanzania, 3.4 Ma Formed by 3 individuals walking in wet volcanic ash Analyses show pattern of footfalls similar to modern humans 17  A. afarensis and Laetoli Tracks Laetoli tracks and modern analyses Take 3D pictures of footprints left in wet sand, compare to Laetoli depressions Heel and toe depressions equally deep, not so in BHBK à Lucy did not walk with BHBK gait. More modern type of bipedalism 18  Australopithecus africanus First hominin species ever found in Africa “Taung baby” – Raymond Dart, first discovery in 1924! – Said hominin because of foramen magnum position – Rejected by most scientists as too “Taung baby” primitive and brain too small South Africa 3 – 2.2 Ma Postcrania similar to A. afarensis Dentition different: – smaller canines and incisors – larger molars 20  A. africanus Cranium and body much like A. afarensis, but with even larger cheek teeth and deep mandible = chewing adaptations? 21  Growth and Development in Australopiths Taung Baby and Selam (Dikika Child) are both ~ 3 years old Help us to understand life history patterns Both grew fast, like apes Dental eruption sequence Rates of enamel growth 22  Australopithecus garhi 2.5 Ma in Afar, Ethiopia Name means “surprise!” in Afar language Even larger molars and premolars than A. africanus Found in association with cut- marked animal bones – Evidence of butchery by hominins – Stone tools found in similarly aged deposits – Hunting or just scavenging? 23 Australopithecus sediba Recent find (2010) South Africa, 2- 1.8 Ma Maybe descended from A. africanus and claimed ancestor of genus Homo – Has Homo-like face and teeth – Small brain Two partial skeletons Fully bipedal but still somewhat arboreal (long arms) “Transitional species” or A. africanus? 24 Paranthropus: the “Robust” Australopithecines Separate line that diverged from early hominids Genus Paranthropus – Disputed: Australopithecus also used Paranthropus aethiopicus – Lake Turkana, Kenya, 2.5 Ma Paranthropus boisei – East Africa (w/ H. habilis), 2.2-1.3 Ma Paranthropus robustus P. boisei – South Africa (w/ A. africanus), 2-1 Ma 25  “Robust” Australopithecines Postcranium: same bipedal adaptations as A. africanus and A. afarensis Skull/teeth: specialized dietary adaptations – Massive molars (with molariform premolars) – Large sagittal crests & wide flaring zygomatic arches (leaves room for large temporalis muscle) – Thick lower jaw – Diet likely of very hard or tough foods (seeds, nuts, tubers) 26 MOLAR SIZE HUMAN Paranthropus boisei  Chewing Muscles Gorilla P. boisei P. robustus Temporalis Muscle 28  Australopith Diets Are varied Trend over time for increase in premolar and molar size (post-canine dentition) coupled with thicker enamel Faces and mandibles get larger Bony attachments for chewing muscles get larger Most extreme in Paranthropus à To process harder or tougher food items? 29  Sexual dimorphism in australopiths Recall: sexual dimorphism and social correlates Body size dimorphism: similar to modern gorillas and orangutans (a lot!) Canine dimorphism: Less than chimpanzees but more than humans An odd combination - not seen in any living primate. Male-male competition, but not aggression? 30 Early Hominin Phylogeny Lots of uncertainty as to how species are related Not sure how if/how any of the ‘earliest hominins’ is related to australopiths Some australopith led to the genus Homo but we don’t know which one – Probably Australopithecus and not Paranthropus 31  Another phylogeny From your textbook Klein, 2009 Paranthropus is a clade Who is ancestral to genus Homo? 32  Australopithecus Age (Ma) Location A. anamensis 4.2 -3.9 East Africa A. afarensis 3.6- 3.0 East Africa A. africanus* 3.7 - 2.2 South Africa A. garhi 2.5 East Africa A. sediba ~2 South Africa Paranthropus P. aethiopicus 3 – 2.3 East Africa P. boisei 2.2 – 1.3 East Africa P. robustus 2–1 South Africa 33 * Dr. Cote is skeptical that A. prometheus represents a distinct species from A. africanus.