ANTH 1210: Transition to Hominins

• Lectures cover the transition to hominins
• These are lectures 18 & 19
• Dates for lectures are February 28 & March 3, 2025
• Course code is ANTH 1210 A01

Oldest African Hominin Fossils

• Sahelanthropus tchadensis lived ~7mya in Chad
• Classified as a hominoid
• Had a small brain and elongated skull
• Featured a sloping face and prominent brow ridges
• Classified as a hominin because the foramen magnum is central

Orrorin tugenensis

• Existed ~ 6mya in Kenya
• Were about the size of chimpanzees
• Small teeth with thick enamel
• Overall human-like features
• Bipedal and partially arboreal
• Similar neck length between human and Orrorin femora

Ardipithecus ramidus

• Existed ~4.4mya in Ethiopia
• Considered a possible hominin common ancestor
• Had hominoid dentition
• Displayed hominin bodies
• Had a big toe and rigid foot
• Central foramen magnum
• Bipedal/arboreal

First Hominins from the Great Rift Valley

• Existed from 4-1mya
• Included Australopithecines (Australopithecus)
• Also Paranthropoids (Paranthropus)
• These hominins had small canines and flat, thickly enameled molars
• Fully bipedal and partially arboreal
• Examples of places to find these fossils include Hadar, Ethiopia, Fejej, Ethiopia, and Kromdraai, South Africa

Hominin Diversity

• Diversity an adaptive radiation to dynamic environment
• Forests gave way to grasslands and savannahs
• Hypotheses for hominin evolution include: Savannah or aridity, Turnover pulse, and Variable Selection

Australopithecus anamensis

• Existed ~4.2mya in Kenya
• Was a small bipedal hominin
• Possessed a human-like lower body (e.g., tibia)
• Partially arboreal
• Teeth similar to Au. afarensis
• Ancestral to Au. afarensis
• Had a small brain and a protruding face

Australopithecus afarensis

• Existed from 4-3mya in Laetoli, Tanzania, and Hadar, Ethiopia
• Laetoli specimens date ~3.6mya
• Large number of individuals recovered (n=24+)
• Clear evidence of bipedalism
• "Lucy" is one example from this species, found in Hadar, Ethiopia, approximately 3.2mya.
• Lucy is a 40% complete skeleton
• Completely bipedal (hominin body)
• Occasionally arboreal
• Retained ape-like skull, jaw, and dentition

Australopithecus africanus

• Existed in South Africa ~3-2mya
• Taung Child was discovered in 1924 and is ~3.5 years old
• Rounder cranium, larger brain
• Smaller teeth (similar shape as humans)
• Had an S-shaped lumbar curve
• Bone morphology of hand suggests possible tool making

Australopithecus sp.

• Includes Au. bahrelghazali ~3mya, Chad
• Broadened Au. afarensis distribution
• Also includes Au. garhi ~2.5mya, Ethiopia
• Possible first tool use??

Australopithicus sediba

• Recently discovered in 1999 in Malapa Cave, South Africa ~2mya
• Fairly complete skeletons of juvenile and adult individuals were found
• Mixed Australopithecine and Homo traits
• Small cranial capacity, dentition, long arms, chest more Australopithecine-like
• More regular, human-like bipedal locomotion (leg bones and pelvis)

Paranthropoids

• Found in South Africa and East Africa
• Existed ~2.7m - 1mya
• Body size similar to robust Au. africanus
• Thick jaws, larger molars
• Massive muscle attachments
• Well-developed sagittal crests

Paranthropus aethiopicus

• Found in southern Ethiopia and northern Kenya, & Tanzania, dating 2.7 – 2.3mya
• Roughly contemporary with A. afarensis
• Very robust in jaw size and dentition
• Faces were broad/ dish-shaped
• Large sagittal crests for muscle attachments

Paranthropus robustus

• Existed in the Kromdraai Cave, South Africa
• Dates approximately 2m - 1mya
• Type specimen for Parathropus
• Displayed robust jaw and teeth
• Likely vegetarian diet

Paranthropus boisei

• Found in Kenya, Malawi, and the Olduvai Gorge in Tanzania, dating 2.4 – 1.4mya
• 'Zinjanthropus'- discovered by Mary Leakey in 1959
• Type specimen for P. boisei
• First evidence of early hominins present in East Africa
• Hyper-robust Parathropus sp.
• Possible tool use??

Genus Homo

• Found in western Kenya and Tanzania, Ethiopia, and South Africa
• Features increased brain size and a flatter face
• Similar body to Australopithecus
• Includes Homo habilis (~2.3-1.4mya)
• Also includes H. rudolfensis (~1.9-1.8mya)
• Contemporary with P. boisei and possibly H. erectus

Homo habilis "Handy Man"

• Larger brain size: 630-640cc
• Reduced molars/premolars, thick enamel
• Omnivorous
• Hand bones capable of precision grip
• Body similar to australopithecines
• Still partially arboreal
• Fossils found in same layers as butchered bone and the first stone tools
• Unclear if they actually made and used such tools

Homo rudolfensis

• Larger brain size: ~775cc
• Longer face
• Larger molars/premolars
• Body similar to australopithecines
• Still partially arboreal

Hominin Trends: Bipedalism

• Spinal column centered on foramen magnum
• Spinal column S-curved, acting as a spring
• Pelvis became more bowl-shaped
• Legs angled inward at the knee
• Arch in the foot

Why Bipedalism?

• Adaptation to life in savannahs
  • Advantageous in tall grass, better vision
  • Related to Savannah or aridity hypothesis for hominin diversity and evolution
• Energy conservation by walking on two legs is easier than four
• Thermoregulation: adaptation for better dispersion of body heat with cooling effect
• Adaptation frees hands while body moves for:
  • Efficient foraging
  • Tool manufacture and use
• Bipedal walking existed ~ 1mya prior to tools in archaeological record

Enlarging the Brain

• Brain development occurred after bipedalism
• Started 2 mya
• Selected for tool making and group living etc.

Reducing the Face, Teeth, Jaws

• Simultaneous with increased brain size
• This leads to a flatter face, reduced tooth size, flatter molar cusps, and thicker enamel

Other Trends in Hominin Evolution

• Include hairlessness/ sweatiness
• Increased dependency of infants: evolutionary advantage for physiologically immature infants
• Social living improved survivability of young
• Larger brain is advantageous, but made birthing more dangerous...