Anth 112 - Primate and Hominin Evolution

The Emergence of Primates and the Evolution of Humans - Chpt 3

Primates and their shared characteristics

a member of the taxonomic order primates

• humans belong to this order along with monkeys, apes, and prosimians

• grasping hands (thumb and five fingers) and feet

• flexible wrists (structure of forearm, rotating)

• skull structures (flatter facial profile, forward facing eyes)

• ears on side (rely more on sight rather than hearing)

• fingernails/fingerprints (rather than claws)

• teeth (generalized dentition, teeth size, incisors)

• stereoscopic vision (excellent depth perception)

• large brain relative to body size

Phylogeny 

the evolutionary history of a species

• 65 mya for humans 

• humans and chimps are most closely related, more than chimps to other apes

6-8 mya last common ancestor between humans and chimps

25 mya last common ancestor between monkeys and apes 

Arboreal

adapted to life in the trees

The most early primate

the first animals that possess some primate characteristics appear in the fossil record by 65 million years ago

• Purgatorius is considered to represent the earliest - rat looking

fossils with monkey like characteristics appear between 30-40 mya

primates with ape-like characteristics appear about 20 mya, Miocene epoch

what happened in the Miocene Epoch : 23-5 mya

often called the “Golden Age of Hominoids”

many species with apelike characteristics emerged during this time

thousands of hominoid fossils have been recovered from Africa, Asia, and Europe from this period

Bipedal hominins appear at the end of this epoch

• more than 100 species of apes, really flourished

• now there are only 4 great ape species

• some switched from arboreal to more terrestrial style life

What is a Hominin and Bipedalism 

Hominin - any creature believed to be in the direct human line

Bipedalism - a defining characteristic, upright walking 

Anatomical Characteristics of Bipeds (main 5)

1. vertebral column

2. skull

3. pelvis

4. the leg

5. the foot

the adaptation from 4 limb to two limb walking led to many skeletal changes, dating back to 7 mya

Biped change - Vertebral column

Bi - distinct curve in the back of the neck (cervical region) and lower back (lumbar region)

Ape - more c-shaped curve, body wants to lean forward; vertebrae does not increase in size for weight distribution like humans do

Biped change - Skull

most easily determinable 

the position of the forum magnum; the orientation of spinal connection into the skull, great ape is further back, head leaning forward, while upright walkers is more in the center 

Biped changes - Pelvis

difference in locomotion

biped pelvis is broad - has a short and broad ilium unlike apes who have a long narrow ilium

Biped changes - the Leg

attachment into the pelvis

human - femur leans inward, bringing the knee to the center of the body, femoral neck is longer, leg length relative to trunk is longer, broad articular surface (where two bones connect) where tibia and femur connect

apes - femur goes straight down, trunk longer than legs

Biped changes - the Foot 

Bi - aligned toes (brings stability and better walking movement), have an arch (shock absorbers), more tightly bound muscle and built for strength 

Apes - grasping activity with feet, divergent big toe

Explanations for Bipedalism - the Upright Provider

allowed males to carry food back to camp, providing for the females and children, allowed hands to carry

has been connected to monogamy

Explanations for Bipedalism - the Upright Scavenger 

superposition on bones (carnivore and tool marks), easy and faster to grab food having hands accessible 

Explanations for Bipedalism - the Efficient Walker

faster than walking on 4 limbs, upright uses one quarter of the energy needed for 4, greater distances traveled

Explanations for Bipedalism - the Endurance Runner

not necessarily fast, but can run very long distances, for hunting purposes

Sahelanthropus tchadensis

oldest hominin fossils found - 7mya 

found in Chad, name comes from 

represented by a nearly complete cranium - 320 to 380 ccm 

only a skull was found, forward position of the foramen magnum suggests it is an upright walker

canines were smaller than seen in apes, thickness of enamel was thin

2022 analysis of post cranial elements (anything below head), femur, suggested bipedality 

prior to this discovery, most early hominins were recovered from south and east Africa, after focus was shifted into more central Africa 

Orrorin tugenesis

found in western Kenya, East Africa - dated to 5.6-6 mya

only found a femur, much longer femoral neck

partial humorous, finger, three partial femurs, teeth enamel - only over a dozen fossils found

“original man”

Ardipithicus ramidus

found in Ethiopia - dated to 4.4mya

earliest well-represented hominin - numerous fossils and a remarkably complete reconstruction

had a mosaic of traits, both terrestrial and boreal living

• very ape like upper body; cranial capacity, long curved fingers, divergent toe

lived in a woodland habitat, suggesting that bipedalism developed not on the savannah, which is surprising as most explanations is how much easier savannah movement would become, looking over tall grass, moving faster

took 17 years to remove all sediments, so deeply embedded, many fossils found

“ground ape at the root”

The Australopthecines 

genus Australopithecus is a diverse group of hominins that lived between 4.2 and 1.8mya - same time as genus homo, multiple species of upright walkers at one period

small brains and prognathic faces (juts forward) with large teeth and jaws 

are bipedal but retained the ability to climb trees 

over 400 fossils found, very represented 

hominins still restricted to Africa at this time 

three species within this genus 

• anamensis

• afarensis

• africanus 

A. anamensis 

located in East Africa - dated 4.2 to 3.8mya; the oldest austra 

small cranial capacity - 365ccm 

broad and concave articular surface of tibia, indicative of bipedal locomotion 

recently a skull was discovered (2016), small brain case and prognathic face 

A. afarensis 

found in Afar (namesake), East Africa - dated to 4 to 3mya 

exhibits a high degree of sexual dimorphism - differences in the size and/or physical characteristics of males and females of the same species 

• females 3.5 ft, males 5ft. tall

Jaw : U-shaped, shallow palate, parabolic, big teeth, diastema 

unique set of derived and ancestral traits 

• D - curved lumbar, broad pelvis, arched foot, aligned big toe, knee angle

• A - males larger than females, brain size, relatively long arms 

derived vs ancestral trait 

derived - a feature that is present in a recent lineage but absent in the last common ancestor; evolutionary new traits passed down

ancestral - a feature that is inherited from the common ancestor, primitive trait 

Three big A. afarensis sites

1. Hadar, Ethiopia - Lucy and the First Family

• Lucy is very well known, 40% of body found, pretty small - 3.5ft, all teeth present, full body representation was able to be made, bipedal pelvis shape

• found in volcanic sediment, argon dating method

• First Family - social group, no advanced weathering or carnivore marks present, though to have all been killed at the same time (mudslide), covered very quickly; found adults and children (one year old jaw)

2. Dikika, Ethiopia - Dikika baby / Selam / Lucy’s baby (although 100,000 years older than Lucy)

• a complete child that lived 3.3mya, around 2-3 years old, most of skeleton found (more than Lucy), very well preserved

3. Laetoli, Tanzania - trace fossils, many footprints

• many fossils found but a remarkable amount of footprints found of a variety of sizes, tried to propose sexual relations from the print sizes

A. africanus

found in South Africa - dated 3 to 2mya

• 400-500ccm cranial capacity - larger than an ape but smaller than a human

• “southern ape of Africa”

• Taung Child - found in a stone quarry, neither ape nor human, was seemingly killed by a bird attack, puncture marks on skull

their hand bones indicate possible evidence of tool use, there aren’t any artifacts from the time, we don’t see tools being directly used but we do see the hand structure that can indicate the movement of the use

the Robust Australopithecines 

found in East and South Africa - dated to 2.5 to 1mya

used to be in the genus Australopthecines but are now classified as genus Paranthropus, not considered a direct human ancestor 

multiple lineages of upright walkers, living at the same time as our ancestors 

have a unique set of characteristics that set them apart 

• Megadontia - enlargement of teeth, extremely large molars 

• Sagittal crest - a ridge of bone running from front to back along the top of the skull, anchors their jaw muscles 

• Zygomatic - these bones make up the cheekbone, have a broad flaring region of these 

there are three types : Paranthropus boisei, aethiopicus, robustus 

Trends in Hominin Evolution

• bipedalism

• expansion of the brain - could be with diet, meat, metabolism

• reduction of the face, teeth, and jaws - less prognathic