Lecture 5- Hominid evolution I

Question 1

What is the story so far with the species we’ve discussed?

Answer 1

–at 20 MYA split= haplorrhines and straphorrhines (major differences) halplorrhines= diurnal living and colour vision, smell less important -anthropoids= now most are diurnal, more diversity, development of sexual dimorphism -then hominoidea= great apes and us, tail lost, we see a shift down from the trees

Question 2

What is the Hominoidea phylogeny?

Answer 2

-Hominidae = great apes + humans (c. 6 species - Africa) -Hylobatidae = gibbons (c. 14 species - East Asia) (6 species in Homonidae still alive) -Many people split great apes and humans into two families Pongidae and Hominidae -Pongidae is not a monophyletic group: it does not contain all of the descendents from its common ancestor -Pongidae is paraphyletic: it is missing at least one descent -Hominidae (covering humans and great apes) is phylogenetically more correct

Question 3

What are the differences between the Hylobatidae vs Hominidae?

Answer 3

-Hominids have: • Hair loss • Reduced canines • Brow ridges • Enlarged mammary glands, different mode of raising their offspring • Taste buds (papillae), refined sense of taste

Question 4

When did the Hylobatidae and Hominidae split?

Answer 4

approx. 21 MYA

Question 5

What is the story with Moropithecus bishopi?

Answer 5

• The earliest fossil on the lineage leading to humans and great apes? • 20 Mya - found in Moroto, Uganda • Large body size (femur length ≈ 27cm, estimated weight = 50kg) • Shoulder structure suggests a cautious climber (like great apes), but one that could swing through trees. • Lumbar vertebrae suggest an upright posture (like great apes) -lot of controversy about which fossil is at the base of our tree, which is the earliest ancestor -this might be -from Africa -can use femur length= can estimate size of the individual -probably climbed tree, but not as agile (cautious climber) -lumbar posture= upright posture? maybe, suggests it

Question 6

Has hominid phylogeny always been controversial?

Answer 6

-yes! -• Phylogeny of living hominids has always been (and continues to be) controversial Mya • A close relationship between human and chimps is now mostly accepted •…though exceptions always arise: one study claiming that orangutans are closer to us -close relationship of chimps and humans, we split from chimp-human ancestor -but sometimes people say it is organutan that is -MYA in the numbers

Question 7

What is the distribution of the living hominidae?

Answer 7

-

Question 8

What does the map of the fossil record of our ancestors look like?

Answer 8

• map of a fossil history= think about tools we can use to determine how the timeline looks, -until recently there was a massive gap in the fossil record
• several million years gap in Africa, and explosion in europe, so maybe africa then europe, then died out in africa and some returned

Question 9

What are the possible reasons for the “gap” in fossil record?

Answer 9

1. Not enough sampling, European/Asian sites much more accessible and well worked. 2. Environmental change: conditions in Africa became less amenable to preserve fossils (cooler, drier). 3. The apes weren’t there. -maybe just not enough fossils, also easier to work on in europe -kenyapithacus= harder enamel, change in diet -or else they did die out in africa and returned at some stage

Question 10

What is the hypotheses as to what happened to the movement of hominids the fossil record?

Answer 10

• Hominids split into two lineages

• Eurasian & African
• Hominids spread into Eurasia on several occasions
• Hominids moved into Eurasia, then split into two. ‘African apes’ then moved back into Africa

Question 11

What is the Grihopithecus?

Answer 11

• The earliest Eurasian fossil 16Mya
• Fragments of teeth & jaws found in Turkey & Central Europe
• Hard enamel, similar tooth structure to Kenyapithecus
• Probably from the African Proconsul lineage that died out - a separate European invasion

Question 12

What is the Sivapithecus?

Answer 12

• Specimens found from about 12-8 Mya in Pakistan, India & Nepal

• Hard enamel on teeth, remarkable similarity in skull to orangutans -eurasian lineage?

Question 13

What is the Dryopithecus?

Answer 13

• Specimens found from about 12-8 Mya in Europe
• Thin (soft) enamel like modern chimps and gorillas: diet of soft fruits & leaves • Long fore limbs & grasping hands
• Related to hominines (gorillas, humans, chimps)
• but also lineages that resemble chimps and gorillas
• lot of specimens with different similarities, do not have to remember all the names
• mixed record

Question 14

So what happened with the movements of the hominids?

Answer 14

• people have suggested there are these multiple hypotheses= red= africa, black= europe -suggesting apes originated in africa then to europe and then back = some evidence that this may have happened
• moved through europe and asia
• some of european species back to africa and then humans evolved there

Question 15

What do the recent fossil finds in Africa mean?

Answer 15

-these started to fill the fossil gap -several new species in Africa during the gap period -now the one origin theory makes more sense -Choropithecus 10.5 Mya -Nakalipithecus 10 MYA -Samburupithecus9.5 MYA • Early gorillas? • Early chimps/humans? • Or late hominines from just prior to the split of the African apes?

Question 16

What do people agree on now with how many migrations there have been from Africa?

Answer 16

• so people agree not just one move out of africa, there are multiple migrations out of africa
• sometimes a species doesn’t fit (Oreopithecus)

Question 17

What is the Oreopithecus?

Answer 17

• Descended from pre-hominid ancestor? • Descended from hominine ancestor? • 9-7 Mya • Found only on Sardinia • Very complete fossil, but it’s position remains uncertain -pre split of chimps and humans, on the border, found in a restricted area -some people say it is the early human ancestor /shape of the pelvis etc. but unclear since the skeleton is squished so hard to say

Question 18

What is the evidence for bipedality from the fossil record? (lecture notes)

Answer 18

Changes from quadrapedalism (knuckle walking) to bipedalism

• Big toe reduced, straightened
• Fingers become long and more slender
• Pelvis shortened, more bowl-like than blade-like (helps support base of spine)
• Femur bends inwards, knee straightened, patella central to joint
• Connection with spinal column (foramen magnum) on underside of skull
• Less robust upper arms

Question 19

What is the evidence for bipedality (my notes)?

Answer 19

key indicators for bipedalism:

• big toe in humans is important for balance, no longer grasping
• fingers get longer and more slender, more dextrous
• on all fours pelvis can be longer as it doesn’t have to hold the weight as much
• pelvis in humans support the base of the spine, important for sustained walking
• knee points straight, better stability and can walk for longer! crucial with the pelvis for walking!
• shift of the head, where the connection attaches as the angle is different

Question 20

Was Oreopithecus bipedal?

Answer 20

• Big toe reduced, straightened: No • Fingers become long and more slender: Yes, but could be arboreal • Pelvis shortened, bowl-like Depends who you believe • Knee straightened: Ditto • Foramen magnum on underside of skull: Yes • Less robust upper arms: No -fingers= maybe an intermediate between arboreal and on the ground -the pelvis= depends, it has been squished so hard to tell

Question 21

What is the Toumai?

Answer 21

-Sahelanthropus tchadensis -one of the candidates for the earliest human ancestor? • Skull found in 2001, Chad • 7 mya • Chimp size • Forest living (found by lake) • Intermediate enamel thickness

Question 22

What is the Millenium Man?

Answer 22

-another candidate for the earliest human ancestor -Orrorin tugensis -• Found 2000 in Kenya (6.2 Mya) • Forest living • Thick tooth enamel (like humans –probably after the split of chimps and humans -much more similar femur to humans than chimps

Question 23

What is Ardi?

Answer 23

-another candidate for the earliest human ancestor • Discovered 1994, not described until October 2009, from Afar, Ethiopia • 4.4 mya • Badly crushed (“roadkill”) but almost complete skeleton • Pelvis and hands suggests bipedal • Feet (opposable big toes) suggests that it also climbed • Probably spent most of time in trees?

Question 24

Why did bipedalism evolve?

Answer 24

-Just so stories: -possible explanations for bipedalism -humans are great endurance athletes, not for speed but for endurance • Improved foraging efficiency in grass-land (see above grass) • Improved thermoregulation under the hot savanna sun (reduced surface area and possibly more air movement) • Increased home range = increased foraging success • Increased ability to use tools effectively (e.g. in hunting) • Energetically efficient way of moving between food patches

Question 25

Questions from this lecture:

Answer 25

• What does the fossil record tell us about the origin and evolutionary history of the great apes? • What have been the major anatomical changes involved in the switch to bipedality in the human lineage? • Which fossils have been candidates for being closest to the common ancestor of humans and chimpanzees, and what evidence supports, or argues against, these theories?