evo. lecture 4

Question 1

Time Frame and Climate

Answer 1

Major Epochs of the Cenozoic Era

• Paleocene: 65-56MYA
• Eocene: 56-34MYA
• Oligocene: 34-23MYA
• Miocene: 23-5MYA
• Pliocene: 5-2.59MYA
• Pleistocene: 2.59-0.01MYA
• Holocene: 0.01MYA-Now
• as we move from the Paleocene to present day, global temperatures have gotten colder and colder.

Question 2

Paleocene

Answer 2

• the Paleocene was the end of the age of dinosaurs, whom went entirely extinct, along with many other organisms.
• it was hotter and more humid, and there were no ice caps.
• gave rise to primate-like mammals called Plesiadapiformes.

Question 3

Plesiadapiformes | Paleocene and Primate-Like Mammals

Answer 3

• body size: tiny, shrew-sized to size of a small dog.
• niche: likely solitary, nocturnal quadrupeds, with well-developed sense of smell.
• diet: insects and seeds.
• used to be classified as primates because of primate-like teeth and limbs that are adapted for arboreal life.
• not actually primates because:
  
  • no postorbital bar
  • claws instead of nails
  • eyes on side of head
  • and enlarged incisors.

Question 4

Adapidae | Eocene

Answer 4

• North America and Europe
• from 100-6900g
• diurnal and nocturnal
• arboreal quadrupeds
• smaller ones ate fruit; larger ones ate fruit and leaves
• led to lemurs?

Question 5

Omomyidae | Eocene

Answer 5

• North America, Europe, and Asia
• from 45-2500g, most weighing less than 100g.
• nocturnal and diurnal
• specialized leapers
• dental morphology indicates interspecific variations in diet
  
  • smaller ones eating insects
  • larger ones eating fruits and a few ate leaves
• led to tarsiers?

Question 6

Oligocene

Answer 6

• as the average temperatures decreased, sea levels kept rising and dropping, which isolated lots of plants and animals.
• primates appear for the first time in fossil record of South American towards late Oligocene.
• three haplorhine features: fused frontal bone, full postorbital closure, and fused mandibular symphasis
• three taxonomic groups: Parapithecidae, Propliopithecidae, and Platyrrhini

Question 7

South American Primates

Answer 7

• origins of South American primates unclear.
• may have “rafted” over from Africa.
  
  • computer generations show that Africa and South America were close together, and ocean currents would’ve been travelling from Africa to South America at the time.
• the monkeys found in South America today look at a lot like the moneys in Africa*.
• (*but looking alike doesn’t mean phylogenetic lineage.)

Question 8

Miocene

Answer 8

• it got colder in the Miocene; expansion of the ice fields and dry lands meant less tropical places and more dry places.
• early Miocene (23-16MYA) monkeys and apes (e.g. Proconsul) apparently confined to Africa.
• mid-Miocene (16-11.6MYA) ape-like catarrhines (e.g. Dryopithecus) were widespread and diverse in Europe and Asia.
• late Miocene (11.6-3MYA) apes (e.g. Sivapithecus) became rarer as woodlands and forests replaced by drier and more open habitats.

Question 9

Pliocene

Answer 9

• land masses still on the move; connection between North and South America opened via Panama canal.
• fluctuations in global temperatures.
• Mediterranean Sea dried up at the end of the Miocene and filled up again in the Pleistocene.
• two main taxa: Fossil Cercopithecinae (had cheek pouches) and Fossil Colobinae (gut tract adaptation for leaves).
• phylogenetic relations: unresolved.
  
  • we can only look at the relationships in modern organisms since cheek pouches and digestive tracts don’t fossilize.

Question 10

Transitional Forms (Apes:Humans)?

Answer 10

1. modifications of postcranial skeleton for bipedal locomotion.
2. shape and size of canines, especially in males, changes so not pointy or blade-like. reduction in level of sexual dimorphism in canine size.
3. expansion of brain size.

Question 11

Hominins

Answer 11

modern humans, chimpanzees, and fossil species more closely related to each other than to any other living species.

Question 12

Morphological Trends in Hominin Evolution

Answer 12

• mosaic evolution: major evolutionary changes tend to take place in stages, not all at once.
• bipedalism
• increased brain size: intelligence (but, it’s about connections, not pure size)
  
  • relative vs. absolute intelligence, i.e. intelligence is socially and economically relative.

Question 13

Quadrupedalism vs. Bipedalism

Answer 13

• fingers: power, precision, movability (not locomotion)

Question 14

Hominin Brain Size

Answer 14

steady until 2 million years ago, when brain size started getting larger.

Question 15

Ardipithecus ramidus and Ardipithecus kadabba | Transitional Hominin Fossil

Answer 15

• Middle Awash, Ethiopia
• A. ramidus, 4.4MYA
• A. kadabba, 5.8-5.6MYA
• teeth and fragments of various upper and lower bones.
• both ape-like (thin enamel) traits and hominin-like traits (canines have reduced sexual dimorphism).

Question 16

Key Australopithecines: First “Real” Humans

Answer 16

• Australopithecus anamensis
• A. afarensis
• A. africanus
• A. sediba
• A. aethiopicus, 2.7-2.3MYA in East Africa
• A. boisei, 2.2-1.2MYA in East Africa
• A. robustus, 2.0-1.0MYA in South America
• these were robust creatures; had huge teeth and large top ridges, leading to great bite force

Question 17

Hominin Fossils: Transitional Forms

Answer 17

• Sahelanthropus tchadensis
• Orrorin tugenesis
• Ardipithecus ramidus
• Ardipithecus kadabba
• Kenyanthropus platyops.

Question 18

Laetoli Footprints

Answer 18

• 3.6MYA in Laetoli, Tanzania
• demonstrated that early hominins were bipedal.
• big toes hardly diverged from the rest of the foot.

Question 19

Rise of the Genus Homo

Answer 19

• earliest humans evolved in Africa.
• most date back 2.4-1.8MYA.
• first fossil member of taxon was Homo habilis, which means “handy man”.
• some researchers suggest that H. habilis is just “junk taxon” and that there my be two or more species of Homo by 2.0MYA.

Question 20

Australopithecus afarensis

Answer 20

• ​Ethiopia, 4.2-3MYA
• complex morphology exhibiting some ape-like traits (e.g. sagittal crests) and hominin-like traits (e.g. valgus knee).
• single, sexually dimorphic species or two species? (consensus on the former.)

Question 21

Australopithecus sediba

Answer 21

• 1.98MYA in Malapa, South Africa
• initial discovery by 9 year-old son of a researcher.
• specimens were a juvenile male (MH1) and adult female (MH2).
• very controversial
• brain: human-like in shape, yet smaller than average H. sapiens brain volume.
• hand: good for tree climbing and long thumb with short fingers for precision gripping.
• pelvis: more human-like.
• overall: upright walking humans, but could still climb trees.