Lecture 3- Primate evolution and diversity I

Question 1

What does primate mean?

Answer 1

• first rank
• primates viewed as the highest rank, the name taken from how we refer to heads of churches and archbishops
• controversial nomenclature as Linnaeus identified similarities between monkeys and humans and has hence classified them together

Question 2

What does classification mean?

Answer 2

• groups organisms together into phyla, class, order, genus etc based on shared characteristics.
• e.g.: all bats have wings, all mammals produce milk
• knowing that bats have wings and the ancestor didn’t gives us little information as to where the split occured

Question 3

What does phylogeny mean?

Answer 3

• represents the evolutionary relationships between organisms (it’s an evolutionary tree), based on shared derived characteristics (synapomorphies).
• Shared primitive characteristics (symplesiomorphies) are not considered useful

Question 4

What are symplesiomorphies?

Answer 4

-shared derived characteristics on which a phylogenic tree is based

Question 5

What are symplesiomorphies?

Answer 5

-shared primitive characteristics, not considered useful for establishing a phylogenic tree

Question 6

What is this?

Answer 6

• the mammalian evolutionary tree
• primates are a small portion of the tree (red rectangle)

Question 7

What are the nearest relatives of primates?

Answer 7

-flying Lemurs (Dermoptera)

Question 8

What are the Euarchonta?

Answer 8

• means true ancestors, these are three groups that share a common ancestor from which humans have also eveolved
• the groups are:
  1. Dermoptera (Flying Lemurs)
  2. Primates
  3. Scandentia (Tree shrews)= proposed basal link to primates, separated approx. 80 MYA

Question 9

How old are the earliest primate fossils, where were they found and what were the characteristics of those animals?

Answer 9

• 65-55 MY
• most found in America but also found in Asia and Africa (spread quickly)
• belonged to a now extinct group known as Plesiadapiformes
• small 20-30g, arboreal, insectivorous
• similar in appearance and habits to modern tree shrews -found two species:
  1. Purgatorius (c. 64 MYO)
• maybe the basal link of primates?
  2. Dryomomys (c. 55 MYO)
• maybe the ancestor of tree shrews and the basal link?

Question 10

What are the characteristics of primates in general? (9)

Answer 10

1. Grasping hands and feet
2. Opposable digits
3. Finger nails (instead of claws)
4. Hind limb-dominated locomotion (arms less strong)
5. Reduced sense of smell (small noses
6. Binocular vision
7. Extended maternal care
8. Large brains
9. Relatively small number of teeth

Question 11

What are the three primate characteristics that are related to arboreal living?

Answer 11

1. Grasping hands and feet
2. Opposable digits
3. Binocular vision

Question 12

What is this?

Answer 12

• comprehensive primate phylogeny
• 1st split: Plesiadaformes splitting into Strepsirrhines and Haplorrhines
• 2nd split: Haplorrhines split into Anthropoidea and Tarsiiformes (tarsiers)
• 3rd split: Anthropoidea split into Platyrrhines (New World Monkeys) and Catarrhines (Old World Monkeys)
• 4th split: Catarrhines split into Hominoidea and Cercopithecoidea

Question 13

What was the first split in primate evolution?

Answer 13

• the Plesiadaformes split into Strepsirrhines and Haplorrhines
• this occured approx 78-63 MYA

Question 14

How many species of Strepsirrhines are there and where do they occur?

Answer 14

• 110 species (about a quater of primate species)
• mostly in Madagascar, few in S Africa, SE Asia

Question 15

How many species of Haplorrhines are there and where do they occur?

Answer 15

• 280 species
• spread throughout the world, in Africa, Asia, America

Question 16

In which areas are there differences between Strepsirrhines and Haplorrhines?

Answer 16

1. Nose
2. Eyes
3. Snout
4. Teeth
5. Hand

Question 17

How is the nose different in Strepsirrhines and Haplorrhines?

Answer 17

• Strepsirrhines: wet nose, nose pad (rhinarium) and nose slits
• Haplorrhines: dry nose, no nose pad and have nostrils
• Strepsirrhines have better sense of smell & use scent- marking, possibly associated with nocturnal existence

Question 18

How are the eyes different in Strepsirrhines and Haplorrhines?

Answer 18

Strepsirrhines:

• the back of the retina has a layer (the tapetum) that reflects light which allows for more light to be collected at the retina
• this is believed to be a nocturnal adaptation (increases light gathering abilities of the rod cells)
• mostly dichromatic (not colour vision)

Haplorrhines:

-have colour vision and no tapetum, poorer visual acuity in the dark (as they are diurnal)

Question 19

How is the snout different in Strepsirrhines and Haplorrhines?

Answer 19

Strepsirrhines:

• have larger snout and a better sense of smell

Haplorrhines:

• have a flatter profile and less prominent snouts

Question 20

How are teeth different in Strepsirrhines and Haplorrhines?

Answer 20

Strepsirrhines:

• incisors and canines modified into thin prominent teeth = toothcomb which is used for grooming and chewing off bark

Haplorrhines:

-comparable mammalian dentition

Question 21

How are hands different in Strepsirrhines and Haplorrhines?

Answer 21

Strepsirrhines:

• second digit is modified into a longer claw, used for grooming.
  eg. Aye-ayes (Daubentonia madagascariensis) have extra long claw for food extraction (eat insect grubs)

Haplorrhines:

-“normal” hands

Question 22

What were the key changes in the evolution of Haplorrhines? (4)

Answer 22

1. Reduced sense of smell
2. Development of trichromatic vision
3. Tendency to greater frugivory
4. Loss of ability to synthesise Vit C
   - Single GLO gene mutation that only codes for Vitamin C (this means the mutation only affects vit C and is otherwise non-detrimental, our ancestors survived thanks to having a high fruit content in their diet)

Question 23

What are some of the species that have lost the ability to synthesise Vitamin C and how do they survive?

Answer 23

-selection on the gene is neutral

• Species that have lost Vit C = High dietary vitamin C content (fruit usually)
• Human RDA approx 1 mg/kg/day
• Gorillas (20-30 mg/kg/day)
• Howler monkeys (88 mg/kg/day)
• Spider monkeys (106 mg/kg/day)

Question 24

What is the controversial fossil of a possible early Haplorrhine?

Answer 24

-Darwinius masillae (aka “Ida”)

• Most complete fossil primate ever found
• 47 Mya old - found in Germany
• Lacks toothcomb and second-digit claw (hence Haplorrhine)
• 60cm long - probably 600-900g
• Diet - frugivorous/herbivorous (Fur and stomach contents preserved)
• controversial as the line is there and the time between the find and publishing (1983-2009)
• some say it is a lemur but doesn’t have the basic characteristics!
• probably spread from Siberia then to Europe and then east to the Americas

Question 25

What was the second split in primate evolution?

Answer 25

- Haplorrhines split into the Anthropoidea and the Tarsiiformes (tarsiers) - Tarsiiformes: 9 species, all in SE Asia - Anthropoidea: 270 species, Africa, Asia, Americas

Question 26

What are the characteristics of the Tarsiers?

Answer 26

* Arboreal primates * Eat insects and small vertebrates * Generally small (t have a tapetum * Nocturnal (but no tapetum) * Entirely carnivorous - insects -probably arose in Asia

Question 27

What is a synapomorphy?

Answer 27

-a synapomorphy or synapomorphic character state is a trait that is shared ("symmorphy") by two or more taxa and inferred to have been present in their most recent common ancestor, whose own ancestor in turn is inferred to not possess the trait.

Question 28

Are there any easily identifiable synapomorphies in Anthropoids?

Answer 28

- genuine synapomorphies for Anthropoids are difficult to identify (many are shared with tarsiers) - but anthropoids did evolve a single, "simple" uterus, which is typically associated with a decreased litter size, often means an increase in individual maternal investment

Question 29

What were the earliest Anthropoids like?

Answer 29

* Earliest anthropoids - Tarsier-like (\<100g) * Probably arose in Asia * Insectivorous and arboreal - had shearing plates in their dentition= characteristic of species that need to crush the hard exoskeleton of insects

Question 30

What is the Eosimias and what is its significance?

Answer 30

* At least 3 species * Found in China * 40-45 Mya -link between Anthropoids and Tarsiers - split where primates and monkeys diverge - also a possible candidate for the split (like Darwinius masillae)

Question 31

What were the main changes in Anthropoids?

Answer 31

* Switch to diurnal existence * Relatively stronger upper-arms) * Change in locomotion - less leaping from trees - more swinging (brachiation) • More herbivorous diet - occurred in several lineages • Trend towards larger body size - although they remained small - and, associated with herbivory

Question 32

What was the third split in primate evolution?

Answer 32

- the Anthropoids split into the Platyrrhines (New World Monkeys) and the Catarrhines (Old World Monkeys) - split occurred approximately 43 MYA - the Platyrrhines consist of about 135 species, all occur in the Americas - the Catarrhines consist of about 145 species and occur in Asia, Europe and Africa

Question 33

How did the Platyrrhines (the New World Monkeys) get to the Americas?

Answer 33

- Floated to South America on a raft (distance = 1500km) - Genetic evidence suggests that this happened at least twice! - pregnant female? - female with young? - multiple individuals? - How did they survive without fresh water? - Geological evidence = the rafts may have been “floating islands” - most likely several individuals and probably on the floating island structures

Question 34

How is the nose different in Platyrrhines and Catarrhines?

Answer 34

**Platyrrhines** - wide flat noses - nostrils well separated **Catarrhines** - narrow pointed noses - nostrils close together

Question 35

How is the tail different in Platyrrhines and Catarrhines?

Answer 35

**Platyrrhines** - long,muscular,prehensile - used to hold onto branches **Catarrhines** - less muscular, shorter - sometimes absent

Question 36

How are teeth different in Platyrrhines and Catarrhines?

Answer 36

Catarrhines - lost a pre-molar (they have 2 incisors, 1 canine, 2 [not 3] pre-molars and 3 molars) - Upper canine occludes against the first pre-molar

Question 37

What are some of the other changes that occurred in the Catarrhines?

Answer 37

* General larger body size * Greater sexual dimorphism * Higher levels of sexual selection and competition between males * Higher levels of polygyny * Female sexual swellings

Question 38

What were the earliest Catarrhines like?

Answer 38

-Aegyptopithecus zeuxis and Propliopithecus (2 species) * 34 million years ago * Found in Egypt (African origins) * Body mass about 6kg

Question 39

What is the fourth split in Primate evolution?

Answer 39

- the Catarrhines split into the Hominoidea (c. 20 species, Africa and Asia) and the Cercopithecoidea (Old World Monkeys, c. 125 species, Africa and Asia) - occurred approx. 31 MYA

Question 40

What are the differences between Cercopithecoids and Hominoids?

Answer 40

1. Tail: - lost in Hominoids 2. Arms: - Hominoid arms are long (as long or longer than legs) - Numerous skeletal changes (arm movements more flexible)

Question 41

What was the earliest Hominoid found?

Answer 41

-Proconsul • Found in East Africa - at least 3 species * Earliest fossils ≈ 24 Mya * Rainforest-dwelling, frugivorous, quadrapedal (not full flexibility of arms) * Large monkey - about 30kg

Question 42

What are the questions from this lecture?

Answer 42

1. What are the main groups of primates and how do they relate and differ from one another? 2. When did the major groups of primates originate? What does the fossil record tell us about the evolution of major primate groups? 3. What were the major evolutionary transitions that occurred in the evolution of primates in the lineage leading to man?