Biological Anthropology GWU Exam #2

ANCESTRAL HOMOLOGIES

Features primates share with

other placental mammals

Ex. Mammary glands, expansion of the neocortex

of the brain, Placenta, long gestation

followed by live birth, maternal care, Homeothermy, and Heterodonty

Primate derived homologies

• Petrosal bulla

• High degree of grasping ability in the hands and feet

• Decreased reliance on olfaction (smell), particularly in

haplorhines

• Stereoscopic vision and enhanced depth perception

• Enclosed bony orbits (postorbital bar)

• Large brain relative to body size, expanded neocortex

• Prolonged life history, single offspring

Primate Ancestral homologies

Generalized body plan

• Retention of the collar bone (clavicle)

• Two separate bones in lower arm (ulna and radius)

• Five digits of the hands and feet

• Generalized dentition

• Heterodonty

Quadrupedalism (Terrestrial or Arboreal) Locomotion

•Hind limbs and forelimbs of near equal length

•Arboreal species have long tails to aid in balance on top of branches

•Shoulder blade positioned to the side of the ribcage, and restricted

movement at the shoulder

•Long, flexible lower back

Vertical clinging and leaping Locomotion

Long powerful hind limbs

• Long flexible back

• Long fingers for grasping supports

when they land

Suspensory (incl. brachiation) Locomotion

Short hindlimbs, elongated forelimbs

•Mobile shoulder joint

•Shoulder blade located on the back

•Long and curved fingers for grasping branches

Knuckle-walking

Form of quadrupedalism practiced by great

apes

• Wrist joints are stabilized

Heterodont dentition

Incisors, canines,

premolars and molars

Suborder Strepsirhini Ancestral mammalian traits

Sense of smell is well-developed

- Retain the rhinarium

• Lower jaw (mandible) is not fused

• Eye has a tapetum lucidum - Most are nocturnal

Suborder Strepsirhini Derived Traits

Grooming claw on 2nd digit of hind limb

• Tooth comb

Strepsirhini Superfamilies

LORISOIDEA - Galagos & Lorises

LEMUROIDEA - Lemurs, aye-aye, and

sifaka

Haplorhini tree

Look at pp notes

https://blackboard.gwu.edu/webapps/blackboard/execute/content/file?cmd=view&content_id=_8580083_1&course_id=_293232_1

Infraorder TARSIIFORMES

Tarsiers

INFRAORDER ANTHROPOIDEA

New World monkeys, Old World monkeys, apes & humans

Platyrrhines ('flat-nosed'; New World)

Broad noses, with outward-facing nostrils

Smaller body size

3 premolars in each quadrant (2.1.3.3)

All are arboreal

Some, but not all, have prehensile tail

Most have 2 color vision

Marmosets, Tamarins

Small bodied (< 1kg)

• Omnivorous, insects & plant exudates

• Variety of social grouping patterns:

• Usually only one breeding

female

• Intense female-female

competition, with suppressed

ovulation in subordinate females

• Twinning is common

• Males are principal caregivers

Cercopithecoidea ('down-nose'; Old World)

Narrow nose, downward-facing nostrils

Larger body size

2 premolars in each quadrant (2.1.2.3)

Arboreal & terrestrial

S None have prehensile tails

All have 3 color (trichromatic) vision

Ischial callosities

Old World Monkeys Variations

Colobine monkeys

• Dietary specialist on mature

leaves

• Arboreal quadrupeds; also

adaptations for leaping

long tail and legs

teeth meant for cutting leaves

Cercopithecine monkeys

• Arboreal & semiterrestrial species

• Dietary omnivores

• Cheek pouches

Super Family Hominidae

Apes and Humans

• Loss of the tail

• Relatively large brains

and enhanced cognition

• Prolonged development

• Postcranial adaptations

for suspensory posture and

locomotion

Gibbons and Siamangs

Tropical forests of SE Asia

• Smallest of the apes

("lesser apes")

• Diets focus on fruits

• Socially monogamous

• No sexual dimorphism

• Brachiation

TARSIOIDEA - Tarsiers

Prosmian' traits (i.e., strepsirhine-like):

• Grooming claw

• Unfused lower jaw

• Nocturnal, Small social groups

Haplorhine traits:

• Lack: tapetum lucidum, rhinarium, tooth

comb

Other derived traits:

• Adaptations for vertical clinging & leaping

• Large eyes relative to body size, orbit anatomy

• Nocturnal predators of small vertebrates

Aye-Aye

Diet specialized for woodboring

insect larvae

• Except for thumb and big toe,

all digits have claws;

elongated and thin 3rd digit,

functions like a skewer

• Large continuously growing

incisors

Great Apes (Family Hominidae:

Orangutans, Gorillas,

Chimpanzees, Humans)

Borneo & Sumatra

(Orangutans); Central & West

Africa (Gorillas, Chimpanzees)

• Large body size ('Great Apes')

• Show suspensory adaptations,

but are quadrupedal on the

ground

Insectivore

Primates that eat insects. tend to be

smaller in body size

- Smaller animals have

relatively higher energy

requirements, and eat

small amounts of highquality

foods

Folivore

Primates that eat leafs. Tend to be

larger in body size

- Can afford to eat large quantities of lower quality foods

Brachiation locomotion

Swinging under objects with arms

Costs of sociality

- Greater competition for resources

- Vulnerability to infectious disease

Two main benefits of sociality

- Enhanced access to resources

- Reduced vulnerability to predation

Resource Defense Model

Primates live in groups because groups are more

successful in defending access to resources

than lone individuals. (ex. defending a fruit tree). Leads to between-group competition.

Problems of group living:

- Benefits gained in between-group competition are offset by costs from within-group competition

Predator Defense Model

Group living evolved as a defense against

predators.

-Terrestrial species tend to form larger groups than arboreal species.

-Primates seem to adjust their behavior in response to the risk of

predation (e.g., alarm calling)

Weaknesses of the model: Predation is very difficult to observe, and it is therefore difficult to establish whether it is clearly linked to group size.

Reproductive Asymmetry

Primate mothers are

almost always the

primary (if not exclusive)

caretakers of offspring

• The behavior of fathers is

much more variable

Reproductive Potential

The maximum number of

offspring an individual can produce

Female Reproductive Strategies

1) Invest more care & energy into offspring à

requires food and other resources

2) Be choosy about males fathering offspring

only mate with quality males

Scramble Competition

when resources cannot be

easily monopolized.

first-come, first-serve basis.

o Resources are of low value,

highly dispersed, or occur in

large patches

Contest Competition

occurs when access to a resource can

be monopolized some individuals exclude others, and obtain more of the resources

o Resources patches are clumped, of intermediate sizeand high value

DOMINANCE

Often measured as direction of approach-retreat interactions, or the direction of submissive and aggressive behaviors

When there is competition, dominance rank may determine priority of access to preferred resources

Male Reproductive Strategies

High variance in reproductive success

limited by access to females leads to competition among males for mates.

Solitary

Females live only with their offspring; males are solitary. Social structure usually based on erratic food supply

Monogamous Pairs

Littile sexual selection

• Males do not invest much

energy in courtship or mating

• Males invest heavily in their

offspring and in maintaining

long-term bonds with their

mates

One-Male, Multifemale Groups

• Males compete actively to establish

residence in groups of females.

• Resident males face constant pressure

from nonresident bachelor males; threat of aggression

Multimale, Multifemale Groups

Larger groups of females; one single male cannot monopolize access to all of them

- Male-male competition is mediated though dominance relationships

• Male dominance rank is associated with reproductive success in many studies

• Female preferences can influence male mating success

SEXUAL SELECTION

A form of natural selection that occurs when

individuals differ in their ability to compete with

others for mates or to attract members of the

opposite

Intersexual Selection

Where individuals exert choice among individuals of the opposite sex for mating partners

• Favors traits that:

- (1) provide direct benefits to their

mates

- (2) indicate good genes and thus

increase the fitness of the offspring

- (3) make males more conspicuous

to females (although they can be

maladaptive)

Intrasexual Selection

Competition among same-sex

individuals for access to members of

the opposite sex

Sexual Dimophism

When males and females differ consistently in size or appearance

Sperm Competition

In a social systems where multiple

males have access and male-male

competition is high, sexual

selection favors sperm

competition

Paleontology

The study of extinct organisms based on

their fossilized remains

fossil

Preserved remains of a living organism

The Matrix

Skeletons become fossils by absorbing minerals from their surroundings. The _________ composition is informative for analyzing fossils, and it is critical for the dating of fossils

Relative dating

Using principles of stratigraphy and Biochronology (faunal succession) for dating objects

Absolute dating

- Radiometric methods of dating objects

Paleomagnetism

- Method for linking up to absolute dating

methods

Stratigraphic Laws

• Original Horizontality

• Lateral Continuity

• Superposition

• Cross-Cutting Relations

• Law of Faunal Succession

14C Dating

Estimate age based on proportion of

remaining 14C

Potassium-Argon dating

Based on the decay of 40K to 40Ar

• Argon gas escapes magma, but starts

accumulating as magma cools and

hardens

• Useful for volcanic

rocks up to billions

of years old

early fossil primates characteristics

• Petrosal bulla

• Highly derived hands and feet

nails instead of claws

• Decreased reliance on smell

reduction of snout

• Increased reliance on vision

forward facing eyes

post orbital bar

Arboreal Hypothesis

Mammals evolved into primates as a result of their arboreal lifestyle. Flawed because scientist believe that the ancestors of primates already lived in trees and other mammals that live in trees don't have similar traits to us.

Visual Predation Hypothesis

Primates developed for stalking and grasping insect prey

Angiosperm Exploitation Hypothesis

Primates evolved in sink with adaptive radiation of flowers to exploit their products

Consensus View on Origin of Primates

A combo of arboreal and Visual Predation

Paleocene

Plesiadapiformes:

Primitive, they retain a number of

ancestral mammalian traits

Not clear if they fall within,

or just outside of, the

primate evolutionary tree

Some plesiadapiformes

possessed some, but

not all, derived primate

traits

Eocene

First Primates of "Modern Aspect"

Adapoids

Probably ancestor to strepsirrhines. Lemur

like

Omomyoids

Similar to modern tarsiers

in many respects. Probably ancestor of

haplorrihnes

Oligocene

Anthropoid Origins

Apidium- from pre-divergence of Catarrhines and Platyrrhines. Proof by 2.1.3.3 dental formula

Aegyptopithecus- from after divergence of Catarrhines and Platyrrhines. Is a catarrhine, proof by 2.1.2.3

Miocene

Age of apes

fission-fusion polygyny

Males and females join groups and break those groups very quickly. Males and female mate in this setting

polyandry

mating system where one female mates with multiple males.

taphonomy

the study of what happens to the remains of animals from the time of their death to the time of discovery

Frugivor

Primate that eats fruit