The platypus is a mosaic of mammalian, avian and reptilian traits.
The ability to fly evolved in four groups,
Insects, pterosaurs (extinct), birds and bats
1. The oldest known bird (Archaeopteryx) resembled reptiles in limb bones and other features. (avian traits, including feathers).
2. Birds still resemble reptiles:
horny beaks, scaly legs, and
3. There are greater than 9,000
named species of birds. The
smallest known birds weigh
2.25 gm (0.08 ounces), while
the largest bird, the ostrich, weighs
about 330 lbs.
4. The first birds evolved from reptiles during the Mesozoic era. The feathers were a highly
modified reptilian scale.
1. The body is covered with feathers –
helpful in flight and insulation.
Elastic sacs connected to the
lungs help dissipate excess heat
as they force warmed air out of
2. Construction meets the requirements
of flight: low weight and high power.
a. The bones are lightweight because
of air cavities within them. There is a
honey combed structure and an efficient
mode of respiration and circulation.
b. Powerful muscles are attached
at strategic places on the bones
for maximum leverage.
c. The heart is four-chambered,
and the lungs are highly
efficient because of their “flow-
3. Flight in general and migratory
movements in particular are
amazing feats that birds seem to
accomplish with ease.
FLIGHT: PG 459 gives some explanation of the mechanics. Birds that are migratory move frequently from region to region in response to environmental rhythms. Seasonal change in day length is a cue, that influences internal timing mechanisms and biological clocks. Consequently, causes physiological and behavioral changes which induce birds to make round trips to different regions in different climates.
The Rise of Mammals
Range from: Kitti’s hog-nose bat 1.5 gm to 100 ton
1. Brain capacity is increased, allowing
more capacity for memory, learning, and
2. Milk-secreting glands nourish the young.
3. Hair covers at least part of the
body (whales are an exception).
4. Dentition is extensive and special-
ized to meet dietary habits.
Other amniotes typically swallow their prey whole, but most mammals secure, cut and sometimes chew their food before swallowing it. Four distinctive types of upper and lower teeth serve this purpose – incisors, canines, premolars, and molars.
The amniotes are a microphylum of tetrapod vertebrates that include the Synapsida (mammals) and Reptilia (reptiles and dinosaurs, including birds).
B. Mammalian Origins and Radiations
1. During the Triassic, divergence
from the small, hairless reptiles
called synapsids gave rise to the
therapsids. The early ancestors
2. By Jurassic times, mouse-sized
therians with jaws and hair had
evolved. This was a diverse group
of plant and meat eating mammals
that co-existed with the dinosaurs.
They began to flourish as the
dinosaurs began to vanish.
3. They (therians) had major changes
in the jaws, teeth and body form.
Their four limbs were positioned
upright under the body’s trunk.
It made it easier to walk upright.
Stability however had not yet
arrived. The cerebellum, the
region of the brain, concerned with
balance and spatial positioning
was only beginning to expand.
4. With the demise of the dinosaurs,
diverse adaptive zones opened up
for monotremes (egg-laying
mammals), marsupials (pouched
mammals), and eutherians
Monotremes – “Spiny Anteaters” (egg-laying)
Monotremes – Duck-billed Platypus
Marsupials - kangaroos, koalas, wallabies, wombats, bandicoots, and opossums
Eutherians – placental mammals
5. Egg laying mammals – Platypus/Spiny Anteater
Compared with the monotremes and marsupials – placental mammals had a competitive edge (i.e., higher metabolic rates, more precise regulation of body temperature, and a new way of nourishing their developing embryos).
Evolutionary distant, geographically isolated lineages often evolved in similar ways and in similar habitats and came to resemble each other in form and function.
of convergent evolution.
1. The platypus and spiny anteater,
which survive today in Australia,
differ from other mammals in
a. They are practically toothless
b. Metabolic rates are lower
c. They lay eggs but suckle their
2. The marsupials found in Australia
and in North America are distinc-
tive in that the young are born
tiny, blind, and hairless but find
their way to the mother’s pouch
where they are suckled and
finish their development. 260
species of marsupials are native
to Australia. The Tasmanian devil
the largest carnivorous marsupial.
3. The descendants of therians, placental mammals are found in virtually every aquatic and terrestrial environment.
a. The young are nourished within the mother’s uterus by the placenta – a composite of maternal and fetal tissue.
b. It is the organ of exchange of oxygen, nutrients
and wastes between the maternal blood and
the fetal blood.
We have journeyed about 570 million years, starting from tiny bag like animals to craniates, from jawless and jawed fishes having a backbone. Arriving at the end of the Devonian era we saw the emergence of tetrapods, that possessed skull bones, jaws, a back bone, lungs, walking on four limbs that evolved from fleshy lobed fins, to amniotes – reptiles and mammals to primates and then to humans.
Trends in Primate Evolution
A. Primates include a wide variety of
1. Prosimians (literally: before apes)
are small tree dwellers (arboreal)
that use their large eyes to advant-
age during night hunting.
Prosimians – Mongoose Lemur
2. Tarsiers (tarsioids) are small
primates with features inter-
mediate between prosimians and
3. Anthropoids include monkeys, apes
and humans. Hominoids include apes and humans, where Hominid refers to human lineages only.
Tarsiers – Spectral Tarsier (S.E. Asia)
Anatomically and biochemically apes are closer to humans than monkeys, but chimps are most closely related.
GA Tech conducted a genetic analysis of approximately 63 million base pairs of DNA – 99.4%
Ape and Man – 98 -99% genetic similarity
Five features set primates apart from other mammals:
1. Less reliance on sense of smell and
more on enhanced daytime vision:
a. Early primates had an eye on each
side of the head.
b. Later ones had forward-directed eyes resulting in better depth perception and increased ability to discern shape, movement in three
dimensions, color, and light intensity.
2. Skeletal modification promoted
Bipedalism – upright walking
a. Bipedalism is possible because of
of skeletal reorganization in primates ancestral to humans. This freed the bonds for novel tasks.
b. A monkey skeleton is suitable for
a life of climbing, leaping, and
running along tree branches with
c. An ape skeleton is suitable for
climbing and using the arms for
carrying some body weight; the
shoulder blades allow the arms to
d. Compared to the ape, humans
have a shorter, S-shaped and
somewhat flexible backbone.
Skeletal change favoring
bipedalism was a key innovation
that evolved in ancestors of
3. Bone and muscle changed led to
refinements in hand movements.
4. Power grip and precision grip:
Early mammals spread their toes apart to support the body. Primates still spread fingers and toes. Tree-dwelling primates had modifications to handbones which allowed them to wrap their fingers around object.
a. Opposable thumb and fingers
allowed more refined use of
b. The precision and power grip
movements of the human hand
allowed for toolmaking.
4. Teeth became less specialized.
Jaws and teeth in early mammals
suitable for eating insects and fruits
and leaves later evolved long\ canines, in monkeys and apes and
humans to rip flesh.
5. changes in the brain became inter-
locked with changes in behavior and the
evolution of culture.
6. Brain, behavior, and culture:
is the sum of behavior patterns of
a social group, passed on to
generations through learning and
a. Brain expansion and elaboration
produced a brain of increased mass
complexity, especially for thought,
language, and conscious movements.
b. Human brain development promo-
tion of new neural connections,
led to patterns of human behavior
known collectively as culture.
Maternal core became intense
and offspring started to acquire
longer periods of dependency and
From Early Primates to Hominids
A. Origins and Early divergences
1. The first primates that evolved
from mammals about 60 million
years ago (Paleocene) resembled
small rodents or tree shrews; they had
long snouts and were good foragers
on the forest floor.
2. By the Eocene, their descendants
were living in trees, had larger
brains, were active in the daytime,
and possessed better grasping
movements. Trees offered a
larger quantity of food and safety
from ground-dwelling predators.
3. By the time of the Oligocene,
tree-dwelling ancestors of monkeys
and apes, such as the anthropoid
Catopithecus, had emerged.
4. The first hominoids ape-like forms
appeared between 23 and 5 million
years ago (Miocene)
They evolved and spread through Asia, Africa and Europe. During this time too, shifts in land masses and ocean circulation caused long-terms change climate.
1. Most of the earliest known
hominids lived in the East African
a. Cooler and drier weather in this
region of the world encouraged
the transition of hominids to
mixed woodlands and grasslands.
Food eventually became more
scarce. Hominoids had two choices,
move to adaptive zones or die.
Those who moved survived those
who did not more became extinct. The
lineage of the former became the first
hominids while the latter game rise to the
b. The plasticity of early hominids
was the result of the capacity to
learn to adapt.
2. The first known hominids are designated australopiths (southern
a. The oldest has been designated
Australopithecus anamenis; other forms have been designated Australopithecus afarensis and A. africanus.
b. More robust muscular & heavily built
were A. boisei and A. robustus.
c. Relationship of these species is uncertain, but all shared several characteristics; improved dentition for grinding harder foods, upright walking, bipedalism (leaving footprints), and increased manual dexterity.
Ape vs. Human Fossils
Ape-like featureHominid feature
Jaw shape rectangular dentation U-shaped dentation
Spine shape straight S-shaped
Posture knuckle-walked erect posture, bipedal
Pelvis elongated short
Supraorbital pronounced ridges not pronounced
Plane of face projected forward flat faced
Teeth larger, large canines smaller, smaller canines
Emergence of Early Humans
Modern humans emerged from the traits seen in our tree-dwelling ancestors, relying more on the acute daytime vision than sense of smell. Manipulative skills increased. Bipedalism, omnivorous eating habits and increased brain complexity and behavior.
A. Which traits characterized humans?
1. “Human” is mostly defined by the increased brain capacity which allows
analytical skills, complex social behavior, and technological innovation. These set us apart from apes.
2. The earliest human is designated Homo habilis, signifying “handy man”
B. Homo habilis is associated with the first stone tools.
1. hominids began to use stone tools about 2.5 million years ago to get marrow out of bone & to scrape flesh from bones
2. “Manufactured” tools have been found at Olduvai Gorge.
Emergence of Modern Humans
A. How did Homo erectus become Homo sapiens?
1. H. erectus migrated out of Africa into Europe and Asia.
2. Selection pressures triggered adaptive radiations resulting in physical changes as well as cultural shifts.
a. Homo erectus had a longer, chinless face, thick-walled skull, heavy browridge but narrow- hipped and long-legged.
b. Homo erectus made advanced stone tools and used fired as they migrated out of Africa into Asia and Europe.
B. By about 100,000 years ago, Homo sapiens had evolved from Homo erectus
1.Early H. sapiens had smaller teeth, a chin, thinner facial bones, larger brain, and rounder, higher skull.
2. Neanderthals were similar to modern humans but disappeared about 35,000 years ago.
3. From about 40,000 years ago to today, human evolution has been cultural, not biological.