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IB 202
Agnathan
Vertebrate
diversity
Fig. 34.7
• Amphibian Reproduction
• Non-amniotes - eggs lack a shell and dehydrate
quickly in dry air.
– Mostly external fertilization; eggs shed in ponds or
swamps, or other moist environments.
– Vast numbers of eggs in temporary pools where
mortality is high.
– Some species – parental care.
• Males or females house eggs on their back, in the mouth, or
even in the stomach.
• A few ovoviviparous or viviparous.
• Why didn’t amphibians evolve an amniotic egg ( a water
proof egg) like the reptiles and birds ?????? Evolutionarydevelopmental barrier????
• Inside the shell of the amniotic egg are several
extraembryonic membranes that function in
gas exchange, waste storage, and the transfer of
stored nutrients to the embryo.
– These develop
from tissues
layers that
grow out
from the
embryo.
Fig. 34.19
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Evolution of Amniotes
• Monophyletic group (clade), with all modern
reptiles, birds, and mammals sharing a common
ancestor.
• An evolutionary radiation of amniotes during the
early Mesozoic era (~200mya) gave rise to 3
main groups, - anapsids, synapsids and
diapsids. (holes in temporal region of skull,
none,one and two).
Two Great
Waves of
Adaptive
Radiation
of Amniotes
Extant
taxa
Late Triassic
(206 mya)
Permian
(290-245mya)
Fig. 34.20
• Synapsids - mammal-like reptiles  therapsids 
mammals.
• Anapsids - extinct.
– Turtles – may be anapsid, may be diapsid
descendant.
• Diapsids - extinct and modern reptiles.
• Early Mesozoic (245 mya)  two lineages:
• lepidosaurs (lizards, snakes, and tuataras)
• archosaurs (crocodiles and alligators, dinosaurs, and
birds)
• Birds’ closest relatives are the extinct dinosaurs – the
saurischian dinosaurs.
• Read about the uncertain taxonomy of amniotes – not in exam
and use of reptile as a taxonomic unit.
Fig. 34.21
Reptile Adaptations for Terrestrial Life
– Amniotic egg (leathery).
– Scales containing the protein keratin
waterproof the skin.
– Reptiles obtain all their oxygen with
lungs; no cutaneous respiration unlike amphibians.
• Ectotherm vs Endotherm
• Modern reptiles are ectotherms – i.e rely on
external heat (solar) and shade for adjusting body
temperatures.
• (Endothermy – ability to maintain high body temp
by metabolic heat production).
• Were their reptilian ancestors (dinosaurs)
ectotherms?
• Some anatomical evidence supports endothermy.
• Large dinosaurs have low surface-to-volume ratios 
low body temp fluctuation; functional enothermy.
• The dinosaur that gave rise to birds was certainly
endothermic, as are all birds and feathers on fossil
dinosaurs may have been for insulation.
• Extant Reptiles
• ~ 6,500 species; four groups:
•Testudines (turtles)
•Sphenodontia (tuataras)
•Squamata
(lizards, snakes)
•Crocodilia
(alligators,crocodiles)
Birds Began as Feathered Reptiles
• Theropod ancestor - small, bipedal, carnivorous
dinosaurs, e.g. velociraptor.
• The famous Mesozoic Archeopteryx.
• ~150 mya, during
Jurassic.
• Had clawed forelimbs,
teeth, and a long
tail containing
vertebrae. Too heavy
to fly.
• Not precursor to
modern birds.
• Cladistic analyses of fossilized skeletons
support the hypothesis that the closest reptilian
ancestors of birds were theropods.
– These were relatively small, bipedal, carnivorous
dinosaurs (such as the velociraptors of Jurassic
Park).
– While most researchers agree that the ancestor of
birds was a feathered theropod, others place the
origin of birds much earlier, from an ancestor
common to both birds and dinosaurs.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Without its feathers, Archeopteryx would
probably be classified as a theropod dinosaur.
• Its skeletal anatomy indicates that it was a weak
flyer, perhaps a tree-dwelling glider.
• Archeopteryx is not considered to be the
ancestor of modern birds, but probably an
extinct side branch.
– The evolutionary side branch that includes
Archeopteryx probably stemmed from a common
ancestor that also produced the lineage from which
modern birds evolved.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• In 1998, paleontologists described a diversity of
Chinese fossils that may fill in the gap between
dinosaurs and early birds such as Archeopteryx.
– These include feathered but flightless dinosaurs
which may have evolved feathers for
thermoregulation or courtship displays.
– Others have a much closer kinship to modern birds
with a lack of teeth, a horny bill, and a short stubby
tail (a few fakes, money!).
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 34.28
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Extant Birds
• ~ 8,600 species (~ 28 orders); two major groups.
• Ratites - flightless; lack a breastbone and large
pectoral muscles (except penguins). Eg. ostrich,
kiwi, and emu (recent extinct large birds-moa).
• Carinates – flight birds; have a carina, or sternal keel,
which anchors the large pectoral muscles.
• Nearly 60% of birds are passeriformes, or perching
birds.
Avian Adaptations to Flight
• Reduction of weight:
– The bones are honeycombed to reduce weight without
sacrificing much strength.
– Female has one ovary.
– Air sacs. Frigate bird
skeleton 4 oz (2 m wing)
• Wings and feathers.
• Large strong pectoral muscles
to power flight.
• Endothermic – constant high
body temperature for efficient function.
• Efficient circulatory system – 4 chambered heart.
• Efficient respiratory system – lung with one pass gas
exchange.
• Feathers are among the most remarkable of
vertebrate adaptations.
– They are both extremely light and strong.
– Feathers are made of the protein keratin, the same
material in reptile scales and mammalian hair and
nails.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Feathers may have functioned first as insulation
during the evolution of endothermy and were
later co-opted as flight equipment.
– Birds have downy feathers and contour feathers.
– The downy feathers of birds lack hooks on barbules,
producing a fluffiness that provides excellent
insulation because of the trapped air.
– Contour feathers are the stiff ones that contribute to
the aerodynamic shapes of the wing and body.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The evolution of flight required radical
alteration in body form but provided many
benefits.
– Flight enhanced hunting and scavenging.
• It enabled many birds to exploit flying insects, an
abundant, highly nutritious food resource.
– Flight provides a ready escape from earthbound
predators.
– It enables many birds to migrate great distances to
exploit different food resources and seasonal
breeding areas (Arctic seashores major nesting
areas).
• The Arctic tern migrates round-trip between the Arctic to
Antarctic each year.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Rise of
Mammals
Permian
(290-245mya)
Fig. 34.20
• Evolution of Mammals
• Dinosaurs became extinct at the CretaceousTertiary (K-T)boundary ~ 65 mya (end of
Mesozoic).
• Mammalian evolution began over 220 mya
from reptilian stock – the therapsids.
• Remained small, and “out of the lime light”
until dinosaurs became extinct.
• Extensive diversification in Cenozoic.
• Extant mammals - ~ 4,500 species.
• Characteristics of Mammals
• Amniotes; offsprings born rather than hatched
(except monotremes)
• Presence of mammary glands – mothers produce
milk and nurse newborns.
• Long periods of parental care; long period of
learning by offspring.
• Have hair made of keratin (protein).
• Endothermy.
• Active metabolism supported by efficient respiratory
and circulatory systems.
• Brains larger than other vertebrates of equivalent
size; capacity for learning.
• More complex jaws and teeth types than reptiles.
• 3 ear bones instead of one.
Fig. 34.30
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Cladogram of Mammals
African branch
“Afrotherian”
Endentates
Fig. 34.33
• Monotremes – duck bill playtpus, spiny echindas
are the only living mammals that lay eggs.
• Females produce milk in specialized glands, but no
nipples
• Baby sucks milk from the mother’s fur.
• Found only in Oz and New Guinea.
• Marsupials - opossums, kangaroos, bandicoots,
and koalas.
• Born very early, and completes its embryonic
development while nursing within a maternal
pouch, the marsupium.
• In Australia,
marsupials have
radiated and filled
niches occupied
by eutherian
mammals in other
parts of the world.
• Through convergent
evolution, these
diverse marsupials
resemble eutherian
mammals that
occupy
similar ecological
roles.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 34.32
• Eutherian (placentals) mammals
• Complete embryonic development within the
uterus joined to the mother by the placenta.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Which animal is the closest relative to whales?
Primates and the Evolution of Homo sapiens
• Primates - two subgroups.
– The Prosimii (prosimians) - lemurs of Madagascar
and the lorises, pottos, and tarsiers of tropical Africa
and southern Asia.
– The Anthropoidea (anthropoids) - monkeys, apes,
and humans.
Fig. 34.34
Fig. 34.35
Africa, Asia
S. America
• The oldest
known
anthropoid
fossils, from
about 45 million
years ago,
support the
hypothesis that
tarsiers are the
prosimians most
closed related to
anthropoids.
• Anthropoid -Monkeys
• ~ 40 million years ago, monkeys were established in
Africa, Asia, and South America.
• The Old World and New World monkeys underwent
separate adaptive radiations
• New world monkeys - arboreal, prehensile tail,
nostrils open to side
• Old world monkeys - arboreal and ground-dwelling
species, NO prehensile tail, nostrils open downwards
?? New world??
?? Old world??
bald uakari
• Anthropoid – Apes
• Hylobates (gibbons), Pongo (orangutans),
Gorilla (gorillas), and Pan (chimpanzees and
bonobos).
– Modern apes are confined exclusively to the
tropical regions of the Old World. ?? Which is which??
– They evolved from
Old World monkeys
about 25-30
million years ago.
Fig. 34.37
•
•
•
•
• Characteristics of Apes
With the exception of gibbons, modern apes are
larger than monkeys, with relatively long arms
and short legs, and no tails,
Although all apes are capable of brachiating,
only gibbons and orangutans are primarily
arboreal.
Social organization varies among the genera,
with gorilla and chimpanzees highly social.
Apes have relatively larger brains than
monkeys, and their behavior is more flexible.
Humanity is one very young twig on
the vertebrate tree
•
Paleoanthropology - the study of human
origins and evolution.
– Hominoid is a term referring to great apes and
humans collectively
– Hominid has a narrow meaning, confined to those
twigs of the evolutionary tree that are more closely
related to us than any other living species.
Two main groups of hominids:
Australopithecus – early hominids; extinct
Homo - all extinct except Homo sapiens
• Human evolution is marked by the evolution
of several major features.
– Brain Size - brain size in hominoids tripled over the
past 6 million years.
– Jaw Shape - hominoid ancestors had longer jaws prognathic jaws - than those of modern humans.
• Bipedal Posture - hominoid ancestors walked on all four
limbs when on the ground, like modern apes.
• Reduced Size Differences Between the Sexes –
Gorillas and orangutans, male 2X female by weight.
Chimps and bonobos, 1.35X females.
Humans, males 1.2X females.
Read the rest on paleoanthropology of hominids – not in exam
Fig. 34.38