Chapter 31: Animals: Part II
31-1
Echinoderms
Echinoderms and chordates are
deuterostomes.
In deuterostomes, the second embryonic
opening becomes the mouth and a
coelom forms by outpocketing of the
primitive gut making these animals
enterocoelomates.
A dipleurula larva is found among some.
31-2
Characteristics of Echinoderms
Echinoderms are a diverse group of
marine animals; there are no terrestrial
echinoderms.
They have an endoskeleton consisting of
spine-bearing, calcium-rich plates.
Echinoderms are often radially
symmetrical, although the larva is a
free-swimming filter feeder with
bilateral symmetry.
31-3
Echinoderm Diversity
Echinoderms include:
Sea lilies (class Crinoidea)
Sea cucumbers (class Holothuroidea)
Brittle stars (class Ophiuroidea)
Sea urchins and sand dollars (class
Echinoidea)
Sea stars (class Asteroidea)
31-4
Echinoderm diversity
31-5
Sea Stars
Sea stars are an example of echinoderms
and possess tiny skin gills, a central
nerve ring with branches, and a water
vascular system for locomotion.
Water enters this system through the sieve
plate, passes into a ring canal, then into
ampullae, and into tube feet; expansion
and contraction of tube feet move the
sea star along.
Each of the five arms contains branches
from the nervous, digestive, and
reproductive systems.
31-6
When a sea star eats a bivalve, it everts
its cardiac stomach into the bivalve and
secretes enzymes; partially digested
food is taken into the sea star.
Echinoderms do not have a respiratory,
circulatory, or excretory system.
The water vascular system carries out
these functions.
Sea stars reproduce both sexually, and
asexually by fragmentation.
31-7
Sea star anatomy and behavior
31-8
Chordates
Chordates (tunicates, lancelets, and
vertebrates) have:
a suuporting notochord,
a dorsal hollow nerve cord,
pharyngeal pouches, and a
post-anal tail at one time during their
development.
31-9
Chordate characteristics
31-10
Evolution of Chordates
The lancelets and tunicates are
invertebrate chordates.
Vertebrates include the fishes,
amphibians, reptiles, birds, and
mammals.
Cartilaginous fishes were the first to have
jaws; amphibians evolved legs and
invaded land.
Reptiles, birds, and mammals have means
of reproduction suitable to land.
31-11
Evolutionary tree of chordates
31-12
Invertebrate Chordates
Lancelets and tunicates are the invertebrate
chordates.
Lancelets are small animals found in
shallow water along the coasts; they filter
feed on microscopic organisms.
Tunicates (sea squirts) live on the ocean
floor and filter water entering the animal
through an incurrent siphon.
Adult tunicates lack chordate characteristics
except gill slits, but adult lancelets retain
the four chordate characteristics.
31-13
Habitat and anatomy of a
lancelet, Brachiostoma
31-14
Anatomy of a tunicate,
Halocynthia
31-15
Vertebrates
At some time during their lives, all
vertebrates have the four chordate
characteristics.
The notochord is replaced by the
vertebral column; this endoskeleton
demonstrates segmentation.
The internal organs are well developed
and cephalization places complex
sense organs at the head.
31-16
Vertebrates are distinguished in
particular by these features:
Living endoskeleton
Closed circulatory system
Paired appendages
Efficient respiration and excretion
High degree of cephalization
The evolution of jaws allowed some
vertebrates to take up the predatory
way of life.
31-17
Milestones in vertebrate
evolution
31-18
Fishes
Today there are three living classes of
fishes: jawless fishes, cartilaginous
fishes, and bony fishes – the last two
groups have jaws.
Jawless Fishes
The first vertebrates were jawless fishes,
today represented by hagfishes and
lampreys with no scales or paired fins.
Water moves in and out through gill
openings.
31-19
Cartilaginous Fishes
The cartilaginous fishes include the
sharks, rays and skates which have
skeletons made of cartilage.
Skates and rays are flat fishes that live
partly buried in the sand and feed on
mussels and clams.
Sharks and rays have a sense of electric
currents in water, a lateral line system,
and a keen sense of smell; these
attributes help detect prey.
31-20
Bony Fishes
Bony fishes have jaws and two pairs of
fins and are the most diverse and
numerous of all vertebrates.
Bony fishes include those that are rayfinned (most abundant) and a few that
are lobe-finned; some of the lobedfinned fishes have lungs and likely
gave rise to amphibians.
A swim bladder may provide buoyancy in
ray-finned fishes.
31-21
Most fishes today are ray-finned and
have these characteristics:
Bony skeleton and scales
Swim bladder
Two-chambered heart (one atrium, one
ventricle)
Paired fins
Jaws
Gills
31-22
Jawed fishes
31-23
Amphibians
Amphibians evolved from the lobefinned fishes and are tetrapods with
two pairs of limbs.
They are represented today by frogs,
newts, toads, and salamanders.
Amphibians usually return to the water to
reproduce and require moist habitats.
Frog tadpoles metamorphose into
terrestrial adults with lungs.
31-24
These features distinguish amphibians:
Usually tetrapods
Mostly metamorphosis
Three-chambered heart (2 atria, one
ventricle)
Usually lungs in adults
Smooth, moist skin
31-25
Frog metamorphosis
31-26
Reptiles
Reptiles include the extinct dinosaurs and
today’s snakes, lizards, turtles,
alligators, and crocodiles.
Reptiles have well-developed lungs within
a rib cage; they are covered with scales
that protect them from desiccation and
predators.
Reptiles have internal fertilization and also
lay a shelled egg, which contains
extraembryonic membranes, including
an amnion that allows the embryo to
develop on land.
31-27
Features that distinguish reptiles include:
Usually tetrapods
Lungs with expandable rib cages
Shelled, leathery egg
Dry, scaly skin
Fishes, amphibians, and reptiles are
ectothermic.
Reptiles try to regulate their body
temperature by moving to a warmer or
cooler location as needed.
31-28
The tongue as a sense organ
31-29
The reptilian egg allows
reproduction on land
31-30
Birds
Birds are characterized by the presence
of feathers, which are modified reptilian
scales.
Birds lay hard-shelled eggs rather than
the leathery eggs of reptiles.
Birds are likely closely related to bipedal
dinosaurs, although this is still under
study.
31-31
Bird anatomy
31-32
Anatomy and Physiology of Birds
Features of birds are related to the ability
to fly.
Bird forelimbs are modified as wings.
Bones are hollow and laced with air
cavities; the sternum has a keel to which
flight muscles attach.
A horny beak replaces teeth.
Respiration is efficient due to air sacs.
Birds have a four-chambered heart, and
birds are homeothermic.
31-33
Bird circulatory system
31-34
Classification of Birds
The classification of birds is based on
beak and foot types and to some extent
on habitat and behavior.
These features distinguish birds:
Feathers
Hard-shelled egg
Four-chambered heart
Usually wings for flying
Air sacs
Homeothermic
31-35
Bird beaks
31-36
Mammals
Mammals evolved from reptiles and
flourished after the demise of dinosaurs.
Mammals have hair that helps them
maintain a constant body temperature.
Like birds, mammals have a fourchambered heart.
Internal development in the uterus
shelters the young.
Mammary glands allow mammals to
nourish their young.
31-37
Monotremes
Monotremes have a cloaca that is a
common area for feces, excretory
wastes, and sex cells.
Monotremes lay hard-shelled amniote
eggs.
Monotremes are represented by the
duckbill platypus and the spiny
anteater.
31-38
Marsupials
Marsupials have a pouch in which the
very immature newborn matures.
Inside the pouch, the newborns attach to
nipples of mammary glands.
Marsupials are represented by the
American opossum, and various
Australian animals such as koalas and
kangaroos.
31-39
Monotremes and marsupials
31-40
Placental Mammals
Most mammals are placental mammals,
which retain the offspring inside a
uterus until birth; extraembryonic
membranes are present, including the
chorion that contributes to the fetal
portion of the placenta.
The classification of these mammals is
based on methods of obtaining food,
and mode of locomotion.
31-41
Mammals are adapted to life on land and
can move rapidly.
The brain is enlarged due to the
expansion of the cerebral hemispheres.
Internal body temperature is constant.
Mammals have differentiated teeth; the
specific size and shape of the teeth
may be associated with whether the
animal is a herbivore, a carnivore, or an
omnivore.
31-42
These features distinguish placental
mammals:
Body hair
Differentiated teeth
Infant dependency
Constant internal temperature
Mammary glands
Well-developed brain
Internal development
31-43
Placental mammals
31-44
Primates
Primates are mammals adapted to living in
trees; many have an opposable thumb.
The snout is shortened, enabling
stereoscopic vision, and cone cells give
greater visual acuity.
During the evolution of primates, various
groups diverged in a particular
sequence.
Prosimians include lemurs, tarsiers, and
lorises; anthropoids include monkeys,
apes, and humans.
31-45
These traits distinguish primates from
other mammals:
Opposable thumb (and sometimes great
toe)
Well-developed brain
Nails (not claws)
Single birth
Extended period of parental care
Emphasis on learned behavior
31-46
Human Evolution
The primate evolutionary tree shows that
all primates share one common ancestor
and that the other lines of descent
diverged from the human lineage over
time.
Humans and apes shared a common
ancestor.
Molecular data indicate we are most
closely related to the African apes,
whose ancestry split from ours about 6
MYA.
31-47
Primate evolutionary tree
31-48
Evolution of Hominids
To be a hominid, a fossil must have an
anatomy enabling it to stand erect and
walk on two feet (bipedalism).
Ardipithecus ramidus kadabba is a 5.6 to
5.2 million-years-ago (MYA) hominid
found in Ethiopia; Ardipithecus
ramidus ramidus is a 4.4 MYA hominid
and less apelike than the older fossil.
31-49
Australopithecines
Human evolution continued in eastern Africa
around 4 MYA with the evolution of the
australopithecines, a group that is a direct
ancestor to humans.
Raymond Dart discovered Australopithecus
africanus in southern Africa in the 1920s;
this fossil was the gracile type dated at 2.8
MYA.
A more robust form, (A. robustus), from 2 to
1.5 MYA, had a brain size of 500cc like A.
africanus; these hominids may have been
bipedal but still had longer forelimbs. 31-50
The most famous australopithecine is
“Lucy” or A. afarensis (3.18 MYA)
unearthed in eastern Africa, whose
brain was small (400 cc) but who
walked bipedally.
Since the australopithecines were apelike
above the waist but humanlike below
the waist, it seems that human
characteristics did not all evolve at
once.
This type of evolution of various body
parts at different rates is referred to as
mosaic evolution.
31-51
Australopithecus afarensis
31-52
Australopithecus afarensis, a gracile
type, is believed to be ancestral to the
robust types found in eastern Africas:
A. aethiopicus and A. boisei.
A. boisei had a powerful upper body and
the largest molars of any hominid.
These robust types died out, and
therefore, it is possible that A.
afarensis is ancestral to both A.
africanus and Homo.
31-53
Evolution of Early Homo
Fossils are assigned to Homo if the brain
size is 600 cc or greater, if the jaw and
teeth resemble those of humans, and if
tool use is evident.
Homo habilis
Homo habilis, (handy man) present at
about 2 MYA, is certain to have made
crude flake-like stone tools.
Speech areas of the brain enlarged and
contributed to the beginning of society
and culture.
31-54
Human evolution
31-55
Homo erectus
Between 1.9 and 0.3 MYA Homo erectus,
with a brain capacity of 1,000 cc, a
striding gate, and a flatter face, was the
first to migrate out of Africa into Asia
and Europe about 1 MYA.
Males were about 6 feet tall and females
approaching 5 feet, much taller than
earlier hominids.
H. erectus was the first hominid to use
fire and tools of this time were
advanced axes and cleavers.
31-56
Homo erectus
31-57
Evolution of Modern Humans
Two contradicting hypotheses have been
suggested about the origin of modern
humans, Homo sapiens, from H. erectus.
The multiregional continuity hypothesis
suggests that modern humans
originated from H. erectus separately in
Asia, Europe, and Africa.
The out-of-Africa hypothesis states that
modern humans originated in Africa and,
after migrating into Europe and Asia,
replaced the archaic Homo species
found there.
31-58
Multiregional continuity
hypothesis
31-59
Out-of-Africa hypothesis
31-60
Neanderthals
The Neanderthals lacked a high forehead
and a significant chin and are classified
as Homo neanderthalensis.
They had massive brow ridges; their pubic
bone was long compared to that of
modern humans.
Neanderthals had a brain larger than that
of modern humans, and they lived in
Europe and Asia during the last Ice Age.
Neanderthals lived in caves, made stone
tools, and buried their dead with flowers.
31-61
Neanderthals
31-62
Cro-Magnons
Cro-Magnons evolved about 100,000
years ago and were the first humans
(Homo sapiens) to have a thoroughly
modern appearance.
They made stone tools, including stones
attached to wooden handles; they
threw spears, enabling them to
cooperatively hunt larger animals.
The Cro-Magnon culture included art and
beautiful paintings on cave walls.
31-63
Cro-Magnons
31-64
Chapter Summary
Both echinoderms and chordates are
deuterostomes.
In deuterostomes, the second embryonic
opening becomes the mouth; the
coelom develops by an outpocketing
from the primitive gut.
Echinoderms develop radial symmetry
and have a unique water vascular
system for locomotion.
31-65
Chordates have a notochord, a dorsal
tubular nerve cord, and a post-anal tail;
pharyngeal pouches occur sometime
during the life of chordates, and in
vertebrates, the notochord is replaced
by the vertebral column.
There are three groups of fishes.
One group is jawless, but the
cartilaginous and bony fishes (rayfinned and lobe-finned) have jaws.
31-66
Frogs and salamanders are amphibians
that evolved from lobe-finned fishes;
they have limbs as an adaptation for
locomotion on land.
The shelled egg of reptiles contains
extraembryonic membranes as an
adaptation for reproduction on land.
Both birds with feathers, and mammals
with hair and mammary glands, evolved
from reptiles and are able to maintain a
constant body temperature.
31-67
Primates such as prosimians, monkeys,
apes, and humans are mammals
adapted to living in trees.
Human evolution diverged from ape
evolution in Africa about six to seven
million years ago.
The australopithecines were the first
hominids and were ancestors to
humans.
31-68
Homo habilis could make tools; Homo
erectus migrated out of Africa.
The Neanderthals (H. neanderthalensis)
gave evidence of being culturally
advanced, lived in caves, and hunted
large mammals; they buried their dead
with flowers.
Cro-Magnons are the oldest fossils to be
designated Homo sapiens; they made
sophisticated tools and were
accomplished artists and hunters.
31-69