General Biology 101
Chapter Outlines
Starr & Taggert
10th edition
Chapter 26:
Vertebrate Animals
Introduction to the chapter examines the unique, less familiar animals such as the
platypus, of Australia, that when first brought to the British Museum in 1798 by explorers
and naturalists was considered to be too bizarre an animal and presumed to be a hoax.
A platypus is a mammal but lays eggs – an apparent anomaly.
Salps are small marine plankton thought to be similar to the arliest chordates – a branch
of bilateral coelomate animals. Urochordates have a hollow nerve cord which is one of
the key characteristics of chordates.
They have small rudimentary brains, with an “eye” sitting on top of that brain. The entire
animal is transparent, from the figure they seem like alien ghosts.
Note: Each kind of animal is a mosaic of traits, many conserved from remote ancestors
and others unique to its branch on the animal family tree.
Section 26.1
The chordate heritage
Chordates are:


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Deuterostome
Coelomate
Bilateral
Have defining features at some stage of their development while embryos.
Have a notochord – a long rod of stiffened tissue for support. It isn’t bone or
cartilage though.
 Nerve cord – runs parallel to the notochord it is a dorsal tube. Anterior end
may become a brain.
 Pharynx with slits in them – at some stage in development, though may not be
preserved/visible past the embryonic stage.
 A tail extending past the anus.
There are 2100 species of chordates that are invertebrates without a backbone, but they
do demonstrate features listed above.
48,000 species are vertebrates with a backbone of cartilage or bone.
I. Urochordates – salps and tunicates (sea squirts).
Characteristics:
 Baglike with a caudal notochord.
 Usually very small – a few centimeters long at best.
 All are marine
 Sea squirt larvae are bilateral swimmers.
 Undergo a process of metamorphosis with tail reabsorption and the notochord
is lost as larvae become adults.
 Tunicates are filter feeders.
 Tunicates have no coelom
II. Cephalochordates - lancelets
Characteristics:
 Fish shaped animals with a head end containing a brain with nerve cells.
 Common name is lancelets because of being blade shaped – also called
“Amphioxus”
 Side to side swimming motions.
 Filter feeders that live in the sand.
 Pharynx has numerous gill slits that act as a food trap.
III. Early Craniates – animals with skulls
These are animals that have their brain enclosed in a cranium of bone or cartilage.
Ostracoderms (jawless fishes) some of the earliest forms.
Placoderms were the earliest jawed fishes.
Section 26.2
Trends in Vertebrate Evolution
Vertebrates have bone tissue that become hardend with minerals.
The vertebrae bones replace the notochord, working in conjunction with muscles for agile
movement.
Jaws formed from the first series of structural supports for gill slits.
This allowed better hunting capabilities.
Coevolving features of other fishes such as complex sensory structures evolved to keep
pace with more efficient hunters with teeth.
Other trends seen in vertebrates:
 Paired fins in fish – to propel and guide and stabilize the animal.
 In most early vertebrates gills evolved for respiratory structures.
 Later terrestrial organisms developed lungs that served for gas exchange.
 More efficient circulatory system with heart modifications to accommodate
pumping needs.
Section 26.3
Existing Jawless Fishes
Hagfish and lampreys
I. Hagfish
Characteristics:
 Partial cranium
 Cartilage backbone
 Cylindrical body
 No jaws or paired fins
 Secrete sticky slime for defense
 Can survive when no food is present for long time periods
 Very slow metabolism
 Scavengers
II. Lampreys
Characteristics
 Parasitic lifestyle
 Have horny mouth parts
 Aggressive fish that attach to larger fish like trout, salmon and catfish.
 One lamprey can kill up to 40 pounds of host fish in its lifetime, even though
it is fairly small (generally one foot or less).
 A scourge to the Great Lakes region where it has invaded.
Section 26.4
Existing Jawed Fishes
Fishes are the world’s dominant vertebrate group. Their numbers exceed all other groups
combined.
21,000 Species
Characteristics of Fishes:
 Many are stream lined for pursuit or escape.
 Swim bladder is an adjustable flotation device exchanging gases with blood
inside the body to maintain buoyancy.
I.
Cartilaginous fishes (Chondrichthyes)
850 species
Include sharks, skates and chimaeras/rat fishes
Characteristics:
 Marine predators
 Have a skeleton of cartilage
 5-7 gill slits
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II.
Some have protective scales
Some have very sharp teeth inset in jaws.
Some produce venom
Some produce electrical volts to stun their prey.
Boney fishes
96% of fish
Most numerous and diverse
A. Ray-finned fish –fins supports derived from the skin, help make fins
more maneuverable.
B. Lobe-finned fishes – Coelocanths are the only living forms. They
respire by gills but have boney extensions into their fleshy, ventral
fins. (Give transitional evidence of weight supporting structures).
C. Lung fishes – Gills and lungs, all are found in the Southern continents.
There are numerous body shapes in the boney fishes. Walking probably originated in the
water during the Devonian period (age of fishes) among the aquatic forerunners of
tetrapods on land.
Section 26.5
The Rise of Amphibians
Characteristics:
 Mostly bony endoskeleton
 Have 4 legs or a four legged ancestor.
It is thought that the movement to land by amphibians may have coincided with an
asteroid impact during the Devoniana that may have drastically changed the available
oxygen in the sea.
The movement to land was both dangerous and promising.
- Drier
- Less support for body weight
- More oxygen available
- Less competition for resources (not given in text but a common assumption)
Animals with better senses, sight, hearing and balance were favored because they were
better hunters.
Amphibians can exchange gases by both lungs and across skin surface.
Eggs must still develop in moist places.
I.
Frogs and Toads
4000 species
Characteristics:
 Well adapted for jumping
 Catch prey with a sticky tipped tongue.
 Some are poisonous
Note: Frog populations world wide are plummeting in part due to parasite attacks,
predators, UV radiation, habitat loss and pollution.
II.
Salamanders and Newts
380 species
Live in N. temperate zones and tropical regions of Central and S. America
Characteristics:
 Have 4 limbs and as they walk they bend from side to side.
 Carnivorous
Note: Axolotyl is a salamander (from Mexico) that retains gills as an adult and can breed
i.e. is an adult and sexually reproductive even though their body is larval like.
III.
Caecilians
160 species
Worm shaped amphibians
Live in moist soil (usually tropical or subtropical)
Section 26.6
The rise of amniotes
Amniotes were the first vertebrates to form eggs with internal membranes that conserve
water and cushion the embryo. The early amniote laid leathery or calcified eggs.
Amniotes allow reproduction away from aquatic habitats.
Amniotes fertilize the eggs internally.
They also have a pair of kidneys to help conserve water.
Groups of Amniotes
I.
Synapsids – mammals and early mammal like reptiles.
II.
Sauropsids – reptiles and birds
Unique aspects:
 Greater cunning and speed.
 Well muscled jaws
 Cerebral cortex originates with reptiles
 Crocodilians were first reptiles/Sauropsids with a 4 chambered heart.
 Well developed lungs
 Some dinosaurs in the past left fossil evidence of parental behavior
particularly eggs in nests.
Section 26.7
A sampling of existing reptiles
“Repto” is Latin for “to creep”
Not a monophyletic group – a conglomeration of animals with some traits in common.
95% of living reptiles are lizards or snakes.
I. Turtles:
250 species still exist
Characteristics:
 Live in a shell attached to their skeleton i.e. vertebral column.
 Don’t have teeth but instead have horny beak, which is suitable to gripping
and chewing food.
 Lay eggs on land and then leave them – generally no parental care.
II. Lizards
3750 kinds
Characteristics:
 Various adaptations that aid their survival.
 Aggressive disposition
 Do displays to court and to warn
 Some drop their tails if attacked to escape predation.
III. Snakes
2300 existing species
Characteristics:
 Slither in S-shaped waves (except side winder)
 All snakes are carnivorous
 Have flexible skull bones and jaws that allow them to swallow relatively large
prey items.
 Some have fangs
 Some are venomous
IV. Tuataras
1 species
Characteristics:
 Lizard like animals of New Zealand
 More similar to amphibians with respect to their brain and manner of walking.
 Have a third “eye” under the skin with a retina, lens and nerves to the brain,
which they use for monitoring day length.
V. Crocodilians
Closest relatives of birds and dinosaurs
Characteristics:
 Live in or near water
 Powerful jaws
 A long snout
 Sharp teeth (don’t match)
 Some parenting of young occurs, building nests and assisting hatchlings into
the water.
Section 26.8
Birds
Feathers are a unique trait to birds.
Lightweight structures derived from the skin.
Important in flight and insulation.
28 orders of birds
9000 species
Bird songs also a special feature of this group.
Birds evolved during an adaptive radiation of reptiles in the Mesozoic.
Evolved from theropod dinosaurs – 2 legged dinosaurs.
Characteristics:
 Feathers evolved as highly modified scales - useful for insulation.
 They still have scaled feet.
 Engage in parental behavior
 All lay amniotic eggs.
 Air sacs connected to lungs, help to dissipate excess heat from flight exercise.
 Bones are adapted to flight by being light weight.
 Have a four chambered heart.
 The wings are especially adapted to be aerodynamic and very light for
maximum lift.
Migration – a recurring pattern of movement between 2 regions in a response to
environmental rhythms.
Section 26.9
The rise of Mammals
Vertebrates with hair and mammary glands
“mamma” means breast in Latin.
Diversity of size, amount of hair coverage is quite astonishing, with aquatic forms having
very little hair and enormous sizes.
Mammals also have a furry coat of underhair which is dense, soft and insulative.
Guard hairs are longer and protect from wear and tear the more delicate underhair.
Highly developed cerebral cortex offers a wide range of behaviors, including learning.
Dentition – the type, number and size of teeth. 4 distinct types:
Incisors – to nip or cut food.
Canines – piercing points for food capture especially in carnivores
Premolars and molars – (cheek teeth) grind and crush food.
Mammalian orders and radiations:
Triassic was 200 million years ago (mya)
Therapsid reptiles  therions
Early Therions in the Jurassic were small and walked on all fours – under their main body
trunk.
Three lineages of mammals:
1) Monotremes (egg layers)
2) Marsupials (pouched mammals)
3) Placentals (placental/womb bearing animals)
Different radiations (expansions) of mammals occurred since 150 mya to the present
having shifted in prevalence and location according to shifting land masses during
continental drift.
Section 26.13
Emergence of Early Humans
How do we know the ancestral forms became characteristically human i.e. members of
the genus Homo?
Determination is made primarily based on physical traits.
 Bipedalism
 Manual dexterity
 Larger brain volume
 Smaller face
 Smaller, more thickly enameled teeth.
Originated in the late Miocene
Homo habilis means “handy man” and may have been the earliest form of the genus.
Used tools but other hominids may have as well.
At some point they started shaping the tools that they used in food gathering.
Tools did not change much in ½ million years.
Section 26.14
Emergence of Modern Humans
Homo erectus was a traveling species, leaving the home origins of Africa and migrating
to Europe, Asia and N. America as the ice sheets advanced.
This species had a larger brain and was a more creative tool maker.
Speculation that it had strong social organization and communication skills.
Homo erectus
Used and built fires
Used clothing
Modern Homo sapiens arrived only 100,000 years ago.
Features:
 Chin
 Facial bones smaller
 Skull was higher and rounder
 Brain had a large volume
Neaderthals existed in Europe 200,000 – 30,000 years ago. They were adapted to colder
climates. They went extinct when H. sapiens arrived through the reason is not clearly
understood.
Currently cultural evolution has predominated and humans have adapted to many
environments and spread quickly.
Section 26.15
Out of Africa – Once, Twice, Or…..
Africa is the origination area for all hominids.
Fossil evidence suggests that Homo erectus left Africa in waves between 2 mya and
500,000 years ago.
Two different hypothesis exist about the origins of H. sapiens.
1) Multiregional model – H. erectus spread through many regions by about 1 million
years ago. Different populations evolved in regionally distinct ways due to
different selection pressures.
2) African emergence model.
Holds that modern humans originated in sub-Saharan Africa between 200,000 –
100,000 years ago. Moved out of Africa and migrated where they settled, they
replaced H. erectus populations.
Oldest known H. sapiens fossil is found in Africa.
Chinese Human Genome Diversity Project looking at gene patterns suggests modern
humans moved into central Asia, moved into SE Asia and later into N. America.