Week 13: Vertebrates
Phylum Chordata
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Class Amphibia
Class Reptilia
Class Aves
Class Mammalia
4 Characteristics:
1. Notochord
2. Dorsal Hollow Nerve Cord
3. Pharyngeal
4. Post Anal Tail
Tetrapods:
Derived Characteristics:
 Limbs – used to support
on land (replacing pectoral/pelvic fins!)
 Feet with digits: muscle generated force can be transmitted to ground when
walking
 Bones of pelvic girdle (
) fused to backbone
 Pharyngeal clefts gave rise to ears and glands, not gill slits
 Ears can now detect
!
Class Amphibia – “Dual Life”
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Order Urodela
 Body with head, trunk and
 Ex. Salamander
Order
 Body with fused head and trunk, NO tail
 Ex. Frog
Order Apoda
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-like body, NO legs or limbs
 Ex. Caecilian
Amphibian Life:
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Primarily found in damp habitats
Utilize moist skin for gas exchange
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does NOT persist
3-chambered heart
“
” – adapted to both terrestrial and aquatic habitats
Metamorphosis
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Aquatic larvae transform into
adult frogs
Tadpoles (larvae) develop lungs, legs and external eardrums
At the same time, the
and lateral line disappear
Adaptations in Frogs
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Powerful hind legs used to hop along terrain
Long, sticky tongue to capture
Skin glands capable of secreting poisonous mucus for defense
Many poisonous species are
but some utilize colors for
camouflage
Amniotes:
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A group of
including reptiles, birds and mammals laying eggs
The amniotic egg no longer requires water for reproduction
Shells (if present) decrease dehydration of the egg, allowing amniotes to inhabit a
wider range of terrestrial environments
Amphibian eggs lack a
Eggs of birds have calcareous and inflexible shells
Non-avian reptiles’ eggs have
flexible shells
Amniotic Egg:
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The egg have four structure elements used to protect the embryo:
 Allantois – disposal of metabolic waste
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– gas exchange between embryo and air
 Amnion – fluid filled cavity that cushions against mechanical shock
 Yolk Sac- contains nutrients that are transported to the embryo via
Amniote Adaptations to Terrestrial Life:
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Less
skin
Well-developed limbs and lungs for breathing
Stance is more elevated than earlier tetrapods
Early amniotes most likely lived in drier environments as evidenced from
Body Temperature Regulation
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Endothermic – Maintain homeostasis through
metabolic production of
heat.
Ectothermic – Body heat obtained from external sources. These animals use
energy rather than cellular metabolic reactions.
Class Reptilia
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Possess tough, dry skin with
Have well-developed lungs and limbs
Most have
-chambered hearts, except alligators and crocodiles, which have a
4-chambered heart.
Ectothermic heat regulation
Utilize a
as the single opening for digestive, reproductive and excretory
systems.
4 Orders of Class Reptilia:
Four orders of Extant Reptiles:
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Order Rynchocephalia – includes tuatara (2 extant species)
Order
– snakes and lizards
Order Testudines – turtles and tortoises
Order Crocodilia –
and alligators
**Dr. Frazier classifies tuatara as SQUAMATES**
Class Aves
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Highly evolved
?
Notochord does not persist
Distinguished by a
, epidermal feathers, scales on their legs, and a cloaca
Possess a light skeleton with
bones for flight
Have 4-chambered heart
Endothermic
Class Mammalia
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Notochord become vertebral discs
Possess
glands (milk)
Have hair/fur and fat layer under skin to retain heat.
Efficient respiratory and circulatory system with 4-chambered heart
Larger brains than other vertebrate – capable of
Large variety of
– specialized to chew different foods
Endothermic with high metabolic rate
Subclass Prototheria
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Order Monotremata
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and Reptile-like
 One species of platypus and four species of
 Possess a cloaca, hair and can secrete milk but lack
(spiny anteaters)
Subclass Theria
Metatherians =
(opossums, kangaroos & koalas)
 Short gestation period
 Embryo begins development in uterus but completes development in a maternal
pouch called
 Marsupium contains nipples to provide milk
 Marsupials have relatively
metabolic rate
Eutherians =
(monkeys, dogs, humans, zebras, etc.)
 Commonly called placental mammals because placenta is more complex than
marsupials
 Longer
period than marsupials
 Young eutherians complete development inside
 Exhibit parental care and some display intricate social behaviors
Order Primates
(Homo sapiens – humans and other apes)
Distinguishing Characteristics of Humans:
 Stand erect & walk on two legs (
)
 Much larger brain than other hominids
 Capable of language,
and manufacture and use of complex
tools
 Reduced jawbones and jaw muscles
 Shorter digestive tract than other hominids
Bipedalism
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Ability to walk on
– requires less energy than walking on four
Adaptation to aid in travelling over open ground more efficiently and allows for
the use of
to complete other tasks
In humans, the spine is located directly underneath the skull, allowing us to hold
our heads directly above our bodies.
Earliest Humans
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is the name of the fossil skeleton of Austalopithecus afarensis (3mya)
Lucy represents one of the earliest bipeds
Less famous, but more recently discovered is Ardipthecus ramidus (4mya)