The Amniotic Egg Secret to the Reptile’s Success

Unlike the eggs of amphibians and fish, the amniotic egg of reptiles,
birds and monotremes is internally fertilized (through sexual contact) and has
a protective outer membrane or shell that prevents it drying out.
 It contains enough nutrients in the yolk to nourish the embryo.
 The allantois is a sac that holds wastes until the embryo hatches, and also
provides some oxygen.

The amniotic egg freed the reptiles of the

need to return to the water to reproduce.

Evolution of the heart

 As reptiles evolved, so did their hearts. Early reptiles had a 3 chambered
heart, just like the amphibians.
 As they became more active, a “septum” began to appear in their hearts.
At first the septum served little purpose, but slowly it became an
advantage..
The septum prevented oxygen-rich blood from mixing as much with the
oxygen poor blood. This allowed a higher activity level for the reptiles. The
septum evolved to divide more and more of the heart. Most reptiles today
have a fairly significant septum. In a few reptiles, like crocodiles, the septum
completely divided the heart.
This four chambered heart was passed on to
the most successful descendants of the reptiles, the
birds and mammals.
 Reptile Facts
*Smallest reptile is the Jaragua Sphaero a dwarf gecko
*The largest (living) reptile is the salt water crocodile.
*Tuataras have a tiny “third eye” on the top of their
heads, related to a human’s pineal gland.

Class Aves
The Birds
Evolution of the Birds
The earliest accepted fossils of birds date back to 150 million years ago.
Recent finds of dinosaur fossils with feather-like scales suggest an
earlier evolution of birds, but this is still debated.
Archaeopteryx lithographica is the oldest confirmed bird species.
→It had several reptilian features, including claws on its wings, teeth and a
long bony tail.

Features of Modern Birds

*Skin covered in feathers
*Wings in place of the forelimbs
*Light-weight rigid skeleton
→many of the bones are hollow to reduce weight
 Endothermic metabolism (warm blood)
→Birds maintain a high body temperature (40-41 degree)
*Unique respiratory system
*A beak in place of teeth
*Amnoitic eggs with hard shells
Birds have many sacs attached to their
lungs. As they inhale, air passes through
lungs and fills the sacs.
Lungs
As they exhale, the air passes through
Air sacs lungs again. Essentially they pass twice
as much air through the lungs with each
breath.
 Flight
*Over 90% of all birds are able to fly.
*Flight has been made possible by many adaptations:
– Wings with an “airfoil” shape.
– “Keel” shaped breast bone with attachment
points for large muscles that operate the
wings.
– Hollow bones to reduce weight
– Feathers insulate and propel.
Down feathers for insulation
Contour feathers give birds shap
Flight feathers give propulsion

Diversity in Birds
• There are 29 different orders of birds
-Only the twelve most common are described in the
textbook
The smallest bird is a Cuban hummingbird not much
larger than a bumblebee (5 cm long including tail, about 1/20
ounce or just over 1 gram)
The largest bird is an African ostrich (9 ft tall, 350 lb, or 2.7m,
160 kg) It is flightless, but a good runner.
Penguins are the fastest swimming birds (Penguins are also flightless, the BBC
video that showed flying penguins was an expensive Computer Generated
April fool’s joke)

A Few Orders of Birds

1) Falconiformes: Birds of prey or raptors
2) Anserformes: Ducks and Geese
3) Strigiformes: Owls
4) Passeriformes: Songbirds
*there are 25 more orders…
 The Mammals
Origin of Mammals
Mammals probably evolved from the synapsids, an early reptile family
that included Dimetrodon,
The Therapsids, like this Lycaenops were a later type of synapsid that looked
more mammal-like. The first true mammals that appeared about 150 million
years ago were small, shrew-like organisms

Characteristics of Mammals
 Endothermy (warm-blooded)
 Skin covered in hair or fur
→in whales and humans the h
 air is reduced to small patches

Four chamber heart →with fully divided

ventricle and separate circulation
 Mammary glands → mammals secrete milk to help nourish their young
 Single jawbone →eptiles have a split lower jaw, mammals have a fused
one.
 Specialized teeth →whereas reptile teeth are all similarly pointed,
mammals can have different shapes (molars, canines, bicuspids
 Diaphragm: a specialized muscle that makes breathing more efficient

Three Subclasses of Mammals

1) Monotremes (Prototheria) 0.2%
→The monotremes are egg-laying mammals (1 order with 3 species)
2) Marsupials (Metatheria) 5.8%
→give birth to immature offspring, and then carry them in pouches. (1
order, 334 species)
3) Placental Mammals (Eutheria) 94%
give birth to well developed offspring after a longer gestation period.
(18 orders, over 5400 species)
The Monotremes
Kingdom Animalia, Phylum Chordata, Class Mamalia, (Subclass
Prototheria)
 Order Monotremata: (only 3 species exist)
“Duck-billed” Platypus
“Short-beaked” Echidna
“Long-beaked” Echidna (aka. “Spiny Anteater”)
 Monotremes lay eggs, but they nurture their young with secretions from
nippleless mammary glands.

The Marsupials
Subclass Marsupialia (about 280 species in 8 order)
Including :
1.) Kangaroo 2.) Wallaby
3.) Tasmanian Devil 4.) Tasmanian wolf(believed extinc)
5.)Marsupial mole 6.) Koala
7.)Wombat 8.) Opossum (only native marsupal in North America)

Interesting facts about marsupials

 Most female marsupials have 2 vaginas within a single cloaca
 Most male marsupials have a forked penis
 Marsupials have a gestation period of less than 5 weeks (some of
them much less).
 Kangaroos don’t fart, (or more accurately, they produce no methane
gas from their digestion)
 A baby kangaroo is about an inch long when born. It crawls to its
mother’s pouch and stays there for about 9 months.
Placental Mammals
→Can produce a placenta.
→Give birth to well-developed offspring.
– In fact, some species offspring can be standing
and running minutes after being born.
→Have longer gestation periods

Main Orders of Placental Mammals (about 5500 species in )

1. Order Rodentia: mice, rats, squirrels, porcupines, beaver
2. Order Edentata: ant While I don’t expect you to memorize all -eaters,
sloths, armadillos
3. Order Lagomorpha: rabbits, hares, pikasthese orders of mammals, I do
give them as
4. Order Insectivora: shrews, moles, hedgehogsexamples of the diversity of
the class.
5. Order Primates:five in bold print are of particular interest, monkeys,
lemurs, apes, humans
6. Order Chiroptera:because they clearly illustrate how different bats
7. Order Carnivora: dogs, cats, bears, seals, sealions
8. Order Artiodactyla: ungulates, deer, cows, pigs, camelsmammals can be.
9. Order Perissodactyla: horses, zebra, rhinoceros, tapirsYou should be
aware of them, as well as
10. Order Cetacea:any other orders that interest you.whales, dolphins,
porpoises, orcas.
11. Order Sirenia: manatees and dugongs
12. Order Proboscidea: elephants, mammoths (extinct)
 Comparison Of Vertebrates
Heart blood limbs covering
chambers

Class 2 Ectotherm None Skin/

(cold) scales

Chondrichthyes 2 Ectotherm Fins Plaquoid

(shark) (cold) scales

Osteichthyes 2 Ectotherm Fins Wet skin

(fish) (cold) and/or

scales

Amphibia 2, 3 Ectotherm No Moist

(cold) claws skin

Reptilia 3, 4 Ectotherm Claws Dry skin

(cold) (except
snakes)
and/or

scales

Aves 4 Endotherm Wings

(warm)
Claws Skin and
Feathers

Mammalia 4 Endotherm varies Skin and

(warm) hair / fur
Mammal Organ Systems
 All vertebrates have well developed organ systems, but those of mammals
are among the best developed.
 Organ systems include:
Integumentary system (skin, with hair or fur)
Muscular system (muscles– skeletal, cardiac, smooth)
Skeletal system (bones, cartilage, connective tissues)
Digestive system (esophagus, stomach, intestines etc.)
Cardiovascular or circulatory system (heart, blood vessels)
Lymphatic and Immune systems (nodes, vessels)
Respiratory system (fully developed lungs, trachea)
Excretory or Urinary system (kidneys, bladder)
Reproductive system (most species have a uterus)
Endocrine system (glands)
Nervous system (brain, dorsal spinal cord)

How a Mammal is Organized

Levels of organization:
Cells→ tissues→ organs→ organ-systems
Many similar cells working together form a tissue
Several tissues working together form an organ Several organs working
together form a system

Major Tissue Types

The four major tissue types are:
1.) Muscle tissues: movement
2.) Nervous tissue: communication
3.) Epithelial tissue: covering organs and surfaces
4.) Connective tissue: connecting and supporting.
Each tissue type has several sub-types:
for example, muscle tissue could be skeletal muscle, cardiac muscle or smooth
muscle tissue.
Body Cavities
 Body cavities are compartments within the body that house organs.
 Humans, like most mammals have four main body cavities:
 Cranial Cavity: Holds the brain
 Spinal Cavity: Surrounds the spinal cord
 Thoracic Cavity: Contains the heart, esophagus, lungs, and other
respiratory organs.
 Abdominal Cavity: Contains the organs of the digestive, reproductive
and excretory systems
The cranial and spinal cavities are often referred to as dorsal cavities because
they are mainly at the back of the body.
The thoracic and abdominal cavities are the ventral cavities because they are
on the front or stomach side of the body.
Sometimes the lower portion of the abdominal cavity is called the pelvic
cavity.

diaphragm
 Geological Timescale (Birds)

Dinosaur
s
Bird
s
Feathere Archeopter
dinosaur yx
s

543 510 439 409 363 290 245 206 144 65 2

Paleozoic Mesozoic Cenozoic

Geological Timescale (Mammals)