Reptiles, Birds and Mammals
Our scaly, feathered and hairy
3 Key Adaptations for Life on Land
• 1. Amniotic Egg
• 2. Internal Fertilization
• 3. Water-tight skin
• An amniotic egg is a waterproof egg with a shell.
• It is named for a particular membrane called the
• The amnion protects the embryo from drying out
and surround a fluid filled cavity that cushions it.
• The other membranes formed during development
of the embryo function in gas exchange, waste
removal and supplying nutrients.
• The amniotic egg makes it possible to lay an egg on
land without needing to return to the water like an
• In internal fertilization, the male deposits sperm within the
• The sperm then swims inside the reproductive tube towards
• This allows for reproduction to take place outside of water.
• Amniotes have a water-tight skin enriched with a
waterproofing protein called keratin.
• The keratinized skin prevents dehydration.
• Reptile skin has scales which are hard,
overlapping structures made of keratin.
• Birds have feathers made of keratin.
• Mammals have hair, nails and horns made of
• Ectotherms-main source of body heat is the
• Endotherms-body heat generated internally
by cell metabolism, warm-blooded
History of Reptiles
• The oldest reptile fossils have been found in rocks dating from
the Carboniferous period about 300 mya.
• Reptiles diversified in the Mesozoic era.
• At that time, dinosaurs occupied every habitat and ecological
• Some were very quick and agile indicating that they might
have been endotherms.
• Some fossils of dinosaurs have been found with feathers.
• Dinosaurs became extinct 65 mya from a massive collision
with a comet or asteroid.
• Rare, old species
• Different structures than lizards, vestigial third
eye and slowest metabolism in reptile class
• Live only on islands near Australia and New
Turtles and Lizards and
Hard shell Can be legless or Rare
Made of scutes Have limbs endangered
Longest lived Snakes evolved Related to
reptiles From lizards dinosaurs
History of Birds
• Molecular and fossil evidence indicated birds
and crocodilians are more closely related to
dinosaurs than any other reptiles.
• Feathers-modified scales made of keratin used
for flight and insulation
• Birds have a system of branching air sacs that
function with their lungs in respiration.
• The air sac system helps supply the high levels of
oxygen that support a high rate of metabolism.
• Air sacs also reduce the overall body weight of the
• Bird bones are honeycombed and mostly hollow but
are still structurally strong.
Bird’s Adaptations to Decrease Body
• 1. Air sac system
• 2. Honeycombed bones
• 3. Absence of many internal organs
• 4. Absence of teeth
• Gizzard- muscular organ often containing small
stones that grind seeds and other food
• Crop- sac like organ used for temporarily storing food
• 4 chambered heart is efficient by keeping oxygen rich
blood completely separate from the oxygen poor
Origin of Birds
• Many paleontologists agree the ancestor of
birds was a small, feathered dinosaur.
• A famous bird fossil, Archaeopteryx lived 150
• It had a mixture of bird and reptilian features.
• Rapid altitude changes-finches, cardinals
• Soar and glide on air currents-falcons and albatrosses
• Flap or buzz quickly and can hover or go backwards-
• Flightless swimming/diving birds-penguins
• Flightless running birds-ostriches, emus
• Made of keratin
• Modified to the food source
• Toothless and cannot chew
• Grasping-woodpeckers, nuthatches
• Raptors-eagles, hawks
• Swimming-ducks, geese
Perching grasping raptors swimming
Cardinals Eagles Duck
songbirds hawks geese
• Complex courtship behaviors
• Complex song communications
• Caring for offspring
• Nest building
Origin of Mammals
• The oldest fossils of mammals date back about 200 mya to
early Mesozoic era.
• Fossil evidence indicates mammals evolved from reptiles
• Early mammals coexisted with dinosaurs but were mouse-
sized and ate insects.
• These early mammals were nocturnal and endothermic.
• Mammals took over all habitats and diversified once the
dinosaurs went extinct.
• Mammal-endothermic vertebrate that possesses
mammary glands and hair
All Mammals have:
• 1. Mammary glands
• 2. Hair
• 3. Lungs
• 4. Muscular diaphragm that separates lungs and
heart from the rest of the body
• 5. 4 chambered heart
• 6. Reproduce sexually with internal fertilization (a
• 7. Most give live birth with few exceptions
Placentals Monotremes Marsupials
Lay eggs Have a pouch
In a uterus
Only live in
Australia and Young born before
Neighboring Fully developed
Most live in
Contains amnion Mixture of reptilian Australia and
like bird and reptile And mammalian Neighboring
eggs characteristics Islands, except
Platypus and Koalas
• Oldest evidence for bipedalism or upright
walking was Australopithecus about 4 mya.
• Famous fossil called Lucy.