Reptiles, Mammals, and Birds

Reptiles, Birds, & Mammals

Amphibians

~400 MYA

Early Reptiles: Reptilomorphs

• The earliest ancestors of reptiles are reptile-like amphibians.

• Remember: what is THE defining characteristic of an amphibian?

• The first “amphibian” that laid eggs on land… that’s our first reptile.

AMNIOTES: Reptiles, Mammals and Birds• An amnion is the

membrane “sac” in which an embryo develops.

• Labeled 2

• Both egg-laying and live-birthing animals may have an amnion

Reptiles: What is a Reptile?• Includes lizards, snakes,

crocodiles, turtles, and similar species.

• Aerobic, ectothermic amniotes with scales.

• The Komodo dragon (pictured) is the largest living reptile – it can grow to over 10 feet.

Oviparous Animals Lay Eggs

• For land-dwellers, fertilization is internal.

• Almost all embryonic development happens inside the egg.

Dinosaurs: Famous Reptiles

• The group of reptiles from which all true dinosaurs evolved includes crocodiles as well as ostriches…

• Appear around 250 MYA, during the Triassic period of the Mesozoic Eon… and some survive today!

Mammal-like Reptiles• Cynognathus (shown) is an example of one of

several fossil species that show divergence from the reptile line.

• The first true mammals (with mammary glands, fur, etc.) arise in the Triassic, about 200 MYA.

More about

mammals tomorrow

…

Class Aves: For The Birds

• Birds are close relatives to the dinosaurs

• This bird is preening – a feather cleaning activity that keeps them working just right.

Birds = Surviving Therapod Dinosaurs• Wishbone• Hollow bone structure• 3-toed foot• Oviparous and brooding (nesting)

What’s a Bird?

• Wings, two legs• Endothermic• Oviparous

• Modern birds all have:– Feathers– Toothless beak– Hard-shelled eggs– 4 chambered heart– Hard endoskeleton