Aves birds most scientists refer to this group as

Aves: birds
• Most scientists refer to this group as Sauropsida
• Birds are a part of the Dinosauria clade. Why?
• This means dinosaurs are still around!
• All non-avian dinosaur clades
died off in the Cretaceous extinction

Tetrapods: Reptiles
Emerald tree boa Vestigial hind limb bones
Broad-tailed hummingbird

Xiatingia zenghi
• Birds are thought to have evolved from theropod dinosaurs during the
Jurassic period
• Archaeopteryx and Xiaotingia are pre-birds which were close relatives (but
not the ancestors) of modern birds
Archaeopteryx lithographica
Reptiles: Birds

• Synapomorphies which contribute to flight:
• Feathers – modified scales
• Air sacs – pump air through lungs and bones
• Reduction of organs
• Lightweight bones
Reptiles: Birds

Reptiles: Birds
• Tons of diversity – over 10k species!

National Geographic, 2013
• Tons of diversity – over 10k species!
Reptiles: Birds

Mammals

Mammal Phylogeny
• Over hundreds of millions or years, synapsids eventually
give rise to mammals

Mammals
§ Synapomorphies that arose in the
mammal MRCA:
• Mammary glands – secrete milk
(fats + sugars + proteins +
vitamins + antibodies!)
• Hair – made of keratin (also
makes up reptile scales and
feathers!)
•