Transitions in Evolutionary History

1
Transitions in Evolutionary History

• Or, why is there no such thing as a crocoduck?
• Paleozoic four on the floor
• Mesozoic flying high
• Cenozoic walking tall

2
Euramerica aka Laurussia
3
Origin of Tetrapods
Eusthenopteron

• Eusthenopteron was lobe-finned fish
• early Devonian (ca. 408 MYA)
• Ichthyostega early amphibian
• late Devonian (ca. 350 MYA)
• Many homologies
• appendages
• skull structure
• Consider transition to land what predictions?

Ichthyostega
4
Tiktaalik

• 375 MYA
• Fish-like characters
• scales
• fins
• gills and lungs
• Tetrapod-like characters
• neck
• enlarged ribs
• flattened head
• functional wrist

5
Tetrapod Phylogeny
6
Mesozoic
7
Amniote Phylogeny
8
Dinosaur Diversity
9
Therapod Dinosaurs
10
Feathered Dinosaurs
11
Birds are Living Dinosaurs

• T. rex more closely related to birds than to most
  other dinosaurs
• Numerous homologies
• hip structure
• hollow bones
• feathers
• genetic evidence
• What was original purpose of feathers?