Evolutionary History

Birds first evolved about 155 million years ago from a reptilian ancestor and still share many characteristics

with reptiles.

First Bird

Archaeopteryx lithographica

Archaeopteryx lithographica

First Feather found 1861

This complete fossil found 1877

Archaeopteryx lithographica

Feathers not symmetrical in modern flying birds and in Archaeopteryx

Feathers symmetrical in flightless birds

Comparison of Feathers

Europe, Asia, Africa - Rail

New Zealand - Rail

Thecodonts

Some Reptilian Features of Birds

Skull

Nucleated Red Blood CellsFemales: W and Z chromosomesMales: Z Z chromosomes

One ear boneScalesEggs

Comparison of Skeleton

Archaeopteryx Pigeon

Thecodont Reptile Longisquama

Thecodont Reptile Longisquama

Theropod hypothesis of the origin of birds

1862 – Thomas HuxleyExamples of evidence:

Toes

Wristbones fused, e.g. Oviraptor (+ eggs!)

Theropod Dinosaur Oviraptor

Oviraptor Eggs

Theropod hypothesis of the origin of birds

1862 – Thomas HuxleyExamples of evidence:

Toes

Wristbones fused, e.g. Oviraptor (+ eggs!)

Shoulder socket

Louis Chiappe: “Take any bone in theropods and birds, and I can show how it links birds to dinosaurs.”

Theropod dinosaur Compsognathus

Theropod dinosaur Compsognathus

(Tyrannosaurus rex was a Theropod)

Some theropods and other dinosaurs in action

http://www.youtube.com/v/VQbNdWnuitY

(from Ritchison’s Website)

Some Theropod Dinosaurs had Feathers

1. Caudipteryx zoui

Some Theropod Dinosaurs had Feathers

2. Microraptor

Some Theropod Dinosaurs had Feathers

3. Sinosauropteryx

Part of Theropod Proposal

Feathers first evolved as thermoregulatory structures from modified reptilian scales.

Proposals of Evolution of Flight – Dichotomy(?)

Arboreal Hypothesis

Cursorial Hypothesis

Proposals of Evolution of Flight – Arboreal and Cursorial Dichotomy (?)

Arboreal Hypothesis Walter Bock

Alan Feduccia

Proposals of Evolution of Flight – Arboreal and Cursorial Dichotomy (?)

Arboreal Hypothesis

1. ancestral ground-dwelling quadrapedal reptile

2. bipedal ground-dweller

3. bipedal and arboreal life

4. leaping between trees

5. parachuting

Proposals of Evolution of Flight – Arboreal and Cursorial Dichotomy (?)

Arboreal Hypothesis

6. gliding

7. active powered flight

Feathers first evolved as stabilizers for gliding.

Proposals of Evolution of Flight – Arboreal and Cursorial Dichotomy (?)

Cursorial Hypothesis J. H. Ostrom

Feathers on forelimbs became “insect nets” to catch prey. (excellent example of pre-adaptation for flight later)

Proposals of Evolution of Flight – Arboreal and Cursorial Dichotomy (?)

Cursorial Hypothesis J. H. Ostrom

Selective pressure would lead to increase in forelimb (wing) size to increase prey capture – leading to short and then longer flights from the ground.

Combination