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

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

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Thecodonts

Some Reptilian Features of Birds Skull Nucleated Red Blood Cells Females: W and Z chromosomes Males: Z Z chromosomes One ear bone Scales Eggs

Comparison of Skeleton Archaeopteryx Pigeon

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Thecodont Reptile Longisquama

Theropod hypothesis of the origin of birds 1862 – Thomas Huxley Examples of evidence: Toes Wristbones fused, e.g. Oviraptor (+ eggs!)

Theropod Dinosaur Oviraptor

Oviraptor Eggs

Theropod hypothesis of the origin of birds 1862 – Thomas Huxley Examples 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

(Tyrannosaurus rex was a Theropod)

Some theropods and other dinosaurs in action (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.

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