Video Assignments

Microraptor—PBS

The Four-winged Dinosaur—Mark Davis

SUNY Cortland Library Online

Radiolab Apocalyptical

http://www.youtube.com/watch?v=K52vD4WBdLw&feature=youtu.be

Minute 13 through minute 60

Link to this video will be emailed—but you can search on Youtube for

“Radiolab Apocalyptical”

Evolutionary Origin of Birds Outline

• Why birds are reptiles

• Archaeopteryx—the link to reptiles

• Birds as dinosaurs

• What kind of dinosaur

• Theropods as bird precursors

• Feathered dinosaurs

• Molecular evidence

Characteristics that Define Birds

• Feathers

• Bills

• Lightweight Bones

• Furcula

• Opposable Hallux

• Efficient Respiratory

System

• External Eggs & Parental

Care

• Finely-tuned Nervous

Systems

Why Birds are Reptiles

Thomas Huxley—19th Century Naturalist regarded birds

as “Glorified Reptiles”

Cladistics—classification application that attempts

to group organisms based on shared derived traits.

(i.e., novel traits that were inherited through a common ancestor)

Species A

Species B

Species C

Ancestor of A, B, & C

Ancestor of A & B

Evolutionary Origins

Species A Species B Species C

Ancestor of A, B, & C

Ancestor of A & B

Why Birds are Reptiles Shared Derived Traits

• Single Occipital Condyle

• Single Middle Ear bone

• Fused Jaw Bones

• Epidermal Scales

• Female Heterogametic Sex

• Sclerotic Eye Ring

• Nucleated Red Blood Cells

Archaeopteryx as a Missing Link

• Archaeopteryx

lithographic fossil

from lithographic rock

quarries in Germany

• 150 MYA

• Reptile-like traits

– Reptilian teeth

– Long tail

– Separate pelvic, hand,

head, and foot bones

– Dinosaur-like hip

– Skull osteology of

reptiles

– Floating gastric ribs

Archaeopteryx as a Missing Link

• Bird-like traits – Asymetrical feathers on wings

– Furcula

– Reversed hallux (?)

• What was the life-style of Archaeopteryx? – Arboreal or ground-dweller?

– Volant?

Archaeopteryx as a Missing Link

More Specimens of Archeopteryx 2005--Science 310:1483

• Pterosaurs

• Pre-dinosaur, pre-crocodilian ancestor

(Archosaurs)?

• Theropod dinosaurs

Who were the

direct

ancestors to

birds?

Ornithischians (Stegosaurus, Ankylosaurus,

Corythosaurus, Iguanodon)

Saurischians—Lizard-hipped (Brachiosaurus, T. rex,

Velociraptor, Deionychus)

DINOSAURS

Thecodonts--Archosaurs

Birds????

Dinosaur-Bird Connection

Backward tilted pelvis,

Predentary bone,

Ossified vertebral tendons

Hands rotate around digits

III, IV, and V

Pelvis tilted forward,

No predentary

No ossified tendons

Digits II, III, and IV

Ornithischians (Stegosaurus, Ankylosaurus,

Corythosaurus, Iguanodon)

Saurischians—Lizard-hipped (Brachiosaurus, T. rex,

Velociraptor, Deionychus)

DINOSAURS

Potential Theropod Precursors

Hollow bones

Three-toed foot (digit I rotated backwards)

Semilunar carpal

Pectoral girdle enlargement

Bipedal

Reduction in digits and arms

Feathers???

Caudipteryx

Elongated feathers

worthy of flight

Arms and legs of

equal length

Enlarge pectoral girdle

Fusion and reduction of bones

Reduction in tail

Motor system development

Beak development

Respiratory efficiency

Why Birds are Reptiles Cladistics of Morphology and Molecular Data

Shark

Mammals

Amphibians

Turtles

Crocodilians

Birds

Reptiles

Snakes

Lizards

Habits of Archaeopteryx (Feduccia, 1993)

Glen & Bennett, 2007.

Cuckoos and Road Runners Pigeons

The first birds (Mesozoic) were very

likely ground foragers and not arboreal foragers.

Feathered Dinosaurs

Hot bed of dinosaur fossils in

Chinese Liaong Province

New species of feathered

theropod dinosaurs-120 MYA

Sinosauropteryx

(first Chinese dragon feather)

Caudipteryx

Caudipteryx zoui

Filamentous

tail feathers

Other specimens that blur the line

between dinosaurs and birds include

Protoarchaeopteryx, Confuciusornis

Birds as Theropods

• Feathered Theropods

– Feathers evolved

before flight

– Feathers are no longer

a novel feature of birds

• Share large numbers of

advanced traits

• Evolutionary trends in

theropods are consistent

with bird evolution

The Four-winged Dinosaur

Microraptor

Significance?

What about non-avian

dinosaur feet and Chukars?

Opposition to Theropod-bird lineage

• Feduccia--birds share an ancestor

with an Archosaur

• Bird-theropod similarities are due to

convergent evolution

– Bipedalism

• Flight evolved from the trees down.

• Deinonychus is 40 MY more recent

than Archaeopteryx. “Temporal

Paradox: you can’t be your own

grandmother”

Comparative Embryology

Feducia’s strongest argument.

• Assume: Digit IV forms the

central axis of modern hands in

birds, turtles, and crocodiles

• Counting backward it appears

that birds retain digits II, III,

and IV and not digits I, II, and

III as in Theropods

Photo from Burke and Fedducia, 1997

Top row-alligator

Middle row-chicken

Bottom row-turtle

Who cares about finger number? (Pennisi-2005, Science 307:195)

• Digit I in terrestrial vertebrates

has unusual development

• Digit I depends on the

developmental gene Hoxd13

and not Hoxd12

• Molecular genetics suggests

that Digit I in birds is indeed

Digit I

Amino Acid Sequence from Bone

Collagen of Dinosaurs

C, G, I are from Ostrich

Amino Acid Sequence

of Dinosaur Collagen

Birds share a more recent common ancestor

with dinosaurs than to early reptiles.

Concluding Remarks • The origin and evolution of birds is

one of the greatest modern day debates in evolutionary biology

• Birds are reptiles

• Theropod origin of birds is gaining strength from many biological disciplines

• Remaining Questions; How did flight arise and & why did feathers evolve?