Origin
and Evolution
Consider for a minute the diversity of birds. There are nearly 10,000 species! Is it possible to trace these birds back to one common ancestor, and if so, who is it.
One of the major criticisims of Darwin's Origin of Species was the apparent lack of any evidence showing the evolution of birds. Then, as luck might have it, only two years after he first published his book Archaeopteryx appeared.
Today there are 8 preserved fossils of Archaeopteryx in various museums of the world. What an amazing find for since though as it stirred scientists to try and figure out how birds were related to other creatures.
Archaeopteryx was amazing for a few reasons. First it looked like a dinosaur. Infact, except for the feathers and the fact that it had a wishbone it didn't really look like a bird. The jaws had teeth in them, of which no bird today has teeth. Clearly this bird had features of dinosarus AND birds. So where did birds evolve?
Three hypothesis on origin of birds finally arrose:
- Therapod dinosaur hypothesis: The first was a hypothesis that they came from the theapod dinosarus.
- Crocodiles - the second hypothesis was that they came from crocodiles because they had an endolymphatic duct. Yet, as more research was conducted, they discovered that there was a tremendous amount of variation in this duct even amount the lizards and other reptiles. Not many people today give much attention to this hyptohesis
- Neither crocodiles or dinosaurs:Neither on the dinosaur line or the crocodile line. Reasoning because several dinosaurs were very specialized already.
Today we can show that birds are related in many ways to Dinosaurs. By using key characters we can relate them generally to Ornithodira and more specifically to Manirapterans.
• Relationship of different Diapsids (cladogram).
o Include snakes and lizards
o Includes Archosaurs (Crocodiles etc.)
o Each section of the diagram represents a character or a clade.
Dinosaur cladogram:
Looking in particular at the Ornithodira, Dinosaurs, Saurischian
dinosaurs, Therapods, Tetanurae, Coelesaurs, Manirapterans. (list
heirchial) (then Aves
- Archaeopteryx can be traced back to the dinosaurs
- Birds ore Ornithodira because birds have the same type of Ankle. (ankle diagram). Pterosaurs have this as Ornithodira.
- Ornithician dinosaurs compared to Saurischian dinosaurs.
o Shape of the pelvis makes them similar, but independently evolved. - Birds are Dinosaurs because of the pelvis.The advanced bipeds have changed the joints of the legs. Dinosaurs have a perforated acetabulum: (very important between dinosaurs and birds).
- Saurischian because the ankles have an ascending process on one of the bones in the ankle.
- Therapod because it has at least 5 sacral vertebrae in the pelvis.
- Tanuraens (Allosaurus etc.), has a tooth row on the upper row that doesnot extend back past the orbital (eyes). Also has a antorbital fanestra.
- Coeleasaur cause it has large hands. This is the basal group for wishbone dinosaurs.
- Manirapteran because has a semi-opisthopedic pelvis. Means that the pubis bone of the pelvis is rotating backwards and has a foot.
- Half-moon shape bone in the wrist.
Summarize of set of derived characters that link them throughout
the dinosaurs:
• Pelvis
• Clavicles
• Wrist
Caudipteryx
fossil picture:
• Has feathers and a wing but too small for it to be able to fly!
• Created huge news!
• Initial function of feathers may not have been for powered flight!
• Feathers symmetrical around the shaft around the shaft.
• Forced a reconfiguration of the systematics of the group.
• Now a bird is a manurapterean with arms as long as the legs, but
still doesn’t deal with the feathers.
Feathers
• Were widespread among dinosaurs (distribution of known feather
types).
• Could have been more like ‘down’ feathers’
Microraptor
• Found around 2000 AD
• Tiny fossil of about only around 10 cm long.
• Showed that these dinosaurs could be very small. Even smaller
than Archaeopteryx
• This dinosaur looked like it was arboreal.
How
changes occurred from Archaeopteryx to modern birds
• Figure14: Mesozoic birds
• Can look at evolution of modern birds through the Mesozoic.
• Neornithes- Ichthyornithiformes- Hesperonithiformes – Patagopteryx
– Enantiornithes – Iberomesornis – Monoykus - -
Metornithes:
• Somebirds were will evolving flightlessness.
• Fusion of the metacarples and carples
• Carpometacarples.
Ornithotherasces
• represented by Iberomesornis
• shows characters of modern birds
• strut-like caraicoid.
• Must shorter tail
• Some caudal vertebrae are fused into structure called pygostyles.
Allowing for modern structures of the tail feathers.
Sinornis
• now has 8 sacrum vertebrae.
• Changes in the wrist that causes better flight.
Spanish birds: look for picture.
• alula on its wings … has a midwing slot.
Patagopteryx (from Alvarenga and Bonaparte 1992).
• closest known bird to Ornithurae. Bone near ankle is a fusion
of some carpel elements. Tarsal – metatarsal.
Ornithurae
• pelvis has become fused and quadrate bone of the skull has a spike.
• (underside of the skull (see spike).)
• Hesperornis. First known foot propelled divers.
• Ichthyornis has a shorter back more like modern birds. …
nature of the humorous on its arm (Fig 5-17). Convex lob-shaped head.
Carinatae (Ichthyornis and modern birds)
Evolution of specializations for flight (Figure 15.1). This is a great slide.
ORIGIN OF FLIGHT.
How did it evolve?
• Because of the ancestry they think it might have evolved from
the ground up.
• 1 theory was that they use the wings to catch insects.
• Archeopteryx wing reconstruction is used for flight.
Figure 9: leaping for prey
• Think a leaping bird could allow it to come down in one piece.
• Try to show that there could be a function of a wing even before
the wings evolved to fly.
Arm movement
• capturing prey was the same movement for flight
Wing-Assisted Incline running. (Study ‘lit the world on fire’).
• Used chucker partridges.
• Inclines of different grades.
• From 0-45 degrees they just used their legs.
• But greater than 45 they used their wings too.
• So when they flap their wings, some of if it puts more traction
on the surface.
Links about on Evolution of flight:
By Rob Nelson
