Origin on birds Flashcards
How do birds process their food?
- With a gizzard
- Gizzard contains stones that help break up food
Was flightlessness (ratites) the origin of birds?
- Ratites are distributed over the southern land masses
- First suggested they were a monophyletic group
- More recently it has been suggested that they are a polyphyletic group that have evolved convergently
When did birds arise and then when did they diversify
?
Arose in the Jurassic
Diversified in the Cretaceous
What are the suggestion of what birds evolved from?
- Early archosaurs
- Crocodilians
- Theropods (main accepted hypothesis)
What were theropods?
- Small carnivorous dinosaurs
- Diverse group
- Most diverse group of saurischians
- Huge size variation
- Not just the t-rex
- Spinosaurus ← giant theropod (18m long)
- Obligate bipeds
What were the diets of theropods?
- Wide branch of diets in later diversifications
- Insectivores, carnivores, herbivores
What did the birds share a common ancestor with?
Dromeosaurs
Sister group to the clade aves
What did thomas huxley suggest?
Said there was an evolutionary link between birds and theropods
What were the shared derived characteristics of dromeosaurs?
- Modification of fore limb, allows seizing action (flexible)
- Suggested feathers were for insulation or sexual selection (maybe)
- Not flight
How did small birds evolve from giant dinosaurs?
50 million years of miniaturisation
What other features changes alongside Miniaturisation?
- Skull is large relative to the rest of the body
- Reduction in number of digits
- Paedomorphic dinosaur skull in birds - skull shape remains similar between juvenile and adults
What are the dinosaur features found in birds?
- Egg laying
- Scales (feathers are derived scales)
- S shapes neck
- Tridactyl foot
- Bipedal
- Toes bearing weight of body
- Wishbone (evolved in the theropods)
- Fused sternum (also found in theropods)
What is Archaeopteryx?
- First fossil with well-developed feathers from jurassic deposits
- 150 mya
What is special about Archaeopteryx?
Shows a transitional form between birds and reptiles
What are Archaeopteryx reptilian features?
- Stong thick bones
- Teeth
- No fusion of vertebrae
What are the bird features of Archaeopteryx?
- Well developed feathers
- Three fingers
- S shaped neck
What do Arcchaeopteryx feathers show?
- Asymmetrical feathers - typical of flight feathers
- Had a similar moulting strategy to modern birds - helps to maintain feathers for flight
- Primitive shoulder that would have limited ability to flap wings
- Glide - lived in areas without trees - would glide not flap wings
- Closed structure that suggested they weren’t climbing
- Similar flight to a pheasant
Archaeopteryx hind-foot
Similar to hind-foot of modern birds
Archaeopteryx Furcula
- Wish bone
- Fused clavicle
- Found in theropods and birds
Archaeopteryx had a hyper extendable second toe, what group also showed this?
- Seen in dromaeosaurs
- Not seen in modern birds
- The terrible claw
- Believed to be used for hunting
Differences between Archaeopteryx and modern birds?
- Archaeopteryx had a smaller brain case than modern birds
- Individual vertebrae (not fused like in modern birds)
- Longer tail compared to modern birds
- Modern birds has large sternum
- Modern birds have 2 digits - Archaeopteryx 3
Was Archaeopteryx the first bird?
- Recently new species of small feathered dinosaurs have been found
- Unsure if its convergent evolution / closely related cousins etc?
- Rahonavis, auromis, scansoriopteryx - other small feathered dinosaurs
- Unsure where Archaeopteryx belongs in the phylogeny
