Birds Flashcards
What was the first discovered dinosaur?
Megalosaurus.
Main two groups of dinosaurs?
Ornithischia (bird hipped) - herbivorous bipeds and quadrupeds.
Saurischia (lizard hipped) - sauropods (long necked herbivorous quadrupeds) and theropods (mostly predatory bipeds). Includes birds.
Diversification of dinosaurs?
Peak diversity in the Cretaceous.
Burrowing dinosaur has been discovered, as well as evidence of a semi-aquatic dinosaur.
Breakup of Pangaea in the Cretaceous. This isolated groups of dinosaurs, and they underwent separate adaptive radiations in the Cretaceous.
Describe the K-Pg extinction event?
Occurred at the Cretaceous Paleogene boundary.
Non avian dinosaurs disappear from the fossil record (65 mya) along with pterosaurs, ammonites, and most marine reptiles.
High iridium content in clay between the two rock boundaries, but couldn’t be volcanic, as the impact was worldwide. Therefore this deposition must have been due to an extra-terrestrial impact. Crater was found in gulf of Mexico.
Large amounts of ferns in the pollen record, which indicates that photosynthesis was slowed. Perhaps due to a world embracing dust cloud.
Other contributing factors…
Marine regression - Late Cretaceous showed a fall in sea level. All 5 mass extinctions are associated with marine regression.
Consequences - loss of coastal planes, marine habitats, habitat fragmentation, establishment of land bridges (biotic interchange).
Volcanoes - Just before the impact, there was a massive episode of volcanism. Lava flows could have covered 2 million km^3
How did dinosaurs get so big?
By growing faster or living longer?
T Rex got bigger by growing faster than its smaller cousins - can be seen by looking at growth rings in the bones
Thermoregulation in dinosaurs?
We know that some therapods were endotherms. Some large dinosaurs lived in the polar regions (maybe migrated or burrowed in winter).
Can regulate temperature by pumping bood through the long neck to decrease temperature.
Locomotion in dinosaurs?
Biomechanical simulations of 40m long sauropod suggests a max walking speed of 2m/s.
Modern analyses suggest that T Rex could only walk at 5 m/s
Reproduction in dinosaurs?
Most basal birds retain an intromittent phallus, as do the crocodiles (closest living relatives) so its reasonable to conclude that dinosaurs did too.
Oviparous (eggs which hatch after laying). Some species carefully arranged their eggs. Some sauropods positioned eggs next to hydrothermal geysers for incubation.
Origin of birds?
Unclear how some birds, mammals, crocodiles, turtles and lepidosaurs survived the KPg boundary.
Birds first appear in fossil record 150 mya.
Archaeopteryx recognised as the first bird for over 150 years. Fully formed wings with asymmetric feathers, claws on wings, elongated forearms, toothed jaw, long bony tail with tail feathers.
Origin of feathers?
Decoupled from the origin of flight, as proto-feathers (similar to hair) were used for insulation. Linked to origin of endothermy as body size was getting smaller.
Possible that vaned feathers could have been used for display.
Insulation -> Display -> Flight
Main features of birds?
10,000 recognised species.
Endothermic - 40/42 degrees due to high metabolic rate
Feathers - present in all birds but can be highly modified. Evolved in dinosaurs.
Flight - 98% are capable of powered flight (basal character)
Eggs - hard shelled eggs in a nest with parental care.
Bones - light, air filled structure
Keratinaceous beak - no teeth.
Did the current avian radiation occur pre or post KPg?
Pre:
Relatively poor fossil size pre KPg, the phylogeny suggests an explosive radiation, and we know there was a large mass extinction of T Rex. Molecular evidence doesn’t match up.
Post:
Clear evidence that the majority of the avian radiation occurred between 60-55 mya.
What are the Palaeognathae?
Few species which are either flightless or poorly flying.
Ostrich, Rhea, Emu and Kiwi.
From Gondwana, original theory was that they diversified as Gondwana split up due to the fact they couldn’t fly between the islands.
New theory is that they aren’t monophyletic, meaning flight was either lost three times independently, or gained in 2 lineages. Losing flight more times is more likely, as no known case of birds regaining flight.
What are the Neognathae?
Globally distributed modern birds - 99.3% of all bird species.
Why do birds show a restricted body form compared to other vertebrate groups?
Only 5 log difference.
This could be due to the need for light bones for flight. High BMR might place a lower limit on body mass due to excessive heat loss in smaller birds.
