week 7

Question 1

features of birds

Answer 1

• strong bipedal stance
• absence of a bony tail
• feathers
• fused limb bones
• forelimbs decoupled from terrestrial locomotion (usually specialised for powered flight)

Question 2

why was the archaeopteryx imporant

Answer 2

• it had a mix of ‘reptilian’ and avian features
• semi-lunate wristbone
• long arms
• reduction and fusion of digits
• retroverted pubis
• tibia longer than femur
• clavicles
• feathers

Question 3

describe the postcranial pneumaticity of living birds and non-avian therapods

Answer 3

• in living birds, posterior trunk vertebrae are only ever pneumatised by abdominal air sacs and lungs
• pneumatised non-avian theropods possessed abdominal air sacs and therefore possibly avian-like flow-through ventilation
• i.e. evolved a long time ago

Question 4

what is the medullary bone

Answer 4

• when laying eggs, female birds grow a special type of bone in their limbs
• this medullary bone forms as a calcium-rich layer inside the outer bone and is used as a calcium source to make eggshells
• equivalent structures are interpreted in several non-avian theropods

Question 5

what are gastroliths

Answer 5

• in living birds, gastroliths ( =stomach/ gizzard stones) are retained in the muscular gizzard and used to grind food

Question 6

describe feathers

Answer 6

• composed of a unique form of keratin derived from the epidermis
• clearly evolved initially for another purpose and were exapted for flight

Question 7

hypotheses for the origin of avian flight

Answer 7

1. the ‘ground up’ cursorial model - being on the ground and running until you take off
2. the ‘trees down’ arboreal model - being in a tree jumping from one branch to another

Question 8

discussion on whether archaeopteryx can fly

Answer 8

• hindfoot not suitable for perching
• lived in an environment lacking tall trees
• hindlimbs suited to running
• no keeled sternum
• feather morphology suggests weak flyer

Question 9

when did crown group birds evolve

Answer 9

cretaceous

Question 10

evidence to suggest that birds are descendants of non-avian theropods

Answer 10

• post-cranial pneumacity
• medullary bones
• gastroliths

Question 11

behavioural similarities in extant birds and non-avian theropods

Answer 11

• tucked-in sleeping position
• non-avian dinosaurs brooding - sitting/nesting on eggs

Question 12

describe the origin of flight

Answer 12

• answer appears to lie closer to cursorial than arboreal hypothesis but not necessarily an either/ore explanation
• feathers clearly evolved initially for another purpose (thermoregulation and/or display) and were exapted for flight
• development of flight unlikely to have been a simple linear process (evolved many times in different lineages)

Question 13

when was the cretaceous/paleogene boundary

Answer 13

66Ma

Question 14

what did the end-cretaceous world look like

Answer 14

• distribution of continents similar to present-day
• high sea levels
• ice-free poles
• warm greenhouse world
• although a greenhouse world, long-term global cooling trend fro ~90Ma

Question 15

describe the K/Pg (or end-cretaceous) extinction

Answer 15

• famous for the extinction of all non-avian dinosaurs
• ~75% of all species lost
• as well as dinosaurs, K-Pg boundary witnessed the extinction of the pterosaurs, plesiosaurs, mosasaurs, ammonoids and belemnites
• many surviving groups also suffered heavy losses, including sharks, bony fishes, insects, bivalves and plants

Question 16

extinction theories

Answer 16

• high CO2 levels destroyed dinosaur embryos
• climate too cold/wet/dry/hot
• a meteorite struck the earth

Question 17

evidence for meteor theory

Answer 17

• when studying a clay layer at the K/Pg boundary, a large iridium anomaly was discovered
• only meteorites have iridium levels orders of magnitudes more abundant than terrestrial sediments
• chicxulub impact crater discovered in gulf of mexico
• ‘shocked’ quartz grains found in the crater which indicates intense pressure
• evidence for mega-tsunamis (tsunami deposits)

Question 18

effects of chicxulub impact

Answer 18

• global heat pulse that ignited large wildfires near impact site
• impact occurred in sulphate-rich region cuasing aerosols to be released into the atmosphere
• aerosols trap longwave solar radiation resulting in earth cooling for years following initial heat pulse
• ‘impact winter’ scenario
• ‘dust cloud’ scenario, blocking sunlight for a year, depressing photosynthesis

Question 20

what are deccan traps

Answer 20

• a large igneous province in India containing multiple layers of flood basalts indicating great volcanism
• may imply that chicxulub triggered increased volcanism

Question 21

what are disaster taxa

Answer 21

an opportunistic species that rapidly becomes abundant in a wider range of habitats after a biotic crisis than before

Question 22

what role did food chains play in extinction

Answer 22

• for marine phytoplankton, suppression of photosynthesis was likely the major killing mechanism
• loss of diverse vegetation on land would have led to destruction of diverse forest communities
• knock-on food-chain effects in both cases
• detritus-based food chains (e.g. in lakes) were seemingly less affected

Question 23

what was K-Pg extinction selectivity

Answer 23

• freshwater amphibians, small-bodied, non-picky eaters and organisms that lived multiple environments were more likely to survive
• fully terrestrial, large-bodied species didn’t have a chance