Avian evolution and the origins of flight

Question 1

what did Padian K 1998 say about birds and their relation to dinosaurs

Answer 1

bird were once thought to have a large number of features exclusive to the group. One by one those features have also been identified in fossils of certain theropod dinosaurs
= backed up by Thomas Huxley who stated birds where nothing more than glorified dinosaurs

Question 2

what are sauropsids and diapsids

Answer 2

S= The reptiles e.g.tutrles, lizards, snakes, crocodylia and birds

D= true reptiles = include birds

Question 3

what are the main diagnostic characters of diapsids

Answer 3

translates to ‘two arches’ = bones that form the arches are very distinctive although have been lost in many forms e.g. snakes
two arches also known as two post orbital fenestrae which can be found at the back of the skull behind the eye

Question 4

what features do birds have which are also found in reptiles

Answer 4

• egg laying
• scales = feathers are modified scales
• soft anatomy (brain, heart, other organs and musculature

Question 5

outline the history of proving birds to be true repitles/diapsids

Answer 5

T.Huxley 1825-1895 saw similarities between birds and theropod dinosaurs
1970 = began to be accepted birds were dinosaur decendants
1990 = still some debate due to differing molecular and morphological evidence

Question 6

why was the evolutionary trend towards bipedalism important

Answer 6

evolution showed general trend for hindlimbs to move under the body and bringing up the forelimns for functions other than locomotion = a precursor to flight
1) increased locomotor efficiency
2) freed forlegs for functions other than walking

Question 7

what are coelurosaurs

Answer 7

a small, slender, bipedal carnivourous dinosaur with long forelimbs and believed to be an evolutionary ancestor to birds
made up of
1) Tyrannosaurids = early forms were small and derived froms were large with shortened necks, large heads and tiny forelimbs
2) Dromeosaurs = carnivorous, elongated claw on second toe of hind food, collective hunter, large brain

Question 8

what did lee et al 2014 find out about the theropod lineage

Answer 8

the theropod lineage leading to birds was the only dinosaur lineage to get continuoulsy smaller
- sustained miniaturisation of these theropods for about 50MY
- skeletons also changed four times faster than other dinosaurs including evolution of feathers and wings

Question 9

what is some evidence to prove than birds are coelurosaurs

Answer 9

1) large orbits (eye openings in the skull)
2) flexible wrists with a semilunate carpal bone
3) erect, digigrade stance with feet below body
4) elongated forelimbs and clawed hands
5) Hollow, thin- walled bones
6) fused bony sternum
7) reduced and posteriorly stiffened tail

Question 10

what is the semilunate carpal

Answer 10

an enlarged element covering the proximal ends of the two medialmist metacarpals aka a wrist joint

= this structure allowed them to flex their wrists sideways while roatining it allowing arms to be lifted up and back as well as down and forwards
- this trait is the functional basis of the power of stroke in flight

Question 11

outline the role of feathers in basal theropod dinosaurs

Answer 11

ornithomimosaurs and maniraptorans showed a range of complex feather types involoved in
1) social interaction and display
2) cover eggs in nests shielding them from the sunn and insulating them from the cold
3) retained heat produced by movement and feeding

= orginal functions didnt involve flight

Question 12

what are some theories as to how birds survived when all other dinosaurs died out?

Answer 12

1) The Wulst
= extinct and extant birds have an extremely dense area of brain tissue called the wulst
= this structure is associated with an increase in intelligence without increasing mass

2) The diet
= not all birds survived only a few types of more advances birds called neornithines did
= these birds lacked teeth and many were seed eaters

Question 13

why is the diet theory thought to be better than the wulst theory when explaining why birds survived

Answer 13

wulst doesnt explain why not all birds survived as all spp had this structure
if birds which survived lacked teeth and ate different foods = more niches available as well as the fact seeds proven to be able to survive extremes so more food for these birds and less for others which didnt have this adaptation

Question 14

what are the two groups which evoloved flight within the archosaurs

Answer 14

1) pterosaurs
2) Birds

Question 15

outline pterosuars and flight

Answer 15

appeared 50MY before birds in the late Triassic
- wing formed by skin membrane
- showed convergenent evoloution of hollow bones, well developed sternum, large eyes, large cerebellum and some spp with no teeth

Question 16

outline the history of the first birds

Answer 16

1) birds appeared in the late jurassic (170 MYA)
2) Archaeopteryx lithographica 130 MYA = this was a size of a crown and had a mix of reptilian and avian features

Question 17

outline some derived avian features

Answer 17

1) bill
2) loss of teeth as food ground in the gixxard
3) Fused manibular bones
4) loss of bony tail
5) loss of wing claw
6) fused hand and finger bones
7) large oectoralis muscles
8) sternum enlarged with keel
9) asymmertirc vaned feathers

Question 18

outline the role of the pectoralis muscle, supraoracoideus muscle and the keel in bird flight

Answer 18

P = pulls wings down
S= raises wing
K= anchor point coming of the sternum for the two muscles to attach

Question 19

what did Mckellarf et all 2011 find about the feather eovlutionary developmental model

Question 20

outline the advanatges of flight

Answer 20

1) once powered flight is attained, lying lineages tend to evlove quickly and radiate into diverse niches

2) allows animals to extend foraging or breeding territories, migrate seasonally between divergent habitats and inhabit environments with sparse resoruces

Question 21

Name the different hypothesis which explain the origins of flight

Answer 21

1) tree-down/ arboreal hypothesis
2) Ground up/cursorial hypothesis

Question 22

outline the tree down hypothesis

Answer 22

1) gliding precursor = flying forms progressed through gliding stages, weak flapping fliers to fully airborne flapping fliers

2) flapping precursor = arboreal ancestors flapped limbs to control descent

FOR = Over 60 spp of arboreal mammalian gliders along, models show tranition from gliding to flapping flight is feasible

AGAINTS= the dromaesaurs were bipedal, fairly cursorial and terrestrial, no evidence that they were arboreal

Question 23

outline the ground up hypothesis for flight

Answer 23

Ground running biped evolved into an active flier without an intermediate gliding phase
1) jumping higher to catch insects = enlarged forelimbs can provide stability in running and jumping, better control and lift afforded greater access to insects, limb movements similar to those needed for flight

2) to run up slopes = wing assissted incline running theory = partridge flap wings when running up slopes permitting them to run up tree trunks and reach refuge