Final Exam Flashcards
Describe mammalian Homologies
Hair Mammary glands External Ears Diaphragm Left aortic arch Enucleated erythrocytes 3 middle ear bones Single lower jaw bone -dentary Dentary/squamosal jaw articulation Diphyodont teeth (allows precise occlusion,shows tooth wear and allows mastication)
Describe, in detail,the evolution of mammal ears and jaws.
Pelycosaurs had a joint between the large quadrate and small articular. The angular formed a large portion of the lower jaw.
A transitionary form, a therapsid called the diarthrognathus was found with two jaw joints, one on the reduced quadrate and articular and one between the squamosal and dentary. The angular was still present, just slightly reduced.
Early mammals had very reduced versions of these bones, with the quadrate forming the incus of the ear, the articular the malleus, and the angular part of the tympanic bone. Only one jaw joint is found, between the squamosal and dentary.
What do birds have in common with derived theropods? Describe some molecular evidence for their relation
Digit one is on the back of the foot in derived theropods and birds (as the hallux in birds).
Derived theropods and birds both are elongate, mobile, and have S-shaped necks. The ankle joint is with the tarsals (not tibia/fibia). Both have hollow, pneumatic bones. Both had furcula and a fused sternal plate. There is also evidence suggesting that theropods had air sacs.
Molecular evidence: T-rex bone was found with soft tissue inside, and the tissues were found to be similar to that of chickens.
What were the bird-like theropods called? Describe their characteristics
Called dromeosaurs. They had grasping arms, swivelling wrist joints, and a posteriorly directed pubis. There is evidence suggesting that they had feathers.
Discuss the importance of the discovery of Anchiornis to the understanding of bird evolution.
The feathers of anchiornis are very well-preserved. The shapes and distribution of melanosomes in the feathers were identified by SEM and their colours were determined. It was found that they had several different colours similar to modern birds.
Explain the evolution and formation of feathers using the evo-devo model.
Feathers are fundamentally different in morphology from scales, as they arise from follicles and are tubular. Both feathers and scales are formed from epidermal placodes. Differences in expression of the “bone morphogenic protein 2” gene and the “sonic hedgehog” gene determine what is produced by those placodes.
It has been found that feathers evolved over a series of forms: filament -> tufts of barbs -> rachis and simple barbs -> barbules -> asymmetric veins and alula
What is archaeopteryx?
Thought to be the first bird
Compare the bird-like features and non-bird-like features of Archaeopteryx and explain why it is classified as an early bird.
Bird-like: Large furcula, rectangular sternum for flight muscle origin, structure similar to hallux, rearward pubis
Non bird-like: No carpometacarpus, free digits, no pygostyle, no skull fusion, has teeth.
Classified as an early bird because of fossil feather imprint in soft sediment, asymmetrical flight feathers, a long neck, and a tail.
What are the major evolved traits that contributed to flight in birds?
Reduction in body size helped to enable flight. Even a slight ability to fly or glide is a beneficial trait, which likely explains how it evolved.
List the following from most ancestral to most recently evolved: compognathus, velociraptor, caudipterix, archaeopteryx, enantiornithes, ichthyornithes, and neoaves.
Note major physical changes in each.
Velociraptor, neoaves, archaeopteryx, enantiornithes,
Describe the two hypotheses used to explain the origin of bird flight
“Trees down” hypothesis - Thought that ancestors of birds were arboreal and may have glided down from trees
“Ground up” hypothesis - Thought that ancestors of birds were bipedal runners that flapped their wings to catch prey. This is evidenced by the fact that archaeopteryx had a terrestrial foot and not a perching foot.
Give some evidence for the “ground up” cursorial hypothesis for origin of flight in birds
- Archaeopteryx had terrestrial feet.
- Makes sense given theropod ancestry
- Wings could assist in horizontal jumps after prey (increased airfoil surface could assist in lift and manoeuvreability)
- Can help in either hunting or fleeing
What are the names of the two major groups of modern birds?
Paleognathae (flightless ratites), Neognathae (all others)
Describe the skeletal adaptations of birds for flight
Bones are pneumatic in many species (hollow with supporting structures in the middle). But divers and many small birds have solid bones.
Teeth were lost, and skulls take up very little body weight (thin bones and lots of fusion).
Fused thoracic vertebrae and uncinate processes to reinforce ribs.
Pelvic bones fused into synsacrum. Many caudal vertebrae fuse into pygostyle.
Tibiotarsis and tarsometatarsus. Sternum serves as attachment site. Forelimbs reduced - carpometacarpus formed and phalanges loss/fusion.
There are tight articulations between bones so they require as few and as small muscles as possible.
Describe the muscular adaptations of birds for flight
Jaw muscles and hindlimb muscles reduced in many species. Rigid skeleton provides so much support that less musculature is needed. Flight muscles (pectoralis and supracoracoideus) are extremely large and located near the centre of gravity.
Describe the muscle composition in the bodies of birds of prey, fliers like hummingbirds, and aquatic birds. Describe the two different types of muscle.
Birds of prey - Need strong leg muscles (10%) and flight muscles (20%)
Hummingbirds and swallows - Flight muscles take up 25-35% of body weight
Aquatic birds - Equal muscle mass between wings and legs (need them for paddling). In totally they take up 30-60% of body mass.
Red muscle has a high level of myoglobin for aerobic metabolism; used in sustained flight.
White muscle is used for short bursts of activity; anaerobic metabolism.
Compare the feeding preferences and adaptations (beak, digestive system) of a pigeon, hoatzin (forgut fermentor), and hawk.
Pigeon - Seed eater with a large crop and gizzard, average sized round beak.
Hoatzin - Twig and leaf eater with huge foregut (crop).
Hawk - Animal eater with an average sized beak. May have a piercing lip on the end of the beak.
Describe the pathway of air through two respiration cycles in a bird’s lung.
Cycle 1:
Inspiration: Thorax volume increases and air flows through the trachea and into posterior air sacs.
Expiration: Air flows from anterior air sacs into the parabronchus (site of gas exchange)
Cycle 2:
Inspiration: Same unit of air is drawn into the anterior air sacs
Expiration: Air sent out via the trachea.
Bird hearts are ___% larger than mammal hearts
40%
What makes faveolar lungs so efficient?
Within the faveoli, air and capillaries flow in opposite directions (counter current). This results in a higher degree of oxygen retention than mammals have.
What are the function of air sacs?
Air sacs are certainly not necessary for flight (considering bats don’t have them), but they do function in expanding and contracting with barometric pressure, allowing birds to fly at much higher altitudes than bats.
Flying at higher altitudes is advantageous because of higher wind speed, and colder wind to assist in heat loss. Air sacs can also, as a result of their pressure sensing abilities, indicate a change in weather.
Explain the evidence for the presence of air sacs in sauropods and theropods.
There is a theory that because oxygen levels dropped so much between the Permian and the Triassic and then again later on, the dinosaurs may have lived through it because of their air sacs (and faveolar flow). Bones of dinosaurs were also pneumatic, and showed signs of connections to potential air sacs
In what way is oviparity and the reproductive system of birds an adaptation for flight?
Oviparity developed because it is near impossible to fly when carrying young. The reproductive organs of birds have only one side, the other remain undeveloped throughout life. The remaining organs shrivel up in the non-breeding season as well.
Define profile and induced drag. What factors affect each type of drag and how do birds counteract the forces of drag?
Profile drag - Occurs due to friction between the air and the body of the bird. This decreases with streamlining but increases with bird size and air speed
Induced (pressure) drag - Occurs when air flow separates from the surface of the wing. This is a problem at the wing tips and can be fixed by wing tip vortices.
