17: Birds Flashcards
2 theories of where birds came from
Birds evolved from theropod dinosaurs (most probable)
Birds evolved from earlier thecodont reptiles
Similarities between birds and reptiles
Lay eggs Lower jaw consists of several bones Scales on legs Pneumatised bones Single middle ear bone
Differences between birds and reptiles
Birds are endothermic Have a 4 chambered heart Have feathers (only different to extant non-avian reptiles)
What is the semilunate carpal?
The ‘half moon shaped’ bone in the therapod wrist
Formed by the fusion of distal carpals 1 and 2
What is the function of a semilunate carpal?
Flexible wrist
What was the first feathered non-avian dinosaur?
Sinosauropteryx prima
Features of Sinosauropteryx prima
Small theropod dinosaur
Up to 1.07m, 0.55kg
Had downy filamentous feathers, probably for insulation
Another important feathered dinosaur
Protarchaeopteryx
Features of protarchaeopteryx
A non-avian theropod 1m in length, 4kg Pneumatised feathers (air cells/cavities) Feathers with symmetrical veins Also had a furcula (wishbone)
What was the earliest bird?
Archaeopteryx lithographica
Features of Archaeopteryx lithographica
Both bird and reptile features (transitional form)
Reptile: long bony tail, claws on forelimbs, small sternum
Gastralia
What is a gastralia?
Dermal bones found between sternum and pelvis
Provide support for abdomen
Attachment for abdominal muscles
Skulls of Archaeopteryx vs extant birds
Long nasal opening in birds
Birds have much larger brains relative to body size
Many cranial bones in birds are fused
What is a pygostyle?
Triangular plate made of fused caudal vertebrae
Supports tail feathers
What were the Enantiornithines?
Toothed jaws (a few had beaks)- reptiles
Shortened hand with claws- reptiles
Pygostyle
No keeled sternum
What was the K-Pg extinction event and who survived?
Cretaceous-Palaogene
Water birds and crocodiles survived
How many extant species of bird are there?
9,000-10,000
What are the two super orders of bird?
Palaeognaths
Neognaths
What do Palaeognaths include?
Ratites and tinamou
What do Neognaths include?
Game birds and ducks
Water birds and soarers
Forest birds
Features of palaeognaths
The vomer is fused with the palatine bone (morphology of the palatte)
Mostly flightless eg. ostrich, but the tinamou can fly
What is a ratite?
Bird with a keel-less breastbone
So can’t fly
What was the moa?
Extinct ratite
Endemic to New Zealand
Human driven extinction
Features of the bird skull
One occipital condyle
Large optic lobes and cerebellum, well developed brain
Single bone in the middle ear- the columella
What is the columella?
Single bone in the middle ear
Equivalent to our stapes
Bird vision
Very good vision
3 eyelids- upper and lower, and a nictitating membrane
Membrane keeps out dirt and water in diving birds
Large eyes relative to skull
Supported by sclerotic eye ring- bony plates also seen in reptiles and icthyosaurs
What is an indented fovea?
Magnifies central part of visual field
Some have 2 fovea in each eye
What can birds see that we can’t?
UV part of light spectrum
Used in mate choice in starlings- look drab to us
Bird beak structure
Upper jaw (maxilla) and lower jaw (mandible)
Both made of bone, usually hollow or porous
Sheath of keratin over the bone called the rhamphotheica
Continuous growth
What is special about a toucan beak?
Vascular controlled thermal radiator
Open capillaries to heat up/cool blood
Only adults
Bird circulatory system
Heart has 2 atria and 2 ventricles (4 chambered)
There are separate pulmonary and systemic circuits
What is the syrinx?
How birds produce sound
Change diameter where the trachea branches
Vibrate a pressulus
Can generate more than one sound at once
Bird respiratory system
No diaphragm
Air moves in and out of lungs by pressure changes in air sacs
Air sacs are only involved in air movement, not gas exchange
Air sac hypothesis
Inhalation:
Air moves into posterior air sac, lungs, through parabronchi andinto anterior air sacs
Exhalation:
Out of posterior airsacs, through parabronchi, out of anterior and out of body
Would require valve
What is the crop?
Part of digestive system
Softens and regulates flow of food
Can store food temporarily
In some birds, produces milk to feed young
Bird stomach features
2 parts:
Proventriculus- glandular stomach
Produces mucus, pepsin and HCl for digestion
Gizzard- muscular stomach
Some contain stones/grit to ‘chew’
Safety valve blocks bits that might damage- owl pellets
What is the caeca?
Part of the digestive system
Contains bacteria that break down cellulose
In birds that digest fibrous plant food
eg. pheasants
What is the cloaca?
Opening for intestinal, urinary and reproductive tracts
Excrete as uric acid, like reptiles
Bird skin features
Thin epidermis and dermis
No sweat glands
Feathers
Antibacterial secretion for cleaning
How did feathers evolve?
From reptilian scales
For insulation or display originally
Flight came after
2 types of feather
Vaned feathers- exterior
Down feathers- not vaned
What are feathers made of?
B-keratin
Feather functions
Flight/contour feathers- flight
Filoplumes- sensory information
Downy feathers- insulation
Also visual display, sound, nest lining
Pigmentation
Melanins- water and bacterial resistant, blacks, browns, greys
More melanin in tips to protect from wear
Carotenoids- died derived, yellows, orange, reds
Porphyrins- greens, pinks
Reproduction in birds
Internal fertilisation
Amniotes
Oviparous
What is an egg shell made of?
Calcium carbonate
What are altricial young?
Born undeveloped, require care and food from parents
eg. robins
What are precocial young?
Born developed, can feed themselves immediately
Eg. mallard ducks
