17: Birds Flashcards by Rebecca Crummett

2 theories of where birds came from

Birds evolved from theropod dinosaurs (most probable)

Birds evolved from earlier thecodont reptiles

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Similarities between birds and reptiles

Lay eggs
Lower jaw consists of several bones
Scales on legs
Pneumatised bones
Single middle ear bone

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Differences between birds and reptiles

Birds are endothermic
Have a 4 chambered heart
Have feathers (only different to extant non-avian reptiles)

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What is the semilunate carpal?

The ‘half moon shaped’ bone in the therapod wrist

Formed by the fusion of distal carpals 1 and 2

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What is the function of a semilunate carpal?

Flexible wrist

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What was the first feathered non-avian dinosaur?

Sinosauropteryx prima

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Features of Sinosauropteryx prima

Small theropod dinosaur
Up to 1.07m, 0.55kg
Had downy filamentous feathers, probably for insulation

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Another important feathered dinosaur

Protarchaeopteryx

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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)

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What was the earliest bird?

Archaeopteryx lithographica

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Features of Archaeopteryx lithographica

Both bird and reptile features (transitional form)
Reptile: long bony tail, claws on forelimbs, small sternum
Gastralia

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What is a gastralia?

Dermal bones found between sternum and pelvis
Provide support for abdomen
Attachment for abdominal muscles

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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

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What is a pygostyle?

Triangular plate made of fused caudal vertebrae

Supports tail feathers

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What were the Enantiornithines?

Toothed jaws (a few had beaks)- reptiles
Shortened hand with claws- reptiles
Pygostyle
No keeled sternum

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What was the K-Pg extinction event and who survived?

Cretaceous-Palaogene

Water birds and crocodiles survived

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How many extant species of bird are there?

9,000-10,000

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What are the two super orders of bird?

Palaeognaths

Neognaths

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What do Palaeognaths include?

Ratites and tinamou

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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