Birds

Amniote - animal whose embryo develops in amnion and chorion and has allantois

Includes mammals, reptiles and birds

Diverged early in history into synapsids and reptiles

Birds = dinos 

Birdiness evolved in theropod dinosaurs - complex feathers, gliding flight, beak tissie

Birds emerged during Jurassic - 1 of many lineages of small, feathered theropod dinosaurs

• Only in evolving tiny size and true flight
• Only group to survive beyond end of Cretaceous

Evidence of evolution from dinos:

• Bird-like sleeping postures in fossils
• Semi-lunate joint used in flapping wings also found in velociraptors to grasp prey

Suggestion that:

• Sauropods are grouped with early, carnivorous herrerasaurs
  • Sauropods = t-rex and diplodocus
• Ornithischins grouped with theropods
  • Ornithopods = iguanodon and armoured e.g. triceratops, stegosaurus 

Since early 1980s, knowledge of Mesozoic birds increased exponentially

Archaeopteryx = ancient wing

Originated ~140mya in Bavaria, Germany

11 know specimens - vary in form and size

Long bony tail, long claws and lack of beak

Exhibited 'bird-like' features called feathers

• Long feathers on legs and probably feet
• Thickly feathered

Melanosomes (used to determine colours of fossils) - show black feathers

From Lower Cretaceous of China

Long-tailed archaic birds

• Weird, frond-like array of feathers at end of tail
• Not aerodynamic - display structure
• Second fan of large feathers close to tail base
• Suggests Archaeopteryx tail fan not homologous with distal part of frond

Reduced dentition

• Few lower jaw teeth and robust jaw
• Indicates seed eating diet - confirmed by specimens w/ seeds in stomach

Lower Cretaceous China

First bird:

• Toothless jaws and keratinised beak
  • Evolved indpendently from toothlessness in modern birds
• Pygostyle - triangular plate in birds formed of fused caudal vertebrae, support tail feathers
  • Not anchors tail fan

• Huge thumb claw
• Window in humerus
• Long wing feathers
• Tail streamers in males

Social creatures - specimens found together

Stomach contents = fish diet

Debate if flapping flier or glider

Smallest non-avian theropod dinos

Found in groups

Symmetrical feathers on arms and legs

Arboreal - evidence of 'trees-down' evolution of flight

Evolution of flight isn't linear - many branches off

Feathers on tails, arms and legs

• Tetrapteryx - four winged
• Proof of 'trees-down' flight

Wing feathers asymmetrical, leg feathers symmetrical

• Hind leg feathers dragged on ground - problematic
• Microraptors glided?

Originally removed Archaeopteryx from phylogenetic grouping 

From further along in geological time

Black with white striped feathers

Unsuitable feathers for flight - more display

Evidence of very long forelimbs and wrists like birds

• Developments that later descendants use for fully functional flight wings

Numerous Mesozoic lineages evolved across Jurassic and Cretaceous = large diversity of bird lineages in Mesozoic

Toothlessness and flightlessness evolved >3 times

Moden birds (neornithines) - evolved late Cretaceaous

• Filled many dino niches when they died

Two major groups - Palaeognaths and Neognaths

• Classification due to jaws

Neognaths = higher birds, 4 major clusters:

• Galloanserae - gamebirds and waterfowl e.g. duck, geese, swans
• Metavians - new group with little in common, waterbirds and seabirds
• Aequornithes - waterbirds and seabirds e.g. loons, penguins, tubenoses, storks
• Higher landbirds

Palaeognaths = basal birds, exhibit primitive characteristics, 2 groups:

• Ratites - ostriches, emus, cassowary, rheas, kiwis
• Tinamous

Enlarged premaxilla = most of snout/upper jaw (top of beak)

Interorbital septum = vertical plate of bone, acts as wall in between eyes

Kinetic zones = base of rostrum, in palate

• Associated with quadrate = whole rostrum can flex up and down

Increasing bones in jaw = jaw less flexible

Neognaths - basipterygoid processes reduced/absent

• Palate lightweight and flexible

Palaeognaths - basipterygois processes contact pterygoid

• Palate reinforced and stiffer

Introduced idea of dinosaur relatioships to birds

5 main things about birds:

• Feathers - fluffy body coating
• Bipinnate feathers - fly
• Brood their nests
• Take care of young
• Hollow bones w/ air sac system

Function as anchorage for large flight muscles

Larger sternum = large muscle attachment = more powerful flight

Enormous pectoalis muscles - attach to sides of sternal keel

• Depress humerus in flight

Supra coracoideus - anchords to sternum in both muscles

• Attaches to side of sternal keel
• Loops up into trisseal canal
• Attaches back to dorsal surface of humerus
• Responsible for humeral elevation is flight

Wisbones - elastic

• Springs
• As wings come down = compressed chest 
• Elasticity springs wings back
• First seen in theropod dinos like velociraptor

Three toed feet - seen in theropod dinosaurs

Airspces for bones - prerequisite for flight

• Inheritance of light skeleton
• Hollow and air-filled bones = pneumatic (no marrow)
• Tubes connect air-sacs inside bones to other air-sacs and lungs
• Pneumaticity = well-developed in large, flying species e.g. pelicans
• Reduced/absent in diving birds e.g. penguins

Hollow bones = bendable and squishable

• Cross structures - light but stable and less energy required to produce them

Air sacs 

• Used to increase surface area for gaseous exchange
• Flight energetically expensive
• Flight draws air into air-sac system

Pneumatic bones

Skull with large brain cavity and big eye sockets

Toothless and extensive fusion of skull bones

Shin/ankle bones fused = tibiotarsus

Metatarsals and ankle bones fused = tarsometatarsus

• Birds walk on toes

Reduced hand - 4 toes

• Digit I reverse and opposable to II-IV

Shortened tail skeleton - pygostyle

Tridactyl hand and wrist fused = carpometacarpus

• Highly flexible

First digit form = mobile and feathered alula

Highly flexible wrist allows hand to be folded against ulna - storing wing feathers

Wing claws:

• Hoatzin (S. America) - has claws on digits I and II of chicks, used for climbing
• Claws on digits I and II common in modern birds - gulls, swans, quails, vultures

Controversy - are digits I-III or II-IV

3 fingered hand of theropod dinosaurs = I-III digits

Discovery of ceratosaur - small, beaked pirimitive theropod from ~155mya Jurassic period

• Strongly reduced I digit (manus) alongside II-IV digits
• Manual phalanges abbreviated more associated with II-IV
• Finger bones more like I-III

Suggests bird fingers are II-III-IV and II digit became shrunken and similar to I digit

Several groups of birds evolved weapons on carpometacarpus - long, sharp-tipped spikes or bony clubs

Used in combat - intraspecifically or against predators

Screamers, ducks, plovers, jacanas, pigeons

Xenicibis

• Extinct ibis from Jamaica
• Expanded, thick-bones carpometacarpus 
• Functioned as club - intraspecific combat

Solitaire

• Giant flightless pigeon of Rodriguez Island
• Males = large bony calluses on radius
• Carpometacarpus sheathed in keratin
• Functioned for fighting
• Pronounced sexual dimorphism

Mostly hollow bones of upper and lower jaw

Sheathed in casing of keratin

Lightweight, durable and change shape according to wear

Flexible, sensitive

Huge radiation for adaptations - use to manipulate environment

Birds had teeth ~100my of time alive (out of 160my)

Small and conical 

Lined jaws or restricted to jaw tips

Large, anteriorly projective teeth at jaw tips evolved several times

Outgrowths from beak itself

Advantageous for catching fish

Evolved at least twice in extinct modern birds - waterfowl (moa-nalos) and giant, oceanic pelagornithids

Multiple bird lineages, merganser, hoatzin, motmot = tooth-like structures along keratin edge of beak = gripping, cutting and crushing

Rhamphoteca - keratinous sheaths covering jaw/beaks of birds

Originally rhamphoteca was compound (2+ parts)

• Found in primitive birds and extant neornithes

Pieced together during evolution - simple rhamphothecae result from loss of softer keratinous grooves between components

Examples of transitional forms - grooves remain as shallow depressions w/ pronounced edge

Essential bird behaviour - feathers need constant maintenance

Use bills and claws - feathers keep clean and barbs/barbules in good condition

Overhanging sections of beak in upper jaws = maxillar overhangs

• Crucial to parasite control

Seabirds

Nostrils exist via single tube on top of bill 

Part of keratinous beak

Acts as nozzle - squirt stomach oil at enemies or in chick mouths

Potential use in salt balance 

Relate to seabirds good smelling abilities and pressure-detection

Two-tubed albatross must have evolved from single-tubed condition

Short, hooked reinforced beaks - often deep

Small, dorsaly positioned nostrils

Advantagous when holding prey

Convergently evolved ~4 times - hawks and eagles, owls, falcons and shrikes

Don't rely alone on beak - feet and talons crucial

Falcons - special notch and tooh-like structure used in dispatching prey

Giant hooked beaks evolved in extinct lineages:

• Use = kill and dismember vertebrate prey
• ~55-2mya
• Mostly South America
• Phorushacids - grow >2m tall

Poorly mineralised sections of bone = jaws bow outwards

Pelicans can scoop jaws through water

• Lower jaws can widen to catch prey

Variation in beak length and curvature - depends on lifestyle

• Short-billed waders = surface organisms
• Long-billed waders = deep in sediment

High nostiles - don't clog them with sediment

Beaks sensitive

• Special organs on tips = Herbst corpuscles
• Detect organsisms

Sticking a bill into shells = dangerous = drowning and starving

Spear-like bills (slender with pointed tips)

Spear into/through prey

Elongated jaws

Long, flexible neck with strong joints and muscles = lightweight skull can be thrown around

Horn-covered bony crests - sit on top of bill on top of skull

Hornbills, cassowaries and curassows

Used in

• Visual display
• Resonating devices 
• Foliage-manipulators
• Potentially microphones

Foot begins as paddle in embryo - controleld apoptosis during cell cucle causes webbing to disappear

Webbing is advantagous - escape and catch food

Typical anisodactyl foot - 4 toes

• Digit I (hallux) = reversed

Ancestral foot morphology for modern birds

Tarsometatarsus - long and slender

Toes long and slender (except for cursoirial/running birds)

Webbing, claw length and hallux length variable

Some fossil bird tracks have interdigital angles >50' = typical of waders 

Extreme waders - rely on shallow-water invertebrates

• Elongate tarsometatarsi and tibitotarsi
• High digital divergance angles
• Fully webbed feet

Tarsometatarsus - long and slender

Toes long and slender (except for cursoirial/running birds)

Webbing, claw length and hallux length variable

Some fossil bird tracks have interdigital angles >50' = typical of waders 

Extreme waders - rely on shallow-water invertebrates

• Elongate tarsometatarsi and tibitotarsi
• High digital divergance angles
• Fully webbed feet

Relatives of gulls, waders, auks

Specialised for foraging on floating vegetation and soft mode

Long, slender unwebbed toes - long, straight claws

• Suited for supporting weight

Extremely long hallux

Individual toes (+ claws) probably longer than entire body

Divers/loons dive and apddle with webbing

Gulls/terns paddle at surface and do shallow dives with feet

Wing-propelled divers (auks, penguins) use feet for steering and diving

• Wings = propulsion

Waterfowl = extensively webbed feet with webs extending to toe tipes but not including hallux

• Paddling and slow swimming

Seaducks - partially opened wings to provide thrust during swimming

Fully webbed feet - webbing between all toes including hallux

Pelicans, gannets, boobies, cormorants, tropicbirds, frigatebirds

Used to groop bird species

Used in paddling, diving and airbrakes when landing

• Useful surface to push through water
• Provide thrust

Sexual display - blue-footed booby

Grebes - lobed feet, not webbed

• Feet move from beneath and side of body to above and behind body
• Generate lift as mulit-slotted hydrofoils

Hesperornithines - extinct bird

• Homologous to grebe swimming
• Cretaceous toothed birds
• Long, slender toothed jaws
• Grebe/loon-like skull shape
• Found in marine deposits worldwide
• Flattened toe bones
  • Toes folded up during recovery stroke
  • Shape suggestive of lobes on toes, not webbing
• Skin impressions = evidence of lobes

Specialised for running

Long, slender legs with long tibiotarsi and tarsometatarsi

Reduced/absent hallux = tridactyl foot

• Less chance of tripping over

Ostriches - lost digit as well = didactyl

Include ratites, bustards, coursers but also shorebirds

Strong, powerfully muscled legs + large body size = kicking and jumping at enemies

Cassowaries use flying kicks with enlarged, spike-like claws of digit II in combat

• Hawks
  • Enlarged talons on digits I and II
  • Strong grip - pin prey and kill with beak
• Falcons
  • Slightly enlarged claws
  • Use bill to kill prey
• Owls
  • Long, weakly curved claws
  • Rely on contricting power of long toes
• Ospery
  • Strongly curved claws on all toes
  • Spicules - calcareous protusions on feet
  • Opposable digit IV
• 4

Woodpeakers, parrots and cuckoos

Digit IV rotated to posterior - opposes digits II and III

• Two toes point forwards, two backwards

Percher or climber foot

Some of most specialised climbers have modified zygodactyl foot pamprodactyl foot or lost hallux to become tridactyl

All 4 toes point anteriorly in pamprodactyl arrangement

In climbing or clinging 

• Digits I and II oppose II and IV 
• Forms pincer-like arrangement 
• Similar to feet of chameleons/koalas

What happened at end of Cretaceous period (65mya)

• Major global extinction - 65% Family-level diversity wiped out

Holy grail of avian evolution - K-Pg (Cretaceous-Paleocene) event = success of modern Aves

• Loss of egg size constraint
• Proliferation of avian reproductive strategies
• Evolution of altriciality (young dependent on parents)
• Neornithine (mass extinction) survivorship

Changed body mass, relative egg size and environments of preservation