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- Forelimb converted to wing - fused hand bones support flight feathers
- Rigid shoulder joint with fused clavicles (furcula)
- Keeled sternum to support huge breast (=flight) muscles
- Trunk vertebrae and pelvis fused into solid but light structure
- Tail bones fused - support tail feathers
- Some fused leg bones
- Teeth lost - keratin beak
- Entire body adapted for flight
- Trunk solidified and neck elongated
- Forelimbs reduced to flight feather supports
- Keeled sternum for attachment of pectoralis (downstroke) and supracoracoideus (upstroke) muscles (similar to pterosaurs)
- Supracoracoideus tendon runs through triosseal (3-bone) canal in coracoid, scapula and furcula.
Bird's Respiratory System
- Includes air sacs that allow lungs to operate more efficiently than in mammals, also act as air conditioning - dissipate excess heat from high metabolism animals. Air sacs also lighten body and bones.
- Some dinosaur bones may have air sacs, suggesting a flow through respiratory system.
- intricate structures - provide effective flight surface and excellent insulation with lightweight materials.
- Bird bones hollow to reduce weight, but have internal struts to enhance their strength. Some have air passages connected to lungs.
- Archaeopteryx="ancient wing"
- a Jurassic bird
- Bird features:
- -wing and body feathered
- -Possible streptostyle movable quadrate)
- Furculum (also in some dinosaurs)
- Reptile features:
- -Dinosaur-like (theropod-like) skeleton
- -toothed jaws; long lizard-like tail
- Clawed forelimbs
- -No sternal keel, strong muscles for sustained flight.
- -Quadrate appears flexible as in later birds (parallel to lizards)
- -long tail (no pygostyle)
- Interdental plates on medial side of jaw as in some dinosaurs and basal archosaurs
Theories of Bird Relationships
- -Share endothermy, 4-chamber heart, large brains
- -clearnly convergence
- Basal Diapsids
- -Traditional view, previously no good specific candidates for close bird relatives identified
- Dromeosaurid Dinosaurs
- -Similarities that appear to be synapomorphies
- Archaeopteryx compared to a theropod dinosaur (above) and a modern bird (below)
- Basically a small theropod dinosaur with feathers!
- Most bird specilizations came later.
Archaeopteryx and Compsognathus
first discovered skeleton of Archaeopteryx lacked feathers and was misidentified as Compsognathus
If theropods didn't give rise to birds, then what did?
- Thecodonts (basal archosaurs) - similarities between birds and theropods represent convergence.
- Primitive crocodiles - birds share features of jaw and ear with early crocodiles, but could be convergence - otherwise very different.
- Birds share more similarities with theropods than other reptiles, so some paleontologists consider them ancestors.
The other side of the bird argument
- Alan Feduccia and others argue birds and theropods do not share special close relationship.
- Each=three fingers; theropods=1-2-3, birds=2-3-4 NON HOMOLOGOUS reduction pattern!
- Strongly suggests convergence rather than common ancestry.
- Conclusion=based on homology arguments although those with too much invested in birds=dinosaurs idea refuse to accept it.
The problem with Bird Fingers
- Evidence against homology, Coelophysis lower left forelimb showing reduced fourth and fifth fingers (ventrolateral view; arrows). b)Transient appearance of fifth digit condensations as chick limb develops. Finger IV (forms first, as in all tetrapods) labeled. Digit V condensation shown my arrowhead. (Burke and Feduccia, 1997.)
- Advocates of dinosaur-bird connection argue that frameshift occurred, only in the case of coelophysis.
- Timing of ossification of repeating elements controlled by Hox genes - no necessary linkage between cartilage precursors and bone.
- Phesant-sized animal (late Triassic of west Texas), bird-like theropod - or earliest bird? Sankar Chatterjee (Texas Tech University) argues for bird, but few convinced.
- A bird this early casts doubt on theropod origin of birds.
- Fragmentary remains may come from >one species.
A Chinese farmer created this forgery, sold it on the black market. Front half=bird skeleton, back half=slab and counter-slab of a theropod dinosaur. Intent= to show a close link between dinosaurs and birds (and make more money).
Why did birds develop feathers?
- Flight origin from the ground upward?
- Gliding from treetops downward?
- Catching insects?
- Archaeopteryx claws well-adapted for tree climbing - easier at first to glide out of a tree than take off from the ground (GRAVITY!!).
Bird Flying Styles
- Marine soarers and aerial predators
- -High aspect ratio, low wing loading
- -Albatrosses, gulls, swallows, falcons, kites
- Diving birds
- -High aspect ratio, high wing loading
- -Penguins, auks, gannets, some ducks and grebes
- Thermal soarers
- -Low aspect ratio, low wing loading
- -Eagles, hawks, vultures, storkes, herons, large owls
- Poor flyers
- -Low aspect ratio, high wing loading
- -Turkeys, grouse, peacocks, pheasants, cormorants
How well could Archaeopteryx fly?
- Ostrom: could not or hardly fly - because no keeled sternum or triosseal canal.
- Rayner: good flyer - well-formed wings and flight feathers, even with no strong upstroke.
- Could probably fly well at high speed but poorly at low speed, so takeoff and landing would have been biggest problems.
- May have climbed trees and glided away for escape (typical of gliders) then developed flapping flight to extend that ability.
- Earliest Cretaceous Birds
- Rahonavis - Madagascar=bird based on reversed hallux and ulnar feather papillae. It retains all primitive features of Archaeopteryx.
- Jeholornis of China retains most primitive features but has begun specilization of hand that would continue in later birds. Seeds preserved in stomach area clearly indicate diet.
- confuciusornis sanctus
- Earliest toothless (beaked) bird, from early Cretaceous of China, still has clawed hands.
- Earliest birds lacking teeth
- first with pygostyle (8-9 fused caudal vertebrae) and synsacrum (7 fused sacral vertebrae)
- Slight keel on sternum
- Considered earliest memebers of the Pygostylia
- Beautiful preservation from Liaoning Province, China
- Lack of teeth, claws on fingers, pygostyle, and tail of long feathers. Males with much longer tails than females.
- "egg stealers"
- Upper Cretaceous of Mongolia
- Short snouts, toothless jaws
- Large fenestrae in mandible
- Deep, strong lower jaws
- Crest of sponge-like bone on tip of snout
- Fused clavicles (as in birds)
- Evidence of brooding their eggs
- alternately aberrant flightless birds or coelurosaurs (related to ornithomimosaurs).
- The puzzle of Monoykus
- Late Cretaceous of Mongolia
- Either a flightless bird or bizarre theropod.
- Radically reduced, specialized forelimbs hide most of the evidence.
- Basal group of new clade: Ornithothoraces
- -Short trunk fewer than 13 thoracic vertebrae
- -Strut-like coracoid with triosseal foramen
- Major group of Cretaceous birds (40+ species)
- Fossils found nearly worldwide
- Sparrow-sized to 1-meter wingspan
- Mid-grade of birds with a mix of modern and primitive characters.
- Early Cretaceous of China, had keeled sternum and perching feet but retained teeth and small wing claws.
- Smallest of the Enantiornites, from China
- A small Enantiornithes from Spain
- Eight free caudal vertebrae and a plate-like pygostyle
- Specialized for perching with a reversed hallux
- Retains claws on wings
- Hesperornis - flightless marine bird
- Late Cretaceous, Niobrara Chalk
- Large flightless foot-probelled diving birds
- Retained teeth for eating fish
- Wings reduced from lack of use
- Pointed anterior process of the quadrate and other features in common with modern birds
- Hesperornis found in Niobrara Chalk from Kansas to South Dakota
- Found just before Archaeopteryx and hailed as a missing link ( a bird with teeth)
- Gull-sized flying bird also from Niobrara Chalk
- Relatively large head and long bill and strong recurved teeth for catching fish
- Probably dove for fish like modern terns, pelicans and boobies
- Deeply keeled sternum to support large flight muscles
- Tail more reduced than in Hesperornis
- Icthyornis - a flying marine bird
- Late Cretaceous of North America, still has teeth but otherwise like modern birds. Marine birds well known because of good chance of preservation. Other Cretaceous birds known from fewer/ more fragmentary fossils.
- Pointed orbital process of the quadrate
- Shortened back
- Pelvic elements run nearly parallel as pubis rotates fully posteriorly
- First seen in Hesperornis and Ichthyornis
- Loss of teeth
- Pneumatic foramen in humerus
the Cretaceous Neornithes Controversy
- Neornithes radiated in Tertiary after competing birds died out at the end of Cretaceous.
- Neornithes lineage back to early Cretaceous (based on disputed fragmentary remains), and molecular clocks supported early Cretaceous diversification.
- Proponents of Tertiary radiation claim that molecular clocks sped up after big extinction or are miscalibrated.
- Polarornis is the most convincing neornith, from latest Cretaceous of Antarctia.
- Wings not found but feet suggest food-propelled diver ?=a loon.
- Controversy not ended, truth may be in the middle: that neornith radiation begain in late Cretaceous.
Modern Bird Clades (within Neornithes)
- -Large vomer attached to pterygoid
- -Joint between pterygoid and braincase
- -Flightless ratites and tinamous
- -Vomers reduced or lost
- -Joint between palatine and pterygoid
- -Most modern birds
- =old palate Birds
- Tinamous - small flightless birds from South America
- Ratites - flightless birds with no keel on sternum
- -Ostriches of Africa
- -Emus and Cassowaries of Australia
- -Kiwis of New Zealand
- Rheas of South America
- Extinct Elephantbirds of Madagascar
- Extinct Moas of New Zealand (up to 3 meters tall)
- Paleognathus Birds
- Extinct moas of new Zealand
- Flightless ground-dwelling birds, reduced wings and a distinct palate, some giant, mostly on southern continents.
- Previous controversy: Paleognaths=monophyletic or= polyphyletic derivatives (degerates) of various Neognaths.
- now considered monophyletic from palate synapomorphy and DNA>
- No early fossil record allows ongoing debate over how long ago they diverged and whether it predated Gondwana breakup.
- DNA evidence suggests older (Gondwana) origin even though a fossil group (Lithornithiformes, which were flyers) found in N. America/Europe.
- Most modern birds (9,000 species)
- Neognathous palate with considerable flexibility.
- Ankle axis shifted from astragalus - calcaneum (prior to fusion of bones of tibiotarsus)
- New ankle structures-synapomorphy for the Neognathae, unclear when it first developed.
- A distinct group among neognaths
- -Anseriformes - ducks, geese, swans (waterfowl)
- -Galliformes - turkeys, grouse, chickens, quails, pheasants (land fowl)
- -Gastornithiformes - giant flightless carnifores from the early Cenozoic of North America/Europe
- Based on similarities in skull bones, supported by DNA relationships
- Some workers still dispute this grouping.
- Giant flightless birds of he cenozoic
- While large flightless birds of today are mainly plant eaters, several lines in the early Cenozoic became giant and predatory.
- Diverse Neognaths
- left - Presbirnis, an early Cenozoic duck
- middle - Diatryma
- right - swimming penguins
- bottom - Teratornis, and extinct giant vulture
- These are all considered part of the "waterbird assemblage"
Giant Carniforous Flightless birds
- Diatryma of North America is traditionally considered a carnivore, but some have argued for herbivory becasue it lacks a hooked bill like other carnivores.
- Phorusrhacos of South America and elsewhere was definitely a carnivore (mostly in the absence of mammalian carnivores). It survived until the isthmus of Panama developed.
- the Hoatzin
- Small south american ground bird ?=related to doves
- Juveniles have claws on two wing fingers for climbing back to nests.
- Probably atavism (accidental genetic return to former feature) rather than persistent primitive trait.
- The hoatzin also odd - uses crop as a fermentation vat similar to the rumen of cows!
Messel oil shales
- Rich fossil bird deposits in Eocene lake sediments of Germany.
- Parrot (Psittacopes) shows all the modern bird characters.
- 13/24 bird orders represented at Messel.
Darwin's Finches and Island biogeography
Variation in beaks among finches on various islands led Darwin to believe that they evolved from a common ancestor that colonized the islands.