Vertebrate Paleontology

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Angdredd
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267491
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Vertebrate Paleontology
Updated:
2014-03-22 19:14:42
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The Birds
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  1. Bird Characters
    • 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.
  2. 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.
  3. Feathers
    • 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.
    • Anatomy:
    • -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
  4. Theories of Bird Relationships
    • Mammals
    • -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.
  5. Archaeopteryx and Compsognathus
    first discovered skeleton of Archaeopteryx lacked feathers and was misidentified as Compsognathus
  6. 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.
  7. 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.
  8. 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.)
  9. Bird fingers
    • 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.
    • Protoavis
    • 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.
  10. "Archaeoraptor" Forgery
    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).
  11. Why did birds develop feathers?
    • Flight origin from the ground upward?
    • Gliding from treetops downward?
    • Catching insects?
    • Insulation?
    • Archaeopteryx claws well-adapted for tree climbing - easier at first to glide out of a tree than take off from the ground (GRAVITY!!).
  12. 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
  13. 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.
  14. Confuciusornithids
    • 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. ┬áMales with much longer tails than females.
  15. Oviraptors
    • "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).
  16. mon
    • The puzzle of Monoykus
    • Late Cretaceous of Mongolia
    • Either a flightless bird or bizarre theropod.
    • Radically reduced, specialized forelimbs hide most of the evidence.
  17. Enantiornithes
    • 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.
    • sinornis
    • Early Cretaceous of China, had keeled sternum and perching feet but retained teeth and small wing claws.
    • Smallest of the Enantiornites, from China
    • Iberomesornis
    • 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
  18. Hesperornithiformes
    • 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)
  19. Ichthyornithiformes
    • 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.
  20. Ornithurae
    • Pointed orbital process of the quadrate
    • Shortened back
    • Pelvic elements run nearly parallel as pubis rotates fully posteriorly
    • First seen in Hesperornis and Ichthyornis
  21. Neornithes
    • Loss of teeth
    • Pneumatic foramen in humerus
  22. 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.
  23. Modern Bird Clades (within Neornithes)
    • Paleognathae
    • -Large vomer attached to pterygoid
    • -Joint between pterygoid and braincase
    • -Flightless ratites and tinamous
    • Neognathae
    • -Vomers reduced or lost
    • -Joint between palatine and pterygoid
    • -Most modern birds
  24. Living Paleognathus
    • =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.
  25. Paleognath Origins
    • 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.
  26. Neognathous Birds
    • 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.
  27. Galloanserae
    • 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"
  28. 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!
  29. 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.
  30. 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.

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