Chapter 13 Outline

WHAT IS A BIRD?

• HIGHER LEVEL CLADES
  • VERTEBRATA, TETRAPODA, AMNIOTA
    • Nerve cord & backbone; Have four limbs; Eggs have amniotic membranes
  • DIAPSIDA, ARCHOSAURIA
    • Upper & lower temporal openings; Antorbital openings
• DERIVED CHARACTERISTICS
  • FEATHERS
    • Flight feathers & downy feathers
      • DOWN IS GOOD INSULATION
    • Evolved only once - Birds are a monophyletic group
  • ABSENCE OF TEETH
    • Possess rhamphothecae; do not chew food - internal processing
  • LARGE BRAINS & ADVANCED SIGHT
    • Large brain developed through possession of endothermy
    • Large brain & advanced sight developed for flight
  • CARPMETACARPUS
    • Fusion of wrist and hand bones and digits I, II and III
  • FOOT
    • Three toes in front & one toe in back
    • Digits II, III and IV in front & digit I in back
    • Foot & some ankle bones fused to form TARSOMETATARSUS
  • PNEUMATIC BONES
    • Hollow bones
    • Walls thin & supported by splintlike buttresses internally
    • Pneumatic foramina - openings in the wall of the bone for air sacks to enter
      • USEFUL FOR FLIGHT, BUT EVOLVED PRIOR TO FLIGHT (PREADAPTED!)
  • RIGID SKELETON & ADAPTATIONS FOR FLIGHT
    • Pelvis
      • FUSION OF SACRAL VERTEBRAE & HIP INTO SYNSACRUM
    • Chest
      • WELL-DEVELOPED BREASTBONE (STERNUM) WITH BROAD, DEEP KEEL
      • STERNUM CONNECTED TO FUSED BACKBONE BY SEGMENTED RIBS
    • Shoulder
      • PILLARLIKE CORACOID BONES BUTTRESS AGAINST THE FRONT OF THE STERNUM, THE SHOULDER BLADES & WISHBONE (FURCULA = FUSED CLAVICLES)
    • Flight muscles
      • DIFFERENT MUSCLES FOR DOWNWARD STROKE & FOR RECOVERY STROKE

ARCHAEOPTERYX LITHOGRAPHICA AND THE ANCESTRY OF BIRDS

• HISTORY OF DISCOVERY
  • FOUND ONLY IN LATE JURASSIC SOLNHOFERN LIMESTONE FROM BAVARIA (SE GERMANY)
    • Very fine grained carbonate mud that can be etched & used for printing plates
  • FIRST SPECIMEN WAS AN ISOLATED FEATHER IMPRESSION FOUND IN 1860
  • SECOND SPECIMEN FOUND IN 1861 CONSISTED OF FEATHER IMPRESSIONS & AN ASSOCIATED SKELETON
    • Two years after Darwin published "On the Origin of Species"
    • Sold to Sir Richard Owen & for the British Museum of Natural History
  • THIRD SPECIMEN FOUND IN 1877 ALSO CONSISTED OF FEATHER IMPRESSIONS & AN ASSOCIATED SKELETON (& IS ILLUSTRATED IN YOUR TEXT IN FIGURE 13.4, PAGE 300)
    • Spectacular specimen
    • Retained in Germany (in Berlin)
  • AN ADDITIONAL FIVE SPECIMENS HAVE BEEN FOUND SINCE
• ANATOMY OF ARCHAEOPTERYX
  • SKULL
    • Features include conical, recurved teeth
  • ARMS & HANDS
    • Relatively long arms
    • Each hand bears three fully movable, separate fingers, each tipped with a recurved claw
    • The wrist bears a semilunate carpal
  • LEGS & FEET
    • Three toes symmetrical about the middle digit in front & one toe behind
      • STRONG CURVATURE TO REAR TOE, SUGGESTING TREE-DWELLING
    • Ankle is a modified mesotarsal joint
    • Astragalus has an ascending process
    • Femur is considerably shorter than tibia & fibula and has a gentle S-shape
      • FEMUR SHAFT AT 90° TO HEAD
  • LONG BONES
    • Thin-walled and hollow
  • TRUNK & TAIL
    • Vertebrae are not foreshortened or fused as in modern birds
    • Sternum is relatively small and a large, strong furcula is present
      • GASTRALIA, OR BELLY RIBS, ARE PRESENT
    • Synsacrum is absent and pubis points down, not back
      • PUBIC FOOTPLATE IS PRESENT
    • Tail is long, straight and stiffened by zygopophyses
  • FEATHERS
    • Well-developed flight feathers
• BIRDS AS DINOSAURS
  • T. H. HUXLEY RECOGNIZED RELATIONSHIP BETWEEN DINOSAURS & BIRDS
    • Fell into disfavor during the early 20th Century
      • SIMILARITIES ATTRIBUTED TO CONVERGENT EVOLUTION
      • DINOSAURS THOUGHT TO BE TOO SPECIALIZED
      • NO CLAVICLES WERE KNOWN FOR COELUROSAURS
  • G. HEILMANN ARGUED THAT BIRDS EVOLVED FROM "THECODONTS"
    • Fell into disfavor during the 1970's
      • THECODONTIA DISBANDED
      • COELUROSAURS FOUND TO HAVE CLAVICLES
  • JOHN OSTROM DOCUMENTED THE RELATIONSHIP BETWEEN COELUROSAURS & ARCHAEOPTERYX
    • Bakker & Galton propose that birds should be included within a new Class Dinosauria in 1974
    • Cladistic analysis showed Archaeopteryx (& hence birds) are coelurosaurs
  • HIGHER TAXONOMIC RELATIONSHIPS OF ARCHAEOPTERYX & BIRDS
    • Ornithodira
      • FULLY ERECT POSTURE
      • MESOTARSAL ANKLE
      • FOUR-TOED FOOT WITH THREE DIGITS (II, III & IV) FORWARD, SYMMETRICAL ABOUT DIGIT III, AND ONE DIGIT (I) BEHIND OR TO THE SIDE
      • TOES HAVE LARGE, ARCUATE CLAWS
    • Dinosauria
      • FIVE SACRAL VERTEBRAE AND PERFORATE ACETABULUM
      • REDUCTION OR LOSS OF DIGITS IV & V IN HAND
      • REORIENTATION OF SHOULDER
    • Theropoda
      • HOLLOW LONG BONES
      • ENLARGED 3-FINGERED HAND
    • Tetanurae - STIFFENED TAIL
    • Coelurosauria - SEMILUNATE CARPAL IN WRIST
    • Maniraptora
      • GRASPING 3-FINGERED HAND WITH ELONGATED DIGIT III
      • LARGE, ROBUST FURCULA
    • Dromaeosauridae
      • DROMAEOSAURIDS & ARCHAEOPTERYX ARE UNITED BY THEIR SEMIOPISTHOPUBIC PELVIS & A PUBIS MISSING THE FRONT PORTION OF THE FOOTPLATE
    • Dissent
      • BASED ON POSITION OF PUBIS
      • REJECTION OF PARSIMONY BECAUSE OF ABUNDANT CONVERGENT EVOULTION WITHIN ARCHOSAURIA
      • DERIVE BIRDS FROM CROCODILES
• PNEUMATIC BONES & FEATHERS: ADAPTATION VS. INHERITENCE
  • PNEUMATIC BONES
    • Hollow bones characteristic of theropods
  • FEATHERS
    • Modification of reptilian scales
    • Probably developed for insulation first; later adapted for flight
      • SINOSAUROPTERYX - DOWN; CLOSE TO COMPSOGNATHUS , NOT A MANIRAPTORAN
      • CAUDIPTERYX & PROTARCHAEOPTERYX - TRUE FEATHERS; COULDN'T FLY; MORE PRIMITIVE THAN ARCHAEOPTERYX
      • NEW FROM CHINA
• FLIGHT
  • FEATHERS NECESSARY FOR FLIGHT, BUT FLIGHT MAY NOT BE NECESSARY FOR FEATHERS
  • ARBOREAL (TREES DOWN) VS. CURSORIAL (RUNNING) HYPOTHESES
    • Arboreal - first birds glided down from trees & developed powered flight later
      • INTUITIVELY APPEALING
      • MOST ARBOREAL GLIDERS ARE QUADRUPEDAL WITH FLAPS OF SKING BETWEEN HIND- AND FORELIMBS
    • Cursorial - first birds were runners & developed powered flight to avoid obstacles
      • BIRDS ARE BIPEDAL & ULTIMATELY EVOLVED FROM A CURSORIAL ANCESTOR
  • FLIGHT IN ARCHAEOPTERYX
    • Probably not a great flyer

THE EARLY EVOLUTION OF AVES

• EARLY CRETACEOUS
  • SINORNIS FROM CHINA - ONLY 15 MILLION YEARS YOUNGER THAN ARCHAEOPTERYX
    • More modern than Archaeopteryx
      • PYGOSTYLE
      • SHORTENED BODY (REDUCED NUMBER OF VERTEBRAE)
      • MODERATELY LARGE STERNUM
      • PILLARLIKE CORACOIDS
      • WRIST ALLOWS WING TO BE FOLDED TIGHTLY AGAINST BODY
      • FEET FOR PERCHING
    • Retains some primitive features
      • TEETH
      • UNFUSED FINGERS (NO CARPOMETACARPUS)
      • GASTRALIA
      • UNFUSED PELVIS
      • SEVERAL OTHER FORMS FROM THE EARLY CRETACEOUS
• LATE CRETACEOUS
  • FLYING & MARINE DIVING BIRDS, AS WELL AS SOME ENIGMATIC FORMS
  • HESPERORNIS FROM WESTERN NORTH AMERICA
    • Still retains teeth
    • Specialized features for diving
  • MONONYKUS FROM GOBI
    • Looks like a typical theropod from the center of the back toward the tail
    • Digits fused into short stout carpometacarpus
    • Arms very short
      
      

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