Tetrapod Similarites The Origins of Birds Birds Reptiles Mammals Integument Feathers, scales Scales Hair Digestive Horny bill Teeth Teeth Skeletal Fusion of bones Some fusion Some fusion Reduction in number Some reduction Some reduction Pneumatization Some pneumatization Some pneumatization Bipedalism & digitigrade Digitigrade Plantigrade Single occipital condyle single occipital condyle double occipital condyle Single middle ear bone Single middle ear bone 3 middle ear bones Jaw of 5 fused bones Jaw of 5 fused bones Single jaw bone (dentary) Circulatory 4-chambered heart 3-/4-chambered heart 4-chambered heart Nucleated rbc Nucleated rbc Anucleated rbc Endothermic Poikilothermic Endothermic Respiratory Flow-through lungs Blind sac lungs Blind sac lungs Nervous Vision & hearing Olfaction & hearing Olfaction, vision, hearing Urogenital Oviparity Ovi-, ovovivi-, viviparity Vivi-, oviparity Female heterogametic Both Male heterogametic Cloaca present Cloaca present No cloaca (ex. Monotremes) Metanephric kidney Metanephric Metanephric Features shared with reptiles: 1. Scales 2. Single occipital condyle 3. Lower jaw with quadrate 4. Single middle ear bone 5. Pecten present in eye 6. Nucleated red blood cells 7. Oviparity & egg structure Lecture Outline Fossil History of Birds Origins of birds from reptiles Principal bird fossils Reptilian lineages Current zoogeography Evolutionary history of ratites Heilmann (1926) conclusively established this link Class Aves Subclass Archosauria Cotylosaur Reptiles Class Mammalia Subclass Synapsida Amphibians 1
Archaeopteryx lithographica 6 specimens 145 million yr old Characters intermediate between reptiles & birds Which lineage of reptiles? Skeleton of Archaeopteryx Pneumatic bones Normally no; limited to some genera Disagreement on presence Many pneumatic bones in all but cursorial & some diving species Teeth In sockets In sockets Replaced by bill Skull Heavy Intermediate Light-weight Facial bones Broad Reptilian but narrower Narrow Vertebrae Amphicoelous; not fused Amphicoelous; disagreement on fusion Heterocoelous; fused Pelvic Girdle Reptiles Archaeopteryx Birds Separate ilium, ischium, pelvis (pointing forward & down) Separate ilium, ischium, & pelvis (pointing back as in birds) Fused (ilium, ishcium & pubis) in synsacrum Thoracic Ribs Unjointed; not attached to sternum; 11 pairs unjointed; not attached to Jointed thoracic ribs attached to some with uncinate processes; often sternum; no uncinate processes; 6 small sternum; uncinate processes; with cervical & abdominal ribs cervical ribs & 11 pairs of abdominal ribs cervical but no abdominal ribs Sternum Unkeeled Unkeeled Keeled in most Clavicles Fused to sternum or missing Fused into furcula Fused into furcula Forelimb Claw; fused hand & wrist bones Claw; reduced but not fused hand & wrist bones Highly fused & reduced hand & wrist bones; claws occasional Hindlimb Unfused joint Intertarsal joint partially fused Intertarsal joint fused Origins, Feathers & Flight Theropod dinosaurs Archaeopteryx (~ 150 mya) Protoavis texensis (~225 mya) Feathers first function in thermoregulation Then, develop flight capabilities Cursorial origins of flight Thecodonts Feathers first function for gliding flight Later, serve in thermoregulation Arboreal origins of flight Pseudosuchian Thecodonts Thecodont Origins Crocodiles Proto-birds Sauropods Dinosaurs Theropods Ornithischians Birds 245 mya 208 mya 144 mya 2
Microraptor zhaoianus Theropod Origins Status of the Debate Crocodiles Pseudosuchian Thecodonts Sauropods Dinosaurs Theropods Ornithischians Birds Prum (2002) 8 recent theropod fossils with feathers Hypothesized phylogeny 245 mya 208 mya 144 mya Continuing Issues in the Debate Methods of analysis Characters used Digits: 1-2-3 vs. 2-3-4 Temporal paradox Implications of Theropod Origin Feathers diagnostic?! Flight & terrestrial locomotion Nesting biology, oviparity & sequential egg laying 3
Zoogeography of Birds Cosmopolitan distribution No species with worldwide range Distinct avifaunas in zoogeographic realms Region Endemic Families Examples Nearctic 0 Many shared groups with Palearctic Palearctic 1 Hedge Sparrows many shared groups with Nearctic Neotropical 26 Screamers, Hoatzin, Toucans, Motmots, Potoos, etc. Ethiopian 13 Secretary bird, Mousebirds, Turacos, Hammerkop, etc. Oriental 1 Fairy Blackbirds Austral-Asian 21 Megapods, Birds of Paradise, Bowerbirds, Butcherbirds Zoogeography of Birds 31 families have worldwide distribution including 1. Ducks, hawks, swifts, sandpipers, corvids 2. Some exceptions: Woodpeckers aren t present in Australia Cranes don t occur in South America Evolutionary History of Ratites Old theory: postulated independent evolution of flightlessness Elephant Bird Ostrich Rheas Tinamous Kiwi Moa Cassowary Emu Evolutionary History of Ratites New theory: biology corresponds to plate tectonics South America Gondwana 80 mya 80 mya Madagascar -Africa Austral -Asia New Zealand Gigantism Flightlessness? 4
Evolutionary History of Ratites New theory: biology corresponds to plate tectonics South America Tinamous Rheas Male incubation Gigantism Flightlessness Madagascar -Africa Gondwana 80 mya 80 mya Elephant Bird Austral -Asia New Zealand Ostrich Cassowary Emu Moa Kiwi All other birds Neognathe palate Paleognathe palate Conclusions Birds evolved from reptiles Dispute over which reptilian lineage Competing hypotheses argued for >150 yrs Birds distributed worldwide Most families confined to one or a few zoogeographic realms Ratite evolution parallels plate tectonics 5