The Evolution of Birds & the Origin of Flight

Transcription

1 The Evolution of Birds & the Origin of Flight

2 Archaeopteryx Solnhofen quarry Oldest known bird, but not ancestral to modern birds Inhabited coastal habitats where it probably glided between conifers, cycads, ginkos, etc. with its limited flying ability

3 Archaeopteryx Solnhofen quarry Oldest known bird, but not ancestral to modern birds Inhabited coastal habitats where it probably glided between conifers, cycads, ginkos, etc. with its limited flying ability

4 Primitive traits: 3 manual digits with claws teeth long bony tail no expanded breastbone no fusion in skull or girdles hyperextensible second toes ("killing claw") Derived traits shared with modern birds: furcula ( wishbone - fused clavicles) asymmetric flight feathers partially reversed hallux flapping flight, but no supracoracoideus pulley

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6 125 mya 150 mya

7 Bird Origins 2 hypotheses Basal Diapsid Archosaurs Crocs Thecodonts Dinosaurs Birds?? (~230 MYA) Saurichians (reptile-hipped) Thecodont Hypothesis Alan Feduccia Pterosaurs NOT BIRDS - no furcula - wings supported by 4 th digit - patagium wing surface (bats) But convergent - large braincase - ossified, keeled sternum - hollow skeleton - reduced fibula - loss of teeth, tail - fused vertebrae Sauropods Carnosaurs Theropods Coelurosaurs Birds?? (~180 MYA) Theropod Hypothesis Most everybody else

8 What does it mean to call birds dinosaurs? they belong to this monophyletic clade Similarity of T-rex collagen DNA to Chickens (Asara et al. 2007) Bone cell size correlates to genome size Organ et al. (2007) and supports a Saurichian but not Ornithiscian lineage

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11 Feather Evolution KNOW THESE STAGES and REPRESNTED MEMBERS Prum 1999 Undifferentiated Tubular collagen Beipiaosaurus inexpectus Differentiated Barbed ridges Undifferentiated Tubular collagen Caudipteryx zoui Differentiated Barbed ridges Microraptor gui Fully developed: Barbs and interlocking barbules; asymmetrical Sinosauropteryx prima Anchiornis huxleyi

12 Feathered Theropods Sinosauropteryx First dinosaur discovered with feathers in 1996 filamentous body covering. Coloration as indicated by melanosome distribution in feathers (Nature 2010) So far all feathered dinosaurs are known from Liaoning, China lake beds with periodic depositions of fine volcanic ash (mid-jurassic to Early Cretaceous) Scansoriopteryx: arboreal adaptations

13 Why so controversial for years? Bird: II, III, IV Developmental frame-shift hypothesis Theropod: I, II, III At 3.5 days of embryonic development, a shift occurs, causing cells in the progenitor region for digit 4 to move forward and grow into digit 3.

14 Developmental frame-shift hypothesis At 3.5 days of embryonic development, a shift occurs, causing cells in the progenitor region for digit 4 to move forward and grow into digit 3.

15 Paleontological temporal paradox (Alan Feduccia) Haplocheirus and Caudipteryx postdate Archaeopteryx

16 Paleozoic Era, Permian Period (>250 MYA) Basal archosaurs like this Euparkeria flourishing Mesozoic Era, Late Triassic (220 MYA) Small (< 10kg) basal theropods, Staurikosaurus Primitive pro-avian body Increased aerobic capacity Long-fingered w/ sig. climbing skills

17 Mesozoic Era, l. Triassic/e. Jurassic (200 MYA) bird-like avepods (bird-footed dinosaurs); Syntarsus short-armed, runners tridactyl nearly avian foot pulmonary airsacs to increase aerobic capacity feathers?

18 Mesozoic Era, mid Jurassic (180 MYA) Averostra and Avetheropod (bird-snouted); Sinornithosaurus simple feathers all over body did not evolved to fly or glide better climbing skills elongated arms and hands with 3 fingers furcula larger brains and eyes better aerobic capacity All of these are pre-adaptations for flight Ornitholestes Sinornithosaursus

19 Mesozoic Era, late Jurassic (150 MYA) Avepectora (bird-shouldered) have arrived. Birds and avian flight have arrived and w/ flight were changes to pectoral girdle and increased in sternum

20 Yixian formation in China e. Cretaceous ~125 MYA) Early birds abundant and clothed in feathers Thousands of specimens of Confuciusornis (earliest toothless bird) uncovered and suggest they lived in large flocks Possibly the first evidence of sexual dimorphism in birds Confuciusornis

21 Anchiornis huxleyi

22 enozoic Era esozoic Era Modern Ornithurines Caudipteryx Enantiornis Ichthyornis Hesperornis Enantiornithines: once abundant, these Opposite birds die out with the dinosaurs at the end of the Mesozoic Primitive Ornithurines Birds quickly diverged into different lineages

23 Transitional shorebirds Thick knee; Tinamou

24 How To Define Birds? Traits inherited from archosaurs (previously used to define birds): Wings Feathers Light and hollow bones Small lungs and extensive air sac system (one-way respiration) Enlarged brain (encephalization) Endothermy, including with the highest metabolic rates of all animals Four-chambered heart - oxygen-rich and oxygen-depleted blood kept completely separate Derived (unique) traits: Opposing hallux (1 st digit) for grasping and perching Skull kinesis (mobile upper jaw)

25 The Origin of Flight (1) Cursorial (ground-up) Theory (2) Arboreal (tree-down) Theory (3) Combination e.g., protofliers ran into strong winds or down steep slopes, using gravity as the initial power source

26 The Origin of Flight (1) Cursorial (ground-up) Theory: Flight originated in cursorial dinosaur Primitive feathered wings/airfoils arose for: - for capturing food, including Ostrum s insect net hypothesis protofliers were aerial insectivores that ran, hopped, or leaped after prey - for display; increasing height and duration of sexual displays - for safety

27 There is a velocity gap Archaeopteryx can run at 2m/sec, but flight require speeds of 6 m/sec think power curves

28 (2) Arboreal (tree-down) Theory: flight originated in arboreal dinosaurs

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30 WHAT S COMMON?

31 All Membranes

32 Well, birds had FEATHERS & how do you develop the Power Stroke?

33 (2) Hybrid: feathers arose in land-based dinosaurs and flight as they moved into trees - closest pre-birds small and adapted to climbing (e.g., reverse hallux for perching) - drag induced airfoils distally placed - wings enlarged to transform falls into horizontal glides

34 Microraptor The major obstacle is getting through the transition from gliding to flapping flight

35 (3) Wing-assisted inclined running

36 How about Archaeopteryx: Glider or flyer? Species like the Kakapo does use small, slow wing beats to extend glides

37 How about Archaeopteryx: Glider or flyer? Pigeon Power-Flyer perhaps better than the Kakapo, by still crude by modern standards - Wing span and wing loading within the general avian range - Feathers possess aerodynamic properties - Furcula, ossified keeled sternum Archaeopteryx - No quill nodes to anchor feathers - Outer arm not rigid - Lacked full flapping extension - Lacked rigid ribcage - Partially develop supracoracoides

38 Bird origins: Theropod origin, When: ~180 MYA Evolution of feathers: First present in Dromaeosaurs (180 MYA) as simple filaments all over the body; likely had an initial thermoregulatory function Origin of flight: Cursorial (or Ground-up Hypothesis) versus Arboreal (or Tree-down Hypothesis) Primitive feathered wings likely evolved first for controlled leaping, distal airfoils expanded leading to longer distance glides, flapping airfoils increased the length of glides and as the pectoral girdle developed eventually powered, flapping flight arose. However, alternative hypotheses are possible: airfoils evolved for more impressive and sustained intersexual displays or wing-assisted running to escape predators. In other words flight evolved out of selection pressures to efficiently and effectively: travel (arb), capture prey (arb), attract mates (cur), or avoid predators (wing-assisted)