The Evolution of Birds & the Origin of Flight

1. The Evolution of Birds & the Origin of Flight

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

3. Basal Diapsid Archosaurs Thecodonts Birds ?? (~230 MYA) Dinosaurs Thecodont Hypothesis Alan Feduccia Saurichians (reptile-hipped) Sauropods Theropods Coelurosaurs Carnosaurs Birds ?? (~180 MYA) Theropod Hypothesis Most everybody else

4. Who’s correct? (1) Scientific concensus  theropod origin (2) Evidence  theropod origin (All phylogenetic evidence supports the same position for bird, a lineage derived from Dromaeosaurs (3) A priori versus ad-hoc explanation  theropod origin “This paper will stand as an exemplar of manipulation of information to conform to preconceived ideas, but it is otherwise insufficiently credible or comprehensible to constitute a lasting addition to knowledge” Storrs Olson (quoted by Feduccia in the Auk 119:1188) “By offering no testable alternative to the theropod origin of birds and maintaining that the origin of birds is potentially unsolvable, Feduccia and other critics of the theropod hypothesis of avian origins reject science itself. One-sided rejections of the theropod origin reflect not on the hypothesis itself, but on intellectual weaknesses of the critiques….My conclusion is that this is not science, but a rhetorical sham. Richard Prum (Auk 120:559)

5. Why so controversial for years? No clear single morphological feature that distinguishes the lineages of birds NOT FEATHERS which are a primitive state within the lineage of Coelurosarian theropods (velociraptors)… Similarly, pygostyle found in oviraptors, wishbone (furcula) in theropods (T-rex) Pneumatization of bones in theropods, feathers Rather, it is the possession of a combination of characters that separate birds from their closest relatives within Dinosauria… …..possession of flight, contour and down feathers, and other skeletal features

6. 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

7. Paleozoic Era, Permian Period (>250 MYA) Basal archosaurs – like this Euparkeria flourishing Only flying animals are dragonflies w/ 1m WS • Mesozoic Era, Late Triassic (220 MYA) Small (< 10kg) basal theropods, Staurikosaurus Primitive pro-avian body Increased aerobic capacity Long-fingered w/ sig. climbing skills

8. 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? (none found, but neither on any Mesozoic mammals)

9. Mesozoic Era, mid Jurassic (180 MYA) Averostra and Avetheropod (bird-snouted); Sinornithosaurus, Microraptor 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

10. 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

11. Yixian formation in China - 1995 e. Cretaceous ~125 MYA) Early birds abundant and almost always clothed in feathers Thousands of specimens of Confuciusornis (earliest toothless bird) uncovered and suggest they lived in large flocks Confuciusornis Possibly the first evidence of sexual dimorphism in birds

12. Modern Ornithurines Cenozoic Era Mesozoic Era 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

13. Transitional shorebirds Thick knee; Tinamou

14. Early Cenozoic (50 MYA) “Terror Birds” such as this Diatryma were huge, flightless top carnivores

15. Phorusrhacids Were relatives of cranes (Gruiiformes) Titanis walleri

16. What about Chatterjee’s Protoavis? …would predate Archaeopteryx by >100 MY…

17. What is a bird? Dromaeosaurs – In the last 6 years no fewer than 8 non-avian theropods with filamentous appendages homologous to avian feathers have been found in early Cretaceous deposits in China and Mongolia Sinornithosaurus and Microraptors have pennaceous (interlocking) feathers with vanes and barbs indistinguishable from birds “Could anyone imagine better evidence that birds evolved from a lineage of theropod dinosaurs than the presence of modern pennaceous feathers in a theropod dinosaur lineage that was independently hypothesized to be most closely related to birds?” Prum 2003 Sinornithosaurus – A feathered dinosaur or early bird??

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

19. The Origin of Flight (1) Cursorial (ground-up) Theory 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 Food: But, leaping after flying insect seems inefficient, always fighting gravity, no contemporary examples (bats and pterosaurs arose from non-leapers), there are no running gliders or leaping aerial insect specialists Display: ?? Safety: Wing-assisted running in Chukar chicks 50° incline after hatching, 60° incline at 4 days, vertical ascent at 20 days

20. http://dbs.umt.edu/flightlab/videos.htm

21. (2) Arboreal (tree-down) Theory Primitive feathered wings arose for controlled leaps/gliding, faster descent, and increased travel between high places - 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 The major obstacle is getting through the transition from gliding to flapping flight e.g., flying squirrel

22. Species like the Kakapo does use small, slow wing beats to extend glides

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

24. Bird origins: Theropod origin, specifically a lineage derived from Dromaeosaurs 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 (cur)