The Evolution of Birds or What Makes a
The Evolution of Birds: or What Makes a Bird, a Bird?
Common characteristics in birds and reptiles 1. Single occipital condyle 2. Single middle ear bone 3. Scales similar http: //www. aquatic. uoguelph. ca/birds/morphevol/page 2. htm
Common characteristics in birds and reptiles 4. Sclerotic ring supports eye 5. Lower jaw composed of several bones 6. Females heterogametic sex http: //www. arctic. uoguelph. ca/cpl/organisms/birds/biolo gy/morphphys/page 4. htm Moore and Roberts (2013): https: //doi. org/10. 1016/j. cub. 2013. 04. 004
Birds evolved from a group of bipedal Theropod dinosaurs, specifically Maniraptors
Evolution of feathers Feathers were once thought unique to birds. - Theropod dinosaurs had feathers, so feathers must have evolved first for reasons other than for flight. - insulation - communication - camouflage e. g. , Sinosauropteryx
Evolution of Flight Three theories: 1. Arboreal Model = flight evolved in tree dwelling species 2. Cursorial model = flight evolved from ground dwelling species
3. Wing Assisted Inclined Running http: //www. youtube. com/user/UMflightlab https: //www. youtube. com/watch? v=JMuzl. EQz 3 uo Flight evolved as an exaptation for running up steep surfaces and safely descending from heights.
http: //www. nature. com/nature/journal/v 451/n 7181/full/nature 06517. html
Archaeopteryx lithographica “Ancient wing” (150 mya) - Existed 150 mya - Discovered in the 1860 s - One of the most important fossils ever discovered - Shared traits in common with birds and reptiles, as well as some traits unique to birds and to reptiles.
Since the discovery of Archaeopteryx
Sinornis santensis 140 mya Advances over Archaeopteryx 1. Pygostyle 2. Reduced digits 3. Strengthened pelvic girdle 4. Foldable wings 5. Perching foot http: //www. livescience. com/bestimg/index. php? url=Avian_Sinornis_00. jp g&cat=avianancestors http: //the_dinosauria. tripod. com/sinornis. html
Evolution of pygostyle https: //evodevojournal. biomedcentral. com/articles/10. 1186/2041 -9139 -5 -25
Early Cretaceous (130 -120 mya) Jehol Biota of northeastern China
Other Cretaceous-era birds • Hesperornis (100 -65 mya) Uncinate process on the ribs http: //www. oceansofkansas. com/baptornis. html
Other Cretaceous-era birds • Confuciusornis (125 mya) Toothless, horned beak http: //www. nhm. ac. uk/jdsml/nature-online/dinodirectory/detail. dsml? Genus=Confuciusornis
Brusatte et al. 2015 Current Biology
Cretaceous extinction
Modern birds • Quarternary (2. 58 mya – present) – Extinction of most older lines – Expansion of Passeriformes • Many interesting forms recently extinct – Teratorns (6 mya) • 4 -8 m wing span • Largest 175 lbs Argentavis magnificens
Diatrymas
Moas - huge cursorial species endemic to New Zealand. - only species of bird with no wings. - largest – 12 ft tall, 500 lbs. - hunted to extinction by humans http: //eatmorecookies. wordpress. com/2009/07/0 2/using-dna-to-reveal-extinct-moas/
Haast’s eagle (Harpagornis moorei)
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