Brusatte et al., 2015 (origin of birds) Flashcards
Birds evolved from theropod dinosaurs during the … (around 165-150 Myr ago)
Jurassic
Their lightweight, feathered, large-brained, winged body plan evolved …, rather than in one burst of innovation.
gradually (over ~100my of steady evolution alongside dinosaurs before diversifying into modern birds (neornithes)) - shown by the fact scientists have hard time determine where the transition from non-birds to birds occurred, despite the wealth of fossils
Early birds diversified throughout the … and …, becoming capable …. However, they were severely impacted by the KT mass extinction event, leaving modern birds to explosively … into the species and groups seen today.
Jurassic, Cretaceous, fliers, diversify
What types of evidence have been developed/found to improve our knowledge of bird evolution?
- wealth of new fossil discoveries (e.g. Jehol Group yielded thousands of almost complete, fully articulated skeletons w/soft tissue)
- molecular phylogenetic analyses
- quantitative macroevolutionary analyses
It is now widely accepted that birds evolved from …, with the two groups linked by hundreds of shared features of the …, soft tissues, growth, …, and behaviour. It is now known that many non-avian dinosaurs were … and looked more like birds than lizards or crocodiles.
dinosaurs, skeletons, reproduction, feathered
Birds are nested within the … dinosaurs (as they evolved from them). This includes…
theropod, T. rex but also more bird-like (and closely related) deinonychus and troodon
Birds’ very closest relatives are the..
Dromaeosaurids and troodontids (feathers, large-brained, generally small-bodied)
The Jehol biota demonstrates that many major lineages were already well-established in the … …. Although highly diverse, this primitive avifauna demonstrated less … diversity than modern lineages. There were …, semiaquatic taxa and larger generalists for example, but certain extant ecomorphs were absent, such as … specialists and large aerial foragers.
Features such as a … …, narrow furcula (…) and reduced … were starting to evolve and can be observed in certain early avian groups within the Jehol Biota, suggesting the evolution of … ….
Early Cretaceous, ecological, arborealists, aquatic,
keeled sternum, wishbone, hand, powered flight (though these birds still greatly differed from modern birds, e.g. in the construction of the shoulder girdle, retention of large teeth and jaws)
+elongated arms
True modern birds (neornithes) are mostly a …-… redation, though there is some fragmented fossil evidence for … species.
post-Cretaceous, Cretaceous
Simple, hair-like … called “…”, found in many primitive theropods and a growing number of plant-eating ornithischian dinosaurs are widely considered to be the early stages of feather evolution and elaboration (e.g. branching).
More modern, complex, branched, vaned feathers are found in … theropods, e.g. microraptor (almost indistinguishable from some modern flight feathers).
It is clear that feathers evolved in …-… dinosaurs for functions other than … (e.g. … or …), later being optimised for ….
filaments, protofeathers,
maniraptoran
non-flying, flight, thermoregulation (or egg-brooding), display, flight
Microraptor had four wings and probably was capable of … rather than muscle-driven powered flight.
gliding (e.g. from trees) - prob evolved in parallel to birds
- hind leg feathers are asymmetrical - not found in other non-bird dinosaurs (suggesting in these the feathers had a function other than flight, e.g. display)
Many non-bird theropods had very … tail feathers. This suggests that … … may have been an initial driving force in the evolution of elaborate feathers
ornamented, sexual selection
It is probable that powered flight evolved after the…
origin of birds themselves - as early birds lack many characteristics apparently required for this
- e.g. archaeopteryx lacked bony sternum and the right anchorage for large flight muscles
Modern birds possess an efficient “…-…” lung in which air flows unidirectionally, linked to a complex system of air sacs. Recent work has shown that this system first began to evolve in …, and even extant … and … … exhibit unidirectional breathing (but without system of air sacs - which evolved in early …, becoming more elaborate during the course of … evolution)
flow-through, reptiles, crocodiles, monitor lizards, dinosaurs, theropod
Most dinosaurs had … … more similar to that of modern birds than living reptiles. A recent comprehensive study found that dinosaurs had so-called “…” physiologies, intermediate between “cold-blooded” ectotherms and “warm-blooded” endotherms.
high metabolisms, mesothermic
