The first bird is traditionally thought to have been Archaeopteryx, which lived in what is now Germany around 150 million years ago. While a somewhat poor flyer it could nevertheless fly. It may also have been able to use its wings to climb and to swim (Paul, 2010). Archaeopteryx's status of "first bird" has however been challenged by China's Aurornis, thought to have lived around 160 million years ago. As well as potentially revising knowledge of bird origins, Aurornis has also added to phylogenetic data suggesting birds are actually most closely related to troodonts rather than to dromaeosaurs (Godefroit et al, 2013).
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| Figure 1: Archaeopteryx (left) and Aurornis (right) arguing over who gets the title of "first bird". Artist: Emily Willoughby. |
Archaeopteryx and Aurornis still had long tails and lacked such avian features as a beak and a sternal keel (like non-avian flying dinosaurs they used deltoid muscles instead). The first known tailless, beaked, sternal keel possessing bird was Confuciusornis, who lived in China around 142-121 million years ago. Though lacking tails, male Confuciusornis possessed long tail feathers for display, like many birds today (Shipman, 1998).
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| Figure 2: A male Confuciusornis perches on a tree branch. Though it still had wing claws, Confuciusornis was recognisably avian. Artist: Kevin Yan. |
Confuciusornis belonged to an extinct group of birds called the enantiorniths. However, most known birds, including all modern birds and many extinct groups, belong to another group called the ornithurines, of which the oldest known member is China's Liaoningornis, which was contemporary with Confuciusornis. Interestingly, Liaoningornis and other early ornithurines had toothed jaws. All modern birds belong to a group of toothless ornithurines called the neorniths. The earliest known neornith groups, present by the late Cretaceous, were things like ratites, water fowl, loons, and wading shorebirds (Shipman, 1998). There is also possible fossil evidence of late Cretaceous parrots and possible molecular evidence for many other modern groups having a Cretaceous origin (Stidham, 1998). This is far from conclusive though.
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| Figure 3: A loon carries its chicks across some water. Loons are a group of birds that have been around since the Cretaceous. Photographer: Bill Maynard. |
Birds have gone on to be the dinosaurs' greatest success story, with more than 10,000 known living species. They have filled numerous niches including fishers, divers, predators, insectivores, frugivores, folivores, nectarivores, filter feeders, and oppurtunists.
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| Figure 4: Hummingbirds are an excellent example of how modern birds have filled an amazing variety of niches. Photographer: Finca Lerida. |
Next post shall discuss how many birds lost their ability to fly.
References
Godefroit, P., Cau, A., Dong-Yu, H., Escuillie, F., Wenhao, W. & Dyke, G. (2013). A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature. 498 (7454).
Paul, G. S. (2010). Dinosaurs: A Field Guide. A & C Black Publishers Ltd: London.
Shipman, P. (1998). Taking Wing. Touchstone: Rockefeller Center.
Stidham, T. A. (1998). A lower jaw from a Cretaceous parrot. Nature. 396 (6706), pp. 29-30.
Image sources
Figure 1: Accessed April 21, 2015, from http://emilywilloughby.com/gallery-data/images/full/the-earliest-birds.jpg
Figure 2: Accessed April 21, 2015, from http://fc06.deviantart.net/fs9/i/2006/015/3/e/Confuciusornis_sanctus_by_yty2000.jpg
Figure 3: Accessed April 21, 2015, from http://coolwildlife.com/wp-content/uploads/galleries/post-357/Loon%20Pictures%20012.jpg
Figure 4: Accessed April 21, 2015, from http://phenomena.nationalgeographic.com/files/2014/08/Hummingbird-990x618.jpg
Another really great post. Again, I am curious as to how they know the tail was used for display, and not to provide stability during flight? I’m also curious how a sterna keel is better than strong deltoid muscles? It seems that this bone structure would be fairly fragile compared to a strong, interlocking muscular complex.
ReplyDelete"I am curious as to how they know the tail was used for display"
DeleteAre your referring to Confuciusornis? If so, its not a tail but just tail feathers (as said in the post, Confuciusornis was, unlike even earlier birds, tailless). As for how we know they were display, it is because two types of Confuciusornis fossils have been found together- those with and those without the long tail feathers. It is thought the ones with the long tail feathers are the males and that these are for display. After all, in many modern birds males have far longer tail feathers than the females for exactly this purpose.
On the sternal keel, this attaches to a ligament that helps spring the wings upward after a down stroke, thus allowing for flight strokes to be performed with less effort than they would if only muscle power alone were involved.
That said, very early birds, many flying non-avian dinosaurs, and also pterosaurs and bats, all flew just fine without sternal keels. Though in the case of pterosaurs and bats, they did have wing designs far more effective than any feather wing.