What kind of bird has teeth
The "other" birds had teeth and claws
Berkeley - Today we would almost describe a bird like this: can fly, is feathered all around, has a beak ... and in this beak there are teeth and the wings have fingers with claws. At least that's what the average bird looked like during the Cretaceous Period - from a purely mathematical point of view.
From today's point of view, the enantiornithes that exhibited all these characteristics are a side branch of bird evolution that has left no offspring. During the Cretaceous period these "other" birds still formed the majority. For many millions of years they lived alongside their toothless cousins, from whom all of our birds today are descended. The fact that they disappeared was due to a catastrophic coincidence: the asteroid impact 66 million years ago.
A fine specimen
Except in the naturally little explored Antarctica, fossils of enantiornithes have already been found on all continents. They came in a wide variety of sizes and shapes, which suggests that the toothless bird world occupied as many different ecological niches as the toothless of today. US researchers recently described a particularly handsome representative in the journal "PeerJ".
The animal named Mirarce eatoni lived in North America about 75 million years ago. The site of discovery, the Kaiparowits Formation in Utah, was likely to have been a large river delta at the time, in which Mirarce lived next to or above dinosaurs, crocodiles and turtles. According to researchers working with Jessie Atterholt from the University of California, the bird was about the size of a turkey vulture or a great horned owl. These are species with a wingspan of one and a half to two meters: remarkable for a time when the enantiornithes had to share the sky not only with the actual toothless birds, but also with the pterosaurs.
Atterholt points out that Mirarce Eatoni must have been a good flyer. The sternum had a pronounced crest on which strong flight muscles could attach. In addition, elevations were found on the forearm bones, to which the flight feathers were apparently anchored: These are typical features of today's birds. The fact that this has now been discovered for the first time in an enantiornith shows that the "other" birds were in constant development and came to the same evolutionary problem solutions independently of the actual birds.
The problem they could not solve was the asteroid impact at the end of the Cretaceous Period: With it, the 60 million year history of the enantiornithes came to an abrupt end, while their toothless cousins continued. Why not a single one of the many types of Enantiornithes survived the catastrophe is still a mystery.
Atterholt refers to the claws of animals for one possible explanation. Most researchers take these as climbing aids - so the enantiornithes were tree dwellers. That would have been their undoing in the world fire after the asteroid impact: At that time, all forests must have burned down and took centuries to regenerate. Only a few ground-dwelling bird species would have survived then, reported an international research team in "Current Biology" in the spring.
In the same journal, Canadian researchers two years earlier had presented a hypothesis that had a different focus, but could be combined with it: They suspected that the survivors of the fall specialized in eating seeds. Seeds are a resilient resource that would have remained available for much longer after the disaster than fruits or leaves, for example. And seed-eaters would have got along very well without teeth - an ideal niche for the actual birds.
Whatever the final selection factor, the "other" birds didn't have it, and our current definition of the word bird looks accordingly. (jdo, December 2, 2018)
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