The result is a menagerie of non-avian dinosaurs and their primitive bird contemporaries, often accompanied by feathers, scales, and skin that are sometimes so detailed they even retain traces of pigment. Like Archaeopteryx , many of these animals are surreal mash-ups between the standard notion of a modern bird and classic images of a predatory dinosaur.
Ostriches descend from a group of birds that arose in the late Cretaceous period and somehow lived through a mass extinction event 66 million years ago, according to the latest genetic data and fossil clues.
With feathers dark as an oil slick, the non-avian dinosaur Microraptor gui probably glided between branches using stiff feathers on all four of its limbs. Nearby, the primitive bird Longipteryx chaoyangensis was flitting along waterways, snapping up fish with its reptilian, tooth-studded jaws. And Anchiornis huxleyi, a charcoal-hued dinosaur with a crown of rusty fluff, was stalking the forest floor like a goth pheasant, unable to truly fly because of its stubby, three-clawed wings. Despite this bounty of finds from Liaoning, paleontologists still faced gaps in the fossil record, which they sometimes tried to fill based on patchy data from mere fragments of bone.
Some DNA work put the origin of modern birds deep in the Cretaceous, with many of the avian groups that exist today springing up very early in the time line. This implied a tale of mega survivorship, with a bunch of modern bird ancestors somehow making it through the mass extinction in one giant flock. Other experts argued that all birds living before the cataclysm were of the more primitive persuasion, like the ones whose fossils were found in China. For years the debate was as contentious as asking whether cheesecake is cake or pie. But in bones from Antarctica threw an exciting new ingredient into the mix: a bird that lived just before the Chicxulub event and looked stunningly similar to a modern duck.
Julia Clarke at the University of Texas at Austin first described Vegavis iaai based on a fossil dated to around 67 million years ago, just before the asteroid strike. Clarke and her team place it in the same group that includes present-day ducks and geese. In they examined a second, more complete skeleton of Vegavis and found that the animal not only looked like a duck, it may have also quacked like a duck.
Closer looks at fragmentary bones, combined with more advanced methods of genetic backtracking, are fleshing out the story. In a study published in , a team led by Yale University ornithology professor Richard Prum combed through the genes of living bird species and calibrated their results against the latest fossil finds. Their detailed avian family tree suggests that only three modern groups got their start just before the asteroid strike. The picture emerging now shows animals that looked very much like modern birds, flying and diving and pecking in the shadow of the dinosaurs.
The exact relationship of Vegavis iaai to. Birds are exceptionally diverse, with more than 10, known species—all of them. Early birds evolved from theropods, the fierce, three-. The latest genetic clues. Cretaceous period and survived a mass extinction 66 million years ago. In the wake of.
Living Dinosaurs: The Evolutionary History of Modern Birds - كتب Google
Kemmerer, Wyoming, is built on bones. About a hundred miles northeast of Salt Lake City as the crow flies, the town sits among crumbling buttes packed with billions of fossils. Known for these riches since the 19th century, the land hosts about a dozen commercial quarries that supply trade shows and gift shops around the world. Whole family dynasties rise and fall and engage in understated rivalries over the discovery, preparation, and sale of animals that died some 52 million years ago.
In the heart of Kemmerer, a couple of doors down from the first store opened by J. As her safety glasses pin down parts of her spiky blond hair, Adams uses a compressed air chisel and needles to painstakingly remove the pale rock surrounding tea-brown bones. This dry, rugged land is mostly known for its abundant fossil fish. As with the much older wetlands in China, this lake left an entire ecosystem frozen in time, including a valuable collection of ancient birds.
Quarry workers and scientists here have unearthed partial bones, stray feathers, and well over a hundred complete bird skeletons. He and his team have studied 3-D scans of thousands of beaks and have added to the evidence that birds likely diversified rapidly after the rest of the dinosaurs died.
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Grande has been coming to this paleontological wonderland, prosaically known as Fossil Lake, for more than 40 years. He usually spends a few weeks each summer mining privately held land leased by the Tynskys. The most scientifically valuable finds return with him to Chicago, and the Tynsky family keeps the rest for commercial sale. For a blistering week in late June I join him up on the butte, where a cadre of enthusiastic high school students and museum volunteers teach me how to lift large slabs out of the earth and check them for signs of past life.
About midmorning on one achingly bright day, Grande asks me to pause my sweaty efforts and come see something amazing: A worker from a neighboring quarry has brought us a bird. Grande has built relationships with several other local families, and they often share their most interesting finds in case he wants to make a purchase on behalf of science; some they donate. This time, though, the potential prize came to us, lovingly displayed from the back of a dusty pickup truck.
Living Dinosaurs: The Evolutionary History of Modern Birds
The animal is only partially uncovered from its limestone tomb, but I can clearly see delicate bones and the impression of a feathered wing. Grande wants a closer look, so we wrap it for transit and race down to the local hospital to get an x-ray. The radiology techs greet us with less surprise than I would have expected—this is clearly not their first fossilized patient. In this way, many of the birds from the hills around Kemmerer have come to roost in Chicago, held in the display cases and storage rooms of the Field Museum.
During a visit to the storied institute a few weeks after our dig, I get a closer look at an early parrot, a perching songbird, and a type of mousebird that have all been recently described by scientists. These remains show that the postimpact ecosystem was an exceptionally diverse aviary. The past few years have been a boon to researchers trying to capture an image of bird life recovering after planetwide disaster. In New Mexico, paleontologists recently extracted parts of a different mousebird that lived 62 million years ago.
It joins a million-year-old giant penguin found recently in New Zealand that looks different from other penguins that lived around the same time. All these fossils seem to fit with the latest genetic puzzle pieces.
A number of papers released in looked at the full genomes of 48 living bird species and concluded that modern birds saw a rapid boom in diversity soon after the asteroid impact. The genetics study came to a similar conclusion. The million-year-old rock layer of Fossil Lake in Wyoming holds abundant, exceptionally preserved fossils, such as this early songbird Eozygodactylus americanus , and is intensively excavated from May through October.
The dinosaur renaissance
The tougher question is why these particular ancestors of modern birds made it through. With more fossils and faster gene sequencing, theories about survivorship abound.
Examining the lifestyles of species that lived before and after the asteroid, Daniel Field and his colleagues think the widespread disappearance of forests may have had something to do with it. In the last days of the Cretaceous, the world as a whole was a warmer, wetter place than it is today. Lush forests were abuzz with all types of exotic birds, including many that might have passed for contemporary species at first glance.
Many of these once abundant birds have feet suited for perching in trees, suggesting they were largely arboreal. So far, not a trace of them has been found beyond the Cretaceous. Instead, the surviving bird species seem to be more at home on scrubland or at sea.
Another attractive notion is that certain birds were better at proliferating in a disaster zone. In a team led by Gregory Erickson at Florida State University presented evidence that egg-laying, non-avian dinosaurs took months to incubate and hatch their young. Since many modern-style birds generally reproduce quickly and mature in a matter of days or weeks, they might have had a competitive edge over their more reptile-like cousins in the grim aftermath of the asteroid strike.
Today mousebirds like this museum specimen are found only in sub-Saharan Africa. The rare fossil helped scientists better pinpoint when different bird lineages split from each other, in turn supporting the notion that birds experienced an evolutionary boom soon after the asteroid strike. Depending on whom you ask, smaller bodies, polar adaptations, seed-based diets, and even nest designs may have played roles in determining who lived and who died.
Solving the mystery will almost certainly require exhaustive hunts for animals that lived even closer in time to the impact. Ongoing fieldwork in places like South America, New Zealand, and the frosty deserts of Antarctica already hint at fresh discoveries in the near future. And richer genetic clues should flood the field in the coming years.
At the China National GeneBank in Shenzhen, scientists are using faster, more precise techniques to churn out drafts of entire genomes for all living bird species by The most likely answer to the question of survivorship is that it took a suite of characteristics for certain birds to be successful. Roughly are migrants, spending the winter in the region or just passing through on their way between hemispheres.