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联系方式 What scientists thought was the tiniest dinosaur ever may actually have been a lizard
UPDATE: July 22, 2020, 10:20 a.m. PDT The international team of scientists who discovered what they originally described as the tiniest dinosaur in the world now think they made a mistake. They retracted their research from Nature on July 22, 2020. "Although the description of Oculudentavis khaungraae remains accurate, a new unpublished specimen casts doubts upon our hypothesis," the scientists wrote in the retraction notice. The specimen preserved in amber 99 million years ago may actually be a lizard rather than a dinosaur according to Retraction Watch, which monitors scientific retractions.
Original story:
An international team of scientists have discovered a tiny new species of dinosaur, believed to be the smallest on record.
Named Oculudentavis khaungraae, the diminutive bird's skull measures only 14.25 millimetres — less than the width of a thumbnail and smaller than that of the minuscule bee hummingbird. The team's findings were published Wednesday in Nature.
"It’s lucky this tiny creature was preserved in amber, as such small, fragile animals aren’t common in the fossil record," said the Natural History Museum of Los Angeles County's senior vice president of research and collections, Dr. Luis Chiappe. Oculudentavis' skull was trapped in Burmese amber 99 million years ago. "This finding is exciting because it gives us a picture of the small animals that lived in a tropical forest during the Age of Dinosaurs."
Oculudentavis'size isn't the only thing curious about it. Typically when animals evolve to become smaller, their eyes become proportionally large and they lose teeth. However, this pint-sized predatorhas more teeth than any other fossil bird, running all the way up to below its eye.
Further, the bones supporting Oculudentavis' eyes are spoon-shaped like some lizards, rather than square like a bird's. The diurnal dinosaur's sharp, owl-like eyes faced sideways rather than forward and bulged out, making it unlike any other animal alive today. In fact, Oculudentavis' eyes are so strange that scientists are struggling to understand exactly how they would have worked.
"It’s the weirdest fossil I've ever been lucky enough to study," said Dr. Jingmai O'Connor, senior professor at the Chinese Academy of Sciences and lead author on the study. "I just love how natural selection ends up producing such bizarre forms."
A CT scan of the skull of Oculudentavis by Li Gang. Oculudentavis means eye-tooth-bird, so named for its distinctive features.Credit: Natural history museumOf course, there's only so much you can tell from a single skull. Though it certainly has the smallest head on record, it's theoretically possible Oculudentavis isn't the smallest dinosaur since scientists have no body to examine. Still, O'Connor told Mashable via email she estimates its body was around 5–7 centimetres long. “But this is just a guess!”
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The smallest dinosaur on record prior to Oculudentavis' discovery was the bee hummingbird, which lives in Cuba. It's also the world's smallest living bird, with males measuring up to 57 millimetres in length and weighing 1.6 grams, while females are larger. "The smallest non-avian dinosaur of the Mesozoic was probably a scansoriopterygid," said O'Connor. "There were Mesozoic birds that are smaller than these non-avian dinosaurs though, things sparrow sized. But nothing hummingbird sized!"
Despite its missing body, the team of scientists from the U.S., Canada, and China are fairly confident in labelling Oculudentavis a bird, as its pointed beak and large eye socket have previously only been seen in birds. They are also confident that, despite its minuscule size, the fossil is an adult.
“We know its not an infant from the proportions of the skull (the eye is not proportionately large for its size and the rostrum [beak] is not short), the high degree of fusion between many of the skull bones, and the morphology of certain elements like the maxilla [upper jaw],” O'Connor told Mashable.
If an adult Oculudentaviswas already so small, the babies must have been practically microscopic.
An artistic rendering of Oculudentavis by Han Zhixin, imagining what it looked like while alive 99 million years ago.Credit: Natural History Museum