Some dinosaurs laid colored, speckled and spotted eggs boasting exquisite hues of blue and brown, scientists said on Nov. 1, in a discovery that scrambles the notion that such exceptional traits originated with birds. An analysis of 12 fossilized dinosaur eggshells from Europe, Asia, North America and South America detected the same two pigments present in colorful birds eggs in a dinosaur group called eumaniraptorans, which includes well-known meat eaters like Velociraptor and the small feathered dinosaur ancestors of birds.
“We discovered that egg color is not a trait unique to our modern birds, but evolved in their non-avian dinosaur ancestors,” said Yale University paleontologist Jasmina Wiemann, who led the study published in the journal Nature. “Our study fundamentally changes our understanding of egg color evolution, and adds color to dinosaur nests in the real ‘Jurassic World’.” For example, the sickle-clawed predator Deinonychus had a blue egg with brown blotches and the bird-like Oviraptor, known for its toothless beak, had eggs that were dark blue.
Birds evolved from eumaniraptoran dinosaurs in the Jurassic Period. The earliest-known bird, Archaeopteryx, lived about 150 million years ago in Germany. Eumaniraptorans, part of the larger theropod assemblage of two-legged meat-eating dinosaurs, generally were small and bird-like, covered in colorful plumage. They included predators up to 9 meters long and as small as a house cat, but did not include behemoths like Tyrannosaurus rex and Giganotosaurus.
Photo: Reuters
照片：路透
Egg color provided an evolutionary advantage to dinosaurs that had exposed nests for their eggs, rather than burying them as alligators and turtles do, in part by providing camouflage to protect against egg-eating predators, the researchers said. All the other dinosaurs studied produced plain white eggs, indicating a single evolutionary origin of egg color in eumaniraptoran dinosaurs that was passed on to their bird descendants.
In the eumaniraptorans, the researchers found evidence of a blue-green pigment called biliverdin and a red-brown pigment called protoporphyrin IX structurally integrated into the crystal matrix of the eggshell, as they are with birds. “Some were uniformly colored,” said paleontologist and study co-author Mark Norell of the American Museum of Natural History in New York. “Some were spotted and speckled. It was just like in living birds. A robin’s egg is uniformly blue, but a quail’s is spotted and speckled.” Other traits once assumed to have originated in birds, like feathers and wishbones, also were inherited from their dinosaur forebears, Norell said.
(Reuters)
科學家在十一月一日指出，有些恐龍會產下有顏色的蛋，外觀帶有斑點和色塊，呈現出細緻的藍色與褐色光澤。這份發現打破了舊有概念，認為如此特殊的生物性狀並非起源於鳥類。科學家分析了歐洲、亞洲、北美洲與南美洲出土的十二顆恐龍蛋殼化石，並在「真手盜龍類」這個群體的蛋裡偵測到兩種有色物質，同樣可見於色彩繽紛的鳥類蛋中。「真手盜龍類」包含「伶盜龍」等知名肉食恐龍，以及鳥類祖先的小型披羽恐龍。
發表於《自然》期刊的這份研究由耶魯大學的古生物學家亞斯米娜‧維曼擔任主持人，她表示：「我們發現蛋殼顏色並非是現代鳥類獨有的生物性狀，而是從非鳥類的恐龍祖先演化而來。」維曼進一步指出：「這份研究徹底改變我們對於蛋殼顏色演化的理解，也為真實『侏儸紀世界』中的恐龍巢增添色彩。」舉例而言，爪子呈鐮刀狀的掠食者「恐爪龍」，蛋殼呈現藍色，帶有褐色斑點；身型與鳥類相似、以無齒的喙狀嘴著稱的「偷蛋龍」，則會產下深藍色的蛋。
鳥類演化自侏儸紀時期的真手盜龍類。目前所知最早的鳥類──始祖鳥──大約生活在一億五千萬年前的德國地區。真手盜龍類隸屬於涵蓋範圍更廣的獸腳亞目群體，該群體主要由肉食性的雙足恐龍組成。一般而言，真手盜龍類的恐龍體型偏小且與鳥類相似，全身披覆色彩繽紛的羽毛。該類恐龍包含不同大小的掠食性恐龍，有的身長可達九公尺，有的則小如現代家貓，但不包括諸如暴龍或南方巨獸龍等史前巨獸。
研究人員表示，對於把巢暴露在光天化日下，而不像短吻鱷或烏龜把蛋埋入土中的恐龍而言，蛋的顏色具有演化上的優勢，部分原因來自於提供保護色，防止蛋遭到食蛋型掠食者攫取。研究分析的其他類型恐龍則全數產下純白色的蛋，這表示真手盜龍類的蛋顏色屬於單一演化來源，後來傳遞給它們的鳥類後代。
研究人員在真手盜龍類化石中發現證據，顯示藍綠色的膽綠素與紅褐色原紫質IX這兩種有色物質，在結構上被結合到蛋殼的晶體基質中，同樣的情況也見於鳥類。紐約美國自然史博物館的古生物學家馬克‧諾瑞爾是這份研究的共同作者，他指出：「有些蛋的顏色均勻，有些則帶有班點或色塊的花紋，就像是今日鳥類會有的現象。比如說，旅鶇（美洲知更鳥）的蛋呈現均勻的藍色，但鵪鶉蛋就充滿班點和色塊。」諾瑞爾也表示，其他本來被認為起源自鳥類的生物性狀，像是羽毛以及V字形的鳥類鎖骨「許願骨」等，都是遺傳自它們的恐龍遠祖。
（台北時報章厚明譯）
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