Эрдэмтэд Юрийн галавын эхэн үед хамаарах, үр хөврөл бүхий хамгийн эртний бөгөөд маш сайн хадгалагдсан үлэг гүрвэлийн өндгийг илрүүлжээ.
Хятадын Юньнань мужийн Луфэн бүс нутгаас 2008 онд олдсон, тахианы өндгөөс жижиг чулуужсан олдворт хоёр декэйд орчим судалгаа хийсний эцэст дотор нь үлэг гүрвэлийн үр хөврөл байгааг тогтоожээ. Хэбэйн их сургуулийн судлаач Ди Жиюн тэргүүтэй баг өндгийг гэмтээлгүйгээр доторх бүтцийг нь судлахын тулд өндөр нарийвчлалтай микро-КТ сканнер ашигласан байна. Судалгааны үр дүнд уг өндөг нь кальцийн карбонатын маш нимгэн давхаргатай, зузаан мембранаар бүрхэгдсэн, хатуу болон зөөлөн бүрхүүлийн завсрын шинж чанартай болохыг илрүүлжээ.
Палеонтологчид уг олдворыг “Давагийн хэв гажилттай өндөг” буюу “Dawa bianxingdan” хэмээн нэрлэж, үүнийг Bianxingdanidae хэмээх шинэ овог, төрөлд багтаав. Уг үр хөврөл нь Brachiosaurus, Diplodocus зэрэг урт хүзүүт аварга үлэг гүрвэлүүдийн эртний төрөл болох суурь сауроподоморф бүлэгт хамаардаг байна. Энэхүү олдвор нь үлэг гүрвэлийн өндөгний хальс эрдэсжиж эхэлсэн хамгийн анхны шатыг харуулж байгаагаараа шинжлэх ухааны өндөр ач холбогдолтой юм.
Өмнө нь тус бүс нутгаас үлэг гүрвэлийн яс олддог байсан ч бүтэн өндөг олдох нь ховор байжээ. Судлаач Ван Таогийн тайлбарласнаар, Юрийн галавын эхэн үеийн өндөгнүүд нь кальцийн давхарга маш нимгэн байсан тул хүчиллэг орчинд амархан уусаж, зөөлөн мембран нь хурдан ялзардаг байсан нь чулуужсан олдвор олдоход хүндрэлтэй байсны шалтгаан болсон байна. Энэхүү нээлт нь эртний амьтдын өндөгний бүтэц, үр хөврөлийн хөгжил болон хувьслын явцыг ойлгоход шинэ мэдээлэл өгч байна.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
Inside a lump of rock slightly smaller than a chicken egg, found in 2008 at Lufeng in China’s Yunnan province, lies a dinosaur egg that took nearly two decades to study. Its shell is thinner than that of any hard-shelled dinosaur egg and is wrapped in an unusually thick membrane. Inside, the tiny bones of the animal that was growing there are still in place.
Chinese paleontologists have named it Dawa bianxingdan, which translates as the “Dawa deformed egg,” and placed it in a new family and genus of fossil eggs. At about 190 million years old, it is the oldest well-preserved dinosaur egg known to contain an embryo.
The shell sits between the two kinds of early eggs paleontologists already knew: soft, leathery eggs made almost entirely of membrane, and firmer eggs reinforced with a layer of mineral, like those of birds. It holds only a trace of mineral, the earliest stage of hardening ever found in a dinosaur egg. No fossil had shown that step before.
A Shell That Was Mostly Membrane
A chicken egg gets its strength from a thick layer of calcium carbonate, the same mineral found in chalk and seashells. In the Lufeng egg, that layer is extremely thin, made of tiny mineral units that sit side by side without locking together. Over it lies a thick protective outer coat, and under it a membrane built from three thick layers. Most of the shell’s thickness came from soft tissue rather than mineral.
To look inside without breaking the rock, a team led by Di Zhiyong of Hebei University scanned the fossil with high-resolution micro-CT, a medical-style X-ray technique that builds a 3D picture of a fossil’s interior. Preparing and analyzing the specimen took years.
The egg is preserved as two halves of shell facing each other, like a walnut cracked open. The mineral units in each half grew in opposite directions, and each half wraps around a cluster of embryonic bones. Those bones made it possible to identify the kind of dinosaur that laid it.
Tiny Bones of a Long-Necked Dinosaur
The embryo belonged to a basal sauropodomorph, an early relative of giant long-necked dinosaurs such as Brachiosaurus and Diplodocus. These early cousins were far smaller, often walked on two legs and were the most common plant-eaters of their time. During the Jurassic, they roamed what is now southwest China in large numbers.
Lufeng, nicknamed “Dinosaur Valley” in China, is one of the richest places to find them. Its rocks have produced skeletons of Lufengosaurus, a plant-eater about 8 meters (26 feet) long, and a bonebed holding the remains of about 20 of its embryos. That site yielded more than 200 embryonic bones and scraps of eggshell less than 0.1 millimeter thick, but no complete egg.
“This is the first time we’ve been able to track the growth of embryonic dinosaurs as they developed,” said Robert Reisz of the University of Toronto Mississauga, who led the 2013 study of the bonebed.
Why Dinosaur Valley Had So Few Eggs
For decades, Lufeng produced skeletons and embryo bones but not one clearly identified dinosaur egg. The Dawa egg survived thanks to unusual burial conditions in the Zhangjiawa Member of the Lufeng Formation, a band of rock laid down in the Early Jurassic, and it is now kept at Hebei University’s School of Life Sciences.
“The discovery of the Dawa deformed egg provides a scientific explanation for this phenomenon,” said Wang Tao, a former director of Lufeng’s dinosaur fossil protection center and a member of the research team. “Dinosaur eggs from before the early Early Jurassic had extremely thin calcium layers, which were easily dissolved as their environment turned acidic, and their shell membranes, though thick, rotted easily, which made them extremely difficult to fossilize.”
Soft eggs were common among early dinosaurs. Mussaurus, a long-necked plant-eater from Argentina, laid soft-shelled eggs similar to a turtle’s, and hard shells evolved separately in at least three groups of dinosaurs later on. Paleontologists had assumed that the earliest dinosaur eggs carried no mineral at all, a view the Lufeng egg revises with its thin but real mineral layer.
A New Egg Family Named for a Soft Shell
Fossil eggs are classified separately from the animals that laid them, because eggs and skeletons are rarely found together. That is why this egg receives its own scientific names even though its parent is known only as a basal sauropodomorph. The study creates the new family Bianxingdanidae and the new genus Bianxingdan, both built from the Chinese words for “deformed egg.”
The name refers to a shell soft enough to change shape, unlike the rigid eggs of later dinosaurs. Di said the egg offers new clues about the shell structure, embryo development and reproduction of early egg-laying animals, and about the many factors that drove the evolution of their eggs. His team will continue studying how early dinosaurs reproduced and how their eggs evolved.
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