Хятадын Гүйжоу мужаас олдсон шинэ төрлийн үлэг гүрвэлийн чулуужсан олдвор нь тэдний нөхөн үржихүйн онцлог болон өндөгний бүрхүүлийн хувьслын талаарх шинэ баримтыг дэлгэлээ.
Хятадын Шинжлэх ухааны академийн Сээр нуруутан амьтдын палеонтологи ба палеоантропологийн хүрээлэнгийн судлаачид “Qianlong shouhu” хэмээх шинэ төрлийн үлэг гүрвэлийн олдворт шинжилгээ хийжээ. Ойролцоогоор 6 метр урт, 1 тонн жинтэй энэхүү амьтны гурван насанд хүрсэн бодгаль болон үр хөврөл бүхий таван үүр олдсон нь үлэг гүрвэлүүд үүрээ хамгаалдаг байсныг харуулах хамгийн эртний нотолгоо байж болзошгүй юм.
Судлаачид электрон микроскоп болон химийн шинжилгээний олон төрлийн аргыг ашиглан өндөгний бүрхүүлийн бүтцийг судалсан байна. Үр дүнд нь уг үлэг гүрвэл нь хатуу биш, харин арьсархуу бүрхүүлтэй өндөг гаргадаг байсныг тогтоожээ. Энэ нь үлэг гүрвэлийн өндөгний анхдагч хэлбэр нь арьсархуу бүрхүүл байсан гэх таамаглалыг дэмжиж байна.
Тус баг 210 зүйлийн үлэг гүрвэл болон амьд амьтдын нөхөн үржихүйн шинж чанарт харьцуулсан судалгаа хийжээ. Судалгаагаар өндөгний бүрхүүл зузаарах болон хэлбэрийн томоохон өөрчлөлтүүд нь шувуудын үүслийн үед бус, харин теропод үлэг гүрвэлийн хувьслын эхэн үед явагдсан болохыг тогтоов. Энэхүү олдвор нь үлэг гүрвэлийн нөхөн үржихүйн биологийн өмнө нь бүрхэг байсан түүхийг тодруулахад чухал ач холбогдолтой юм.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
Eight fossils from a Chinese dig site are rewriting what we know about how dinosaurs reproduced. A new Early Jurassic species, found with adult skeletons and nests of embryo-filled eggs, points to a leathery shell as the ancestral dinosaur egg, and shows that the big change design came earlier than anyone had pinned down.
Over the last three decades, a handful of exceptionally preserved reproduction-related specimens have deepened what scientists understand about dinosaur reproductive biology. Even so, fossil evidence has stayed thin, and there has been little quantitative analysis across a broad evolutionary range. Much about the subject, especially the pre-Cretaceous chapter, remained murky.
That is where researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences come in. Their work, published in National Science Review, combines a spectacular fossil site in Guizhou with a sweeping comparison of reproductive traits across many species. The results suggest the major transition in egg morphology occurred early in theropod evolution, rather than near the origin of birds.
A Guarding Dragon from Guizhou
The centerpiece is Qianlong shouhu, a new early-diverged sauropodomorph represented by three adult skeletons and five egg clutches. The name is a small story in itself: Qianlong means “Guizhou dragon,” while shouhu means “guarding,” a nod to adults preserved alongside embryo-containing eggs. The researchers say this may be the earliest fossil record of adult dinosaurs associated with nests.
Qianlong was a medium-sized basal sauropodomorph, about 6 meters long and weighing around 1 ton. The embryos differed from the adults in a few ways: a proportionally longer skull, a more vertical front edge of the snout, and fewer teeth. Analyses of limb ratios indicate adults could walk on their hindlimbs, while the babies were likely quadrupedal.
The taphonomical and sedimentary features of the site also suggest colonial nesting, a behavior similar to that of other basal sauropodomorphs such as Massospondylus and Mussaurus.
Reading the Shell
To work out what kind of eggs Qianlong laid, the team turned to a battery of techniques: histological thin-sectioning, electron backscatter diffraction, energy-dispersive spectroscopy, and scanning electron microscopy. According to the study, the eggshell microstructure resembled that of other Cretaceous dinosaur egg fossils, probably consisting of two layers, the mammillary layer and the continuous layer, with fully developed eggshell units.
The calcareous layer was much thicker than in most soft-shelled eggs but thinner than in hard-shelled ones. The surface told a similar tale. It featured small fragments, like a leathery eggshell, unlike the folded surface of soft-shelled eggs or the large-fragmented surface of hard-shelled eggs. These observations indicate that Qianlong laid leathery eggs.
Zooming Out Across 210 Species
The researchers then widened the lens, assembling data from 210 fossil and living species representing all major reptilian clades and testing evolutionary trends against multiple time-scaled phylogenies. The aim was to follow selected reproductive traits across the dinosaur-bird transition.
Relative size decreased from the base of the Diapsida to that of the Saurischia, then trended upward from early theropods to the crown bird node, with the most significant increase early in theropod evolution. Eggshell thickness followed a comparable arc: it tended to fall from the base of the archosaurs to the base of the Saurischia, then rose significantly early in theropod evolution. An increasing trend in thickness also appeared within sauropodomorphs.
Its shape, meanwhile, was generally conserved from diapsids to living birds. Theropod egg elongation peaked in oviraptorosaurs, which had the greatest elongation among diapsids, but it later returned to its ancestral state. Only slightly elongated ones were therefore inherited by all crown bird clades.
Reconstructing the ancestral state of various eggshell types, the authors conclude that the first one was probably leathery, relatively small, and elliptical. A leathery shell was also probably the ancestral state of Avemetatarsalia, Archosauria, and Testudines, as reported by Li Yuan of the Chinese Academy of Sciences.
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