Эрдэмтэд 520 сая жилийн өмнөх үе хөлийн амьтны авгалдайн чулуужсан олдвороос тархи болон хоол боловсруулах эрхтний бүтцийг бүрэн бүтэн илрүүлжээ.
Судлаачид үе хөлийн амьтдын хувьслыг ойлгохын тулд тэдний авгалдайн хөгжлийн үе шатыг судлахыг эртнээс зорьж ирсэн ч, биеийн бүтэц нь маш жижиг, эмзэг тул ийм олдвор олдох боломж бараг үгүй гэж үздэг байв. Гэтэл Мартин Смитээр ахлуулсан судалгааны баг уг хорхой мэт биет амьтны арьсан дор хадгалагдан үлдсэн нарийн бүтцүүдийг илрүүлсэн нь палеонтологийн салбарт ховор тохиолдол боллоо.
Синхротрон рентген томографийн 3D дүрслэлийн аргаар уг олдворыг шинжлэхэд тархи, хоол боловсруулах булчирхай, цусны эргэлтийн системийн анхдагч хэлбэр, мөн мөч болон нүдний мэдрэлийн судал зэрэг нь тодорхой харагджээ. Энэхүү гайхалтай хадгалагдалт нь эртний амьтдын зөөлөн эд эсүүд хагас тэрбум жилийн турш ялзрахгүй үлдэж чадсаныг харуулж байна.
Судалгааны үр дүнд эртний үе хөлийн амьтад Кембрийн тэсрэлтийн үед төсөөлж байснаас илүү нарийн бүтэцтэй байсныг тогтоов. Тухайлбал, олдвороос илэрсэн “протоцеребрум” буюу тархины хэсэг нь өнөөгийн үе хөлийн амьтдын толгойн урд хэсгийн хөгжилтэй холбоотой болохыг тогтоосон нь уг бүлэг амьтад дэлхийн өнцөг булан бүрт тархан амьдрах чадвартай болсныг илтгэж байна.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
A fossilized larva from 520 million years ago has been found with its brain and digestive system still intact, something almost unheard of in the fossil record. When most people picture a fossil, they think of bone turned to stone. Dinosaur remains are the classic example, ideally found in large enough collections to be reassembled into something resembling the whole animal. Other fossils are simply impressions that small creatures left in rock.
What nearly all of them share is that only the hard parts survive. Unless the environment is unusually good at preserving things, soft tissue breaks down over time and leaves stony remains. This larva, one of the earliest ancestors of the arthropods, a group that includes insects, crabs and lobsters, broke that rule.
Soft Tissue, Against The Odds
Martin Smith, the study’s lead researcher, has said that if he could discover any one fossil, he would pick an arthropod larva, because developmental data are so central to understanding how these animals evolved. The catch is that larvae are tiny and fragile, so the chances of finding one fossilized seemed practically zero to him.
He already suspected the simple, worm-like specimen was special. According to Smith, seeing the structures preserved beneath its skin left him stunned.
“When I saw the amazing structures preserved under its skin, my jaw just dropped – how could these intricate features have avoided decay and still be here to see half a billion years later?” he said in a statement.
Looking Inside With 3D Scans
The researchers studied 3D images generated from scans made with a technique called synchrotron X-ray tomography. As reported in the same statement, the images revealed a brain, digestive glands, a primitive circulatory system, and even traces of the nerves supplying the larva’s simple legs and eyes. Katherine Dobson, a co-author of the study, said that:
“It’s always interesting to see what’s inside a sample using 3D imaging, but in this incredible tiny larva, natural fossilisation has achieved almost perfect preservation.”
What Early Arthropods Really Looked Like?
That level of detail changed the picture of what early arthropods were like. Scientists had dramatically underestimated their complexity, and the group came into being during the Cambrian Explosion. Its members today include crabs, lobsters, insects and millipedes.
The scans also let researchers link the ancient animal to modern ones. As said in Nature, the larva preserved a region of the brain called the protocerebrum, and scientists can now see that it evolved into the small protruding part of arthropod heads. That feature has helped the group thrive in a huge range of environments, from the depths of the ocean to every continent on Earth, and that also includes Antarctica.
The study team are simply counting themselves lucky that the creature was preserved at all. Their find gives a rare window into what life looked like in the distant past.
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