Эрдэмтэд 165 сая жилийн тэртээх хөхтөн амьтны өвөг болох Megacauda sungei-ийн бүрэн бүтэн олдворыг илрүүлснээр амьсгалын болон хоол боловсруулах системийн хувьслын нууцыг тайлж байна.
Өвөр Монголын нутгаас олдсон Megacauda sungei хэмээх энэхүү олдвор нь Юрийн галавын үед амьдарч байсан хөхтөн амьтны бүлгийн хамгийн том төлөөлөгч болохыг Nature сэтгүүлд нийтэлсэн судалгаа харууллаа. Докодонт (docodont) хэмээх уг амьтан нь хүн, кенгуру, нугасан хошуут зэрэг орчин үеийн хөхтөн амьтдын шууд удамд орохгүй ч тэдний өвөг дээдэстэй ойр төрлийн бүлэгт багтдаг. Олдвор нь яснаас гадна зөөлөн эд, үс болон ам, залгиурын бүтэц маш тодорхой хадгалагдсанаараа палеонтологийн салбарт ховор тохиолдох нээлт болж байна.
Судлаачдын үзэж буйгаар, уг амьтан нь нугасан хошуут болон халиуны эрлийз мэт гадаад төрхтэй, усанд сэлэхэд зохицсон хүчирхэг хойд хөл, хавтгайвтар сүүлтэй байжээ. Энэхүү амьтан нь голын эрэг дагуу амьдарч, орчин үеийн халиуны нэгэн адил усанд шумбан хооллодог байсан байх магадлалтай. Шинжилгээгээр Megacauda нь зөөлөн тагнай болон залгихад тусалдаг хэлний ясны нарийн бүтэцтэй байсан нь тогтоогдсон байна.
Чикагогийн их сургуулийн судлаач Жэ-Ши Луогийн тайлбарласнаар, зөөлөн тагнай нь хөхтөн амьтдын эволюцийн хамгийн чухал шинэлэг өөрчлөлтүүдийн нэг юм. Энэхүү бүтцийн ачаар амьтад хамраараа амьсгалахын зэрэгцээ хоолоо зажилж залгих боломжтой болсон нь хоол тэжээлийн олон төрлийн эх үүсвэрийг ашиглах, улмаар төрөл зүйлээ өргөжүүлэх үндэс болжээ. Мөн энэхүү анатомийн өөрчлөлт нь үр төлөө хөхөөр тэжээх чадварыг хөгжүүлж, тархины хөгжил, цаашлаад хүн төрөлхтөн үүсэхэд чухал үүрэг гүйцэтгэсэн гэж Боннын их сургуулийн профессор Томас Мартин тэмдэглэжээ.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
A newly described fossil from Inner Mongolia, named Megacauda sungei, is the largest Jurassic mammaliaform found so far. Preserved in exceptional detail, it shows how the soft palate, a key mammalian innovation, evolved more than 165 million years ago.
The animal is a docodont, a group that evolved before true mammals, the lineage that includes humans, kangaroos, platypuses and echidnas. It sits just outside that lineage, yet it already had a complex soft palate.
That matters because this fossil discovery suggests the feature may have allowed our own ancestors to develop diverse ways of eating and exploit new environments.
A Landscape That Would Barely Seem Familiar
Go back 165 million years and Inner Mongolia looked vastly different from today. Freshwater rivers crossed forests that held some of the earliest redwood trees, and long-snouted pterosaurs soared overhead. Among the ferns, small feathered dinosaurs dashed about, picking off little reptiles and amphibians scuttling through the leaf litter.
Somewhere along one of those riverbanks, there might have been the splash of a tail as an early mammaliaform dived to escape. Picture a cross between a platypus and an otter. The animal had a tapered snout full of sharp, shearing teeth, a thickset, furry body, powerful hind legs with webbed feet, and a long, slightly flattened tail covered in scaly skin. In modern mammals, these are the perfect adaptations for swimming.
All of this fossil evidence points to a semi-aquatic lifestyle. The animal likely lived along riverbanks, or possibly even within them, slipping into the water to hunt aquatic creatures such as salamanders, much as modern platypuses, otters, and minks do.
Soft Tissue That Rarely Survives
What makes this fossil specimen remarkable is that it preserved more than bones. The study, published in Nature, revealed that good deal of soft tissue survived too, including the outline of shaggy fur around the body and, importantly, the internal structures of the mouth and throat. As Zhe-Xi Luo of the University of Chicago said:
“Docodonts are the most speciose group of the stem mammals across North America, Europe, and China, and this is probably one of the two most complete specimens for the group.”
The fossil also shows, he explained, in a university statement that:
“the intricate structures of the throat are starting to come together, long before modern mammals split off from their predecessors, and they are very important to the evolutionary innovation that underlies later adaptive radiation.” Even at this stage, Megacauda had a soft palate and a complex hyoid bone that aided in swallowing.
Why A Soft Palate Changed Everything?
So what does a soft palate actually do? It allows mammals to take off small chunks of food and chew them before swallowing, all while still breathing through the nose. Crocodiles, by comparison, have to swallow large pieces of food while tossing their heads back.
Luo called it “an incredibly important evolutionary innovation.” After mammals chew their food, be it plants or meat, they all swallow it in the same efficient and effortless way. Once early mammals had this apparatus, each group could develop specialized teeth and diversify into a tremendous range of food resources, as carnivores, insectivores, herbivores, omnivores, or anything in between.
The soft palate and complex hyoid structure also play a key role in letting young mammals suckle milk from their mothers, even when upside down. According to Professor Dr. Thomas Martin of the University of Bonn:
“It was this adaptation that made brain development, eventually leading to humans, possible.” He added that the shaping of the oral cavity and pharynx is directly linked to the evolution of mammals.
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