10月19日消息：西伯利亚的一处洞穴曾因出土了已灭绝人类谱系丹尼索瓦人的首批遗骸而闻名，这些人类曾广泛活动于欧亚大陆；如今，该洞穴又出土了一种此前未知的冰河时代大型哺乳动物的证据，它与今天的牦牛有着密切的亲缘关系。
Oct 19 : A Siberian cave already famous for yielding the first remains of an extinct human lineage called the Denisovans, who once roamed widely in Eurasia, has now produced evidence of a previously unknown large Ice Age mammal closely related to today's yak.
研究人员表示，他们在俄罗斯西伯利亚南部阿尔泰山的丹尼索瓦洞穴中发现了该动物的小块骨骼碎片，并获取了DNA，表明这些遗骸属于一种不同于以往已知现存及已灭绝物种的牛科动物。
Researchers said they discovered small bone fragments of the animal in Denisova Cave in the Altai Mountains of southern Siberia in Russia, and obtained DNA that showed these remains belonged to a bovine species distinct from others already known, living and extinct.
研究人员总共研究了该物种的20块骨骼碎片——其中14块来自丹尼索瓦洞穴，6块来自更广泛地区的其他遗址。最古老的标本可追溯至大约25万至20万年前，最年轻的标本则约为2万7千年年前。
In all, the researchers studied 20 bone fragments from this species — 14 from Denisova Cave and 6 from other sites in the broader region. The oldest specimen dated to about 250,000 to 200,000 years ago, and the youngest to about 27,000 years ago.
这些骨骼本身极其零碎，仅凭其形状无法看出它们属于一种此前未知的大型哺乳动物。但研究人员成功从这些骨骼中提取了20个古代基因组，结果显示这是一个独特物种，其演化谱系在大约40万年前与现代牦牛的祖先分道扬镳。
The bones themselves were so fragmentary that their shape alone did not reveal that they belonged to a previously unknown large mammal. But the researchers were able to generate 20 ancient genomes from the bones, and these showed that this was a unique species whose evolutionary lineage diverged from the ancestors of the modern-day yak approximately 400,000 years ago.
该研究发表在《当代生物学》杂志上。研究的资深作者、来自斯德哥尔摩大学和瑞典自然历史博物馆合作机构古遗传学中心的演化遗传学家洛夫·达伦表示：“这很不寻常，特别是从无法辨认的小块碎片中识别出一种大型哺乳动物物种。”
"It is unusual, especially to recognize a large mammal species from small, unidentifiable fragments," said evolutionary geneticist Love Dalén of the Centre for Palaeogenetics, a collaboration between Stockholm University and the Swedish Museum of Natural History, senior author of the research published in the journal Current Biology.
古遗传学中心博士生、与该中心博士后研究员乔纳斯·奥本海默共同担任该研究第一作者的亚历山大·吉拉尔代表示：“我想这与古DNA领域的进展有关，因为遗传学作为一项强大的新信息层被应用到了古代材料上。”
"I'd say that this is related to the advances in the field of ancient DNA, as genetics is a powerful new layer of information applied to ancient materials," said Alexandre Gilardet, a doctoral student at the Centre for Palaeogenetics and co-lead author of the study, along with Centre for Palaeogenetics postdoctoral researcher Jonas Oppenheimer.
仅凭遗传证据尚不足以为新物种赋予科学名称，因此研究人员将其称为“牦牛X”（Yak X）。冰河时代景观达伦表示，牦牛X曾与包括草原野牛以及现代家牛已灭绝的野生祖先原牛在内的其他牛科动物共同生活。达伦说，它还与长毛猛犸象、披毛犀、马以及洞鬣熊和棕熊等大型捕食者共享了冰河时代的景观。
Genetic evidence alone is not sufficient to allow for giving a scientific name to a new species, so the researchers are calling this one "Yak X." THE ICE AGE LANDSCAPE Dalén said Yak X lived alongside other bovines including steppe bison and the aurochs, the extinct wild ancestor of today's domesticated cattle. It also shared the Ice Age landscape with woolly mammoths, woolly rhinoceroses, horses and large predators such as cave hyenas and brown bears, Dalén said.
“考虑到它与现代牦牛的近亲关系，我预计它的外表会更像牦牛而不是野牛，”达伦说。
"I'd expect it to have looked more like a yak than a bison, given its close relationship to modern yaks," Dalén said.
牦牛是体格健壮的动物，长有角、长毛和肩峰，外表有点像多毛的公牛。最大的雄性体重可达一吨。野生牦牛仅限于青藏高原的高海拔地区。
Yaks are sturdily built animals with horns, long fur and a hump at the shoulders, looking a bit like a hairy ox. The largest males can weigh as much as a ton. Wild yaks are restricted to higher elevations of the Tibetan Plateau.
牦牛X的发现加深了人们对冰河时代大型哺乳动物多样性的理解，并为在该纪元结束前后灭绝的长长物种名单又添了一个新物种。
The Yak X discovery deepens the understanding of the diversity of large Ice Age mammals and adds another species to the long list that disappeared at around the end of that epoch.
“利用我们长达20万年的采样时间跨度，我们可以看到该物种可能在约12万年前的一个变暖时期经历了一次种群数量下降，并在我们最年轻的样本（约2万7千年前）之后的一段时间灭绝了，”奥本海默（Oppenheimer）说。
"Using the long, 200,000-year time span of our sampling, we can see that the species may have undergone a population decline during a period of warming around 120,000 years ago, and went extinct some time after our youngest sample, about 27,000 years ago," Oppenheimer said.
广袤的西伯利亚旷野是一个被称为猛犸象草原的草原生态系统，因其最大的居民而得名。该地区的大部分未被覆盖北美和欧洲大片土地的巨大冰盖所覆盖。
The vast Siberian expanse was a grassland ecosystem called the mammoth steppe, known as such for its largest denizens. Most of the region was left uncovered by the immense ice sheets that had blanketed large swathes of North America and Europe.
牦牛X谱系与现代牦牛祖先的分化时间，大约与导致今天棕熊和北极熊的熊科谱系之间发生的演化分裂在同一时期。
The Yak X lineage diverged from the ancestors of modern yaks around the same time as the evolutionary split that occurred between the ursine lineages that led to today's brown bears and polar bears.
丹尼索瓦人 2008年，科学家正是在丹尼索瓦洞中发掘出一块指骨，这块指骨首次提供了丹尼索瓦人存在的证据。丹尼索瓦人是尼安德特人以及我们自身所属物种智人的已灭绝近亲。自那以后，人们在那个洞穴以及亚洲几个遥远地区发现了更多丹尼索瓦人的遗骸。
THE DENISOVANS It was in Denisova Cave in 2008 that scientists unearthed a finger bone that offered the first evidence of the existence of Denisovans, extinct cousins of Neanderthals and our own species, Homo sapiens. Since then, more remains of Denisovans have been discovered in the cave and in several far-flung parts of Asia.
一些现代人群，尤其是美拉尼西亚和巴布亚新几内亚的人群，携带着一小部分来自丹尼索瓦人的DNA，这表明在丹尼索瓦人于尚不完全清楚的情况下灭绝之前，他们曾与智人杂交。
Some modern populations of people, especially those in Melanesia and Papua New Guinea, carry a small percentage of DNA from Denisovans, indicating interbreeding with Homo sapiens before the Denisovans became extinct under circumstances that are not well understood.
丹尼索瓦人是狩猎采集者，曾在许多不同类型的环境中生存下来。Yak X物种可能曾是他们猎杀的猎物之一。
Denisovans were hunter-gatherers who survived in many different types of environments. The Yak X species might have been among the prey that they hunted.
“Yak X出现在丹尼索瓦人的菜单上，似乎是合理的，”达伦说。
"It seems reasonable that Yak X was on the Denisovan menu," Dalén said.