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当前位置: Science » 古生物学 » Science:淡水豚的祖先被找到了?


摘要 : 古生物学家可能已经发现亚马逊淡水豚的一个祖先,或者至少是一个久违的近亲。该物种(Inia geoffrensis)只有一个通用名,但它同时也在南美洲北部的其它几个水系中生活,它的进化起源同那些挟沙水域一样模糊不清。大约600万年前,当海平面上升,开辟出新的栖息地时,它的祖先就可能已经离开海洋前往淡水生活。


古生物学家可能已经发现亚马逊淡水豚的一个祖先,或者至少是一个久违的近亲。该物种(Inia geoffrensis)只有一个通用名,但它同时也在南美洲北部的其它几个水系中生活,它的进化起源同那些挟沙水域一样模糊不清。大约600万年前,当海平面上升,开辟出新的栖息地时,它的祖先就可能已经离开海洋前往淡水生活。但2011年,研究人员在巴拿马的沿加勒比海海岸的一个地点挖掘出了一只海豚的零碎化石——解剖学层面的比较发现海轮海豚至少同亚马逊淡水豚密切相关。那些尚未被侵蚀的保存完好的部分包括一部分头骨、下部颚骨、一些零星的牙齿,和一块髆骨(在人类中俗称肩胛骨)。周围岩石中发现的化石帮助研究小组将这只海豚的年龄缩小到580万年前到610万年前之间,那时巴拿马地峡还没有从海里隆起。这只海豚(请见上方艺术家的重现图片)被称为Isthminia panamensis,这个名字结合了今天的亚马逊淡水豚的属名和这个新物种被发现的地点的名字;这只海豚长约2.85米(9.4英尺),因此比它当代的同名物种要略小,研究人员今天在PeerJ的网络版上报告说。它那36厘米(1.2英尺)长的吻直指前方,而不像今天的淡水豚是稍微向下的,这个形状表明,这种哺乳动物大部分时间呆在海中,可能靠食鱼为生,科学家们说。根据化石的解剖学特点,Isthminia要么是今天的亚马逊淡水豚的近亲或是祖先(当600万年前海平面上升,扩大了南美河流体系的栖息地,亚马逊淡水豚或许因此得以侵入),要么它是一种更加古老的、尚未发现的、后来回归大海的淡水豚的后代。


River dolphin’s ancestor unearthed?


Paleontologists may have found an ancestor, or at least a long-lost close cousin, of the Amazon river dolphin. Despite its common name, that species (Inia geoffrensis) also inhabits several other river systems in northern South America, and its evolutionary origins are as murky as those sediment-laden waters. Its ancestors may have left the ocean for fresh water when sea-level rise opened up new habitats about 6 million years ago. But in 2011, researchers excavated the fragmentary fossil of a seagoing dolphin—one that anatomical comparisons reveal is, at the very least, closely related to Inia—at a site along the Caribbean coast of Panama. The preserved bits that hadn’t been lost to erosion include a partial skull, lower jawbones, a few scattered teeth, and a scapula (which in humans is commonly known as the shoulder blade). Distinctive fossils in the surrounding rocks helped the team narrow down the age of the dolphin to between 5.8 million and 6.1 million years ago, a time when the Isthmus of Panama hadn’t yet risen from the sea. Dubbed Isthminia panamensis—a blend of the genus name of today’s Amazon river dolphin and the location wher the new species was found—the dolphin (artist’s reconstruction above) was about 2.85 meters (9.4 feet) long and is thusslightly smaller than its modern-day namesake, the researchers report online today in PeerJ. The shape of the creature’s 36-centimeter (1.2-foot) snout, which points straight forward rather than slightly downward like today’s river dolphins, suggests the mammal spent most of its time at sea and likely fed on fish, the scientists say. based on the anatomical features of the fossil, Isthminia was either a close relative or ancestor of today’s Amazon river dolphin (which probably invaded South America’s river systems when sea-level rise expanded those habitats about 6 million years ago), or it was a descendant of an older and as-yet-undiscovered river dolphin that went back to sea.

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