a two-inch-long, worm-like sea creature is the earli-est-known animal to have the beginnings of a backbone。
cambridge university scientists have confirmed. this makes pikaiagracilens, which evolved more than 500 million years ago, a precursor of modern vertebrates, including humans. the latest study resolves a debate about whether it is the first member of the chordate family. humanbeings, as well as fish, amphibians, birds, reptiles and mammals are all descended from this two-inch creature--pikaiagracilens which lived in the sea 505 million years ago.
发现人类亲缘最古老的祖先——一种2英寸长类似蠕虫，聚集在海床上的生物。剑桥大学的科学家证实，一种2英长类似蠕虫的海洋生物是目前已知的最早的脊椎动物。
这使得5亿多年前就进化完成的一种生物——pikaiagracilens(皮卡虫)，成为了现代脊椎动物的祖先，甚至还包括人类。这项最新的研究终结了一场关于它是否是脊椎动物家族中第一个成员的争论。人类，还有鱼、两栖动物、鸟、爬行动物和哺乳动物等等，都起源于这种2英寸的生物——pikaiagracilens，一种5.05亿年前生活在海洋的生物。