神秘海洋动物的化石浮出水面

New fossil finds reveal that an enigmatic seafloor dweller first described more than a decade ago was armored and much larger than its modern-day kin. Cotyledion tylodes had a goblet-shaped body that surrounded a U-shaped gut (dark feature in fossil at left; arrows denote flow of food), and the animal spent its life anchored to the seafloor or to hard objects that had settled there, such as the molted exoskeletons of trilobites (artist's representation at right). C. tylodes was first described in 1999 based on a couple of fragmentary fossils unearthed from 520-million-year-old rocks in southern China. Previously, some scientists have proposed that the tentacled creatures were related to cnidarians, a group that contains jellyfish. But analyses of the new fossils—hundreds of well-preserved specimens extracted from the same ancient rocks—reveal that the animals belong to a group called entoprocts, aquatic creatures that attach to surfaces and filter their food from passing currents, the researchers report online today in Scientific Reports. The oldest undisputed fossils of entoprocts are less than one-third the age of C. tylodes, so the new fossils push back the origin of the entoproct lineage all the way back to the so-called Cambrian explosion, an interval when life diversified very quickly to produce most of the groups seen today or their ancestors. C. tylodes, which measured between 8 and 56 millimeters tall, dwarfed its modern kin, which typically range between 0.1 and 7 millimeters. Also unlike modern-day entoprocts, C. tylodes was covered with distinctive, scalelike features called sclerites—a hint, the scientists say, that such armor may have been more common among ancestral entoprocts than has been previously recognized. 

 新发现的化石表明：十多年前曾经描述过的神秘海底动物是一种披甲动物，比当今同类动物的体型要大得多。瘤状杯形虫拥有杯状身体，周围环绕着U形肠道（见左侧化石中黑色部分，箭头所指为食物流），这种动物一生都固定在海底，或者固定在落在海底的坚硬物体上，如：三叶虫脱毛后的外骨骼上（见右侧艺术家的再现图）。1999年，根据几块破碎的化石首次描述过瘤状杯形虫，那些化石发掘自华南5.2亿年之久的岩石。以前，一些科学家提出这种触须动物跟刺胞动物是亲属。刺胞动物是包括水母在内的一类动物。今天，研究人员在《科学报告》在线版上报告说：然而，对取自同样古老岩石中几百块保存完好的新化石样品所进行的分析表明，这种动物属于一类被称为内肛动物的水生动物，这种动物依附于表面，从经过的水流中滤取食物。毫无异议的最古老的内肛动物不到瘤状杯形虫年龄的三分之一，因此这些新化石将内肛动物家族的起源一直提前到所谓的寒武纪大爆发期，当时生物多样化速度极快，产生了当今看到多种动物或它们的祖先。据测量，瘤状杯形虫的高度在8至56 毫米之间，比其当今的亲属体型更大，其当今亲属的高度范围通常在0.1至7毫米之间。瘤状杯形虫跟当今的内肛动物也不尽相同，它们身上披着独特的鳞片状外衣（被称为骨片）。科学家们说：跟以往的认识不同，这种披甲动物可能在内肛动物祖先当中更为常见。