Department of Geology and Geophysics, Yale University, New Haven, CT, USA.
Geobiology. 2011 Jan;9(1):24-33. doi: 10.1111/j.1472-4669.2010.00259.x. Epub 2010 Nov 2.
The mid-Ediacaran Mistaken Point biota of Newfoundland represents the first morphologically complex organisms in the fossil record. At the classic Mistaken Point localities the biota is dominated by the enigmatic group of "fractally" branching organisms called rangeomorphs. One of the few exceptions to the rangeomorph body plan is the fossil Thectardis avalonensis, which has been reconstructed as an upright, open cone with its apex in the sediment. No biological affinity has been suggested for this fossil, but here we show that its body plan is consistent with the hydrodynamics of the sponge water-canal system. Further, given the habitat of Thectardis beneath the photic zone, and the apparent absence of an archenteron, movement, or a fractally designed body plan, we suggest that it is a sponge. The recognition of sponges in the Mistaken Point biota provides some of the earliest body fossil evidence for this group, which must have ranged through the Ediacaran based on biomarkers, molecular clocks, and their position on the metazoan tree of life, in spite of their sparse macroscopic fossil record. Should our interpretation be correct, it would imply that the paleoecology of the Mistaken Point biota was dominated by sponges and rangeomorphs, organisms that are either known or hypothesized to feed in large part on dissolved organic carbon (DOC). The biology of these two clades gives insight into the structure of the Ediacaran ocean, and indicates that a non-uniformitarian mechanism delivered labile DOC to the Mistaken Point seafloor.
纽芬兰的中埃迪卡拉纪米斯特克角生物群代表了化石记录中最早出现的形态复杂的生物。在经典的米斯特克角化石产地，生物群主要由神秘的“分形”分支生物群——范围形态生物所主导。范围形态生物的身体结构很少有例外，其中之一就是化石 Thectardis avalonensis，它被重建为一个直立的、开放的锥体，顶点在沉积物中。这个化石没有被认为与任何生物有关，但在这里我们表明，它的身体结构与海绵水通道系统的流体动力学一致。此外，考虑到 Thectardis 生活在光区下方，而且似乎没有原肠胚、运动或分形设计的身体结构，我们推测它是一种海绵。在米斯特克角生物群中识别出海绵为这个群体提供了最早的身体化石证据之一，尽管它们在宏观化石记录中很少见，但根据生物标志物、分子钟以及它们在后生动物生命树中的位置，它们一定在埃迪卡拉纪中广泛存在。如果我们的解释是正确的，这将意味着米斯特克角生物群的古生态学主要由海绵和范围形态生物主导，这些生物要么已知，要么假设主要以溶解有机碳（DOC）为食。这两个分支的生物学为埃迪卡拉纪海洋的结构提供了深入的了解，并表明一种非均变机制将不稳定的 DOC 输送到米斯特克角海底。
