Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, U.K.; Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS81RJ, U.K.
Biol Rev Camb Philos Soc. 2014 Nov;89(4):972-1004. doi: 10.1111/brv.12090. Epub 2014 Apr 29.
Twenty candidate fossils with claim to be the oldest representative of the Phylum Porifera have been re-analysed. Three criteria are used to assess each candidate: (i) the diagnostic criteria needed to categorize sponges in the fossil record; (ii) the presence, or absence, of such diagnostic features in the putative poriferan fossils; and (iii) the age constraints for the candidate fossils. All three criteria are critical to the correct interpretation of any fossil and its placement within an evolutionary context. Our analysis shows that no Precambrian fossil candidate yet satisfies all three of these criteria to be a reliable sponge fossil. The oldest widely accepted candidate, Mongolian silica hexacts from c. 545 million years ago (Ma), are here shown to be cruciform arsenopyrite crystals. The oldest reliable sponge remains are siliceous spicules from the basal Cambrian (Protohertzina anabarica Zone) Soltanieh Formation, Iran, which are described and analysed here in detail for the first time. Extensive archaeocyathan sponge reefs emerge and radiate as late as the middle of the Fortunian Stage of the Cambrian and demonstrate a gradual assembly of their skeletal structure through this time coincident with the evolution of other metazoan groups. Since the Porifera are basal in the Metazoa, their presence within the late Proterozoic has been widely anticipated. Molecular clock calibration for the earliest Porifera and Metazoa should now be based on the Iranian hexactinellid material dated to c. 535 Ma. The earliest convincing fossil sponge remains appeared at around the time of the Precambrian-Cambrian boundary, associated with the great radiation events of that interval.
已经重新分析了 20 个候选化石，它们声称是多孔动物门最古老的代表。使用三个标准来评估每个候选者：（i）在化石记录中对海绵进行分类所需的诊断标准；（ii）假定的多孔动物化石中是否存在这些诊断特征；以及（iii）候选化石的年龄限制。这三个标准对于正确解释任何化石及其在进化背景中的位置都至关重要。我们的分析表明，没有任何前寒武纪化石候选者能够满足这三个标准，成为可靠的海绵化石。最古老的被广泛接受的候选者是来自约 5.45 亿年前的蒙古硅六方晶，它们现在被证明是十字砷铁矿晶体。最古老的可靠海绵遗迹是伊朗下寒武统（原赫茨纳巴里克区）索坦尼赫组的硅质刺，本文首次对其进行了详细描述和分析。广泛的古杯海绵礁在福提安阶的寒武纪中期出现并辐射，表明它们的骨骼结构逐渐组装，与其他后生动物群的进化同时发生。由于多孔动物在后生动物中是基础的，因此它们在前寒武纪末期的存在已被广泛预期。最早的多孔动物和后生动物的分子钟校准现在应该基于伊朗的六射海绵材料，其年代约为 5.35 亿年前。最早令人信服的化石海绵遗迹出现在前寒武纪-寒武纪边界附近，与该时期的大辐射事件有关。
