Sansom Robert S, Randle Emma, Donoghue Philip C J
Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK.
Proc Biol Sci. 2015 Feb 7;282(1800):20142245. doi: 10.1098/rspb.2014.2245.
The fossil record of early vertebrates has been influential in elucidating the evolutionary assembly of the gnathostome bodyplan. Understanding of the timing and tempo of vertebrate innovations remains, however, mired in a literal reading of the fossil record. Early jawless vertebrates (ostracoderms) exhibit restriction to shallow-water environments. The distribution of their stratigraphic occurrences therefore reflects not only flux in diversity, but also secular variation in facies representation of the rock record. Using stratigraphic, phylogenetic and palaeoenvironmental data, we assessed the veracity of the fossil records of the jawless relatives of jawed vertebrates (Osteostraci, Galeaspida, Thelodonti, Heterostraci). Non-random models of fossil recovery potential using Palaeozoic sea-level changes were used to calculate confidence intervals of clade origins. These intervals extend the timescale for possible origins into the Upper Ordovician; these estimates ameliorate the long ghost lineages inferred for Osteostraci, Galeaspida and Heterostraci, given their known stratigraphic occurrences and stem-gnathostome phylogeny. Diversity changes through the Silurian and Devonian were found to lie within the expected limits predicted from estimates of fossil record quality indicating that it is geological, rather than biological factors, that are responsible for shifts in diversity. Environmental restriction also appears to belie ostracoderm extinction and demise rather than competition with jawed vertebrates.
早期脊椎动物的化石记录在阐明有颌类动物身体结构的进化组合方面具有重要影响。然而，对于脊椎动物创新的时间和节奏的理解，仍然深陷于对化石记录的字面解读之中。早期无颌脊椎动物（甲胄鱼）局限于浅水环境。因此，它们在地层中的出现分布不仅反映了多样性的变化，还反映了岩石记录中岩相表现的长期变化。利用地层学、系统发育学和古环境数据，我们评估了有颌脊椎动物的无颌近亲（骨甲鱼类、盔甲鱼亚纲、鳍甲鱼目、异甲亚纲）化石记录的准确性。使用古生代海平面变化的化石恢复潜力非随机模型来计算类群起源的置信区间。这些区间将可能起源的时间尺度扩展到了上奥陶统；鉴于骨甲鱼类、盔甲鱼亚纲和异甲亚纲已知的地层出现情况和干群有颌类系统发育，这些估计改善了为它们推断出的长期幽灵谱系。发现志留纪和泥盆纪期间的多样性变化处于根据化石记录质量估计所预测的预期范围内，这表明是地质因素而非生物因素导致了多样性的变化。环境限制似乎也掩盖了甲胄鱼的灭绝和消亡，而不是与有颌脊椎动物的竞争。
