BUOYANCY MECHANISMS LIMIT PRESERVATION OF COLEOID CEPHALOPOD SOFT TISSUES IN MESOZOIC LAGERSTATTEN
BUOYANCY MECHANISMS LIMIT PRESERVATION OF COLEOID CEPHALOPOD SOFT TISSUES IN MESOZOIC LAGERSTATTEN
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DOI：
10.1111/pala.12267
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发表时间：
2017-01-01
期刊：
影响因子：
2.6
通讯作者：
Vinther, Jakob
中科院分区：
文献类型：
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作者：
Clements, Thomas;Colleary, Caitlin;Vinther, Jakob
鞘状头足类以壳内化为特征，分为十臂十足目(鱿鱼和墨鱼)和八臂食足目(章鱼和吸血乌贼)。它们拥有丰富的化石记录，主要是它们拥有的有限的生物矿化骨骼元素：臂钩、雕像、口器(口腔质量)和内壳(剑骨或笔)，尽管在世界各地的几个Lagerstatten中都发现了保存精美的软组织角突。最近的研究表明，尽管现存的十臂纲化石与化石样本在形态上存在相似之处，但目前还没有已知的十臂纲化石样本。然而，分子时钟数据和系统发育分类表明，它们应该存在于盛产吸血鬼足类软组织化石的Lagerstatten(即黎巴嫩白垩纪的Hakel和Hadjoula Lagerstatten)。我们认为，迄今为止未知的丝状偏向与不同方法的浮力控制有关，限制了保藏潜力。负浮力和中性浮力的十臂足纲动物都使用化学浮力控制(氨)，而吸血鬼足类则不使用。在有利于特殊保存的环境中快速掩埋的情况下，氨极大地降低了十臂虫身体产生自生磷酸钙置换所需的pH的能力，限制了其保存潜力。此外，更大的表面积和相对脆弱的真皮进一步降低了石化的可能性。这种丝状偏向可能是导致其他头足类动物如菊科动物缺乏保存的不稳定软组织的原因之一。
Coleoid cephalopods are characterized by internalization of their shell, and are divided into the ten-armed Decabrachia (squids and cuttlefish) and the eight-armed Vampyropoda (octopuses and vampire squid). They have a rich fossil record predominantly of the limited biomineralized skeletal elements they possess: arm hooks, statoliths, mouthparts (the buccal mass) and internal shell (gladius or pen), although exquisitely preserved soft tissue coleoids are known from several Lagerstatten worldwide. Recent studies have shown that although morphological similarities between extant decabra-chian gladii and fossil examples exist, no known examples of fossil decabrachians are currently known. However, molecular clock data and phylogenetic bracketing suggest that they should be present in Lagerstatten that are rich in vampyropod soft tissue fossils (i.e. Hakel and Hadjoula Lagerstatten, Cretaceous, Lebanon). We propose that a hitherto unknown taphonomic bias pertaining to the differing methods of buoyancy control within coleoid groups limits preservation potential. Both negatively and neutrally buoyant decabrachians use chemical buoyancy control (ammonia) whereas vampyropods do not. In the event of rapid burial in an environment conducive to exceptional preservation, ammonia dramatically decreases the ability of the decabrachian carcass to generate the required pH for authigenic calcium phosphate replacement, limiting its preservation potential. Moreover, the greater surface area and comparatively fragile dermis further decrease the potential for fossilization. This taphonomic bias may have contributed to the lack of preserved labile soft-tissues in other cephalopods groups such as the ammonoids.