The ‘living-fossil community’ of the cyrtocrinid Cyathidium foresti and the deep-sea oyster Neopycnodonte zibrowii (Azores Archipelago)
The ‘living-fossil community’ of the cyrtocrinid Cyathidium foresti and the deep-sea oyster Neopycnodonte zibrowii (Azores Archipelago)
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DOI：
10.1016/j.palaeo.2008.09.015
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
M. Wisshak;C. Neumann;J. Jakobsen;A. Freiwald
中科院分区：
文献类型：
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作者：
M. Wisshak;C. Neumann;J. Jakobsen;A. Freiwald
从陡峭的海底斜坡的南部Faial通道（亚速尔群岛），一个显着的archibenthic社区的两个“活化石”，包括长达30厘米大小的深海牡蛎Neopycnodonte zibrowii和无柄海百合Cyathidium foresti，被描述。两者都在相对稳定的环境条件下（12.3±0.25 °C和开放的海洋盐度）隐藏在420-500米水深的基岩悬突下的特别高的密度中茁壮成长。其他动物区系包括各种海绵、苔藓虫、蛇形蠕虫和大型藤壶。潜水调查表明，C. foresti和N. zibrowii不是强制性的。海百合通常会在死牡蛎和活牡蛎上定居，这为海百合提供了底物可用性和/或参与牡蛎主动摄食电流的好处。这两个物种的颠倒位置提供了保护，从背景沉积和可能的庇护，从捕食者。在死亡和部分断肢后，海百合通常会被其他牡蛎或随后的海百合世代过度生长，反映了有限的基质可用性。这两个属，以模式种Cyathidium holopus和Pycnodonte sp.为代表，在丹麦的Faxe的中丹尼世（古新世）也发现了6000多万年前的化石。与珊瑚灰岩共生的C.偶尔也会发现数量可观的全齿贝，它们要么是孤立的，要么是定居在各种基质上，比如石珊瑚、其他杯状珊瑚，以及类似于亚速尔群岛的密齿牡蛎的内表面。C.全珊瑚虫，如假浮游附着漂流木材或附着在光珊瑚礁的洞穴天花板，被拒绝，赞成解释这种协会蓬勃发展的小硬地悬崖和悬伸下的深架古环境，与最近的古环境评估提出的冷水和深水珊瑚生物礁。我们假设一个栖息地的迁移的aprotocrinids从假定的浅palaeoenvironments在晚白垩世向深陆棚设置在大年，这反映了逃避增强的捕食压力在“中生代海洋革命”。固着海百合几乎完全从浅水沃茨消失，取而代之的是移动的，往往严格夜间comatulids。Cyathidium/（Neo）pycnodonte组合不仅在白垩纪/古近纪大灭绝中幸存下来，而且在整个新生代中都幸存下来，今天可以作为“活化石群落”进行研究。
From the steep submarine slope of the southern Faial Channel (Azores Archipelago), a conspicuous archibenthic community of two ‘living fossils’, comprising the up to 30 cm sized deep-sea oyster Neopycnodonte zibrowii and the sessile cyrtocrinid Cyathidium foresti, is described. Both thrive in particularly high densities concealed underneath bedrock overhangs in 420–500 m water depth under comparatively stable environmental conditions (12.3±0.25 °C and open marine salinity). Other faunal elements include various sponges, bryozoans, serpulid worms, and large barnacles. Submersible investigations showed that the direct association of C. foresti and N. zibrowii is not obligatory. The crinoid is commonly encountered settling on dead as well as live oysters, which provide benefits for the crinoid in terms of substrate availability and/or participation in the oysters' active feeding current. The upside down position of both species provides protection from background sedimentation and possibly shelter from predators. After death and partial disarticulation, the crinoids are commonly overgrown by other oysters or subsequent crinoid generations, mirroring limited substrate availability. Both genera, represented by the type species Cyathidium holopus and Pycnodonte sp., respectively, are also found as fossils more than 60 million years old in the Middle Danian (Paleocene) of Faxe in Denmark. Associated with coral limestone, C. holopus was found occasionally in impressive numbers either isolated or settling on various substrata, such as scleractinian corals, other Cyathidium calyxes, and – analogous to the Azorean occurrence – the inner surface of pycnodontine oysters. Previous palaeohabitat models for C. holopus such as the pseudoplanktonic attachment to drifting wood or attachment to cave ceilings in a photic reef, are rejected in favour of an interpretation of this association thriving on small hardground cliffs and under overhangs in a deep-shelf palaeoenvironment, associated with the cold- and deep-water coral bioherms proposed by recent palaeoenvironment assessments. We assume a habitat-shift of the cyrtocrinids from presumable shallow palaeoenvironments in the Late Cretaceous toward a deep shelf setting in the Danian, which reflects the escape from enhanced predation pressure during the ‘Mesozoic Marine Revolution’. Sessile crinoids almost completely vanished from shallow waters and were replaced by mobile and often strictly nocturnal comatulids. The Cyathidium/(Neo)pycnodonte association did not only survive the Cretaceous/Palaeogene mass extinction, but the whole of the Cenozoic and can today be studied as a ‘living-fossil community’.