镰鳍鲨属
镰鳍鲨属（学名：Falcatus）为已灭绝的镰鳍鲨科软骨鱼，生存于石炭纪早期，化石发现于美国蒙大拿州的熊谷石灰岩矿床。
镰鳍鲨属 | |
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| 镰鳍鲨化石，发现于奥地利维也纳 | |
科学分类 
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| 界： | 动物界 Animalia |
| 门： | 脊索动物门 Chordata |
| 纲： | 软骨鱼纲 Chondrichthyes |
| 目： | †西莫利鲨目 Symmoriiformes |
| 科： | †镰鳍鲨科 Falcatidae |
| 属： | †镰鳍鲨属 Falcatus Lund, 1985 |
| 种 | |
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描述
镰鳍鲨体长约25至30 cm（9.8至11.8英寸），约与现今的小型鲨鱼体型相当，例如侏儒乌鲨[1]。牠们身上最明显的特征在于背上朝头部前方弯伸出去的长鳍棘。最初发现镰鳍鲨化石时，仅有发现鳍棘，于是科学家于1883年依据发现于圣路易石灰岩矿床的鳍棘标本进行发表命名，学名为 Physonemus falcatus。然而，于1985年时，科学家于美国蒙大拿州发表了一种具有明显两性异形的软骨鱼，而部分标本背上就长有这样的长鳍棘，而这些标本均属于雄性个体（于标本上也可发现存在鳍足），也因此将镰鳍鲨移置至独立的镰鳍鲨属下[2]。
分类学
尽管镰鳍鲨外型与鲨鱼十分类似，但牠们与其他西莫利鲨目物种均是属于全头类[2]，这意味着比起鲨鱼，牠们与银鲛的关系更为紧密[3]。其他包含于镰鳍鲨科的物种包括生存于石炭纪美国阿肯色州的奥扎克鲨属[4]以及白垩纪奥地利的白垩拟裂齿鲨属[5]。
古环境学
熊谷石灰岩矿床位于美国蒙大拿州的大雪山，地层年代为石炭纪中期，在当时这个地区的环境是由半咸水及淡水的泥滩与潟湖所构成[6]。为何当地能保存那么多完整的化石，科学家提出了许多假说，其中之一为这些动物是在低含氧量的水中窒息而死的，且尸体很快地就沉入沉积物中，过程中并未遭到其他动物啃食[7]。另外一个假说则认为是豪雨造成土石流冲至下游，快速地将这些动物掩埋[8]。于当地发现的鱼类化石普遍带有膨胀的鳃，这意味着牠们可能是因窒息而死[9]。
与镰鳍鲨生存于同一时期的鱼类包括软骨鱼纲的阿格赛兹鲨属、利斯塔克鲨属[10]及宫齿鲛属[11]，条鳍鱼总纲的迪斯科锯鱼属[12]及副鳗鳕属[13]，肉鳍鱼总纲的吮虾鱼属[14]及Strepsodus[15]，以及七鳃鳗亚纲的哈迪斯蒂鳗属，是目前已知最古老的七鳃鳗[16]。
熊谷也出产了十分多样的无脊椎动物化石，包括了掠虾亚纲物种[17]、头胸足类的Anderella[18]、分类地位不明的提丰怪物属[19]、推测可能属于纽鳃樽科或刺胞动物门的方形遗骸[20]、软体动物门鹦鹉螺亚纲的Tylonautilus[21]、壳上附着有形似马尾藻褐藻的双壳纲莺蛤目物种[22]、腕足动物门的长身贝目物种[23]、Paleolimulus[24]、叶虾亚纲物种[25]、以及许多棘皮动物门物种，诸如海百合、海胆、海星、阳遂足，其中最特别的要属具有许多腕的海星 Lepidasterella montanensis[26]。
参考文献
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- ^ Coates, M., Gess, R., Finarelli, J., Criswell, K., Tietjen, K. 2016. A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes. Nature. doi: 10.1038/nature20806
- ^ Alan Pradel; John G. Maisey; Paul Tafforeau; Royal H. Mapes; Jon Mallatt. A Palaeozoic shark with osteichthyan-like branchial arches. Nature. 2014, 509 (7502): 608–611. PMID 24739974. S2CID 3504437. doi:10.1038/nature13195.
- ^ Iris Feichtinger; Andrea Engelbrecht; Alexander Lukeneder; Jürgen Kriwet. New chondrichthyans characterised by cladodont-like tooth morphologies from the Early Cretaceous of Austria, with remarks on the microstructural diversity of enameloid. Historical Biology: An International Journal of Paleobiology. 2018, 32 (6): 1–14. S2CID 92392461. doi:10.1080/08912963.2018.1539971.
- ^ Bear Gulch Limestone Fossil Lagerstätte. fossilmuseum.net. [2023-08-13]. （原始内容存档于2023-06-04）.
- ^ Grogan, Eileen D.; Lund, Richard. Soft tissue pigments of the Upper Mississippian chondrenchelyid, Harpagofututor volsellorhinus (Chondrichthyes, Holocephali) from the Bear Gulch Limestone, Montana, USA. Journal of Paleontology. 1997, 71 (2): 337–342 [2023-08-13]. ISSN 0022-3360. doi:10.1017/S002233600003924X. （原始内容存档于2023-08-12） （英语）.
- ^ Grogan, Eileen D.; Lund, Richard. The geological and biological environment of the Bear Gulch Limestone (Mississippian of Montana, USA) and a model for its deposition (PDF). Geodiversitas. 2002, 24 (2): 295–315 [2023-08-13]. （原始内容存档 (PDF)于2022-03-08）.
- ^ Hagadorn, James W. Bear Gulch: An Exceptional Upper Carboniferous Plattenkalk. Bottjer, D.J.; Etter, W.; Hagadorn, J.W.; Tang, C.M. (编). Exceptional fossil preservation; a unique view on the evolution of marine life. New York: Columbia University Press. 2002: 167–183.
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- ^ Lund, Richard. The new Actinopterygian order Guildayichthyiformes from the Lower Carboniferous of Montana (USA) (PDF). Geodiversitas. 2000, 22 (2): 171–206 [2023-08-13]. （原始内容存档 (PDF)于2022-07-18）.
- ^ Lund, Richard; Melton, William G., Jr. A new actinopterygian fish from the Mississippian Bear Gulch Limestone of Montana. Palaeontology. 1982, 25 (3): 485–498 [2023-08-13]. （原始内容存档于2023-08-12）.
- ^ Lund, Richard; Lund, Wendy. New genera and species of coelacanths from the Bear Gulch Limestone (Lower Carboniferous) of Montana (U.S.A.). Geobios. 1984, 17 (2): 237–244. ISSN 0016-6995. doi:10.1016/s0016-6995(84)80145-x.
- ^ Lund, Richard; Greenfest-Allen, Emily; Grogan, Eileen D. Ecomorphology of the Mississippian fishes of the Bear Gulch Limestone (Heath formation, Montana, USA). Environmental Biology of Fishes. 2015-02-01, 98 (2): 739–754. ISSN 1573-5133. S2CID 14850973. doi:10.1007/s10641-014-0308-x （英语）.
- ^ Janvier, Philippe; Lund, Richard. Hardistiella montanensis n. gen. et sp. (Petromyzontida) from the Lower Carboniferous of Montana, with remarks on the affinities of the lampreys. Journal of Vertebrate Paleontology. 1983, 2 (4): 407–413. ISSN 0272-4634. doi:10.1080/02724634.1983.10011943.
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