镰鳍鲨属

镰鳍鲨属学名Falcatus)为已灭绝的镰鳍鲨科英语Falcatidae软骨鱼,生存于石炭纪早期,化石发现于美国蒙大拿州熊谷石灰岩矿床英语Bear Gulch Limestone

镰鳍鲨属
化石时期:335–318 Ma
维宪期 - 晚谢尔普霍夫期
镰鳍鲨化石,发现于奥地利维也纳
科学分类 编辑
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
  • 镰鳍镰鳍鲨 Falcatus falcatus

描述

 
雌性(上)与雄性(下)镰鳍鲨复原图
 
雄性镰鳍鲨化石,发现于美国蒙大拿州

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,例如侏儒乌鲨英语Pygmy lanternshark[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英语St. Louis Limestone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奥扎克鲨属英语Ozarcus[4]以及白垩纪奥地利白垩拟裂齿鲨属[5]

 
与镰鳍鲨生存于同一时期的胸脊鲨属物种

古环境学

熊谷石灰岩矿床位于美国蒙大拿州大雪山英语Big Snowy Mountains,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英语Agassizodus利斯塔克鲨属[10]宫齿鲛属[11]条鳍鱼总纲迪斯科锯鱼属英语Discoserra[12]副鳗鳕属英语Paratarrasius[13]肉鳍鱼总纲吮虾鱼属英语Caridosuctor[14]Strepsodus英语Strepsodus[15],以及七鳃鳗亚纲哈迪斯蒂鳗属,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]头胸足类英语ProsomapodaAnderella英语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刺胞动物门的方形遗骸[20]软体动物门鹦鹉螺亚纲Tylonautilus英语Tylonautilus[21]、壳上附着有形似马尾藻褐藻的双壳纲莺蛤目物种[22]腕足动物门长身贝目英语Productida物种[23]Paleolimulus英语Paleolimulus[24]叶虾亚纲英语Phyllocarida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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