Scarce ctenacanthiform sharks from the Mississippian of Austria with an analysis of Carboniferous elasmobranch diversity in response to climatic and environmental changes

The Carboniferous is characterized by drastic climatic and environmental fluctuations, which include multiple phases of glaciation resulting in an icehouse climate. Additionally, dynamic continental reconfigurations forced the contraction of the Rheic Ocean resulting in the closure of the Rheic–Tethyan Gateway, which precluded further faunal exchanges between the North American and Eurasian marine realms. Interestingly, cartilaginous fishes seem to be relatively immune to these drastic climatic and environmental changes. The Eurasian fossil record of Paleozoic sharks is strongly biased towards intensively sampled localities from England, Ireland, Scotland, and the Russian Platform. Here we present rare dental material from the Serpukhovian (early Carboniferous) of Austria, adding new information to the paleogeographic distribution of ctenacanthiform sharks. The new material revealed the first record of the genus <i>Saivodus</i> in Central Europe and allowed us to recognize a new species, <i>Cladodus gailensis</i> sp. nov., and a remnant of fossilized cartilage. In an attempt to identify possible linkages between climatic or environmental fluctuations on shark diversity throughout the Carboniferous, we provide a synopsis of the distribution and diversity of elasmobranchs based on primary literature. This preliminary assessment at genus level indicates two pronounced events of extinction, with the first one occurring during the latest Mississippian and the second one towards the end of the Pennsylvanian. The first extinction event distinctly correlates with the known diversity decline of other marine inhabitants and the second occurred during an unstable period of multiple phases of glaciation.

石炭纪（Carboniferous）以剧烈的气候与环境波动为典型特征，其中包含多期冰川作用，形成了冰室气候。此外，活跃的大陆重组导致Rheic洋（Rheic Ocean）收缩，最终使得Rheic-特提斯通道（Rheic–Tethyan Gateway）闭合，阻断了北美与欧亚海洋域之间后续的生物群交流。值得注意的是，软骨鱼类似乎相对不受这些剧烈气候与环境变化的影响。古生代鲨鱼的欧亚化石记录存在强烈的采样偏差，主要集中在英国、爱尔兰、苏格兰以及俄罗斯地台的高强度采样点位。本文报道了产自奥地利谢尔普霍夫期（早石炭世）的稀有齿类化石材料，为栉棘鲨类（ctenacanthiform sharks）的古地理分布提供了新的研究数据。本次发现的新材料首次记录了中欧地区的Saivodus属（Saivodus），并确立了一个新种Cladodus gailensis sp. nov.，同时还发现了一块石化软骨残体。为探究石炭纪期间气候或环境波动与鲨鱼多样性之间的潜在关联，我们基于一手文献对板鳃类（elasmobranchs）的分布与多样性进行了综述。本次属级层面的初步评估显示存在两次显著的灭绝事件：第一次发生在密西西比世末期，第二次则临近宾夕法尼亚世末期。第一次灭绝事件与已知的其他海洋生物多样性下降存在明显关联，而第二次灭绝事件则发生在多期冰川作用的不稳定时期。