New data on the Late Miocene chondrichthyans from the Western Mediterranean region (Alcoy Basin, Eastern Spain)

The Mediterranean Basin has been subjected to important geological and paleogeographic events that have shaped the evolution of the faunal assemblages that inhabit it. Two main events can be highlighted, the closure of its eastern margin by the <i>Gomphotherium</i> Land Bridge, and the temporal closure of the connection to the Atlantic Basin during the Messinian Salinity Crisis. These two events shaped the diversity of the chondrichthyan assemblages of the Mio–Pliocene Mediterranean, and their consequences can be observed even in the modern faunal composition. To better understand the taxonomic and ecological composition of the Mediterranean chondrichthyan faunas between the aforementioned events, and how they affected their evolutionary dynamics, we have performed a complete systematic and paleoenvironmental study of the chondrichthyan assemblage recovered from various Late Miocene localities at the municipality of Alcoy Basin (Alicante, eastern Spain). Our analysis allowed us to recognize up to 20 taxa of sharks and rays recovered from Miocene deposits. In addition, we reconstruct the paleobathymetry of the El Muro fossil site, based on the estimation of the Oceanization Index for foraminifera, as well as by the elasmobranch fossil assemblage via weighted bootstrap analysis. We expect that this first description and study of the Miocene chondrichthyan taxa from this area of eastern Spain could help us create a comparative framework to compare these communities with other areas, as well as show the changes in the elasmobranch species that have inhabited the Mediterranean Basin during and after the Messinian Salinity Crisis.

地中海盆地曾经历多起塑造其本土动物群演化进程的重要地质与古地理事件。其中两大核心事件尤为关键：其一为盆地东部边缘通过铲齿象陆桥（Gomphotherium Land Bridge）完成闭合，其二为墨西拿盐度危机（Messinian Salinity Crisis）期间地中海与大西洋盆地的连接发生阶段性封闭。这两大事件深刻塑造了中新世-上新世地中海软骨鱼类（Chondrichthyan）组合的多样性，其影响甚至延续至今，可从现代动物群组成中窥见一斑。为更好地理解上述两大事件区间地中海软骨鱼类群的分类学与生态学组成，以及两大事件对其演化动态的影响，我们针对西班牙东部阿利坎特省阿尔科伊盆地（Alcoy Basin）多处晚中新世化石点产出的软骨鱼类组合，开展了全面的分类学与古环境学研究。本次分析共识别出产自中新世地层的鲨类与鳐类共计20个类群。此外，我们结合有孔虫（Foraminifera）海洋化指数（Oceanization Index）的估算结果，以及通过加权自举分析（Weighted Bootstrap Analysis）得到的板鳃类（Elasmobranch）化石组合数据，重建了埃尔穆罗（El Muro）化石点的古水深。我们期望，这项针对西班牙东部该区域中新世软骨鱼类类群的首次系统性描述与研究，能够为该区域群落与其他区域的同类群落搭建对比框架，同时揭示墨西拿盐度危机期间及之后栖息于地中海盆地的板鳃类物种的演化变迁。