A huge wetland (the ‘Pebas system’) covered western Amazonia during the Miocene, hosting a highly diverse and endemic aquatic fauna. One of the most contentious issues concerns the existence, potential pathways and effects of marine incursions on this ecosystem. Palaeontological evidences (body fossils) are rare. The finding of a new, presumably marine ostracod species (Pellucistoma curupira sp. nov.) in the upper middle Miocene Solimões Formation initiated a taxonomic, ecological and biogeographical review of the genus Pellucistoma. We demonstrate that this marine (sublittoral, euhaline), subtropical–tropical taxon is biogeographically confined to the Americas. The biogeographical distribution of Pellucistoma largely depends on geographical, thermal and osmotic barriers (e.g. land bridges, deep and/or cold waters, sea currents, salinity). We assume an Oligocene/early Miocene, Caribbean origin for Pellucistoma and outline the dispersal of hitherto known species up to the Holocene. Pellucistoma curupira sp. nov. is dwarfed in comparison to all other species of this genus and extremely thin-shelled. This is probably related to poorly oxygenated waters and, in particular, to strongly reduced salinity. The associated ostracod fauna (dominated by the eurypotent Cyprideis and a few, also stunted ostracods of possibly marine ancestry) supports this claim. Geochemical analyses (δ¹⁸O, δ¹³C) on co-occurring ostracod valves (Cyprideis spp.) yielded very light values, indicative of a freshwater setting. These observations point to a successful adaptation of P. curupira sp. nov. to freshwater conditions and therefore do not signify the presence of marine water. Pellucistoma curupira sp. nov. shows closest affinities to Caribbean species. We hypothesize that Pellucistoma reached northern South America (Llanos Basin) during marine incursions in the early Miocene. While larger animals of marine origin (e.g. fishes, dolphins, manatees) migrated actively into the Pebas wetland via fluvial connections, small biota (e.g. P. curupira sp. nov.) were phoretically freighted and developed freshwater tolerance over long timescales.

http://zoobank.org/urn:lsid:zoobank.org:pub:886C6476-393D-4323-8C0E-06BB8BD02FD9

中新世期间，亚马逊河西部有一片巨大的湿地（“Pebas 系统”），栖息着高度多样化和特有的水生动物群。最具争议的问题之一是海洋入侵对该生态系统的存在、潜在途径和影响。古生物学证据（身体化石）很少见。在中新世中上层 Solimões 组发现了一种新的可能是海洋介形虫物种 ( Pellucistoma curupira sp. nov.)，这引发了对Pellucistoma属的分类学、生态学和生物地理学回顾。我们证明了这种海洋（亚沿海，真盐），亚热带 - 热带分类群在生物地理上仅限于美洲。Pellucistoma的生物地理分布很大程度上取决于地理、热和渗透屏障（例如陆桥、深水和/或冷水、海流、盐度）。我们假设Pellucistoma起源于加勒比海的渐新世/早中新世，并概述了迄今为止已知物种到全新世的分布。Pellucistoma curupira sp。十一月 与该属的所有其他物种相比，它是相形见绌的，而且壳非常薄。这可能与含氧量低的水有关，特别是与盐度显着降低有关。相关的介形类动物群（主要是多能的 Cyprideis和一些可能具有海洋血统的发育不良的介形类动物）支持这一说法。地球化学分析（δ ¹⁸ O、δ ¹³C）在同时出现的介形阀（Cyprideis spp.）上产生非常轻的值，表明淡水环境。这些观察结果表明P. curupira sp的成功适应。十一月 淡水条件，因此并不表示海水的存在。Pellucistoma curupira sp。十一月 显示与加勒比物种最接近的亲缘关系。我们假设Pellucistoma在早中新世的海洋入侵期间到达南美洲北部（Llanos 盆地）。虽然较大的海洋动物（例如鱼类、海豚、海牛）通过河流连接积极迁移到佩巴斯湿地，但小型生物群（例如P. curupirasp。nov.) 被泳装运输，并在很长一段时间内发展出对淡水的耐受性。

http://zoobank.org/urn:lsid:zoobank.org:pub:886C6476-393D-4323-8C0E-06BB8BD02FD9