Albany Museum and Geology Department, Rhodes University, P.O. Box 94, Makhanda/Grahamstown, South Africa.
South African Institute for Aquatic Biodiversity (SAIAB), Private Bag 1015, Makhanda/Grahamstown, South Africa.
Biol Rev Camb Philos Soc. 2020 Aug;95(4):865-888. doi: 10.1111/brv.12590. Epub 2020 Feb 14.
The Waterloo Farm lagerstätte in South Africa provides a uniquely well-preserved record of a Latest Devonian estuarine ecosystem. Ecological evidence from it is reviewed, contextualised, and compared with that available from the analogous Swartvlei estuarine lake, with a particular emphasis on their piscean inhabitants. Although the taxonomic affinities of the estuarine species are temporally very different, the overall patterns of utilisation prove to be remarkably congruent, with similar trophic structures. Significantly, both systems show evidence of widespread use of estuaries as fish nurseries by both resident and marine migrant taxa. Holocene estuaries are almost exclusively utilised by actinopterygians which are overwhelmingly dominated by oviparous species. Complex strategies are utilised by estuarine resident species to avoid exposure of eggs to environmental stresses that characterize these systems. By contrast, many of the groups utilising Devonian estuaries were likely live bearers, potentially allowing them to avoid the challenges faced by oviparous taxa. This may have contributed to dominance of these systems by non-actinoptergians prior to the End Devonian Mass Extinction. The association of early aquatic tetrapods at Waterloo Farm with a fish nursery environment is consistent with findings from North America, Belgium and Russia, and may be implied by the estuarine settings of a number of other Devonian tetrapods. Tetrapods apparently replace their sister group, the elpistostegids, in estuaries with both groups having been postulated to be adaptated to shallow water habitats where they could access small piscean prey. Correlation of tetrapods (and elpistostegids) with fish nursery areas in the Late Devonian lends strong support to this hypothesis, suggesting that adaptations permitting improved access to the abundant juvenile fish within the littoral zone of estuarine lakes and continental water bodies may have been pivotal in the evolution of tetrapods.
南非滑铁卢农场的拉格斯层提供了一个独一无二的晚泥盆世河口生态系统的保存完好记录。本文回顾、分析并比较了来自类似的斯瓦特弗里特河口湖的生态证据，特别强调了它们的鱼类居民。尽管河口物种的分类亲缘关系在时间上非常不同，但总体利用模式被证明是惊人地一致，具有相似的营养结构。重要的是，这两个系统都有证据表明，居住的和海洋迁徙的分类群都广泛地将河口用作鱼类育幼所。全新世河口几乎完全被肉鳍鱼类利用，而这些鱼类绝大多数是产卵物种。河口定居物种利用复杂的策略来避免将卵暴露在这些系统特征的环境压力下。相比之下，许多利用泥盆纪河口的群体可能是胎生的，这可能使它们避免了产卵类群所面临的挑战。这可能导致在晚泥盆世大灭绝之前，非肉鳍鱼类在这些系统中占据主导地位。在滑铁卢农场发现的早期水生四足动物与鱼类育幼环境的关联与来自北美的发现一致，比利时和俄罗斯，并且可能暗示了一些其他泥盆纪四足动物的河口环境。四足动物显然取代了它们的姐妹群，即肉鳍鱼类，这两个群体都被假设适应了浅水环境，在那里它们可以捕食小鱼。晚泥盆世四足动物（和肉鳍鱼类）与鱼类育幼区的相关性强烈支持这一假说，表明允许更好地进入河口湖泊和大陆水体滨岸带丰富的幼年鱼类的适应可能是四足动物进化的关键。
