The late Cenozoic Viviparidae (Mollusca, Gastropoda) of the Albertine Rift Valley (Uganda—Congo)
The late Cenozoic Viviparidae (Mollusca, Gastropoda) of the Albertine Rift Valley (Uganda—Congo)
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艾伯丁裂谷（乌干达-刚果）的新生代晚期胎生科（软体动物、腹足纲）
作者：
D. van Damme;M. Pickford
在晚新生代裂谷前时代，Bellamya属可能仅产于东非，而在刚果盆地出现了Neothauma属和Kaya属(这里描述的一个新属)。在上新世，卡亚灭绝了，新陶玛成为坦噶尼喀湖的遗迹。上新世期间或之后形成的所有非洲裂谷湖泊都被贝拉米亚人殖民，并演变为湖泊特有物种。贝拉米亚的贝壳形态的变化，例如作为对捕食者的保护作用的装饰，在时间和空间上是适度的和重复的。在最初的适应之后，停滞不前，没有迹象表明该属的猎物和捕食者之间存在军备竞赛。在上新世之前形成的西部裂谷湖泊中，即坦噶尼喀湖和古奥拉克Obweruka湖，Neothauma而不是Bellamya是殖民者。最初，在坦噶尼喀湖和在它存在的最初400万年里，这个属也出现了形态惰性，尽管从一开始这个湖就含有丰富的高度专业化的软体动物鱼类。大约4.5 Ma时，奥布维鲁卡盆地发生了一次大灭绝事件，导致50%的软体动物物种灭绝，但没有软体动物物种灭绝。在这些小蜂中，只有一种存活了下来，它们的种群孤立，数量急剧减少。在这场危机之后，立即发生了一场耳甲量子变化，幸存的血统变成了一个装饰精美的海藻形体。这种戏剧性的形态变化被认为是由于捕食者对孤立的小猎物种群的集中选择。紧随其后的是一个辐射事件，产生了更强烈的装饰性形式。与在其他湖泊中可以观察到的适度和重复的进化模式相比，Obwerukan Neothauma发生的形态变化提供了一个真实或量子进化变化的例子，并为它可能是如何发生的提供了证据。阿尔伯丁盆地淡水软体动物的化石记录，由于其持续时间(约1200万年)、相对较高的分辨率(50万-100万年)和合理的年代地层框架，是了解宏观演化速度和模式的独特资源。
During late Cenozoic pre-rift times the viviparid genus Bellamya was probably confined to eastern Africa while in the Congo Basin occurred the genera Neothauma and Kaya (a new genus described herein). During the Pliocene, Kaya became extinct and Neothauma became a relict in Lake Tanganyika. All African rift lakes formed during or after the Pliocene were colonised by populations of Bellamya, which evolved into lacustrine endemics. The changes in shell morphology in Bellamya, such as ornamentation functioning as protection against predators, are modest and repetitive in time and space. After the initial adaptations stasis followed, and there is no indication of an arms race between prey and predator in this genus. In the lakes of the western rift that were formed prior to the Pliocene, namely Lake Tanganyika and Palaeolake Obweruka, Neothauma instead of Bellamya was the coloniser. Initially morphological inertia also occurred in this genus both in Tanganyika and, during the first four million years of its existence, in Palaeolake Obweruka, although from the outset this lake contained abundant highly specialised molluscivorous fishes. About 4.5 Ma a major extinction event occurred in the Obweruka Basin which led to the extermination of 50% of the molluscan species but none of the molluscivores. Among the viviparids, only one of the Neothauma species survived, its populations isolated and highly reduced in numbers. Immediately after this crisis a conchological quantum change occurred, the surviving lineage changing into a strongly ornamented thalassoid form. The dramatic morphological change is deemed to have been due to focussed selection by the predators on isolated and small prey populations. A radiative event immediately followed, producing still more strongly ornamented forms. The morphological changes that occurred in the Obwerukan Neothauma, in comparison to the modest and repeated patterns of evolution that can be observed in viviparids from other lakes, provides an example of true or quantum evolutionary change and yields evidence as to how it may have occurred. The fossil record of the fresh water molluscs of the Albertine Basin, thanks to its duration (ca. 12 million years), its relatively fine resolution (0.5–1.0 million years) and its sound chronostratigraphic framework, is a unique resource for understanding the tempo and mode of macroevolution.