The late Cenozoic ampullariidae (mollusca, gastropoda) of the Albertine Rift Valley (Uganda-Zaire)
The late Cenozoic ampullariidae (mollusca, gastropoda) of the Albertine Rift Valley (Uganda-Zaire)
复制标题
艾伯丁裂谷（乌干达-扎伊尔）的新生代晚期 ampullariidae（软体动物，腹足动物）
作者：
D. Damme;M. Pickford
艾伯丁裂谷(乌干达-扎伊尔)含有巨大的晚新生代沉积序列。它们沉积在一个广泛的裂谷湖Obweruka湖中，该湖存在于约8 Ma至2.5 Ma之间，在大小和深度上与现在的L.Tanganyik.相当。这些湖沉积中的许多淡水软体动物以其异常的贝壳形态、极端的装饰性和一般的形状为特征，使它们与海洋物种相似。这种在淡水软体动物中罕见的趋同被称为海生型和极端纹饰，在海洋和淡水软体动物中被认为是捕食者/捕食者共同进化的渐进过程的结果。本文从分类上描述了壶腹科Lanistes属和Pila属的艾伯丁代表，其中大多数是科学上新发现的，并根据无型特征给出了它们的系统发育关系。此外，还重建了盆地内淡水钉螺的演化史，在裂谷湖前环境中出现了3种拉尼斯特螺类，没有特殊的贝壳适应捕食能力。在裂谷湖形成后，其中两个在新的湖泊生态空间殖民，改变了形态和辐射。这3条衍生线对捕食表现出较小的适应性。在大约6 Ma左右优势种群灭绝后，唯一幸存的湖相羊群突然辐射，祖先系延续到3个新的子系旁边。这第二个形态变化是壮观的，因为它产生了具有明显海绵体特征的贝壳。在4.5 Ma左右的一次灾难性事件中，奥布维鲁卡的所有兰尼斯特物种都灭绝了。在这一事件之后，Pila属的种群在湖泊栖息地定居，其衍生形式也显示出显著的地中海类群特征。毫无疑问，从地质学上讲，这种强烈的形态变化发生在很短的时间内。因此，软体动物的形态变化程度似乎与时间无关。在突如其来的辐射后，所有谱系在形态上保持稳定，直到大约1 Ma后灭绝。这一模式对应于间断均衡模型。其他类群(小蜂、小蜂)则表现出更渐进的变化。
The Albertine Rift Valley (Uganda-Zaire) contains vast sedimentary sequences of late Cenozoic age. They were deposited in an extensive riftlake, Lake Obweruka, which existed from c. 8 Ma to 2.5 Ma and was comparable in size and depth to the present L. Tanganyika.Many freshwater molluscs that occur in these lacustrine deposits are characterised by their aberrant shell morphology, their extreme ornamentation and general form, making them resemble marine species. This convergence, rare in freshwater molluscs, is called thalassoidism and extreme ornamentation in marine as well as in freshwater molluscs is considered to be the result of a gradual process of prey/predator coevolution.In the present paper the Albertine representants of the ampullariid genera Lanistes and Pila, most of which are new to science, are taxonomically described and their phylogenetic relation, based upon apomorphic characters, is given. In addition the evolutionary history of these freshwater snails in the basin has been reconstructed.In the pre-riftlake environment 3 species of Lanistes occurred, with no special shell adaptations against predation. After the formation of a riftlake, 2 of these, colonising the new lacustrine ecospace, changed morphologically and radiated. The 3 derived lines show minor adaptations against predation. After the extinction of the dominant Lanistes species group around 6 Ma, the sole surviving lacustrine Lanistes suddenly radiates, the ancestral line persisting next to the 3 new daughter lines. This second morphological shift is spectacular as it produces shells with distinct thalassoid features. All the Lanistes species of L. Obweruka became extinct during a cataclysmic event around 4.5 Ma. Populations of the genus Pila colonised lacustrine habitats after this event, the derived form also showing striking thalassoid characters. There is no doubt that the intense morphological change occurred during a brief period, geologically speaking. The degree of morphological change in molluscs appears hence not to be linked with time. After the sudden radiation all lineages remain morphologically stable until they became extinct c. 1 Ma later. This pattern corresponds to the punctuated equilibrium model. Other groups (viviparids, thiarids) show more gradual changes.