Department of Earth and Environmental Sciences, Paleontology and Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner-Strasse 10, 80333, Munich, DE, Germany.
Section Evertebrata Varia, SNSB - ZSM Bavarian State Collection of Zoology, Münchhausen-Strasse 21, 81247, Munich, DE, Germany.
BMC Evol Biol. 2020 Jun 5;20(1):65. doi: 10.1186/s12862-020-01602-x.
The diversification process known as the Lake Tanganyika Radiation has given rise to the most speciose clade of African cichlids. Almost all cichlid species found in the lakes Tanganyika, Malawi and Victoria, comprising a total of 12-16 tribes, belong to this clade. Strikingly, all the species in the latter two lakes are members of the tribe Haplochromini, whose origin remains unclear. The 'out of Tanganyika' hypothesis argues that the Haplochromini emerged simultaneously with other cichlid tribes and lineages in Lake Tanganyika, presumably about 5-6 million years ago (MYA), and that their presence in the lakes Malawi and Victoria and elsewhere in Africa today is due to later migrations. In contrast, the 'melting pot Tanganyika hypothesis' postulates that Haplochromini emerged in Africa prior to the formation of Lake Tanganyika, and that their divergence could have begun about 17 MYA. Haplochromine fossils could potentially resolve this debate, but such fossils are extremely rare.
Here we present a new fossil haplochromine from the upper Miocene site Waril (9-10 million years) in Central Kenya. Comparative morphology, supported by Micro-CT imaging, reveals that it bears a unique combination of characters relating to dentition, cranial bones, caudal skeleton and meristic traits. Its most prominent feature is the presence of exclusively unicuspid teeth, with canines in the outer tooth row. †Warilochromis unicuspidatus gen. et sp. nov. shares this combination of characters solely with members of the Haplochromini and its lacrimal morphology indicates a possible relation to the riverine genus Pseudocrenilabrus. Due to its fang-like dentition and non-fusiform body, †W. unicuspidatus gen. et sp. nov. might have employed either a sit-and-pursue or sit-and-wait hunting strategy, which has not been reported for any other fossil haplochromine cichlid.
The age of the fossil (9-10 MYA) is incompatible with the 'out of Tanganyika' hypothesis, which postulates that the divergence of the Haplochromini began only 5-6 MYA. The presence of this fossil in an upper Miocene palaeolake in the Central Kenya Rift, as well as its predatory lifestyle, indicate that Haplochromini were already an important component of freshwater drainages in East Africa at that time.
被称为坦噶尼喀湖辐射的多样化过程产生了最具物种多样性的非洲丽鱼科鱼类分支。在坦噶尼喀湖、马拉维湖和维多利亚湖发现的几乎所有丽鱼物种，共计 12-16 个部落，都属于这个分支。引人注目的是，后两个湖中所有的物种都是哈氏丽鱼族的成员，其起源尚不清楚。“出自坦噶尼喀湖”假说认为，哈氏丽鱼族与坦噶尼喀湖的其他丽鱼部落和谱系同时出现，大概在 5-600 万年前（MYA），而它们今天在马拉维湖和维多利亚湖以及非洲其他地方的存在是由于后来的迁徙。相比之下，“坦噶尼喀湖熔炉假说”则假设哈氏丽鱼族在坦噶尼喀湖形成之前就已经在非洲出现，它们的分化可能始于 1700 万年前。哈氏丽鱼的化石本可以解决这场争论，但这样的化石极其罕见。
本文介绍了肯尼亚中部上新世沃里尔（9-1000 万年）遗址的一种新的哈氏丽鱼化石。通过比较形态学，结合微计算机断层扫描成像，发现它具有独特的组合特征，涉及牙齿、颅骨、尾骨和可数特征。它最显著的特征是具有独特的单尖牙，在外齿列中有犬齿。†沃里尔丽鱼属，新属新种，与哈氏丽鱼族的成员仅具有这种特征组合，其泪骨形态表明与河流属拟丽鱼属可能存在某种关系。由于其狼牙状的牙齿和非梭形的身体，†沃里尔丽鱼属新属新种可能采用了坐追或坐等狩猎策略，而这种策略在任何其他化石哈氏丽鱼丽鱼中都没有报道过。
化石的年龄（9-1000 万年）与“出自坦噶尼喀湖”假说不符，该假说假设哈氏丽鱼族的分化仅始于 5-600 万年前。这种化石出现在肯尼亚裂谷中部上新世古湖，以及其捕食性的生活方式，表明哈氏丽鱼族在当时已经是东非淡水水系的重要组成部分。
