New haplochromine cichlid from the upper Miocene (9–10 MYA) of Central Kenya

Abstract

Background: 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. Results: 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. Conclusions: 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.

A small cichlid species flock from the Upper Miocene (9–10 MYA) of Central Kenya

“…The present study continues our previous works on the fossil cichlid specimens from the locality Waril (Altner et al, 2017(Altner et al, , 2020. We introduce a new extinct cichlid genus and possible member of the Haplochromini, Baringochromis gen. nov., represented by three species.…”

“…The comparative skeletal material of recent species corresponds to that used in Penk et al (2019, pp. 18-19) and Altner et al (2020).…”

“…Methods concerning preparation of fossils, morphometric measurements, imaging and phylogenetic analysis follow Altner et al (2020). Measurements of the fossil specimens were normalized with reference to body length (BL) as most specimens lack a completely preserved head (BL is the distance from the posterior margin of the opercle to the posterior margin of the hypural plate).…”

“…Their good preservation documents that the ancient lake had anoxic conditions at the bottom. Two fossil cichlid taxa have been described previously: one is an extinct member of the Lake Tanganyika cichlid radiation ( Tugenchromis pickfordi), and the other is an ancient predatory species of the Haplochromini ( Warilochromis unicuspidatus) (see Altner et al, 2017Altner et al, , 2020. In addition, fossils of well-preserved insects and plant remains have been found (Pickford, 1978;Pickford et al, 2009).…”

“…Nevertheless, previous studies of fossil cichlids have considerably extended our knowledge of their ancient diversity and biogeography (Malabarba et al, 2014;Murray et al, 2017;Altner et al, 2017;Kevrekidis et al, 2019 (amongst others)). To date, 22 fossil cichlid species are known from Eocene to Pliocene sediments of Africa, Arabia and Europe, but only a few could be classified as members of extant tribes (van Couvering, 1982;Carnevale et al, 2003;Penk et al, 2019;Altner et al, 2020). This subset testifies to the presence of the tribe Oreochromini since at least the middle Miocene (Penk et al, 2019), and implies at least a late Miocene age, and perhaps even a date in the early Miocene, for the origin of the tribe Haplochromini (Altner et al, 2020).…”