At around 12.5 million years old, the fossil is the oldest known representative of the Tribe Oreochromini.
Image credits Stefanie B. R. Penk et al., 2019, Nature.
Research led by members from the GeoBio-Center at Ludwig-Maximilians-Universitaet (LMU) in Munich has identified an ancient fish related to the tilapia. They christened it Oreochromimos kabchorensis.
Old fry
“Cichlid diversification in East Africa has become a central paradigm in evolutionary biology. As a consequence, dating the onset of the process and understanding the mechanisms that drive it are issues of great interest to evolutionary biologists and paleobiologists,” says LMU paleontologist Professor Bettina Reichenbacher, who is also a member of the GeoBio-Center at LMU.
Cichlids (Cichlidae) are a group of small to medium-sized fish that are native to (and plentiful in) freshwater habitats in the tropics. They’re quite diverse, both in morphology and behaviors, exhibiting many patterns of parental care such as mouthbrooding. Some cichlid species (most notably members of the genus Tilapia) are quite delicious, which makes them popular and of economic value.
Africa is currently home to over 1100 species of cichlids, and the Great Lakes in East Africa’s Rift Valley (Lakes Tanganyika, Malawi and Victoria) has served as a hotbed of evolution and diversification for the group. Fossils in this area are often the only direct evidence paleontologists can use to trace back the evolutionary history of this group through time, the authors report — however, the search for cichlid fossils in the area has proven to be arduous and time-consuming. So far, only about 20 African fossil species of cichlids have been formally described.
The team, led by Bettina Reichenbacher, a Professor of Palaeontology at LMU, describes one new such fossil cichlid discovered in Central Kenya, assigned to the genus Oreochromimos. The name derives from the fact that the specimens show similarities to members of the Tribe Oreochromini (‘mimos’, means ‘mimic’), which are widely distributed in Africa today.
Image credits B. R. Penk et al., 2019, Nature.
“Determining whether or not the fossils could be assigned to any of the extant cichlid lineages was particularly challenging,” says Stefanie Penk, first author of the study and a doctoral student in Reichenbacher’s group. “The architecture of the skeleton in cichlids is pretty conservative. All of them have a similar basic form, which undergoes very little change during speciation.”
In collaboration with Dr. Ulrich K. Schliewen, co-author of the new paper, Curator of Fishes at the Bavarian State Collection for Zoology in Munich (SNSB-ZSM), the team used the ‘best-fit approach’ to classify the fossil specimen. This process entails comparing the fossil material with all modern lineages of cichlids, and was only feasible thanks to Schliewen’s knowledge and the range of comparative material represented in the collection under his care — the strategy succeeded.
The Oreochromimos specimens are about 12.5 million years old, which makes this genus the oldest known fossil representatives of the tribe Oreochromini. This makes it the oldest fossil in the lineage that gave rise to today’s African cichlids and to the East African Cichlid Radiation in the Great Lakes of the Rift Valley
It therefore qualifies as the oldest fossil clade yet assigned to the Haplotilapiini, the lineage which gave rise not only to most of the species that constitute the present-day diversity of African cichlids, but also to the East African Cichlid Radiation in the Great Lakes of the Rift Valley. With their use of an innovative approach to comparative systematics, the authors of the new study have provided a basis for the taxonomic assignment of future finds of fossil cichlid material. “With the aid of this dataset, it will be possible to classify fossil cichlids much more reliably than before and thus to shed new light on their evolutionary history,” says Bettina Reichenbacher.
The Oreochromimos specimens are about 12.5 million years old, which makes this genus the oldest known fossil representative of the Tribe Oreochromini.
The paper “New fossil cichlid from the middle Miocene of East Africa revealed as oldest known member of the Oreochromini” has been published in the journal Nature.