We know the first cichlids appeared some 130 million years ago. Halfway through the history of cichlids, about 65 million years ago, as Gondwana was breaking up, a more advanced cichlid appeared resembling Heterochromis and Hemichromis of Africa.
While this Heteroehromis-Ukc fish was spreading over this large land mass, a giant crack was developing in the tectonic plate below, splitting it in two. As magma rose up, it pushed the plates apart and the land mass began breaking up, one side drifting eastward and the other westward. Between them, the Antarctic Ocean poured into the breach and the South Atlantic Ocean was born, separating the newly born continents of Africa and America. The primitive Hetcrochromis-Ukv cichlid was now broken into two populations that would forever be separated.
As those land masses grew farther apart, other changes occurred. The ocean enlarged, and that early cichlid gave rise to new types.
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In the west, constant rainfall led to the development of great rivers. Here, Africa would see the modern Hemichromis (jewelfish) and similar ciehlids (Pelvicochromis), Lumprologus, and so on evolving within the rivers. Parenting gave ciehlids greaL advantages over other fishes that abandoned their eggs or fry, and ciehlids spread into many habitats.
Discus J'ish lire closely related In iiitiselfisli.
In northeastern Africa, something even more dramatic began to happen. Rainy years were intermittent, alternating with years of drought. Lakes became refuges for fishes to survive periods of decreased rainfall. Here, mouthbrooders, similar to Tilapio, evolved in response to fluctuating water levels. Again these cichlids had the advantage of being parenting fishes, able to move their eggs and young to safe locations as water levels fluctuated. Soon they were doing this irrespective of water levels. It was to be a fortuitous adaptation, for the worst was yet to come.
Soon the weakened plate below began to break apart and east Africa began breaking into subplates. As the split increased, Africa continued long-term climatic changes of drought alternating with excessive rainfall and flooding. As the land above the plates ripped apart, rain and rivers poured into the gouges in the Earth's crust to form the deep lakes known today as the Great Rift Valley lakes (Lakes Albert, Edward, Kivu, Malawi, and Tanganyika). A broad, flat area between two lines of the rift also became massive, shallow Lake Victoria.
During each period of drought, the giant lakes fragmented into isolated smaller lakes. Within each of these smaller lakes, the isolated Tilapia- and Haplochromis-like cichlid populations continued to change, adapting to the major foods, their teeth becoming modified for scraping algae (if that was the major food), plucking insects off the bottom or I he top, attacking other fishes, or even mimicking other fishes for either protection or predation. The fluctuating water levels reinforced mouthbrood-ing as the most successful adaptation.
When the rains came again, the smaller lakes were flooded and reconnected. And the newer fish were different from the ones that had been isolated before. Over thousands of years of drought, flood, and the continued rifting of east Africa, the lake cichlids evolved at a spectacular pace compared to the cichlids of the central African rivers.
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