The oldest know cichlid fossils date back 45 million years and were found in Mahenge, Tanzania. The fossils are made up of different cichlids that lived in a small crater lake centrally located between modern day Lakes Victoria, Malawi and Tanganyika. The fossils are complete and well preserved and demonstrate that cichlids 45 million years ago, like the cichlids today, were able to rapidly evolve from a common ancestor to fit different the niches of their environment. More information can be found in Dr. Alison Murray's publication "The oldest fossil cichlids (Teleostei: Perciformes): indication of a 45 million-year-old species flock" (PDF).