Pharyngeal jaws helped 1,760 cichlid species bloom
Cichlids form one of the largest vertebrate families, with at least 1,760 described species spanning thumb-length shell-dwellers to meter-long predators. All guard or mouthbrood young. African Great Lake radiations rode rift-lake level swings over the past tens of millions of years.
Only the carp family has more described species, and the true count may reach 2,000 to 3,000 because new ones turn up every year. Cichlids live natively in the American tropics, Africa and Madagascar, the Levant, southern Iran and southern India, and they include more endangered species than any other vertebrate family, most of them haplochromines. Tilapia feed millions, Cichla species draw anglers, and angelfish, oscars and discus fill aquariums, though escaped cichlids have become pests in many places.
Their single defining trait is a fused lower throat bone bearing teeth. Worked by its own muscles, this pharyngeal jaw processes food while the ordinary jaws grab it, a division of labour thought to explain their huge dietary range. Sizes run from a 2.5-centimetre shell-dweller to predators approaching a metre, and shapes from disc-flat angelfish to pencil-thin forms. Every species guards its eggs and young or broods them in the mouth.
The African Great Lakes are the showcase. Rifting some 20 to 25 million years ago opened the basins; Tanganyika, the oldest, formed about 12 to 9 million years ago. Sediment cores from Lake Malawi record at least 24 drops of 200 metres and 14 of 400 metres over 1.3 million years. Low water stranded populations apart, and high water reunited them to interbreed, a cycle that fuelled explosive speciation.
Their scattered range once suggested an ancient Gondwanan origin, but molecular clocks now date the family only to the Late Cretaceous, implying ocean crossings no one fully understands. Fossils appear on both sides of the Atlantic in the Eocene, about 48 million years ago in Argentina and 46 million in Tanzania.
Source: Cichlid
