Credit: R. BRITZ

Proc. R. Soc. B doi: 10.1098/rspb.2009.0141 (2009)

Carp-like cypriniform fishes lost their teeth millions of years ago, but a newly described species has come close to redeveloping them.

Males of the tiny Danionella dracula have a series of fang-like pieces of bone projecting from their jaws, report Ralf Britz of London's Natural History Museum and his colleagues. So far, the maximum size reported for the fish, from Myanmar, is 16.7 millimetres. Its development also appears stunted; it retains many larval body features into adulthood and lacks 44 bones or parts of bones seen in its close relative the zebrafish (Danio rerio).

Remaining mysteries include the function of the toothy projections and whether they are formed through the genetic pathway for true tooth formation, which is known to be conserved in zebrafish.