The existence of melanin in extinct marine organisms helps provide clues about the environments in which they lived, Swedish researchers found.

Dark traces on the well-preserved fossilized skin from three distantly related marine reptiles -- a 55-million-year-old leatherback turtle, an 86-million-year-old mosasaur and a 190-million to 196-million-year-old ichthyosaur -- had melanin, allowing Swedish researchers to track the convergent evolution of the melanin.

Convergent evolution is the process in which organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.

Melanin is a pigment found in many animals and plays many roles, from coloration to regulating body temperature. The researchers, led by Johan Lindgren of Sweden's Lund University, said such convergence showed the important evolutionary role melanin had in determining whether such animals could live in colder parts of the world.

The findings were included in this week's edition of Nature.