As a result the creatures have acquired a bizarre body shape, eyes that can look in different directions at once, toothless snouts for sucking in prey, and - strangest of all - male pregnancy.

Scientists who mapped the complete genome, or genetic code, of the tiger tail seahorse, Hippocampus comes, identified numerous unique features that had evolved within a short time.

Both the loss and duplication of genes contributed to the rapid changes, said the researchers led by Professor Byrappa Venkatesh from the Agency for Science Technology and Research (ASTAR) in Singapore.

The seahorse owes its unusual appearance to bony plates that reinforce its body and allow it to stand and swim vertically.

A key feature is the absence of pelvic fins, which share the same evolutionary origins as human legs.

The scientists found that an important limb gene called tbx4, common to nearly all vertebrates, was missing from the seahorse genome.

When the same gene was deactivated in zebrafish, the fish also lost their pelvic fins.

Gene duplication, that can give genes entirely new functions, was thought to be how male pregnancy developed in the seahorse.

Males carry developing embryos in a "brood pouch" from which the offspring eventually hatch.

Regulatory elements of DNA that control gene activity are also believed to have played a key role in shaping the seahorse.

Loss of regulatory elements may have taken the brakes off evolution and allowed the seahorse skeleton to be so greatly modified.

Writing in the journal Nature, the authors concluded: "Our genome-wide analysis highlights several aspects that may have contributed to the highly specialised body plan and male pregnancy of seahorses.

"These include a higher protein and nucleotide evolutionary rate, loss of genes and expansion of gene families, with duplicated genes exhibiting new expression patterns, and loss of a selection of potential ... regulatory elements."