This "most singular group of finches" appeared in Charles Darwin's famous journal from the voyage of the Beagle. Darwin collected specimens which were later classified by the ornithologist John Gould, back in London.
"Darwin was amazed by the beak diversity in species that were otherwise very similar," said the new study's senior author Prof Leif Andersson, from Uppsala University in Sweden.
Only about 1.5 million years ago, these species started branching out from a common ancestor, which colonised the relatively young Galapagos archipelago - thrust from the ocean by volcanic activity.
According to Darwin's now-famous theory of natural selection, the birds rapidly adapted to the different food sources that were available in their new home, where they faced little competition from other birds. Chief among these adaptations were different beak shapes: stronger, blunter beaks for cracking tough seeds or insects