While the red panda, big cats, elephants and giraffes are found in most zoos, there's no place for the pika, the golden mole or the rat kangaroo, researchers found.
Scientists have warned that the focus on attractive species that appeal to paying visitors could have detrimental effects on conservation, with the mammal rated the least attractive, the endangered marsupial mole, not found in any zoo, 'The Independent' reported.
"Selection of species into world zoos is determined by decisions made by humans, and intelligent and beautiful animals seem to be favoured," the researchers said.
Out of 5,334 mammalian species, only 1,048 of them, or 16 per cent, were found in the world zoo collection. The team used data on brain size and attractiveness to humans to see why some species were being left out in the cold.
More From This Section
The researchers rated the 123 mammal families for attractiveness, with the red panda, big cats, giraffes, elephants and bears coming out on top.
However, researchers warn that the proportion of threatened species is increasing rapidly, leaving only few species safe from a possible extinction.