NAIROBI At least six distinct species of giraffe, the world's tallest land animal, may be in existence and some of them are critically endangered, scientists in the United States and Kenya have found.
It had previously been thought that there was only one species of giraffe ranging across Africa's golden savannahs.
"Some of these giraffe populations number only a few hundred individuals and need immediate protection," said the study's lead author, geneticist David Brown of the U.S.-based Wildlife Conservation Society.
"Lumping all giraffes into one species obscures the reality that some kinds of giraffe are on the very brink."
The most threatened potential species include the reticulated giraffe (currently Giraffa camelopardalis reticulate) in Kenya, Ethiopia and Somalia. Its population was estimated at around 27,000 until the 1990s, when poaching and conflicts slashed numbers to just 3,000 individuals.
In west and central Africa, there are thought to be only 160 Nigerian giraffes (Giraffa camelopardalis peralta) left.
But all giraffes -- which can grow up to 19ft tall and weigh 4,400lbs (2,000kg) -- were under threat, Brown said in a statement late on Friday, citing an estimated 30 percent drop in numbers over the past decade.
Classifying what are currently called sub-species as fully-fledged species would force governments and experts to re-examine steps to conserve the most at risk animals, he said.
The study is in the latest edition of BMC Biology journal.