Current estimates predict lions and elephants could be extinct by 2025, tigers by 2035, rhinos by 2040, but charity Care For The Wild has now said all four could vanish by 2035.
The charity, at the launch of its Tooth Fairy campaign, said that from its own on-the-ground experience and reports from conservation experts, these species could be extinct in the wild in 22 years' time.
Chris Pitt, campaign and communications manager, said: "There are so many figures out there that we are trying to take a realistic view of extinction rates.
"Poaching is a serious problem and elephant figures are falling fast - in some parts of Africa elephants are now nonexistent - so we are trying to raise awareness of this issue and raise money to help with protection patrols."
It claims that, to date this year, more rhinos will have been killed in South Africa than in 2012 as a whole - an increase of 30%.
There are currently around 35,000 rhinos in Africa but the current birth rate and poaching could lead to their demise as soon as 2025.
Estimates for elephant deaths vary across Africa due to the nature of poaching, and war and poverty in countries elephants are native to.
However, estimates used by Care For The Wild show more than 25,000 are being killed each year, with Africa having lost 90% of its elephants in the past 50 years.
The number of tigers in the wild has fallen from one million a century ago to estimates from the 2009 Kathmandu Global Tiger Workshop that there are only 3200 tigers left in the wild.
In west and central Africa, lions are classified as "endangered", with Kenya losing around 100 wild lions every year due to human contact.
Money raised from the Tooth Fairy campaign will go to helping protect the animals in order to save them for future generations.
Pitt added: "It is vitally important that we protect these animals. They are part of us - we read stories about them as children, we watch them in films - and just because they are far away does not mean that they don't matter.
"I do not want to be part of the generation that just lets them go. I do not want to have to say to our children when they grow up that these animals are like the dinosaurs and we did nothing to stop that."