Researchers have found a new species of ape that roamed Earth 12.5 million years ago - and weighed just 8lbs when it was fully grown.

The tiny ape, known as Simiolus minutus, was found in the Tugen Hills of Kenya.

Experts believe the mini ape, weighing slightly less than an average house cat, subsisted mainly on leaves, which led to its downfall as it was unable to compete with colobine monkeys that dined on the same leaves. 

The fossil molars were found at three different sites in the Tugen Hills of Kenya. The tiny ape, known as Simiolus minutus,is a new species.

WHY DID THE TINY APE DIE OUT? 

Fossil molars from the tiny ape, now housed in the National Museum of Kenya, Nairobi, show evidence of leaf eating, which suggests that it was in direct competition with the earliest colobine monkeys for food resources. 

Researchers believe it was unable to compete with colobine monkeys that dined on the same leaves.

Stony Brook University anthropologist James Rossie made the find of the first day of a dig in the area. 

Now, a study authored by Rossie and his former doctoral advisor, the late Andrew Hill of Yale University, shows that this belongs to a new species of ape. 

The fossil molars were found at three different sites along the Tugen Hills and Lake Baringo Basin by Rossie and Hill in 2004, just more than a decade before Hill's death in 2015

The find gives important clues about the unexplained decline in diversity of apes during the Miocene epoch.

Rossie said fossil molars from the tiny ape, now housed in the National Museum of Kenya, Nairobi, show evidence of leaf eating, which suggests that it was in direct competition with the earliest colobine monkeys for food resources. 

Rossie said the small ape is also the latest-surviving member yet described of the small apes that flourished in the early Miocene epoch. 

The palate of a chimpanzee, left, compared to a Simiolus minutus molar, center. The figure on the right is the same chimpanzee palate, but scaled down to match the Simiolus molar. 

At the beginning of the Miocene epoch, there were only a few species of monkeys, while apes were represented by a broad radiation of species ranging from 4 to 50 kilograms; today, however, there are only a handful of ape species remaining.

Precisely what caused the decrease in ape diversity and rise of monkey diversity is a mystery that paleontologists have been contemplating for decades, Rossie said, and many suspect that direct competition between the two groups was to blame.

'One thing this shows us is that some apes were leaning toward folivory [leaf eating] at just the time when monkeys were evolving their uniquely effective adaptations for it,' said Rossie, . 

Fossil molars from the tiny ape, now housed in the National Museum of Kenya, Nairobi, show evidence of leaf eating, which suggests that it was in direct competition with the earliest colobine monkeys for food resources.  Pictured, Olivia, a five-year-old Angolan colobus monkey, clutches her baby at the Brookfield Zoo