Do These Fossilized Teeth Belong to the World’s Smallest Great Ape?

If great apes are known for anything, it’s being great in size. A large gorilla can weigh nearly 500 pounds, for example, and the extinct great ape Gigantopithecus was likely a hundred pounds or so heavier, the largest primate of all time. But now paleontologists have identified what might be the smallest of the great apes, a primate that lived in the forests of prehistoric Germany and was the size of a small dog.

Scientists have uncovered the fossils of two teeth and a kneecap that they say represent a new primate, named Buronius manfredschmidi. Paltry as that may seem, the teeth of fossilized mammals are often very distinctive and allow researchers to set species apart from each other. In this case, University of Tübingen paleoanthropologist Madelaine Böhme and colleagues propose, Buronius was a previously unknown species of hominid, or great ape, that lived in warm forests about 11.6 million years ago. The researchers described the fossils on Friday in PLOS One.

The first fossils of the ancient ape were uncovered more than a decade ago. In 2011, Böhme recalls, researchers began searching for fossils at a site called Hammerschmiede in southern Germany. “In the very first year,” she says, “we discovered the upper molar and the kneecap of Buronius right next to each other.”

Böhme and co-authors were confident the initial finds were from a primate, but they didn’t immediately know what sort. “Due to their small size, we initially thought they were pliopithecines,” Böhme says. Pliopithecines were prehistoric monkeys that spread through Eurasia during the Miocene, between 5.3 million and 23 million years ago, and some were quite small. The first tooth and the small bone could have come from such a primate, but too little had yet been uncovered for the researchers to be sure. The fossils waited for additional finds to place them in context.

The identity of Buronius didn’t come into focus until the researchers found the fossils of another ape at the same site. In 2015, Böhme and colleagues found the fossils of a hominid the researchers would eventually name Danuvius guggenmosi. Based on the available fossils, the researchers estimated that Danuvius could get to be about 68 pounds and was a much larger animal than the creature represented by the tooth and kneecap.

Studying the teeth of Danuvius led the researchers to reassess the 2011 finds, and a second mystery tooth had also been found in 2017. The fossils represented an additional ape, Buronius, that would have weighed about 22 pounds in life. “Now published, Buronius is the smallest known hominid,” Böhme says.

But other researchers aren’t entirely sure that Buronius and Danuvius are different species. The fossilized kneecap is small, but it could have come from a juvenile or a different sex of Danuvius, says Brooklyn College paleoanthropologist Kelsey Pugh, who was not involved in the new study. Both modern and extinct apes could greatly vary in size between sexes, she says, and so the small size of the kneecap is not enough to tell what primate species it belonged to.

With the kneecap posing questions, dental details are what principally distinguish the larger and smaller apes. The new study says that the size difference between the Buronius and Danuvius molars are greater than in any one species within the broader group of primates to which apes belong. The significant size disparity adds some support to the case that the molar found in 2011 and the Danuvius fossils represent different species.

In addition to the size difference between the molars, the interior details also distinguish the new tooth from that of Danuvius. The enamel of the Buronius molar is much thinner than that of a comparable Danuvius molar, hinting that the smaller ape was feeding on softer foods, like leaves, than its larger relative. “While enamel thickness is quite variable in living hominoids, the two Danuvius molars are quite distinct in this feature, reasonably indicating a difference in diet,” Pugh says.

The dietary difference hints at what vegetation grew in the Miocene habitat where the apes dwelled. Back when Buronius and Danuvius were alive, what’s now Bavaria was a flat, swampy landscape at the foot of the ancient Alps. The immediate area the fossils were preserved in hosted a meandering stream, Böhme says, surrounded by scrubby plants that grew densely along the banks. And even though the global climate was warmer than today, the area was far enough to the north that there would have been changes through the seasons, the fresh leaves of the spring and summer becoming rarer as the short autumn and winter days set in. How the apes foraged must have changed as the seasons affected how the local plants grew.

Selecting different foods would have allowed the apes of Hammerschmiede to coexist. “There are lots of examples of modern ecosystems where large numbers of primate species manage to coexist,” says University of Toronto Scarborough paleontologist Mary Silcox, who was not involved in the new study. The Kibale forest of Uganda, she notes, is home to 14 overlapping primate species, ranging from bush babies to monkeys and apes like chimpanzees. “Primates are very good at partitioning niche space,” she says, and the fossil record indicates that monkeys, apes and their relatives have been finding ways to coexist in the same forests for tens of millions of years.

Part of what allows multiple monkey and ape species to coexist today is that many live in warm equatorial forests where food is available year-round. The situation at Hammerschmiede is different, showing the resourcefulness of the apes found there. The vegetation where Buronius and Danuvius lived had deciduous trees and changed through the year. “It speaks to the productivity of the Hammerschmiede paleo-ecosystems that they allowed two great apes to coexist despite the seasonal food scarcity,” Böhme says.

The details of that coexistence await more fossils that will allow paleontologists to get a better view at what Hammerschmiede’s apes were like in life. More skeletal pieces will help sort out the relationships of the site’s apes, as well, which in turn will help paleoprimatologists understand how the prehistoric apes lived in a place quite different from the habitats of nonhuman apes today. Despite differences in interpretation, Pugh says, “it takes a lot of work to discover new fossils, and these authors have done an incredible job discovering new ape fossils at Hammerschmiede.” With luck, even more fossils will soon bring these ancient relatives of ours into clearer view.