Denisovan jawbone helps to reveal appearance of ancient human species

A fossil found on the bottom of the sea has dredged up new details about the Denisovans.

Originally discovered by fishermen trawling the Penghu Channel, off the coast of Taiwan, the Penghu 1 jawbone has puzzled researchers for more than a decade. While the fossil been linked to a variety of different groups over time, evidence of its true identity has been hard to come by.

New research, published in the journal Science, hopes to finally put this debate to rest. By comparing the fossilised proteins locked within the teeth and bone to other remains, the researchers believe that it represents the lower jaw of a Denisovan male that lived at some point in the past 200,000 years.

Finding another remnant of this ancient human species, which is only known from DNA and a handful of fragmentary fossils, is an important step towards finding out what the Denisovans were like. Penghu 1 shows that they had a strong jaw full of large teeth with distinctive roots.

Professor Chris Stringer, a human evolution expert who was not involved in the research, has called the discovery “an important result”.

“This fossil supports the idea that the morphologically similar Xiahe and Penghu finds are probably Denisovans,” Chris says. “It also tells us more about how adaptable they were.”

“Denisovan fossils have now been discovered across an area stretching from Siberia to Taiwan, making it apparent that the Denisovans must have had a wider environmental range than the Neanderthals. They must have been able to cope with cold, open environments in northern Asia as well as the subtropical woodlands of southeast Asia.”

What is a Denisovan?

Since being named from a small group of fossils found in Denisova Cave in 2010, the Denisovans have remained an enigmatic branch on the human family tree. Research into the species has been hampered by a lack of well-preserved fossils, with Denisovan remains mostly consisting of skeletal fragments and individual teeth.

Unusually, a lot of what we know about them has instead come from their DNA. While the genetic material of ancient human species has often long since been lost, the cool climate of Denisova Cave allowed high quality genomes to be extracted from the fossils found there, including those of the Denisovans.

Since then, the genetic signs of Denisovans have been found across large parts of Asia. It is thought they passed on genes that help with life at high altitudes to the ancestors of modern Tibetans, and are responsible for as much as much as 5% of the DNA of the Indigenous inhabitants of Australia, New Guinea and the Philippines today.

While there are a number of fossils across eastern Asia that could come from the Denisovans, the warm and humid climate of much of the region means DNA isn’t normally preserved in these bones. Scientists instead compare the proteins in these fossils with those found at Denisova Cave to try and identify potential matches.

Though proteins alone can’t conclusively identify whether a particular bone is Denisovan, it helps researchers to build up a case.

What was found at Penghu?

Before getting to work on Penghu 1, the researchers first tested their approach on the animal bones that were found alongside it.

Over the past million years, periodic Ige Ages would lock up large amounts of water, causing sea levels to fall and connecting islands like Taiwan to the mainland. At Penghu, this would have allowed animals like water buffalo, tigers and the enormous straight-tusked elephants to roam across these land bridges.

It’s not entirely certain when this was, as seawater contamination means that the techniques normally used to date fossils may be unreliable. However, as Taiwan was connected to the mainland between 10,000 to 70,000 years and 130,000 to 190,000 years ago, it’s reasonable to assume that the Penghu fossils come from similar time periods.

Having refined their analysis on the remains of Penghu’s animals, the team turned to Penghu 1 itself. Their results showed that many of the proteins are shared with a Denisovan rib found on the Tibetan Plateau, known as Xiahe 2, and has certain signatures that have only been found in Denisovans so far.

Proteins in the teeth, meanwhile, allowed the team to find out more about the individual. Certain genes involved in the development of enamel are only found on the sex chromosomes, allowing the team to be reasonably confident that the jawbone belonged to a Denisovan male.

The researchers speculate that thick jaws and teeth could have been a sex-specific characteristic of male Denisovans. However, there’s not enough evidence to say for certain so it’s also possible that it could be a trait of the entire species.

As further Denisovan fossils are discovered, scientists are getting ever closer to pinning down the identity of this ancient human species. It’s even possible that we might even know them by another name.

“My wider phylogenetic work with Chinese colleagues further links Penghu, Xiahe and the limited Denisovan fossil evidence with other Chinese fossils, including ‘Dragon Man’ from Harbin,” Chris explains. “Our analyses place all of these fossils together in the Homo longi group.”

“A question for the future will be whether we end up calling Denisovans Homo longi, which is my preference, or if we say that Homo longi is Denisovan. I think that the names will probably end up being used together.”