Gargantuan cranium may reveal a new ancient human species

Earth is like a fruitcake, rich, decorated, and filled with unknowable treasures. All that humans have ever been is squished together like candied fruit under the crust.

This is why, in our modern era, girls may pull Viking swords from lakes and farmers can stumble upon woolly mammoths. It’s also why, in 1933 during the construction of a bridge, workers unearthed an unusual, ancient skull. Scientists dubbed it the Harbin cranium.

It was a chance discovery, but this massive cranium could completely upend what scientists think they know about modern humans and Neanderthals.

What’s new —  In a collection of three papers published Friday in the journal The Innovation, scientists claim that the Harbin cranium represents a new ancient human species.

Called Homo longi, this possible ancient human is named for the place where the bone was found: Long Jiang is another name for the Heilongjiang Province, home to Harbin City and part of China. Long Jiang also means “dragon river” — and Homo longi has picked up a nickname, the “Dragon Man.”

Homo longi is argued to be an Asian contemporary of Denisovans, Neanderthals, and our own species, Homo sapiens. It’s described as a “sister group” to us: If life is an evolutionary tree and the nodes on the tree are common ancestors, two descendants split from the same node are sister groups. The researchers behind this discovery claim this new human lineage is actually our closest relative — closer than Neanderthals or any other ancient humans who show up in our DNA tests.

Chris Stringer, a co-author of two of the papers and the Research Leader in Human Origins at the Natural History Museum London, tells Inverse that the decision to call this a new species is based on a standard set by Neanderthals.

“If Neanderthals are considered distinct enough to represent a distinct species, then the Harbin group also warrants this.”

He predicts some may question its legitimacy as a new species.

“For me, a species name is a label that helps to identify and classify evolutionary lineages — it does not necessarily imply reproductive isolation from closely related species,” Stringer says.

Some may argue Homo longi is actually an archaic iteration of Homo sapiens; others may say there’s too little data to really know. Subsequent DNA testing could even reveal it’s actually a Denisovan.

The confusion is par for the course when you’re working with a 146,000-year-old specimen, let alone working with a controversial subject matter in a field known for its arguments.

The origin of modern humans is a tangled web. We do know that around this time, several human species coexisted across Africa, Europe, and Asia. And this one human, in particular, met his end where other humans would eventually build a bridge over the Songhua River.

The “Dragon Man”

The man whose head once held the Harbin cranium was perhaps 50 years old when he died, though tooth wear suggests he could have been younger, the studies suggest.

Overall, the “Dragon Man” is thought to have been a bigger guy, adapted to live in cold conditions. The word the researchers use to describe his cranium throughout the papers is “massive.”

“His head was huge — containing a large brain — with a long low shape and massive brow ridge over the eyes,” Stringer says. “His face, nose, and jaw were very broad, and he had big eyes.”

“But his face was low in height, with delicate cheekbones, and it was tucked back under the braincase, as in a modern human,” he adds.

The Dragon Man’s image is reconstructed in one of the papers, a portrait of a not-unkind-looking man with laugh lines and thin lips. His skin tone and hair color can only be guessed without genetic information, but the data we have from Neanderthals, Denisovans, and early Homo sapiens suggests they had darker hair and eye color — so this is what our imagined Homo longi has too.

“Considering the high latitude of Harbin, we chose to give the reconstruction a medium-dark skin color,” Stringer says.

“It’s a very striking image and accurate,” he says, “as far as the preserved anatomy goes.”

The discovery — The Harbin cranium has been housed at the Geoscience Museum of Hebei GEO University in China. Exactly what happened to the cranium between its discovery and its placement at the museum is a “long and confused history,” the research team writes.

It is the best-preserved of the human fossils found in eastern Asia, and one of the most completely preserved human fossils ever found dating to the Middle-Late Pleistocene era. The cranium presents a “mosaic” of features — it is distinct from other archaic human taxa, like Homo erectus or Homo heidelbergensis, while still presenting typical details seen in later populations.

“Its enormous overall size sets it apart from nearly every other fossil but, in terms of cranial vault proportions, the braincase clearly overlaps with those of other large-sized late archaic Homo species,” the team writes.

Perhaps most significantly, the closest match to the cranium from the fossil record are Denisovan molars found in Siberia. Previous Asian Pleistocene human specimens, such as the Dali cranium, have been suspected to be Denisovans. More specimens and genetic testing will, in turn, reveal if the new species designation for the Homo longi is correct.

One of the enduring mysteries in ancient human studies is “establishing the full identity of the enigmatic Denisovans,” Stringer says. “The Harbin fossil may contribute to solving this puzzle.”

“The fossil can be assayed non-destructively for organic preservation, and if that looks promising my Chinese colleagues may consider proteomic and DNA testing, which might tell us whether Harbin is a Denisovan or not,” he explains.

But for now, the evidence suggests the cranium represents a new relative. Determining a new species involved studying the external morphology of the cranium, using over 600 traits. Then, Stringer says, “we used a very powerful computer to build trees of relatedness to other fossils.”

“After many millions of tree-building processes, we arrived at the most parsimonious trees,” he says. “These suggest that Harbin and some other fossils from China form a third lineage of later humans alongside the Neanderthals and H. sapiens.”

Finding and changing human history — This “trees of relatedness” process also suggests the divergence time between Homo sapiens and Neanderthals occurred 400,000 years earlier than previous estimates presumed. The earlier estimated divergence date, they hypothesize, could be a product of “recent gene flow events” — the mating between Neanderthals and modern humans, and subsequent DNA exchange.

But it’s difficult to say for sure and “there’s a large time gap between the hypothetical common ancestor of Eurasian H. sapiens and the actual fossil record,” the team writes.

It is clear that several human lineages coexisted, and likely interacted, in Asia — likely because of its “diverse paleoenvironments.” These humans crossed the Gobi Desert, rainforests, and coastal plains — a world the researchers describe as a “varied biogeographic sink for human evolution.”

It’s not known if Homo longi survived long enough to meet Homo sapiens, but they may have, Stringer says. Knowing ancient humans’ tendency to not let species designation stand in the way of procreation, it’s curious to think what may have happened during this meeting — after all, some modern DNA holds traces of ancient, unidentified ancestors.

“If Neanderthals could interbreed with modern humans, then I’m sure that the Harbin group could too,” Stringer says.

“Of course, if the Harbin group are one and the same as Denisovans, then we know that they did interbreed with both Neanderthals and our species, and some of the Harbin group’s DNA could still be in some H. sapiens populations today.”

It is in labs, and excavation sites across Asia, where scientists will continue to look for elucidating details. The study team argues Asian hominins are critical for studying the later evolution of the genus Homo, as well as the origin of our own species, but “advocates of regional continuity” have made it difficult to “integrate them into the wider picture of human evolution.”

This picture includes us. It also includes the Dragon Man.

Abstract: It has recently become clear that several human lineages coexisted with Homo sapiens during the late Middle and Late Pleistocene. Here, we report an archaic human fossil that throws new light on debates concerning the diversification of the Homo genus and the origin of H. sapiens. The fossil was recovered in Harbin city in northeastern China, with a min- mum uranium-series age of 146 ka. This cranium is one of the best-preserved Middle Pleistocene human fossils. Its massive size, with a large cranial capacity (1,420 mL) falling in the range of modern humans, is combined with a mosaic of primitive and derived characters. It differs from all the other named Homo species by presenting a combination of features, such as long and low cranial vault, a wide and low face, large and almost square orbits, gently curved but massively developed supra-orbital torus, flat and low cheekbones with a shallow canine fossa, and a shallow palate with thick alveolar bone supporting very large molars. The excellent preservation of the Harbin cranium advances our understand- ing of several less-complete late Middle Pleistocene fossils from China, which have been interpreted as local evolutionary intermediates be- tween the earlier species Homo erectus and later H. sapiens. Phylogenetic analyses based on parsimony criteria and Bayesian tip-dating suggest that the Harbin cranium and some other Middle Pleistocene human fossils from China, such as those from Dali and Xiahe, form a third East Asian lineage, which is the sister group of the H. sapiens lineage. Our analyses of such morphologically distinctive archaic human lineages from Asia, Europe, and Africa suggest that the diversification of the Homo genus may have had a much deeper timescale than previously presumed. Sympatric isolation of small populations combined with stochastic long-distance dispersals is the best fitting biogeographical model for interpreting the evolution of the Homo genus.