Crime-drama fans know that forensic scientists can ID the remains of long-missing persons by examining their teeth. To solve even more ancient mysteries, anthropologists use the same kind of cutting-edge tooth technology, and a European team may have cracked a very cold case indeed—one that’s almost half a million years in the making.
A fossil tooth study published today in the journal PLOS ONE analyzes some of the oldest human remains ever found on the Italian Peninsula. The teeth, which are some 450,000 years old, have some telltale features of the Neanderthal lineage of ancient humans. Dating back to the Middle Pleistocene, the fossils help to fill in gaps in an intriguingly complex part of the hominid family tree.
The species Homo neanderthalensis shares an unknown common ancestor with our own species, Homo sapiens, but it’s unclear exactly when the lineages diverged. Homo sapiens evolved perhaps 300,000 years ago, according to the fossil record, while Neanderthals’ evolutionary timeline has proven even trickier to pin down. Some genetic studies suggest that their lineage split from our own as long as 650,000 years ago, but the oldest definitive fossil evidence for Neanderthals extends back only about 400,000 years.
To help to take a bite out of that gap, Clément Zanolli of the Université Toulouse III and colleagues used detailed morphological analyses and micro-CT scanning techniques to painstakingly measure the 450,000-year-old teeth. The teeth were then compared, inside and out, to those of other ancient human species, revealing that they have Neanderthal-like features.
“With this work and other recent studies, it seems now evident that the Neanderthal lineage dates back to at least 450,000 years ago and maybe more,” Zanolli says in an email. “This age is much older than the typical Neanderthals, and before our study it was unclear to which human fossil species these Italian remains were related.”
Most Neanderthal fossils are far more recent, dating from about 130,000 to 40,000 years ago, making evidence of the species’ earlier period hard to come by. The Middle Pleistocene Era teeth were found at two different sites, one near Rome (Fontana Ranuccio) and another outside Trieste (Visogliano). Together, these tiny fossils represent an intriguing piece of physical evidence that supports the findings of genetic studies of ancient human ancestry.
“I think that this is an interesting study, demonstrating that many of the features of Neanderthal teeth are present in Europe as far back as 450,000 years ago, which is farther back in time than Neanderthals have yet been identified in the fossil record,” says Ohio State University anthropologist Debbie Guatelli-Steinberg in an email, who wasn’t involved in the study. “This pushes back the ‘hard evidence’ of the split of Neanderthals from modern humans and is entirely consistent with the divergence dates coming from ancient DNA analyses, which suggest that the divergence occurred before 450,000 years ago.”
But the story isn’t as simple as a fork between modern human and Neanderthal lineages. Rather, the ancestral tree of the genus Homo appears wonderfully complex.
“There are other European fossils of comparable age that lack the Neanderthal features of these Italian fossils, and therefore indicate that other kinds of humans, besides Neanderthals, may have been present in Europe during this period of time,” Guatelli-Steinberg says.
One species in particular, Homo heidelbergensis, has been suggested as the possible common ancestor of both Neanderthals and modern humans.
"During the Middle Pleistocene, another species called Homo heidelbergensis was present in Europe, and its relationships either with Neanderthals or with more archaic species like Homo erectus are still unclear,” Zanolli says.
As scientists further untangle the evolutionary pathways of ancient humans, teeth will likely continue to play a critical role. Made of enamel, the body’s hardest biological substance, teeth tend to survive longer than bone. Additionally, the shapes and structures of teeth provide a valuable diagnostic tool to discriminate between our various ancient hominin relatives.
But how does one tell a Neanderthal’s tooth from a modern human’s, or any of the lineages in between? Paleoanthropologist Kristin Krueger of Loyola University of Chicago says that in general, teeth and jaws get smaller as evolution progresses, likely due to dietary changes such as the development of cooking. But when it comes to teeth, size isn’t the only thing that matters.
Cusps, crenulations, ridges and other features can be used to categorize the teeth of early humans. Tooth interiors can differ as well, and variations like enamel thickness and pulp chamber size can yield critical information to the trained eye.
“This study is an excellent example of what we can learn about evolution from teeth in general, and also what we can learn without destructive analysis,” Krueger says in an email. “The dental record from this time period and location is rare, so to have the number of teeth and analyze them to this degree without having to cross-section them or do destructive analysis (which is necessary for DNA analysis) is of paramount importance.”
And teeth can potentially do much more than simply uncover the roots of our evolutionary family tree. Ancient chompers can often teach us about the lives and diets of the ancient humans they belonged to.
“We think of teeth and dental records when identifying a random body in the woods, but what we don’t often appreciate is the scope of information that teeth can reveal. They are like little windows into a person’s life and can tell us about things like age, diet, hygiene, migration patterns, weaning practices, stress episodes and more,” Krueger says.
That such information might endure for half a million years makes the humble tooth an important tool for untangling the complex threads of early human origins.