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An artist's reconstruction of Homo georgicus. Image courtesy of Wikicommons

While I was doing some research this week, I came across a hominid species I hadn’t heard of before: Homo helmei. The name was first given to a 259,000-year-old partial skull found in Florisbad, South Africa in 1932. The skull resembled early Homo sapiens but possessed many archaic features. Today some researchers think many of the African hominid fossils from around this time should be lumped in the H. helmi species; others call them Homo heidelbergensis, considered by some anthropologists to be the last common ancestor of modern humans and Neanderthals. And then there are those who don’t really know what to call them.

It turns out I should have known H. helmei. It’s mentioned once in my college human evolution textbook. I even underlined the passage. Still, it’s not a species name that’s frequently used. And it’s just one of several obscure species of Homo that anthropologists don’t universally accept. These unfamiliar members of our genus are often based on a few fossils—sometimes just one—that don’t fit neatly into existing hominid species. Here are a few examples:

Homo gautengensis (lived about 2 million to 820,000 years ago): Earlier this year, Darren Curnoe of the University of New South Wales in Australia announced the possible discovery of a new species of Homo found in China. It wasn’t the first time he had identified a new type of hominid. In 2010, he reanalyzed fossils from the South African caves of Sterkfontein, Swartkrans and Drimolen and decided that some of the specimens had strangely shaped molar teeth relative to the known South African hominids, such as Australopithecus africanus. He grouped the weird forms into their own species, Homo gautengensis, claiming it was probably the earliest member of the genus Homo.

Homo georgicus (1.8 million years ago): In 1991, anthropologists found the jaw of a hominid in the Caucasus Mountains of Dmanisi, Georgia. The researchers dug up additional hominid fossils as well as stone tools throughout the 1990s. The fossils looked similar to those of Homo erectus. But in 2000, they found an unusual jaw; its size and shape didn’t quite match H. erectus or any other known hominid that lived about 1.8 million years ago. So the team gave the jaw a new name, Homo georgicus. Since then, more bones that might belong to H. georgicus have been unearthed. The researchers speculate that two types of hominids might have lived in Georgia at this time (PDF): H. georgicus and H. erectus (or something closely related to it).

Homo cepranensis (450,000 years ago): Just one fossil, an incomplete skull, represents the species Homo cepranensis. It’s named for Ceprano, Italy, where the fossil was discovered during the construction of a road in 1994. The short, broad, thick skull didn’t quite fit with other hominids of the time, such as H. erectus and H. heidelbergensis, so anthropologists gave it its own name. But the Italian fossil did share some cranial features, like the shape of the brow ridges, with hominids living in Africa a few hundred thousand years ago (about the same time as H. helmei), leading researchers to speculate  H. cepranensis was perhaps ancestral to these African forms.