A new species discovered through skeletons found in a mass grave in Africa may fill the gap between the first truly human-like species and older more primitive primates.

The scientists who’ve been studying the finds have avoided the term “missing link”, but it certainly appears to be a previously unseen blend of human and ape-like characteristics.

The study is of 15 partial skeletons found in underground caves in South Africa. They have enough differences to previously chronicled species that researchers have classed them as a new species in their on right, named naledi and part of the Homo genus.

The skeletons show both differences and similarities to humans. For example, the brain size is about half that of an average human and thus nearer to other primates. However, the skull shape was close to that of a human. While the species was smaller than human at around five feet tall, the head would have looked bizarrely small to our eyes.

Meanwhile the bone structure of the hands is similar in naledi and humans, though the naledi’s fingers were more curved. The pelvis and shoulders were smaller in naledi, but the leg length was proportionally the same as with humans. The foot size is roughly similar, though the proportions of the various bones leading to each toe are different.

It’s not just the physiology that’s excited researchers, however. They believe that the bodies, laid out more than 100 feet from the cave entrance through narrow tunnels may have been part of a burial chamber. That would suggest ritual behaviour of a type that was previously assumed to only exist in later humans.

The age of naledi hasn’t yet been calculated, though it seems most likely they fit in the period between Australopithecus afarensis, the species to which the Lucy skeleton belongs, and Homo erectus. That’s an important position as Lucy and company were more apelike and may have dwelled in trees, while Homo erectus was the first species with a body shape that almost perfectly matches today’s humans.

However, it’s not necessarily a case of a neat evolutionary stepping stone. One theory is that naledi provides further evidence that the Homo genus may have evolved multiple species at the same time in different locations, with only one eventually leading to human beings.

The good news for research is that the identification of naledi is only a starting point. The skeletons are in such good condition and with so many parts that researchers believe they’ll be able to learn about the species in much more detail over time.