Archaeologists have something new to add to the record books: the earliest case of anemia. Two 1.5-million-year-old skull fragments unearthed in Tanzania display tell-tale signatures of the blood disorder—and may offer hints on the meat-eating habits of our ancestors.

The fossil pieces come from Olduvai Gorge and belong to an approximately 2-year-old child. The fragments are not enough to identify the toddler’s species, but based on the age and location, Homo erectus is a good possibility. On certain portions of the fossils Manuel Domínguez-Rodrigo of Madrid’s Complutense University and colleagues noticed the bone was extremely porous. After ruling out several possible causes of the damage, the team concluded the individual had suffered from porotic hyperostosis. This condition causes the outer cranial bone to thin and exposes the spongy inner bone, which starts to grow abnormally. This is the first time porotic hyperostosis has been seen in a hominid from the early Pleistocene, the team reports in PLOS ONE.

Porotic hyperostosis can be a manifestation of anemia, which is caused by a decline in oxygen-carrying red blood cells. The researchers say the most common cause of the anemia that leads to porotic hyperostosis in children is a lack of vitamins B12 and B6 (with parasites and gastrointestinal infections contributing to the disorder). The nutritional deficiency probably occurred either because the child was still nursing and his/her mother lacked the B vitamins herself or the child was being weaned and was not yet getting adequate levels of the vitamins in his/her own food.

How does this relate to eating meat?

Domínguez-Rodrigo and his colleagues suggest the insufficient levels of B12 and B6 were ultimately the result of not eating enough meat, which is rich in those vitamins. The researchers argue that by 1.5 million years ago hominid physiology had become so dependent on meat that not ingesting proper amounts of it led to nutritional deficiencies. (In contrast, anemia-induced porotic hyperostosis is almost never seen in chimpanzees, which consume much smaller amounts of animal protein.) Thus, the researchers conclude, this early case of anemia is one more piece of evidence that meat-eating was a crucial part of the hominid diet by the early Pleistocene.