Taphonomic inferences about Middle Pleistocene hominins: The human cranium of Gruta da Aroeira (Portugal).

Objectives: The aim of this work is to describe the taphonomic signatures of the Aroeira 3 cranium, with a specific focus on cranial breakage, comparing the cranium with other Middle and Upper Pleistocene hominin fossils in order to approximate the cause of death and the biological agencies and geologic processes involved in the taphonomic record of this specimen. Aroeira-3 was recovered from Acheulean layer X of Gruta da Aroeira (Portugal), dated to 390-436 ka.

Materials And Methods: Taphonomic analyses noted surface modifications employing standard methods. The cranial breakage pattern of Aroeira 3 was analyzed to assess the presence/absence of perimortem (fresh bone) and postmortem (dry bone) fractures and the possible causes of perimortem skull bone fractures.

Results: Aroeira 3 presents substantial bone loss of the left supraorbital arch and the outer cranial table of the frontal squama. Most of the fractures present features consistent with postmortem injuries. The fracture to the posterior region of the parietal bone, however, displays features more usually present in perimortem bone fractures. No evidence of anthropogenic activity or of carnivore modification has been identified. None of the expected features of interpersonal conflict are observed. Finally, the bone loss in the frontal squama and the supraorbital arch could be attributed to different agencies, and a traumatic event cannot be totally ruled out as origin of the bone alteration.

Discussion: Cannibalism, secondary treatment of the corpse and accumulation induced by carnivores can all be discarded, making an accident the most plausible explanation for the cranial fracture.