Why is it important?

• Firmly dated to 390–436 ka, this new hominin fossil found in Portugal is the westernmost Middle Pleistocene cranium of Europe.
• It is one of the earliest fossils associated with Acheulean tools in Western Europe.
• Together with the tools, there is also a direct association with a large amount of faunal remains: mainly cervids and equids, also some rhinos and bears, a large bovid, a caprid and a tortoise.
• The presence of burnt bones suggests a controlled use of fire.

Aroeira 3 cranium. Credit: Daura et al, New Middle Pleistocene hominin cranium from Gruta da Aroeira (Portugal)

The site and the discovery

The Almonda karst system (Central Portugal) has yielded since 1987 human evidences from different Paleolithic and Neolithic periods. The excavations at Gruta da Aroeira from 1998–2002 produced many important finds: Acheulean bifaces associated with faunal remains and two human teeth (Aroeira 1 canine and Aroreira 2 third molar), which are very large but within the known variation of the dentition from the European Middle Pleistocene.

In 2013 new works started at the cave, using heavy-duty demolition hammer to excavate the hard breccia of the sediments. The Aroeira 3 human cranium was heavily fossilized and well preserved within the cemented breccia, and was damaged by the hammer, fragmenting several pieces and producing a notorious hole in the main portion. The cranium was restored in Madrid over a period of two years.

Meet Aroeira 3

Aroeira 3 shows several features found in other European early Middle Pleistocene crania. However, the combination of them makes Aroeira 3 a unique specimen, for example:

• Continuous and thick supraorbital torus -> as in the Bilzingsleben skull.
• Short mastoid process -> as in the Steinheim skull.
• Large, triangular postglenoid process -> as in the Sima de los Huesos (SH) skulls.
• Raised articular eminence, which contrasts with the flatter articular eminence generally seen in the SH sample and in Steinheim, which is likely an early neandertal feature.

Aroreira 3 comparison with Steinheim and SH Cranium 5 and Cranium 4. Credit: modified from Daura et al, New Middle Pleistocene hominin cranium from Gruta da Aroeira (Portugal)

Who was this hominin?

Although there are several sites close each other representing the European Middle Pleistocene hominin record, the fossils from those sites conform two big groups of morphological traits (apart from the Neandertals < 200 Ka):

• A group represented by Sima de los Huesos, Swanscombe and now Aroeira 3 which show Neandertal traits in the face, supraorbital torus, temporal bone and mandible, but the general shape of the neurocranium is not Neandertal-like.

• A group represented by Arago 21 and Ceprano which do not show Neandertal-derived traits or the features are more ambiguous. The Aroeira 3 cranium resembles these specimens in its well-developed angular torus (also present in SH Cranium 4) and its lack of a flattened articular eminence.

This is a new specimen which feeds the passionate topic of the settlement of the European continent and the human expansion during the Middle Pleistocene. The hominin record shows a large amount of variability, and Aroeira 3 is not an exception.

The early Neandertal morphology pattern is shown again in this specimen – found at the Western end of Europe, a region potentially subject to extreme isolation at that time. Aroeria 3 shows typical features as seen in other Middle Pleistocene other specimens, but with a unique combination of them, suggesting variable population replacement with varying levels of isolation and admixture.

Moreover, those hominins used two important technologies: the Acheulean industry and the controlled use of fire, demonstrating a quick spread of these innovations throughout Europe.

Aroeira 3 Acheulean tools. Credit: Daura et al, New Middle Pleistocene hominin cranium from Gruta da Aroeira (Portugal)

Reference: Daura et al, New Middle Pleistocene hominin cranium from Gruta da Aroeira (Portugal) [access to full report]