What was the back of Homo antecessor like?

A study conducted by scientists at the CENIEH on two shoulder blades of this species has revealed that it had already completely lost its capacity to climb easily, and confirms that the postcranial skeleton was very similar to that of modern humans.

A new study which has just been published in the Journal of Human Evolution, led by José María Bermúdez de Castro, coordinator of the Paleobiology Program at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), shows that this species from the European Lower Pleistocene at the Sierra de Atapuerca had already completely lost its ability to climb easily, and suggests that it had the skeleton of a hominin that habitually walked.

These two scapulae of Homo antecessor, found during the excavation campaigns of 2005, 2006 and 2007, belonged to a boy or girl about three years old (ATD6-116), and a minor of unknown sex, and age equivalent to that of a modern adolescent (ATD6-118). The two specimens open up a new way of discovering the shape of the shoulder blade and the characteristics of this bone in the back in this species.

“It remains to be checked whether its growth followed the same patterns as in Homo sapiens, on which point investigation is currently under way, but it can still yield a lot of vital information for learning the biological characteristics of Homo antecessor”, comments Bermúdez de Castro.

In addition, the study considers the hypothesis that one of the characteristics of the scapula (width of the glenoid cavity) can tell us whether objects could be thrown long distances: "If that hypothesis were correct, Homo antecessor would not have been able to throw stones or other objects very accurately. As there are hardly any scapulae in the fossil record, this question remains in the air”, he states.

Unique remains unique in the world

In the entire hominin fossil record, there are only four complete specimens of this part of the skeleton for the period between six million years and 100,000 years ago. The remaining scapulae from this vast lapse of time are incomplete and can only furnish partial information.

It has been possible to compare both scapulae with the other two entire specimens: a very complete one of the species Australopithecus afarensis ("Selam", the girl from Dikika, Ethiopia), dated at rather more than three million years old, and the specimen from the skeleton KNM-WT 15000 (the Turkana Boy), attributed to Homo ergaster, and dated to 1.6 million years ago.

“No less than 50% of all the scapulae known from the Pliocene and Pleistocene record have been found in the level TD6 of the Gran Dolina site, which hints at the nature of the human occupation of this level”, adds Bermúdez de Castro.

Scapulae are extremely delicate and break easily after the death of the individual, especially in children and young people. Thus, at Gran Dolina level TD6, there must have existed one or more camps of indeterminate duration, where cannibalism events took place.

“The remains are in practically the same position where they were left over 800,000 years ago. Analysis of this aspect is also ongoing, and in a few months we will learn the results”, he comments.

Complicated restoration

Due to the fragility of these remains, the restoration work carried out at the Instituto de Ecologìa Humana i Evolució Social (IPHES) in Tarragona by Lucía López-Polín, co-author on this study, has been slow and meticulous. In fact, one of the scapulae is so fragile that it could not be extracted from the block of calcified clay where it was found, and the extraction had to be conducted virtually by micro-CT at the Microscopy and Micro-Computed Tomography Laboratory of the CENIEH.