Emiliano Aguirre

The Atapuerca sites and the ibeas hominids

The Atapuerca railway Trench and Ibeas sites near Burgos, Spain, are cave fillings that include a series of deposits ranging from below the Matuyama/Bruhnes reversal up to the end of Middle Pleistocene. The lowest fossil-bearing bed in the Trench contains an assemblage of large and small Mammals includingMimomys savini, Pitymys gregaloides, Pliomys episcopalis, Crocuta crocuta, Dama sp. and Megacerini; the uppermost assemblage includesCanis lupus, Lynx spelaea, Panthera (Leo) fossilis, Felis sylvestris, Equus caballus steinbeimensis, E.c. germanicus, Pitymys subterraneus, Microtus arvalis agrestis, Pliomys lenki, and alsoPanthera toscana, Dicerorbinus hemitoechus, Bison schoetensacki, which are equally present in the lowest level. The biostratigraphic correlation and dates of the sites are briefly discussed, as are the paleoclimatic interpretation of the Trench sequences. Stone artifacts are found in several layers; the earliest occurrences correspond to the upper beds containingMimomys savini. A set of preserved human occupation floors has been excavated in the top fossil-bearing beds. The stone-tool assemblages of the upper levels are of upper-medial Acheulean to Charentian tradition. The rich bone breccia SH, in the Cueva Mayor-Cueva del Silo, Ibeas de Juarros, is a derived deposit, due to a mud flow that dispersed and carried the skeletons of many carnivores and humans. The taxa represented are:Ursus deningeri (largely dominant),Panthera (Leo) fossilis, Vulpes vulpes, Homo sapiens var. Several traits of both mandibular and cranial remains are summarized. Preliminary attempts at dating suggest that the Ibeas fossil man is older than the Last Interglacial, or oxygen-isotope stage 5.

Dépôts fossilifères du karst de atapuerca, premiers 20 ans

Fossiliferous Karst Deposits of Atapuerca. First 20 years of research. The conception of a multidisciplinary research project on the ancient occupants of Spain and Europe, and the ecological contexts of their evolution derived in 1976 from the incidental find of 16 human fossils in a deep pit, SH, well into the ‘Cueva Mayor’ of Sierra de Atapuerca (Ibeas de Juarros, Burgos, Spain), and after visiting several outcrops of deep, well stratified karst deposits in an abandoned railway cut, not far. The human fossils from SH were assigned to the European group of preneandertalians (Aguirre 1976; Aguirre & de Lumley, 1977), and classified as Homo sapiens heidelbergensis (Aguirre & Rosas, 1985). A ‘mosaic’ evolution was then recognized on the morphological traits of human mandibles in Middle Pleistocene, also an African origin of the pre-neandertalians, and the ancestorship of the latter relate to neandertalians. Different approaches led by 1987 to estimate the age of SH hominines c. 300/320 Ka. BP. Paleopathological and taphonomical studies allowed inferring good health overall; cultural factors were suggested for several common deficiencies. In 1990 the SH site was finally cleaned and human bones in situ exposed after removing more than 6 Tm of a mass of accumulated stones, mud and bone fragments removed by searchers of bear teeth. All that overburden washed and shifted yielded thousands of bear fossils and more then 250 human pieces of a MNI = 11. Excavation of untouched deposit between 1990 and 1999 produced more than 2 400 human fossils belonging to a MNI = 27. Studies of paleodemography are published, based on the assumption that the corpses were deposited as death occurred along time and as a behavioural pattern; present author thinks that the simultaneous death of a group taking refuge in a cave under heavy rain, and land-slide following, is more consistent with observed evidences. Two sites on the railway cut were sampled: the Gran Dolina (TD), 18.5 m deep, and Galeria (TG) with a connected vertical shaft (TN) in the ‘Complejo Tres Simas’, yielding abundant microvertebrate fossils and continuous or dicontinuous pollen record. Extension excavation started in both TD and TG sites over c. 24 m2 in each met successive horizons with mammal assemblages known in European sites of the upper third of Middle Pleistocene and evidences of human occupation. Basal beds of TD also were excavated in a talus: these yielded a paleofauna known as Upper Bhiharian, or Early Cromerian. The extreme ages obtained for TD are c. 900 and c. 150 Ka. Lithic assemblages, analysed from the operational viewpoint, belong to Mode 1 in TD6, to a particularly evolved Mode 2 in TG, to early Mode 3 in upper TD beds. Microwear traces were studied on rodent and amphibian fossils to identify consumers, and on tools in search of traces of use. Differences were found in meat consumption and on use and permanence in various cavities. A slit open cut in TD started in 1992 yielded fossil humans with abundant lithic and faunal context in upper Bed TD6 well below the B/M magnetic reversal. Presently debated interpretations are indicated, and future potentials suggested.

Poor fossil record and major changes around 1 MaBP

The abundance of early fossil humans in African sites ceases at dates around 1.3MaBP; there is almost none until nearly 0.8MaBP. Again these are scarce until less than 0.5 Ma. Most of Homo erectus fossils in Java are dated between c.1.3 and 0.70Ma; just a few fossil humans are known in Eurasia for this time span. Questions arise on eventual environmental constraints, that may have influenced evolutionary crises of human populations, but also on geographic conditions adverse to fossilization processes and/or site formation. Records on climate variables, vegetation, sea level, sedimentary conditions and tectonic behavior in regions of the Old World are collected, and correlation traced back in time slices. Continental accretion is related to end of sedimentation in African basins; repeated compressive tectonic activity negatively affected preservation of both fossils and occupation sites widely, before and immediately after the M/B reversal. Lithic artefact assemblages, although derived, are understood as evidence of human occupation in the studied interval. Human populations are exspected to be affected by environmental changes, small, and scattered. Origin of Homo sapeins and divergence of preneandertalians are driven back to those times. Ancestorship to the latter is found probably in African fossils of that time span. Modern traits found in the Atapuerca-TD6 sample and the preceeding considerations urge research on humans and their movements intra- and intercontinental around 1 MaBP.