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Tracks and trackways of newborns, calves and juveniles attributed to straight-tusked elephants were found in the MIS 5 site (Upper Pleistocene) known as the Matalascañas Trampled Surface (MTS) at Huelva, SW Spain. Evidence of a snapshot of social behaviour, especially parental care, can be determined from the concentration of elephant tracks and trackways, and especially from apparently contemporaneous converging trackways, of small juvenile and larger, presumably young adult female tracks. The size frequency of the tracks enabled us to infer body mass and age distribution of the animals that crossed the MTS. Comparisons of the MTS demographic frequency with the morphology of the fore- and hind limbs of extant and fossil proboscideans shed light into the reproductive ecology of the straight-tusked elephant, Palaeloxodon antiquus. The interdune pond habitat appeared to have been an important water and food resource for matriarchal herds of straight-tusked elephants and likely functioned as a reproductive habitat, with only the rare presence of adult and older males in the MTS. The preservation of this track record in across a paleosol surface, although heavily trampled by different animals, including Neanderthals, over a short time frame, permitted an exceptional view into short-term intraspecific trophic interactions occurring in the Last Interglacial coastal habitat. Therefore, it is hypothesized that Neanderthals visited MTS for hunting or scavenging on weakened or dead elephants, and more likely calves.

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In the Iberian Peninsula the fossil record of artiodactyls spans over 53 million years. During the Pleistocene, wild cattle species such as Bison and especially Bos became common. In Late Pleistocene, the aurochs (Bos primigenius) was widespread and the only bovine living along the large river valleys of southern Iberia. Although commonly found in fossil sites and especially in cave bone assemblages, the trace fossil record of aurochs was known worldwide only from the Holocene. Large bovine and roe deer/caprine tracks were found in at least five horizons of the early Late Pleistocene (MIS 5) beach and eolian deposits of Cape Trafalgar (Cadiz Province, South of Spain). The large bovine tracks are formally described as Bovinichnus uripeda igen. et isp. nov. and compared with the record of aurochs tracks, large red deer tracks and steppe bison biogeographical distribution in Iberia. Aurochs were the most likely producers of the newly described Trafalgar Trampled Surface (TTS) and some of the large artiodactyl tracks in the Matalascañas Trampled Surface, representing the oldest aurochs track record known. This new evidence, together with comparisons with the record of possible aurochs tracks in the Mid-Late Pleistocene coastal deposits from the Asperillo cliff section in Matalascañas (Huelva Province, SW Spain) and bone assemblages known in Gibraltar, point to a recurrent use of the coastal habitat by these large artiodactyls in SW Iberia.

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Mammalian hematopoiesis is based on the activity of multipotent hematopoietic stem cells (HSC) that undergo continuous self-renewal throughout the adult life. The self-renewal represents a unique property of adult HSC, and appears distinct from the proliferation of hematopoietic progenitors or from the initial specification and expansion of embryonic HSC. Despite recent progress, little is known about the molecular mechanisms governing HSC self-renewal. Zfx is a broadly expressed zinc finger-containing transcriptional activator that is highly conserved in vertebrates. Using conditional gene targeting in mice, we demonstrate that Zfx is an essential and specific regulator of HSC self-renewal. The expression of Zfx was elevated in HSC compared to progenitors and differentiated cells. An inducible deletion of Zfx from the adult bone marrow (BM) resulted in the specific loss of the HSC population. The short-term proliferation and lodging of Zfx-deficient HSC in the BM were normal, suggesting a specific defect of long-term self-renewal. The deletion of Zfx in pre-established BM chimeras completely abrogated HSC maintenance as reflected by the rapid loss of HSC contribution to hematopoiesis. Furthermore, a constitutive pan-hematopoietic deletion of Zfx spared embryonic HSC in the fetal liver, yet resulted in the loss of adult BM HSC. In contrast, adult erythromyeloid progenitors or differentiated cells were not affected by the absence of Zfx. Genome-wide expression analysis identified candidate target genes of Zfx, some of which were controlled by Zfx in HSC but not in their differentiated progeny. Finally, several immediate-early and/or stress-inducible genes were upregulated specifically in Zfx-deficient HSC, suggesting that the latter undergo increased stress-related signaling. Thus, functional and gene expression analysis establishes Zfx as a novel specific regulator of adult HSC self-renewal. Further studies of the target genes and pathways controlled by Zfx should provide novel insights into the molecular basis of HSC function.

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