First record of the genus Microchoerus (Omomyidae, Primates) in the western Iberian Peninsula and its palaeobiogeographic implications.

In this paper we describe new material of Microchoerus (Microchoerinae, Omomyidae, Primates) from Zambrana (Miranda-Trebiño Basin, northern Iberian Peninsula, Spain), a locality assigned to Reference Level MP18 (middle Headonian, Late Eocene). The specimens studied consist of two mandibular fragments, bearing p3-m3 and p4-m3. The teeth resemble in size and morphology those of Microchoerus erinaceus from Hordle Cliff, England, although some differences prevent us from making a definitive ascription to this species. We therefore refer the material from Zambrana to Microchoerus aff. erinaceus. Some traits, such as the development of the mesoconid and hypoconulid in the m1 and m2, and the shape of the hypoconulid lobe in the m3, are intermediate between those of M. erinaceus and Microchoerus edwardsi. Thus, the material from Zambrana is very similar to other species of Microchoerus present in Europe, representing a transitional form between M. erinaceus and M. edwardsi. The described material represents the first discovery of a primate from the Miranda-Trebiño Basin, and also the westernmost record of the genus Microchoerus in the Iberian Peninsula. Moreover, the identification of this microchoerine, with clear similarities to the representatives of this genus described from other European sites, reinforces the idea of the existence of connections between western Iberia and the rest of Europe in the Late Eocene, previously hypothesized after the discovery of typical European artiodactyls in the site of Zambrana.