A new site with Neandertal lineage fossil remains: the Sima I of the Polvorín cave (Karrantza, Biscay, Northern Iberian Peninsula)

Abstract

We present 16 new human fossil remains found at the Sima I of the Polvorín cave (Karrantza, Northern Iberian Peninsula). The remains probably belong to a single adult gracile individual, that possessed some Neandertal morphological features. The Sima I paleontological site is located in a gallery c. 33 m below the cave entrance. In 2020 we identified 10 human remains in the Arkeologi Museoa (Bilbao). These human remains were found in a purely paleontological assemblage recovered by speleologists in 1983 and 2000. This assemblage mainly consists of cave bears and spotted hyenas. Most of the bear remains were classified as Ursus spelaeus, but a few remains show affinities with U. deningeri. Previous studies suggested that the hyaena remains display morphometric affinities with the MIS 9-8 Crocuta intermedia. The taphonomic analysis of these remains rules out anthropogenic or carnivore activities as the cause of the bear accumulation at the site. In 2021-2022 we recovered 6 additional human and hundreds of carnivore remains. We observed that the sedimentary history of the gallery that contains the paleontological site is very complex, with different phases of infilling and erosion, with perched sediment remnants at different heights. The human fossil collection comprises 2 cranial fragments, 1 scapular fragment, 4 partial-to-complete thoracic vertebrae, 1 fragment of a lumbar vertebra, 2 rib fragments, 1 partial right radius and 1 shaft fragment from the left side, 2 intermediate hand phalanges, 1 partial hallucal metatarsal, and 1 lateral cuneiform. The cranial morphology, the curvature of the radial shaft, the thoracic vertebrae transverse process orientation, the morphology of the hand phalanges, and the shape of the metatarsal shaft are consistent with the morphology present in "classic" Neandertals and also present in Sima de los Huesos (SH) Middle Pleistocene hominins. However, the orientation of the radial tuberosity is primitive (SH-like)