Een afwijkende mammoetschedel uit de Waal

A second case of severe alveolar damage in a skull of Mammuthus primigenius from the Netherlands is described, the first being a left skull half from the river IJssel near Bingerden (’B’ in fig. 1; see also Cranium 3,1,1986, pp. 17-24). The present specimen was dredged from the river Waal near Hurwenen (’H’ on the map). It is a lower half of a skull that was broken just below the nasal aperture. One of the tusk alveoli thus preserved, the left one, is greatly reduced in size: its diameter ranges from 1.5 to 4 cm. Though this very narrow tubular structure is open on either end, the 44 cm that can be measured from end to end may represent just about the length of the alveolus at the time of the event that caused its distortion. The normally developed right alveolus had reached a length of ± 75 cm by the time of the animals death. The inner surface of the left alveolus is corrugated and its lower edge swollen, both signs of an infection that must have caused the loss of the tusk involved. Furthermore, the maxilla and the premaxillary have fused along the lower edge (fig. 4; the loop marked ’Sm’ is part of the maxilla). The relative flattening of the premaxillary in the course of the healing process – as observed in other cases – was counteracted by the growth of cellular structures of the kind normally present in elephant skulls. The proximal part of the actual alveolus, usually expected beneath the line of the highest elevation in the premaxillary, has shifted to a place near the lowest part of the sutura incisiva (fig. 6c, d). Isolated shallow grooves scattered over the left half of the skull are tentatively interpreted as obliterated fractures. Damage as described above was to some extent liable to occur within the first 25 years of a mammoth’s life, when its tusks were still relatively straight and could be used as a tool for rooting up plants or breaking away ice crusts to reach water. Pollen analysis of sediment still present in the skull suggested a pleniglacial period near the middle of the Weichselian (Devensian). The skull fragment is in the collection of the ’Rijksmuseum van Geologie en Mineralogie’ at Leiden, cat. nr.: RGM 170047.