Anatomy, death, and preservation of a woolly mammoth (Mammuthus primigenius) calf, Yamal Peninsula, northwest Siberia

摘要

A well-preserved woolly mammoth calf found in northwest Siberia offers unique opportunities to investigate mammoth anatomy, behavior, life history and taphonomy. Analysis of the fluvial setting where the specimen was found suggests it was derived from eroding bluffs during ice-out flooding in June 2006. It then lay exposed on a point-bar surface until recovery the following May. AMS dating of bone collagen and plant tissues from the intestine provide age estimates that average about 41,800 (14)CyrBP. Anatomical features of interest include a hemispherical mass, apparently composed of brown fat, on the back of the neck. This may have functioned in thermoregulation for the neonate mammoth, born before onset of spring. Abundant subcutaneous fat and milk residues in the alimentary tract demonstrate that this animal was in good nutritional condition before death, making other features of its life history relevant for general studies of mammoth paleobiology. Plant remains from the intestine (mixed with milk residue in a manner consistent with frequent, small meals) show evidence of mastication by adult mammoths, suggesting that this calf ingested fecal material, probably from its mother and presumably to inoculate its intestinal tract with a microbial assemblage derived from a healthy adult. Discrepancies between the season of death we infer (spring) and seasonal indicators from the intestine implicate coprophagy (involving old fecal boli) by the mother. This animal's trachea and bronchi are completely occluded with fine-grained vivianite (hydrated iron phosphate) such as occurs in some lacustrine settings. Because this vivianite does not penetrate the lung beyond the bronchi, we infer that it must have entered as a viscous mass that occluded the airway, causing asphyxia. Nodular vivianite in the cranial region and interiors of long bones must have originated postmortem, but its distribution may be partly controlled by peripheral vasoconstriction, a physiological response to asphyxia. Nodular vivianite may have formed from iron derived from hemoglobin and phosphate liberated by partial demineralization of bones. Demineralization could have been caused by lactic acid, for which the main evidence is loss of tissues dominated by Type 1 collagen (denatured in lactic acid). We propose that this was consequent on postmortem colonization of the body by lactic acid-producing bacteria. These bacteria and their metabolites may have promoted preservation during the time before the body was incorporated in permafrost and could also have inhibited scavenging and bacterial decomposition following recent exposure of the specimen. (C) 2011 Elsevier Ltd and INQUA. All rights reserved.