Four-dimensional virtopsy and the taphonomy of a mole from the Oligocene of Lake Enspel (Germany)

Abstract

A series of actualistic experiments were conducted to reconstruct probable taphonomic scenarios for a fossil mole specimen from the Enspel locality. Extant Talpa europaea carcasses immersed in water initially floated at the water surface then sank after a few hours or remained floating. Soft tissues started to decompose immediately and concomitantly putrefaction gas was produced and accumulated inside the body. Consequently, the carcasses became bloated, and the submerged ones re-surfaced. Gas formation and decomposition of soft tissues accelerated with increasing temperature, as expected. The skeletons of primarily floating specimens successively disarticulated with ongoing decomposition. In moderately warm water (19 °C) disarticulation began with the phalanges of the feet, while in warmer water (27 °C), disarticulation started with the phalanges of the hands and the lower jaws. Skeletal components of the re-surfaced specimens successively sank until the entire skeleton was disarticulated. Applying these experimental results to a partial skeleton of the Oligocene mole Geotrypus antiquus from Enspel (Germany) suggests that carcass sank whole to the bottom of the lake and did not undergo an extended period of floatation. This interpretation is supported by the following characteristics: (1) upper and lower jaws in occlusion, (2) presence of distal hand elements and the left femur and (3) the positions of the elements of the anterior extremities. After decomposition of most or all soft tissues at the bottom of the lake an underwater current from the right side shifted some bones to the left side of the body axis, while the humeri and the still-articulated skull stayed in their original anatomical position.