From tree to shining sea: taphonomy of the arboreal lizard Geiseltaliellus maarius from Messel, Germany

Abstract

Much has been written about the palaeoenvironment of the middle Eocene fossil Lagerstatte of Messel, Germany, and of the taphonomy of the vertebrates found in it, but taphonomic phenomena among the reptiles in this locality are virtually unstudied. The iguanid Geiseltaliellus maarius is the most common lizard species in Messel. We present taphonomic data for this species and analyse it. Specimens of G. maarius can be divided into three preservation classes, one of which is distinguished purely by decompositional phenomena. Most specimens sank quickly to the bottom of Lake Messel after entering it, but one floated for some time prior to emplacement. In theory, overlying pressure should not preclude the accumulation of gases of decay in submerged carcasses. In one specimen, such gases appear to have built up intracoelomically for many weeks, but did not cause the carcass to rise because of overlying water pressure. Eruption of the gases through the oral and cloacal openings, possibly initiated by a coincident turbidity current, scattered the bones of the skull, the pelvic region, and the proximal part of the tail. G. maarius had evolved a form of intervertebral urotomy (pseudoautotomy), which is indicative of arboreal habits. The waxy substance adipocere, formed after breakdown of fat, has been neglected in discussions of taphonomy, but may constitute an important factor in stabilising carcasses and enabling three-dimensional preservation before diagensis.