PhD Student Northern Illinois University Northern Illinois University Mount Charleston, Nevada, United States
Abstract Body : Introduction
A phenomenon recognized primarily by researchers studying specimens recovered from asphalt seeps is colloquially known as “pit wear” and is relatively unknown outside of tar seeps. This type of fossil bone damage results only from circulation in an asphalt seep and is easily distinguishable from other types of surface damage. The damage consists of defects that are smooth-edged gouges and depressions. These depressions often appear different in color from the rest of the bone. Circulation of bones through the viscous medium is reminiscent of the way cooking pasta tumbles in a pot of boiling water, although slower and without heat. Our goal is to inform researchers who may not have interacted with asphalt seeps as to the differences, challenges, and implications of this type of fossil damage.
Materials and methods
Pit wear is a visually observed phenomenon caused by alteration of bone surfaces by taphonomic processes, and differs in relation to those causes. The study tools used were for making measurements: a centimeter ruler, a quarter, a dial caliper, a log book, and a Nikon Z6 ii camera with a 24-70/4s lens.
Results
The appearance of fossil specimen surfaces change, depending on the matrix in which they occur (eg. conglomerate, sandstone, siltstone, mudstone, and asphalt). Pit wear can occur on any bone surface and between bones of different species as the animals became trapped at different times. Other hard materials in the asphalt seep may also cause pit wear.
Plasticity from being in asphalt deforms bone surfaces into raised ridges without shattering, and damage may be deep enough to extend through the spongy bone, creating holes. These specimens are more pliable in situ than during the drying, hardening, and shrinking process that occurs after they are extracted from the matrix. Specimens that have been in close proximity to one another typically show matching concavities each caused by the other.
Conclusions
Detailed study of fossils from asphalt seeps is useful when observing fossils from these locations. Knowledge of how this type of damage occurs and its appearance on bones is critical to the correct identification of taphonomic processes, and can affect research conclusions. Pit wear differs from other forms of fossil damage and can assist researchers because color, deformation, and even how bones fossilize differ from terrestrial matrices. Pit wear alterations could also be misinterpreted as pathology or other forms of damage from many taphonomic processes.
Significance/Implication
Disease and other types of damage could be mistaken for pit wear. Researchers need to be aware of this type of damage and eliminate pit wear before deriving conclusions. Pit wear is a condition that can either hurt or help paleontologists in trying to distinguish types of damage to fossils.
