How physical characteristics of beetles affect their fossil preservation

Although insect size and robustness often have been hypothesized to be factors that lead to tophonomic bias in the insect fossil record, no studies have examined how these factors directly affect an insect's preseruation potential. In this study, laboratory experiments were performed on modern Coleoptera (beetles) to examine the importance of insect morphology on preservation potential. A rotary tumbling barrel was used to determine how insect size and robustness would influence sinking and disarticulation rates. Although size and robustness were not correlated directly, beetles that were larger and more robust were more resistant to disarticulation than smaller, less-robust beetles. Waterlogged specimens gained increased flexibility in their exoskeletons, and were difficult to puncture. Sinking and disarticulation rates were correlated, although it took fewer days for beetles to sink than it took to begin disarticulating. A white-colored film was apparent on all specimens within a few days of their introduction to the tumbling barrel; however, major disarticulation did not occur until the specimens sank to the bottom. An examination of the fossil-beetle literature also suggests the importance of hardness in preservation potential. Although often considered fragile, given the right physical characteristics and environmental conditions, insects can be resistant to disarticulation and decay.