THEY BEND BUT DON’T BREAK: TESTING THE PHYSICAL ROBUSTNESS OF INSECT CUTICLE TO PREDICT PRESERVATION POTENTIAL

Does the physical robustness of insect cuticle influence their preservation potential in the fossil record? Molecular degredation can occur within a matter of days to months (Stankiewicz et al. 1998), however, mechanical degradation begins to occur as soon as the insect dies. Any degree of prior mechanical degradation will highly increase the amount of biological and molecular decomposition. Therefore, those organisms that are physically robust will resist biological decomposition longer. While Briggs and others have measured the chemical composition of fossilized arthropods, nobody has measured the physical robustness of arthropod chitin. To test the importance of physical robustness, I conducted two experiments on modern beetles. Coleoptera are an abundant and diverse group in the fossil record as well as in modern environments. Their resistance to decay has been attributed to their physical and molecular robustness. Beetles were used in this experiment because they are diverse ecologically, taxonomically and morphologically. Chitin can last indefinitely if it was deposited in an environment that was conducive to its preservation (ie. rapid burial and an environment free of chitinofagous organisms and microbes). I focus on lacustrine environments which often have ideal conditions for preservation of many organisms, including a large abundance of beetles. The experiments tested the chitin strength of different beetle taxa, with different degrees of sclerotization as well as their resistance to disarticulation. We found that the hardness and resistance to disarticulation varies with morphotype. Those taxa with physically robust exoskeletons are preserved more often in the fossil record. Finally, if specimens are waterlogged, their resistance to breakage increases, thus increasing their overall preservation potential.