Meeting Abstract

55.4  Sunday, Jan. 5 14:15  Using impression fossils and 3D tomography to investigate the role of oxygen in insect evolution VANDENBROOKS, JM*; HARRISON, JF; Arizona State University; Arizona State University jvandenb@asu.edu

Changes in atmospheric oxygen levels have been hypothesized to have driven evolutionary changes in insect body size, including Paleozoic gigantism. However, the fact that not all insect groups exhibited gigantism coupled with the paucity of the fossil record and the complex interactions between oxygen, organisms and communities makes it difficult to definitively accept or reject the oxygen-size link. We have taken two approaches to address this issue. One approach was the first statistical study of average and maximum body size of insect impression fossils across geologic times of both high and low oxygen levels. The results of these studies support the link between fluctuations in oxygen and insect evolution: 1) the maximal and average size of Protodonata and Paleodictyoptera fossils correlate positively with modeled atmospheric oxygen, 2) Blattodea fossils showed little variation in maximum size, but average size was correlated with atmospheric oxygen, and 3) the Triassic hypoxic event appears to have a larger impact on insect body size than the Paleozoic hyperoxic event. These results support both our previously reported results on modern insects, and the hypothesis that variation in atmospheric oxygen was a key control on insect body size through the Phanerozoic. Secondly, we have used x-ray synchrotron imaging to generate 2D images and 3D tomographic reconstructions of both modern insects and amber fossils, including the tracheal system. Our studies on modern insects have shown that the tracheal dimensions are strongly affected by oxygen variation. The ability to measure fossil tracheae provides a unique look at the impact of oxygen on insect respiratory systems and a possible biological proxy for atmospheric oxygen. Supported by NSF EAR 0746352.