After fossils form, their original shape can become distorted, which makes it hard for scientists to figure out what these ancient creatures really looked like in life. This problem affects many aspects of the study of ancient life forms, including understanding how such organisms moved or how they were related to each other. Scientists try to overcome these distortions by figuring out how the fossils got bent out of shape in the first place. Although we know a bit about how the Earth's tectonic movement can distort fossils, we are still learning about the details of how pressure affects the shape of organisms as they turn into fossils. In this study, we used three-dimensional computer simulations to see how fossils of ancient sea creatures called trilobites might have changed shape when they were buried and distorted over time. We found that trilobites on flat ground stayed more true to their original shape than those on uneven ground. Also, the way a trilobite was positioned when it was fossilized—whether it was right-side up or flipped over—made a big difference in how much its shape changed. This research helps us form a better picture of what trilobites and other ancient animals looked like in real life.

Shape deformation during fossilization can prevent accurate reconstruction of an organism's form during life, hampering areas of paleontology ranging from functional morphology to systematics. Retrodeformation attempts to restore the original shape of deformed fossil specimens and requires an adequate knowledge of the deformation process. Although tectonic processes and retrodeformation are relatively well understood, research on quantifying the effect of compressive deformation on fossil morphology is scant. Here we investigate the factors that can cause changes in the shape of fossil specimens during compressive deformation. Three-dimensional (3D) models of trilobite cranidia/cephala are subjected to simulated deposition and compaction using rigid body simulation and scaling features of the open-source 3D software Blender. The variation in pitch and roll angle is lowest on flat surfaces, intermediate on tilted surfaces, and highest on irregular surfaces. These trends are reflected in the morphological differences captured by principal component scores in geometric morphometric analyses using landmarks. In addition, the different shapes of trilobite cranidia/ cephala according to their systematic affinity influence the degree of angular variation, which in turn affects their posture —normal or inverted. Inverted cranidia/cephala show greater morphological variability than those with normal postures.