EXCEPTIONAL THREE-DIMENSIONAL PRESERVATION OF MUSCLES IN A FOSSIL GHOST SHRIMP

The preservation of soft tissues in the fossil record is a rare phenomenon and requires special circumstances resulting in early diagenetic mineralization. Muscles are seldomly preserved in fossil decapod crustaceans. However, when they do preserve, they tend to occur in Konservat-Lagerstätten and predominantly as compressed specimens so that the three-dimensional structure of the muscles is often obliterated. We report on three-dimensionally preserved muscles in the chelipeds (propodi) of a Pleistocene-Holocene ghost shrimp (Sergio sp.). The specimens were collected ex-situ from the Amador and Farfan beaches at the Pacific entrance of the Panama Canal near Panama City, Panama. Muscle fibers are clearly visible at different magnifications in one spectacularly well-preserved specimen, whereas muscles are less well-preserved in other specimens. The muscular structure closely resembles that of modern ghost shrimps with muscle fibers forming bundles that attach to the inner side of the cuticle. SEM-EDS analyses indicate that the muscles are phosphatized, which is common for fossilized muscles. The presence of muscles indicates that the specimens were corpses instead of molts. We hypothesize that the propodi provided a relatively closed system that enhanced preservation of these soft tissues.