Museum Paleonephrops Lobster Fossil from Montana

Description: This rare, museum grade lobster fossil is superbly preserved in three dimensions The arms and claws are fully extended, and both eye-stalks are preserved. Note the pustulate carapace and well preserved exoskeleton. The tail is tucked under and the legs are not exposed. The concretion was shattered into six pieces when split. With expert curation the lobster has been exposed and repaired; now lying comfortably, as if on a oval serving platter.

Only a few of these specimens have been preserved in this state of preservation. This species is found in the same areas as the more famous and numerous iridescent ammolite ammonites, Placenticeras. Those rare lobsters discovered normally shatter when the concretion is broken, or are in a poor state of preservation. According to the previous owner, this one was obtained from a small collection, and the others went to a university for study.

"The lobsters are preserved in argillaceous limestone concretions that have the shape of slightly flattened prolate ellipsoids. The concretions that contain lobsters generally contain only a single animal. However, a few contain two lobsters, and one was discovered that contained a lobster and a crab. The lobsters are preserved as sediment filled exoskeletons which usually have the claws, cephalothorax and abdomen articulated, and are preserved in an upright position stretched out along the axis of the animal. The abdomen may be enrolled to varying degrees. Most specimens show some evidence of minor dorsal-ventral compression and a few are laterally compressed. Diagenetic changes have altered the chitinous exoskeletons although preservation is delicate enough to have preserved internal (endophragmal) skeletons in some individuals. The lobster corpses and molts decayed on the sea bottom and as the articulating membranes decomposed the surrounding sediment found its way into the interior of the exoskeleton. Calcite precipitated and filled the interstitial spaces in the mud in and around the lobsters forming the argillaceous limestone concretions." (From the Journal of Paleontology, November 1977, Robert F. Feldman).