Re-evaluation of the Mesozoic mantis shrimp Ursquilla yehoachi based on new material and the virtual peel technique

We re-evaluate the Mesozoic mantis shrimp Ursquilla yehoachi, based on the original four specimens and a new exquisitely preserved one. All specimens were documented by application of a new technique, which is introduced here and termed the virtual peel technique. This technique includes two steps: 1) Documentation of low-relief fossils including their 3D information with the aid of a standard flat-bed scanner. 2) Virtual inversion of the negative relief of fossils; the resulting positive relief facilitates a better understanding of the fossil. Unlike the previously known specimens, the new specimen of U. yehoachi preserved most details of the uropod including the exopod, an important feature in stomatopod phylogeny. Remarkably, this exopod bears striking similarities to that of modern stomatopods in being bipartite and having a paddle-shaped distal part, supporting earlier assumptions about the systematic position of U. yehoachi within Squilloidea. Observable morphological differences among the available material of U. yehoachi can now be identified as ontogenetic variation. The telson, for example, attains a proportionally broader shape with increasing size, a result of allometric growth.