PRESERVED INTERNAL MEMBRANES OF DINOSAUR EGGSHELL FRAGMENTS, UPPER JURASSIC MORRISON FORMATION, DALTON WELLS, UTAH

Previous investigations of the soft-shelled component of dinosaur eggs typically focus on completely preserved eggs, which are scarce in the rock record. Eggshell fragments were collected as float from the Upper Jurassic Brushy Basin Member, Morrison Formation. Both modern birds and dinosaur eggshell fragments were observed under the SEM with secondary electron detector which permits distinguishing relative atomic number. Initial analysis of features documented in the eggshell fragments suggest preservation of organic material. This remarkable preservation of the interior membrane opens a previously unrecognized taphonomic window for studying dinosaur egg evolution

The internal membrane of modern bird eggs is composed of type X collagen fibers that vary in lengths and widths and comprise several interlaced layers. Embedded in this fibrous matrix are “calcium reserve” deposits that are utilized for embryonic development. Features common to both modern birds’ eggs and the dinosaur egg fragments include: 1) irregular shaped-calcium carbonate “floating” in an organic matrix, 2) external calcium carbonate molds of fibers in the mammillary bodies that form the foundation for building the egg shell, 3) three-dimensional organic fiber matrix, and 4) organic matrix with oval to circular pore. Unlike modern birds’ eggs, the dinosaur eggs’ calcium carbonate tubes were observed to have organic fibers inside that are traced into a fluidized/gel deposit.

The recognition of well-preserved internal membrane features on fragments of hard-shelled dinosaur eggs from the Morrison Formation indicates newfound opportunities to explore the preservation of probable organic compounds associated with fragmental dinosaur eggs.