Bird-like characteristics of troodontid theropod eggshell

摘要: Description of well-preserved fossil eggshell (oospecies Prismatoolithus levis), recently assigned to the theropod dinosaur Troodon formosus, reveals traits that are shared with both and Recent avians. Bird-like characteristics troodontid include: fibres associated eisospherites attached bases mammillae, fine radiating crystals form spherulites grade into blocky wedges prisms in outer layer exhibit squamatic ultrastructure. The presence two layers (mammillary squamatic) within is either a apomorphy or it arose Theropoda; external crown-group avians apomorphic respect other eggshell. Despite disagreement on putative sister taxon birds, recent phylogenies suggest strongly prismatic ultrastructure evolved independently Troodontidae Neognathae. Our identification eggshell, which was previously thought lack this structure, problems previous assignment dinosauroid-prismatic morphotype concept current parataxonomy. We conclude should be abandoned.