Re-evaluation of a soft crested Edmontosaurin, with implications for hadrosaurid life appearance and diversity

Hadrosaurid dinosaurs are generally regarded as "crested" or "non-crested" depending on the presence or absence of a bony cranial crest. At least one supposedly "non-crested" hadrosaur is known to have possessed a soft tissue cranial crest (or comb), based on an exceptionally preserved "mummified" specimen. Here we redescribe this specimen and identify new features of the skeleton and integument. The comb evidently covered most of the skull roof and appears to have a crenelated anterior margin. Injury of the neck integument is identified for the first time and resembles previously reported hadrosaurid integumentary pathologies. The previously undescribed left side of the specimen shows disarticulated axial elements and detached integument, supporting a slow-burial mummification timeline. New preparation of the specimen reveals a shallow postorbital pocket that lacks a posterodorsal diverticulum, precluding both the original referral to Edmontosaurus regalis and an alternative referral to Edmontosaurus annectens. While we regard the existing skull material to be insufficient for holotype status, the unique morphology of the postorbital pocket warrants the recognition of this specimen as a distinct taxonomic unit from existing Edmontosaurus species, which we designate the Red Willow Edmontosaurin. The smooth, unremarkable skull texture visible beneath the comb shows that the predictive power of surface osteology with respect to soft display features is limited. Apart from this specimen, the distribution of soft-tissue crests in saurolophine and lambeosaurine hadrosaurids is currently unknown.