Adelolophus
Adelolophus (meaning "unknown crest") is a genus of lambeosaurine dinosaur (a crested "duck-bill") from Upper Cretaceous rocks in the U.S. state of Utah. The type and only known species is A. hutchisoni; the type specimen consists only of a broken maxilla. It constitutes the oldest known lambeosaur remains from North America, as well as the only known lambeosaur species from the Wahweap Formation, of which it pertains to the Upper Member. Among its relatives, it seems to be particularly similar to Parasaurolophus, rather than animals like Lambeosaurus; phylogenetic analysis confirms this, finding it in Parasaurolophini (tube-headed lambeosaurs). It would have lived in a wet environment, bordering on the sea but with a more arid season during some times of the year. This environment would have been shared with a diverse variety of fish and turtles, as well as other dinosaurs like ceratopsids and tyrannosaurids.
A fossil bearing locality near Death Ridge in Kane County, Utah was first reported in 1973 by Howard D. Zeller; this locality is part of the Wahweap Formation, found within the Grand Staircase–Escalante National Monument area. The information reported by Zeller would be used by John Howard Hutchison and colleagues to return there to collect fossils in 1999. Among these was the maxilla (a jawbone) of a lambeosaurine hadrosaur.[1] This maxilla was first reported in 2013, in a paper by Terry Gates and colleagues. It was noted as the only known lambeosaur material from the formation (reported as being from the Upper Member), and the oldest known lambeosaur material in North America. They suggested the unique morphology indicated it was a new taxon, but refrained from naming it.[2]
Later, the specimen was described and named in a 2014 study, again led by Terry Gates, published as part of the book Hadrosaurs. The new species was given the name Adelolophus hutchisoni. The holotype is UCMP 152028, an incomplete right maxilla with both ends broken off. The generic name is derived from Greek α~, "not", δηλόω, "to show" and λόφη, "crest", referring to the known anatomy of the species not showing the presumed crest. The specific name is in honor of Hutchison, who discovered the specimen. The study noted that the exact locality of the specimen was unknown, making its referral to the Upper Member tentative, merely surmised by the rock matrix that had surrounded the specimen.[3] The type locality would be clarified by a 2016 study by Hutchison and Patricia A. Holroyd, confirming it came from the lower end of the Upper Member. It was suggested that the locality may bridge the gap in time between the older Middle Member and younger Upper Member of the formation. Fossils of other animals from the same locality were reported in the paper. Among these were fragmentary hadrosaur postcranial specimens, pertaining to various ages, including one very large individual. While the possibility was noted these could belong to Adelolophus, a referral is impossible to confirm.[1]
Several unique morphological traits diagnose Adelolophus as a distinct genus, despite its fragmentary nature. The anatomy of the only known bone, the maxilla (part of the upper jaw, bearing teeth), is identifiable as that of a lambeosaur (a type of dinosaur which possessed large, hollow head crests) based on features such as its triangular shape. Among its relatives, its anatomy is more similar to that of parasaurolophs (tube-headed lambeosaurs) rather than lambeosaurins (casque headed lambeosaurs), two closely related types of lambeosaurine. It differs most prominently from other taxa in its very tall medial wall (a ridge situated along the middle, upper edge of the bone), both on the front and back end of the bone. By comparison, lambeosaurins possess a particularly short medial wall, with that of Parasaurolophus showing an intermediate condition between the two.[3]
