A new paper out this week in Advances in Paleobiology suggests that the Hadrosaurinae, currently comprised of what's thought to be a paraphyletic group of largely crestless duckbill dinosaurs, may have to be renamed as "Edmontosaurinae." To make a long story short, the authors, Francis Boondoggle and Edward Hootenany, have sunk the majority of crestless forms into the already-sizeable Edmontosaurus genus. Such famous forms as Anatotitan, Maiasaura, and Shantungosaurus are now regarded as various species of the widespread North American genus.
"When you look at these creatures, and I mean really look at them, they all basically look the same," said Boondoggle at a press conference. "They all have toothless beaks with grinding teeth and long snouts. To us, that suggests they all fall under the same general category, or in this case, genus."
It's not all Edmontosaurus, though. Gryposaurus, Kritosaurus and Brachylophosaurus will be united under Kritosaurus, as it was the first genus named, in 1910. The three are united by general cranial characters including a shortened face (compared to Edmontosaurus) and a nasal arch. Unlike his colleague, Hootenany believes that, despite the obvious differences between their skulls, Kritosaurus may, too, fall under Edmontosaurus. "You don't call a Bichon Frise something different from an Australian Shepard. They're both Canis lupis familiaris, but most paleontologists would give them different genus names if they were dug out of the ground."
The authors both agree that Saurolophus should remain a separate genus based on its small nasal crest. "In fact," mentions Boondoggle, "Saurolophus may be the genus connecting edmontosaurines with lambeosaurines based on that little crest." But what of Prosaurolophus? "We think that that smaller-crested form is either a subadult or female Saurolophus. It just makes the most sense." Although Edmontosaurus is not the most inclusive genus in the Dinosauria (that would be Psittacosaurus, with about a dozen species), it is now the largest genus to include other taxa previously separated at the genus level. Instead of having four distinct taxa, we now have one big ol' taxon," Boondoggle said with pride.
The new paper recognizes three genera within the Edmontosaurinae: Edmontosaurus, Saurolophus, and Kritosaurus. The authors are now looking at the Lambeosaurinae, which includes the famous crested duckbills like Parasaurolophus and Corythosaurus. "Although our next study is only in the preliminary phase, the lambeosaurines all seem to be the same animal except for crest shape." The duo has plans to refurbish other branches of the Dinosauria as well. "Specifically ceratopsians and early ornithopods," says Hootenany. "Especially in regards to the latter, they all look the same!"