If we look at these new species superficially, they resemble kritosaurins like Gryposaurus but where they differ largely is in the retention of certain plesiomorphic character states in different bones in the animal including the maxilla and jugal bone.
Research, detailed in a new paper in the Journal of Systematic Palaeontology, revealed that the fossils are of a previously unidentified genus and species; the newly named Aquilarhinus palimentus.
The animal would have been shovelling through loose, wet sediment to scoop loosely-rooted aquatic plants from the tidal marshes of an ancient delta, where today lies the Chihuahuan desert.
While sounding odd, duck-billed dinosaurs - also known as hadrosaurids - were actually the most common herbivorous dinosaurs at the end of the Mesozoic Era.
Sure, some beaks were broader than others, but there was no evidence of a significantly different shape, and therefore different feeding style-until Aquilarhinus came along.
The main group of duck-billed dinosaurs in this category are known as Saurolophidae.
The fossil was originally discovered in the 1980s by Texas Tech University Professor Tom Lehman. He collected them with two more scientists at the University of Texas in Austin but it was impossible to conduct the study. In the 1990s an arched nasal crest was identified, thought to be distinctive of the hadrosaurid Gryposaurus. It turned out that it was a more primitive species, similar to the two groups of duck-billed dinosaurs. Their jaws formed a beak shape used for cropping plants.
"Its existence adds another piece of evidence to the growing hypothesis, still up in the air, that the group began in the southeastern area of the United States". Notably, the symphyseal processes of the dentary are elongated and reflected dorsally, causing the dentaries to meet with a "W"-shaped anterior profile", researchers described the Aquilarhinus".
But the latest fossilised find would have eaten in a completely different manner to other known duck-billed dinosaurs.
Dating to approximately 80m years ago, this dinosaur does not fit in with the main group of duck-billed dinosaurs known as Saurolophidae. Instead, the lower jaw of this newly discovered species met in a unusual W-shape to create a wide, flattened scoop. When the dinosaur died, some of its bones were transported downstream by the tide and became lodged in vegetation. Then, over millions of years, the remains were covered in silt, fossilizing the bones in a type of sedimentary rock known as ironstone.