Tom Lehman was researching rock layers at Texas’ Rattlesnake Mountain in the 1980s when he discovered some weathered bones. He had no idea at the time, but the fossils represented the skull of a previously unknown dinosaur species that lived 80 million years ago.
Lehman, a master’s student at the University of Texas at Austin when he found the fossils, collected the bones. But they couldn’t be studied because they were stuck together.
The bones were trapped in ironstone because when the dinosaur died, some of the bones separated and went downstream before becoming lodged together in a silt-filled area.
In the 1990s, a few clues emerged, including an arched nasal crest and a strange lower jaw. But then the fossil took a back seat until recently.
The arched nasal crest was initially thought to indicate that the animal belonged to Gryposaurus, a member of the hadrosaur family that included duck-billed herbivorous dinosaurs.
But a new analysis of the fossil by Lehman, now a professor at Texas Tech University, revealed that the dinosaur was more primitive than Gryposaurus. A study of the fossil was published Friday in the Journal of Systematic Palaeontology.
“This new animal is one of the more primitive hadrosaurids known and can therefore help us to understand how and why the ornamentation on their heads evolved, as well as where the group initially evolved and migrated from,” said lead study author Albert Prieto-Márquez of the Institut Català de Paleontologia Miquel Crusafont near Barcelona. “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 US.”
The jaw mechanism acted like two trowels, which would have been effective considering that the dinosaur would have needed to shovel through tidal marsh sediment in order to reach aquatic plants. The ancient delta where it lived is now the site of the Chihuahuan desert.
The researchers realized that the dinosaur’s curved nose and wide lower jaw set it apart. They named it Aquilarhinus palimentus, which means “shovel-chinned eagle nose.”
Most duck-billed dinosaurs had jaws that met in a U shape, acting like a cupped beak for capturing vegetation. But Aquilarhinus had a jaw that came together in a W shape, meaning it could function in a wider and flatter scoop than a U shape.
This dinosaur also had a solid bony crest resembling a humped nose, but most duck-billed dinosaurs had hollow bony crests.
The researchers believe that this fossil sheds light on the fact that there were other lineages of these dinosaurs before they all evolved to have similar features.