In addition to revealing greater detail of what the faces of tyrannosaurs looked like, the new dinosaur — called Horner’s Frightful Lizard (Daspletosaurus horneri) — helps to solve many other animal-related mysteries, such as why tyrannosaurs tended to have small arms, why today’s birds lack lips, and why alligators and crocodiles possess such sensitive snouts.
The findings are published in the journal Scientific Reports.
“We hypothesize that tyrannosaurs, including D. horneri and T. rex, had a tactile sensory system that was comparable, if not identical, to what is seen in living crocodylians,” lead author Thomas Carr, a vertebrate paleontologist at Carthage College, told Seeker, referring to an order of species that includes alligators, crocodiles, caimans, and the gharial.
“Work done by biologists on crocodylians has found that their faces were extremely sensitive to touch, rivaling that of human fingertips,” he continued. “The sensitivity comes from a combination of multiple branches of the trigeminal nerve that innervate the skin at specialized structures of thin, dome-like coverings of skin where neurons are in high concentration.”
Carr and his team made this determination after studying the new dinosaur’s well-preserved remains, which were unearthed at a site called the Two Medicine Formation in Montana. The remains include the skull and skeleton of a juvenile, the skull and skeleton of an adult, as well as other fossils from the species, which lived 75.1 to 74.4 million years ago.
The researchers conducted work that co-author Jayc Sedlmayr of the Louisiana State University Health Sciences Center New Orleans described as “arm deep in blood and guts,” dissecting birds, alligators, and crocodiles to see how facial nerves and arteries leave traces on bones. The scientists then used this information to flesh out the face of Horner’s Frightful Lizard that included small horns above the eyes.
The dinosaur’s super-sensitive snout likely would have been important “for prey manipulation, feeding, and for reproduction, such as building a nest, manipulating eggs, and safely moving hatchlings,” co-author David Varricchio, a professor at Montana State University, told Seeker.
He added that the snout could therefore function like an arm, given that “the small arms of tyrannosaurs were likely not effective at any of these tasks.”
The tender snout also appears likely to have served a sensual purpose when it came to mating.
“In courtship, tyrannosaurids might have rubbed their sensitive faces together as a vital part of pre-copulatory play,” says the report.
Horner’s Frightful Lizard used its snout skills to help devour prey that included horned, crested duckbill and dome-headed dinosaurs, in addition to much smaller carnivorous dinos, the researchers believe.
Carr said that “killing would have been the work of the jaws,” with their sensitive margins likely giving the hunter “important information regarding how hard to bite, whether or not the prey was still living, and the locations of soft and hard parts.”
The dinosaur’s similarities with today’s crocodiles and alligators are evidence of a genetic inheritance from a shared ancestor.
“Crocodylians are not dinosaurs, and dinosaurs are not crocodylians," Carr clarified, "but they do share a common ancestor.”
Birds, on the other hand, are considered to be living dinosaurs. Birds probably inherited their lack of lips from their equally lipless dino ancestors, according to the scientists.
The researchers further believe that Horner’s Frightful Lizard evolved via a rare form of speciation known as anagenesis, where one species gradually morphs into a new one over time.
Co-author Jason Moore of the University of New Mexico explained that he most common form of speciation, known as cladogenesis, “most frequently occurs by a small population of one species being separated from the remainder of the members of that species and being subject to a different set of environmental conditions, and hence evolving different sets of traits."
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