Paleontologists have unveiled a remarkable new species of tyrannosaurine dinosaur from the Late Cretaceous epoch — a cousin of the fearsome predator Tyrannosaurus rex.
Life reconstruction of the integument of Daspletosaurus horneri, based on the distribution of texture on the facial bones. The face in tyrannosaurs was covered by an extensive mask of large, flat scales, and regions of armor-like skin on the snout, jaws, and ornamental horns. The large horn behind the eye was covered by horn, the same material that makes human fingernails. The small bumps on the flat scales are integumentary sensory organs, as are seen in crocodylians that provide extreme tactile sensitivity. Image credit: Dino Pulera.
The newly-discovered dinosaur is called Daspletosaurus horneri, or the Horner’s frightful lizard. It is named for the renowned paleontologist, John ‘Jack’ R. Horner, formerly curator at the Museum of the Rockies in Bozeman, Montana.
According to the paleontologists who discovered it, this species lived in what is now Montana between 75.2 and 74.4 million years ago.
The beast was a type of tyrannosaur, a group of giant predatory dinosaurs of the Late Cretaceous from Asia and North America.
“Daspletosaurus horneri was the youngest, and last, of its lineage that lived after its closest relative, Daspletosaurus torosus, which is found in Alberta, Canada,” said Dr. Thomas Carr, a paleontologist at Carthage College and lead author of a report published this week on Daspletosaurus horneri in the journal Scientific Reports.
“The close evolutionary relationship between the species taken with their geographic proximity and their sequential occurrence suggests that together they represent a single lineage that changed over geological time, where D. torosus has morphed into D. horneri.”
“It’s about 75 million-years-old, so this animal lived about 9 million years before the extinction of the non-avian dinosaurs,” added co-author Dr. Eric Roberts, from James Cook University.
“In geological terms, the beast was the youngest of the Daspletosaurus clan.”
With a body length of 29.5 feet (9 m) and a height of 7.2 feet (2.2 m), Daspletosaurus horneri had a wide snout, small orbital horns and slit-like pneumatic opening on the inside of the lacrimal bone.
The large horn behind the eye is elevated beyond the side of the head, indicating a covering of keratin, the hard and shiny material that makes up human fingernails.
Its prey were horned dinosaurs (ceratopsians), crested duckbill dinosaurs (hadrosaurs), dome-headed dinosaurs (pachycephalosaurs) and smaller carnivorous dinosaurs (theropods).
Skull and jaws of the holotype of Daspletosaurus horneri: (A) photograph and, (B) labeled line drawing of skull and jaws in left lateral view; (C) photograph and, (D) labeled line drawing of occiput and suspensorium in caudal view; (E) photograph and, (F) labeled line drawing of skull in dorsal view. Scale bars – 10 cm. Image credit: Thomas D. Carr et al, doi: 10.1038/srep44942.
Dr. Carr, Dr. Roberts and their colleagues worked with well-preserved fossils — a skull and skeleton of a subadult, a skull and skeleton of an adult, a partial lower jaw of a subadult, and isolated bones of subadults and juveniles.
In addition to adding a new species to the tyrannosaur family tree, the team’s research provides new information about the mode of evolution and life appearance of tyrannosaurs.
The researchers found evidence for a rare, nonbranching type of evolution in tyrannosaurs and that tyrannosaurs had scaly, lipless faces and a highly touch-sensitive snout.
“It turns out that tyrannosaurs are identical to crocodylians in that the bones of their snouts and jaws are rough, except for a narrow band of smooth bone along the tooth row,” Dr. Carr said.
“In crocodylians, the rough texture occurs deep to large flat scales; given the identical texture, tyrannosaurs had the same covering. We did not find any evidence for lips in tyrannosaurs, the rough texture covered by scales extends nearly to the tooth row, providing no space for lips.”
“However, we did find evidence for other types of skin on the face, including areas of extremely coarse bone that supported armor-like skin on the snout and on the sides of the lower jaws. The armor-like skin would have protected tyrannosaurs from abrasions, perhaps sustained when hunting and feeding.”
The authors found that, like in crocodylians, the snout and jaws of the tyrannosaurs are penetrated by numerous small nerve openings, allowing hundreds of branches of nerves to innervate the skin, producing a sensitivity similar to that of human fingertips.
“This sensitivity is part of a bigger evolutionary story,” said co-author Prof. Jayc Sedlmayr, from the Louisiana State University Health Sciences Center New Orleans.
“The trigeminal nerve has an extraordinary evolutionary history of developing into wildly different ‘sixth senses’ in different vertebrates, such as sensing magnetic fields for bird migration, electroreception for predation in the platypus bill or the whisker pits of dolphins, sensing infrared in pit vipers to identify prey, guiding movements in mammals through the use of whiskers, sensing vibrations through the water by alligators and turning the elephant trunk into a sensitive ‘hand’ similar to what has been done to the entire face of tyrannosaurs.”
_____
Thomas D. Carr et al. 2017. A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports 7, article number: 44942; doi: 10.1038/srep44942
