Scientists at Louisiana State University have identified a new tyrannosaur that directly evolved from its geologically older ancestor through anagenesis.
The international team of scientists discovered the new tyrannosaur Daspletosaurus horneri or Horner’s Frightful Lizard that evolved directly from its older relative, D. torosus.
This rare form of evolution is known as anagenesis and happens when one species gradually changes or evolves over time into a new species.
Researchers also found that the face of tyrannosaurs were covered by a lipless mask of large, flat scales with smaller patches of armor-like skin and horn and a highly touch-sensitive snout.
The Daspletosaurus horneri is believed to have lived in Montana 75.2-74.4 million years ago. The tyrannosaur had a body length of 9 meters, a wide snout, small orbital horns and slit-like pneumatic opening on the inside of the lacrimal bone.
Scientists from LSU’s Health Sciences Center New Orleans School of Medicine collaborated on the study with researchers at Carthage College, Montana State University, James Cook University and the University of New Mexico.
The team examined fossils of 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. They compared tyrannosaur skulls with those of crocodylians, birds and mammals as well as earlier research matching bone texture with various types of skin covering.
“Much of our research went beyond field paleontology — it was generated from lab-based comparative anatomy, the dissection of birds as living dinosaurs and crocodilians as their closest living relatives, and based on the similarities of the facial nerves and arteries we found in those same groups which left a trace on the bone, we were able to then reconstruct in the new tyrannosaur species,” Jayc Sedimayr, anatomist at LSU Health New Orleans, said in a press release.
Sedimayr’s research was based on dissecting birds, alligators, crocodiles, lizards and turtles, injecting their blood vessels and conducting angiographic studies to hypothesize homology based on the dissections. Homology is anatomical features shared from a common ancestry.
“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,” said Thomas Carr, a researcher at Carthage College’s Department of Biology. “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.”
The study was published in Scientific Reports.