Daspletosaurus horneri, New Tyrannosaurus Relative from Montana
Tyrannosaurus rex remains the best known (and maybe the most popular) dinosaur, but the huge meat-eater had relatives that paleontologist are still discovering. The latest new member of the tyrannosaurid family was found in Montana and lived about 75 million years ago, about 10 million years before Tyrannosaurus. Paleontologist have named it Daspletosaurus horneri (in honor of Montana paleontologist Jack Horner!) and published a short description in a new scientific paper (available for free). The genus Daspletosaurus “frightful lizard” was first described from another species (Daspletosaurus torosus) that lived earlier and was found in Alberta in Canada. The new species D. horneri differs in a number of small ways from D. torosus, but may, in fact, be a direct evolutionary descendent of the earlier Alberta species, a process called anagenesis.
The type skull of Daspletosaurus horneri is well preserved and appears to show evidence of nerve openings on the snout, similar to the pressure-sensing organs on the scaly snouts of crocodilians. Such nerves would mean that the dinosaur’s snout was also scaly and that, like in crocodiles, the jaws did not have lips that covered the teeth (as in lizards) as recently proposed for meat-eating dinosaurs by another group of researchers. Such a pressure-sensing surface could have been used to deal with prey or may have been used in courtship, with dinosaurs rubbing or touching with their snouts. (Crocodiles use their pressure-sensing organs to detect prey underwater.)
A number of skulls and parts of skulls of Daspletosaurus horneri have been identified from the Two Medicine and Judith River formations in Montana and form a growth series from juvenile to adult.
Because both Daspletosaurus and Tyrannosaurus rex lived in Canada and the Western United States, some paleontologist proposed that Daspletosaurus might be an ancestor of the later Tyrannosaurus. However, a number researchers now think that the two dinosaurs belonged to different sub-branches of the tyrannosaurid family and that Tyrannosaurus likely migrated from Asia into North America, replacing the native tyrannosaurids. A tyrannosaurid species called either Tyrannosaurus bataar or Tarbosaurus bataar (some scientist think it’s different enough to need a separate genus) is known from Mongolia and closely resembles the larger and heavier Tyrannosaurus rex that lived a few million years later in North America. The Asian species has been in the news in recent years because smuggled fossils (billed as Tyrannosaurus) were collected and sold illegally in the United States and other countries. Mongolia has laws that prevent the unauthorized export of its fossils and has even opened a new museum in its capital city to display some of the returned dinosaur specimens.
Thomas D. Carr, David J. Varricchio, Jayc C. Sedlmayr, Eric M. Roberts & Jason R. Moore (2017)
A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system.
Scientific Reports 7, Article number: 44942 (2017)
doi:10.1038/srep44942
http://www.nature.com/articles/srep44942
https://phys.org/news/2017-03-discovery-predatory-dinosaur-species-insight.html
http://gizmodo.com/this-tyrannosaur-used-a-sixth-sense-to-hunt-its-prey-1793791733
http://tyrannosauroideacentral.blogspot.com/2017/03/introducing-daspletosaurus-horneri-two.html
http://tyrannosauroideacentral.blogspot.com/2017/04/introducing-daspletosaurus-horneri-two_3.html