Smithsonian.com

The restored skull of Azendohsaurus. From the Palaeontology paper.

Parsing the origins and early history of dinosaurs is a challenging task. A number of prehistoric creatures were a lot like some of the earliest dinosaurs, and sometimes evolutionary cousins of early dinosaurs have been mistaken for dinosaurs on the basis of fragmentary material. As a study published in Palaeontology now shows, this was the case with Azendohsaurus. New skeletal material from Madagascar helps to put it in its proper place.

Described by scientists John Flynn, Sterling Nesbitt, Michael Parrish, Lovasoa Ranivoharimanana and Andre Wyss, a complete skull of a new species of this enigmatic creature confirms that it is not a dinosaur. Instead, this creature, which lived between approximately 237 and 216 million years ago and is named Azendohsaurus madagaskarensis, was an archosauromorph—a member of a diverse group in which the dinosaur family tree is nested along with other creatures—which had independently evolved some of the features seen in the precursors of the immense sauropod dinosaurs and early ornithischian dinosaurs. This is shown most prominently by its teeth. They are leaf-shaped and are marked by a series of notches well-suited to chopping up leaves, meaning that this type of tooth evolved in several lineages of creatures which had been diverging from each other for millions of years.

This reassessment of Azendohsaurus has important implications for how paleontologists identify early dinosaurs. Previously the peculiar tooth type seen in this creature was thought to be an identifying feature of some early dinosaur types, but if it evolved more than once then isolated teeth and bits of jaw can no longer be taken as those of early dinosaur without further evidence. By being better able to diagnose fragments from the Middle and Late Triassic sites that harbor early dinosaurs, their ancestors and the disparate creatures they lived alongside, paleontologists will better able to understand the evolution of dinosaurs.

FLYNN, J., NESBITT, S., MICHAEL PARRISH, J., RANIVOHARIMANANA, L., & WYSS, A. (2010). A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible Palaeontology, 53 (3), 669-688 DOI: 10.1111/j.1475-4983.2010.00954.x

A restoration of the ankylosaur Sauropelta by John Conway. From Wikipedia.

Many dinosaurs were adorned with spikes, horns and plates, but it was the ankylosaurs that took armor to the extreme. These dinosaurs were covered in bony armor from snout to tail-tip, yet, as a new study suggests, there may have been more to some of these structures than just attack and defense.

As reviewed by paleontologists Shoji Hayashi, Kenneth Carpenter, Torsten Scheyer, Mahito Watabe and Daisuke Suzuki in the journal Acta Palaeontologica Polonica, the ankylosaurs can be subdivided into three smaller groups. There was the Polacanthidae (a group with large shoulder spikes and a “shield” over the hips), the Nodosauridae (forms with narrow heads and lacking tail-clubs) and the Ankylosauridae (the classic type with heavy armor over the body and tail-clubs). (There is some debate as to whether the Polacanthidae should be thought of as a distinct group, but since the authors separate it from the others I will follow their lead here.) Members of each group can be distinguished from each other on the basis of features which can be seen with the naked eye, but they are also different at the microscopic level. The arrangement of collagen fibers—one of the chief components of bone—differs in each group, as does the thickness of the bone composing the armor.

The differences in the bony armor of each kind of ankylosaur may help paleontologists determine to which group a specimen belongs based upon fragmentary material, but they may also indicate the different ways in which ankylosaurs used their armor. When the scientists looked at pieces of armor (including spikes and clubs) from several different dinosaurs across the three groups, they found that some of what might be thought to be weaponry was not well suited to the task. The outer layer of bone in the spikes of the polacanthids, for example, was relatively thin, especially in comparison to similar structures from the skeletons of the nodosaurids. This may mean that while the large spikes on the nodosaurids were sturdy enough to be used as weapons, the more fragile spikes of the polacanthids may have played a role primarily in display or regulating body temperature instead.

Additionally, the partial ankylosaurid tail club the researchers examined still showed signs of bone growth even though it appeared to have come from an adult animal. Combined with other recent findings, such as a possible lack of tail clubs among some juvenile ankylosaurids, this may mean that this structure developed later in life and was not initially used as a weapon. Perhaps, the authors hypothesize, developing tail clubs were used by juveniles and young adults for display, but it was not until later that the clubs could also be used for defense. Whatever they were doing, this study confirms that scientists are still learning much about dinosaurs by looking inside their bones.

Hayashi, S. (2010). Function and evolution of ankylosaur dermal armor Acta Palaeontologica Polonica DOI: 10.4202/app.2009.0103

A sketch of the skull of Diabloceratops eatoni. From FossilWiki

At the end of last summer, on my way out of Salt Lake City, Utah, I encountered a dinosaur I had never seen before in the halls of the Utah Museum of Natural History. Lying on its side was an impressive skull bristling with horns, and the placard identified it as an as-yet-unpublished creature informally known as the “Last Chance Ceratopsian” for the name of the stream near which it was found in the southern part of the state. (Though, if you read Scott Sampson’s Dinosaur Odyssey, you got a brief preview of it on page 34.) Now, after numerous delays in publishing the book in which its description is contained, this 26-horned dinosaur is ready to make its public debut.

Described by paleontologists Jim Kirkland and Donald de Blieux, the 80-million-year-old dinosaur is called Diabloceratops eatoni, with the genus name evoking its “devilish” appearance and its species name honoring Weber State University paleontologist Jeffrey Eaton. A long-time friend of Kirkland’s, Eaton is a fossil mammal specialist who has eschewed going after a few big dinosaurs in favor of studying the many, many fossil mammal specimens which lived alongside them during the Mesozoic, so it was only natural for Kirkland to “get back” at his friend by naming a dinosaur after him.

Even better, there may be a second species of Diabloceratops waiting to be described from the Cretaceous strata of southern Utah. While Kirkland and de Blieux were not able to confidently give it a taxonomic assignment, they mention a second skull which is very similar to, yet slightly distinct from, the better-preserved “Last Chance” specimen. As Scott Sampson has stressed on his blog, there is still a lot of interesting new material being found from these sites, and who knows what else will be found?

A restoration of Prestosuchus. From Wikipedia.

It’s not a dinosaur, but it may have eaten some of their ancestors.

Last week paleontologists from Lutheran University discovered the nearly complete skeleton of the 238-million-year-old predator Prestosuchus chiniquensis in the Late Triassic rock near the Brazilian town of Dona Francisca. The exceptionally preserved skeleton is immense—the individual would have been over 20 feet long in life—and represents an apex predator from the time after the Permian mass extinction shook up the world’s ecosystems but before large dinosaurian predators evolved. Indeed, even though it might certainly look dinosaur-like, it was instead part of a group of archosaurs more closely related to crocodiles than to dinosaurs, a peculiar lineages of predators called rauisuchians that flourished during the Triassic but became extinct around the end of that period.

It will take a number of years to fully study and describe this new specimen, but I am personally very excited about it. After being enthralled by a mount of Prestosuchus on display at the American Museum of Natural History years ago I found it nearly impossible to find more information about it. Outside of its original description and mentions in a few other studies, relatively little has been done with Prestosuchus, and I am eagerly awaiting the conclusions paleontologists will be able to draw from this exquisite new specimen.

[Hat-tip to Susan at Crurotarsi: The Forgotten Archosaurs for catching this story.]

A cast of this skull, collected by Barnum Brown, has been on display at the NJSM for years. From Wikipedia.

For years the New Jersey State Museum has displayed the cast of a complete Tyrannosaurus rex skull collected by Barnum Brown at the beginning of the 20th century, but now it may be getting a T. rex of its very own.

As reported last week in the Press of Atlantic City, paleontologists from the New Jersey State Museum and volunteers will be headed out to Montana this summer to recover remains of the world’s most famous dinosaur. The broken-up skeleton was found by amateur fossil hunter Joseph Camburn in 2007 while searching for fossils with NJSM paleontologist David Parris. The fossil will allow scientists to further compare specimens of Tyrannosaurus across different times and places. While the bones themselves would belong to the U.S. Department of Interior, they would be on indefinite loan to the museum for preparation and study.

This new skeleton would not be the first tyrannosaur in the New Jersey State Museum collection. During the time that Tyrannosaurus was hunting in what would become the American West, its smaller cousin Dryptosaurus was stalking prey near the coast of what would become southern New Jersey, and the acquisition of the new Tyrannosaurus would help highlight this bit of biogeography. More than that, paleontologists have recently proposed that the tyrannosaurs of the East adapted differently than did those in the West, and by comparing tyrannosaurs from these two regions paleontologists can better understand how the fearsome predators evolved.