On March 12-13, the south-central section of the Geological Society of America held their annual meeting in Little Rock, Arkansas. During that meeting, a session was held on paleontology in honor of Arkansaurus fridayi being named our State Dinosaur, even though it has never been officially scientifically named and it being the only dinosaur that has ever been found in Arkansas other than tracks. That all changed during the meeting. This post will focus on the Arkansas dinosaurs (yes, plural, that was not a typo). A later post will cover more fossil announcements.

The first talk on Arkansas dinosaurs came from our very own Dr. Rebecca Hunt-Foster, who did the initial work on Arkansaurus. She has a new paper that came out right after the meeting. She announced that Arkansaurus fridayi is now the officially recognized scientific name for our dinosaur. She also discussed her findings confirming it as an ornithomimid, one of the bird-mimics, like the Gallimimus made famous in Jurassic Park. That had been the first tentative identification, but her work previously showed that it did not match with other known North American ornithomimids. However, that was from a total known collection of nine specimens. We now have almost two dozen ornithomimids known from North America. When she compared Arkansaurus with the new material, she was able to confirm that the initial identification was indeed correct. Moreover, it showed that ornithomimids had the ability to disperse across the continent at the time. The Late Cretaceous interior seaway that bisected the continent had not yet closed off access by then.

Dr. Celina Suarez from the University of Arkansas at Fayetteville provided the most astounding talk of the session (ed. this was a repeat of the talk she gave at the national GSA meeting in Seattle in 2017). We knew we had titanosaurs and acrocanthosaurs in Arkansas from their foot prints. Now we have their bones as well. She presented a description of the first known Mesozoic multi-faunal vertebrate assemblage in Arkansas. In other words, she reported a collection of fossils that contained several different species. The fossils were found in Howard County within the Holly Creek Formation, a part of the Trinity Group that underlies the DeQueen Limestone. This is the same site which became famous for its dinosaur tracks.

Among the fossils included pieces of a titanosaur that is probably Sauroposeidon, one of the largest dinosaurs ever known. They like to call it Paluxysaurus in Texas, but further work has indicated that Paluxysaurus is a junior synonym of Sauroposeidon found in Oklahoma and now Arkansas. She also found pieces of an Acrocanthosaurus. For those who are not familiar with this dinosaur, it is a carcharodontosaurid, the same family as Giganotosaurus. This family is within Allosauroidea, the group containing Allosaurus and all its kin. Acrocanthosaurus was almost the size of Tyrannosaurus rex and with a small sail or ridge along its back and was the dominant predator of its time.

Drawing of a Sauroposeidon proteles and an Acrocanthosaurus by Mike O’Brien.

That isn’t all though. They also found scutes from an ankylosaur. While it isn’t a lot, Kristy Morgan, one of her students, was able to determine that they likely belonged to a nodosaurid ankylosaur either most closely related to or actually was Borealopelta, a dinosaur from Canada just named in 2017 from the best preserved dinosaur fossil ever found.

   Borealopelta markmitchelli. Image credit: Royal Tyrrell Museum.

Finally, pieces of two other theropods were found. They found pieces identified as Deinonychus antirropus, Velociraptor’s big cousin, as well as Richardoestia. Deinonychus is well known as the archetypal dromeosaur, the dinosaurs with the famed sickle-clawed toe. Richardoestia is much less well known, making this identification curious. All that is really known of this dinosaur is a set of jaws and some isolated teeth. Three species have been named, but at least one has been suggested to be a sebecid crocodylomorph. It is likely that once more of this genus is discovered, some or all of the species will not survive, at least as they are now. But for now, we will count it as an Arkansas dinosaur until shown otherwise.

Richardoestia. CURRIE, RIGBY & SLOAN, 1990

This just touches on the fossils found in this assemblage. We now have a much bigger glimpse into Cretaceous Arkansas. Stay tuned for more. For now, we can say that southwest Arkansas 120 million years ago looked something like this.

https://www.youtube.com/watch?v=ueBM9QxebNsyoutube