At least 10 million years before dinosaurs ruled the world, very large and probably fierce reptiles dominated the muddy coastal plains of what is now Northern Arizona and New Mexico. Scientists say Arizonasaurus babbitti, a primitive crocodile-like meat-eater, was among the very first. Research into the 13-foot-long carnivore has shed light on the Middle Triassic age and paleontologists believe the predator has more to tell.
A leading Arizonasaurus babbitti expert, vertebrate paleontologist Sterling Nesbitt, Ph.D., continues to scour the Southwest looking for more of the creature’s fossilized remains. A Mesa native, Nesbitt grew up hunting for fossils with his parents in Northern Arizona’s vast open spaces. In 2002, while just a sophomore at University of California, Berkeley, he led a team that found an almost complete skeleton fossilized in rock that was 240 million years old near Winslow.
Those remains – the skull, scapula, vertebrae and pelvic bones – became the biggest ever Arizonasaurus babbitti discovery. The findings helped fill in the early evolutionary chapter about the crocodilian branch of the archosaur family tree. The dinosaurs, distant relatives of Arizonasaurus (Arizona lizard), are archosaurs that took a different evolutionary path and eventually gave rise to today’s birds. Arizonasaurus babbitti’s ancient bones also formed the foundation of Nesbitt’s scientific career. Since his finding, he has traveled the world looking for traces of other archosaurs in ancient rocks of the same time period and is an assistant professor of geosciences at Virginia Polytechnic Institute and State University (Virginia Tech).
Characteristics of a Ruling Reptile
“The Arizonasaurus skeleton started to solidify what these early archosaurs looked like when archosaurs really started to diversify,” Nesbitt said. “It’s the first glimpse of the Age of Reptiles where they became the dominant life form on our planet. It’s one of the earliest large reptiles that we know about [during the Middle Triassic].”
Although neither the tail nor limbs have been found, Nesbitt believes the Arizonasaurus babbitti moved pretty low to the ground and was quadrupedal, meaning it walked on all fours, based on the shape of the pelvic and shoulder girdles and what is known about other relatives of the time. The tail is believed to have made up half the length of the creature.
Paleontologist Christa Sadler has written a book, “Dawn of the Dinosaurs,” about the archosaurs of the Middle and Late Triassic in the region. “It’s absolutely an extraordinary time period. This is when the seeds of the modern faunas that we have today really started to appear. And Arizonasaurus is part of that.”
One of Arizonasaurus babbitti’s distinguishing characteristics is the fin on its back. “It had what we call a sail. The protrusions on the vertebrae, which make up the backbone, were lengthened to form long bony spines. There would have been a big flap of skin over those to create this sail,” she said. “And probably these sails had something to do with thermoregulation, that is, maintaining their body temperature.”
Sadler says the skin sail would have had blood vessels in it. “So if it was a cool morning, it could turn sideways and put the sail toward the sun. The sun’s rays would warm up the blood and then circulate it to the whole body. If it starts to get too hot, it could turn perpendicular to the sun, so the sun’s rays don’t hit the sail.”
She says it also might have had something to do with looking more impressive. “Maybe it turned different colors during mating season. We don’t know exactly, but it seems in other organisms it has something to do with this body temperature regulation.”
Tracing Arizonasaurus babbitti Footsteps
Unusually detailed footprints of the large reptile, or something like it, are preserved in a slab of Moenkopi sandstone in the collections repository at the Museum of Northern Arizona, where Sadler has studied.
“What’s fascinating about this track is that you can actually see the scales on the bottom of the animal’s foot, which is amazing,” she said. “So the slab that the museum has here is one of the coolest fossils ever. I love trace fossils because – even though it’s great to find bones and teeth and all that – trace fossils are really interesting because they are remains of a behavior, of something that an organism was doing. So, in this case, the trace fossils are tracks. So this is the remains of animals walking through mud as these guys were wandering the flood plains probably looking for food in this warm subtropical environment.”
MNA Colbert Collections Curator of Vertebrate Paleontology David Gillette, Ph.D., says the footprints were discovered in Wupatki National Monument in 1973. “The Moenkopi is a really beautiful deep red sandstone and mudstone that formed along flood plains of ancient rivers and has preserved skeletons of these early archosaurs and a variety of important trackways.”
Named for James E. Babbitt
Berkeley researcher Sam Welles identified and named the first-known remains of Arizonasaurus in 1947, which were discovered on Babbitt Ranches land near Holbrook. It is believed he was led to the site by Babbitt family members whose relatives had been running cattle, riding horses and operating trading posts on the land since 1886. In his original publication documenting the find, Welles wrote Arizonasaurus babbitti was named to honor “the late James Babbitt of Flagstaff, Arizona, who has extended us many courtesies.” James E. “Jim” Babbitt was an Arizona state senator who died in 1944 from a hunting accident.
“It turns out that Arizonasaurus babbitti is one of the earliest records of the major evolutionary lineage that, in time, would give rise to today’s crocodilians and thus is really important in evolutionary terms,” said Hans-Dieter Sues, Ph.D., senior scientist and department chair of paleobiology at the Smithsonian Institution’s National Museum of Natural History. “It was a large predator that probably dominated the ecosystem in what is now the Southwest some 240 million years ago. So, an animal named after the Babbitt family played a dominant role in Arizona even before the Age of the Dinosaurs!”
“The Babbitt family has always been really supportive of the sciences and the arts and education in this region, so I think it’s really appropriate to have one of these early, very important fossils named after that founding family of Arizona,” said Sadler.
Nesbitt’s Arizonasaurus fossils are at the Arizona Museum of Natural History. He says he cannot wait to get back to his home state for more research into Arizonasaurus babbitti, the Moenkopi Formation and the Age of Reptiles.
Creature Featured at Expo
Arizonasaurus babbitti, along with other creatures of the Triassic age, plus space exploration, golden eagles, the black-footed ferret and rare plants will be part of the Babbitt Ranches Landscape Discovery Expo from 9:30 a.m. to 3 p.m., Saturday, Oct. 1, at Arizona Nordic Village on Highway 180, 15 miles north of Flagstaff. The event is one of more than 100 free activities offered during the Flagstaff Festival of Science, Sept. 23 – Oct. 2. For more information, visit scifest.org. FBN
By Bonnie Stevens, QCBN
Unusually detailed tracks, showing the scales on the bottom of the foot of Arizonasaurus babbitti or something like it, are available for researchers at the Museum of Northern Arizona.
Photo by Christa Sadler and the Museum of Northern Arizona