Alamosaurus: how this massive titan’s neck is impacting relationships of titanosaurs
Remember the Alamo? Well, it’s easy to forget when you are staring at this massive dinosaur. It makes that Tyrannosaurus look like a puppy in comparison.
At least that was how I felt when seeing the Alamosaurus on display at the Perot Museum of Nature and Science. I, along with hundreds of paleontologists at last year’s Society of Vertebrate Paleontology meeting in Dallas, got to admire this beautiful behemoth at the opening social. Alamosaurus has a great and complex history to match its size, and now, with a new study by Ronald S. Tykoski and Anthony R. Fiorillo published open access this week in the Journal of Systematic Paleontology, Alamosaurus now comes with a more complete anatomical and morphological description, and a new hypothesis of how Alamosaurus relates to other titanosaurs.
“Giant sauropods like Alamosaurus have amazed people since the 1800s. Their sheer size boggles the mind, and they have forced scientists to re-think the physical limits of land-living animals,” said Tykoski. “The fossils described in our paper reveal new details about the last sauropods in North America, which helps us better understand who Alamosaurus was related to and how this species made it to southern North America by 67 to 66 million years ago – just in time to go extinct at the end of the Cretaceous!”
Now, Alamosaurus was not named after the THAT Alamo. Rather it was named for the Ojo Alamo trading post in New Mexico, where bones of the sauropod were first discovered in the 1920s. Since then, other remains have been discovered in Utah, Texas, and New Mexico. Most of these discoveries, however, were incomplete sections of the dinosaur, and so the whole picture remained elusive and its relationship to other titanosaurs was difficult to interpret.
In 1997, a joint team of paleontologists from the University of Texas at Dallas (UT-D) and the Perot Museum of Nature and Science found additional remains of Alamosaurus in Big Bend National Park. The scientists and volunteers were excavating a site that produced parts of several immature sauropods when Dana Biasatti, then a student at UT-D, came upon the remains of an adult titanosaur a few hundred yards away. The team was stunned. The nine cervical (neck) vertebrae were the first articulated series of adult Alamosaurus neck bones ever found. The fossils of Alamosaurus from Big Bend National Park currently represent the biggest dinosaurs discovered in Texas.
It would be another four years before they were able to excavate the remains, however. Working with the National Park Service and a helicopter service, several blocks, some weighing over a ton, were airlifted out to a flatbed truck about a mile away, and then transported over 500 miles to the Perot Museum in Dallas. The bones have been prepared and are now on display under the reconstructed Alamosaurus in the museum, which spans over 25 feet.
“This remarkable discovery illustrates the importance of America’s public lands as places where scientists have access to perform research that benefits everyone,” said Cindy Ott-Jones, Superintendent of Big Bend National Park. “While Big Bend National Park is a place that many people enjoy for its scenery and recreational opportunities, visitors should know that a tremendous amount of scientific research is also performed in the park.”
Because of the new anatomical and morphological information provided in the study, the authors were able to propose a a more robust hypothesis of evolutionary relationships of Alamosaurus to other sauropod dinosaurs. And the results of the phylogenetic analysis were novel; the researchers recovered Alamosaurus to the Lognkosauria clade, which includes the genera Futalognkosaurus and Mendozasaurus, both massive titanosaurs from the Cretaceous of Argentina. This new proposed relationship is supported by three shared derived characters—all characters based on the morphology of the cervical vertebrae, made possible by this discovery.
This study also has paleobiogeographical implications, mainly in why Alamosaurus is where it is at the time it is. Tykoski and Fiorillo (2016) discuss several scenarios depending on different studies, and in one scenario suggest a northward dispersal by the ancestors of Alamosaurus from South America—a hypothesis which matches their phylogeny, as its closest relatives proposed by this study are found in Argentina, it is likely their common ancestor was also from South America.
This paper is significant, and has been years in the making. The new data provided by Tykoski and Fiorillo (2016) illuminates possible evolutionary relationships of titanosaurs, and gives Alamosaurus a place on the family tree.
Ronald S. Tykoski & Anthony R. Fiorillo (2016): An articulated cervical series of Alamosaurus sanjuanensis Gilmore, 1922 (Dinosauria, Sauropoda) from Texas: new perspective on the relationships of North America’s last giant sauropod, Journal of Systematic Palaeontology, DOI: 10.1080/14772019.2016.1183150
This post was modified from materials provided by the Perot Museum of Natural History and Science