New research on the Cañadón Tomás Quarry has revealed insights into the end of the Cretaceous, the time period just before the non-avian dinosaurs went extinct.
Matthew Lamanna, a paleontologist and the principal dinosaur researcher at Carnegie Museum of Natural History, presented the research at the Geological Society of America’s GSA Connects 2023.
The Cañadón Tomás Quarry is found in southern Argentina’s Patagonia region. The site was of interest to the oil industry in 2020 before a paleontological impact study revealed fossils at the quarry.
The oil company found bones belonging to hadrosaurs (large-bodied duck-billed dinosaurs). Ever since its discovery, the quarry has been a popular site for paleontologists.
“At the end of 2020, a few bones were recovered in the outcrop that today is Cañadón Tomás, and little by little, we began to expand that excavation hoping to find something interesting,” Noelia Cardozo, a PhD student at the UNPSJB and member of the Cañadón Tomás research team, said.
Lamanna said the discoveries helped correct the imbalance in our understanding of biodiversity, evolution, and paleobiogeography.
“We know enough about continental vertebrates in the Late Cretaceous to know that there were some very different kinds of animals thriving in the Southern Hemisphere,” he said.
“One thing that we’d really like to know is, how did non-avian dinosaurs in the southern half of the world fare at the Cretaceous-Paleogene boundary.”
While the dinosaur fossils at Cañadón Tomás are exciting and provide crucial insight into Southern Hemisphere non-avian dinosaurs before their extinction, it’s other fossil finds of rare and small-bodied vertebrates that have the research team most excited.
The team discovered a vertebra of a snake, likely a madtsoiid, the first Cretaceous snake found in this region of Patagonia known as the Golfo San Jorge Basin. What really put the site high on their radar, according to Lamanna, was the discovery of the upper jaw containing teeth of a small mammal known as a reigitheriid.
“For me, the most exciting discovery from this site so far was the small fragment of the jaw of a mammal,” says Cardozo. “Because this formation is mainly well known for its record of dinosaurs, that’s what I expected to find. But when that little piece [of jaw] appeared, we knew it was different from everything that we had been working on so far.”
In March 2023, Cardozo and fellow UNPSJB student Ivanna Mora had spent only two hours sieving through rocks and sediment when they discovered the mammal jaw—relatively speaking, a lightspeed find in the world of paleontology. The fossil is now the first Cretaceous mammal of any kind found in the Golfo San Jorge Basin. According to Lamanna, the jaw is “one of the best fossils of its kind of mammal ever discovered.”
Mammals in the Cretaceous were typically small, rodent-sized creatures—not as foreboding and as easy to capture the imagination as dinosaurs. However, understanding mammalian life at the end of the Cretaceous is crucial to having a full picture of life leading up to the extinction of non-avian dinosaurs, as well as understanding how mammals expanded and proliferated following the extinction.
While research and excavations at the Cañadón Tomás site are still in a preliminary stage, the fossil discoveries thus far have shown that the site is extremely promising.
“Cañadón Tomás is a site of great interest not only for the great diversity, but also for the great quantity of materials that are being discovered at the site,” UNPSJB Ph.D. student Bruno Alvarez said.
“As excavation work continues, more and more materials are being found. There is still a lot of work left to do at Cañadón Tomás with a lot of field work to complete, and we suspect there will be many more fossils to discover and study.”
Lamanna notes that people should “keep their eyes peeled for new discoveries” from Cañadón Tomás.