The Ohio State University at Marion

Calede discovers now extinct species of horned rodent

Tuesday, July 14, 2020

Ohio State Marion Assistant Professor of Evolution, Ecology, and Organismal Biology, Dr. Jonathan Calede has uncovered a now extinct new species of rodent with horns that lived in Nebraska during the Miocene epoch.

“The new species is part of a genus called Ceratogaulus. The only genus of rodents to ever evolve horns,” said Calede.

The extinct rodent is most-closely related to the sewellel, also known as the mountain beaver, a rodent alive today in the Pacific Northwest. The group it belongs to (the mylagaulids) is completely extinct. The sewellel is the last surviving relative.

A paper recently published in the Journal of Systematic Palaeontology and co-authored by Dr. Calede and Dr. Josh Samuels at Eastern Tennessee State University and the Gray Fossil Site, helps refine scientists' understanding of the evolution of this family of rodents and supports the idea that the horns functioned as a defense against predators.

“The specimen had never been identified beyond just a general identification and he, (Dr. Samuels), knew that I had done prior work on these animals,” said Calede. “Dr. Samuels asked me to look at it and I recognized it as a new species that afternoon based on comparisons with published data.”

The specimen was initially found in the 1970s somewhere in Sioux County, Nebraska, but was not identified.

“We found it in museum collections and have never been to the site where the fossil was excavated. This is not uncommon for fossil specimens that were collected in the past when record keeping was not as good,” he said.

Calede said, he spent many months running analyses and collecting additional data from specimens in his lab that he had on loan from various museums around the country like the University of California Museum of Paleontology.

“I also collected additional data when I visited the American Museum of Natural History last summer and the Smithsonian Institution last Fall,” Calede added.

“I want to acknowledge the help of many folks over the years in my studies of these organisms, mainly Dr. Samantha Hopkins from the University of Oregon.” Calede said.

Mylagaulids are the only group of rodents to ever have evolved horns, so understanding the evolution and function of these horns, Calede said, is important. Mylagaulids are a completely extinct group of rodents that used to be common in the United States.

“I have been working on the paleontology of mylagaulids for many years now and this project is a continuation of these prior studies,” Calede explained. “I am currently working on several collaborative projects to better our knowledge of the rise and fall of these animals.”

“More broadly,” shared Calede, “I am working with colleagues on investigating the pattern and processes of evolution of burrowing in rodents throughout the Cenozoic. This is one small step towards this goal.”

Moving forward Calede plans to have his lab working on the evolution of body size in gophers using similar methods to those used in this paper.

“At the end of the day our goal (my lab’s and colleagues’ labs’) is to really better understand critical ecological and evolutionary processes like radiation, diversification, body size evolution, predator-prey relationships, etc.”, added Calede

Calede said, “burrowing rodents are an excellent study system to investigate these topics. The number of fossils and the quality of their preservation, their patterns of diversification and their ecological adaptations, the succession of clades within the guild, make fossil rodents a good study system for looking at larger processes in evolution.”

“We have so many well-preserved individual fossil specimens from many different sites across the US and across 30 million years,” he said. “We can gather a lot of data and plug that into analyses in order to ask big questions about how a group of animals rises, becomes successful in its environment, how we end up with so many different species of rodents, but also how those groups decline and disappear altogether.”

“If we can understand this well in one group, it gives us hypotheses to test in other groups, groups that maybe don’t have as great a fossil record,” he added.

Calede believes this discovery and the methods used to uncover the new species can provide a great basis for discovery into the classroom.

“I think that this paper is pretty representative of much of the work my lab is currently working on and I could certainly use it as an example in my classroom, particularly in my upper level class EEOB 4510, Comparative Vertebrate Anatomy. In fact, students in my class this fall will be using some of the techniques used in this paper in their own original research project on a different group of burrowing rodents,” said Calede.


Above is a photo of the specimen and a reconstruction of the animal in the flesh by Keila Bredehoeft at the Gray Fossil Site and Museum of Eastern Tennessee State University. Photo by, Dr. Jonathan Calede and illustration by Keila Bredehoeft.