Northern Florida bear fossils reveals new species of Indarctos in North America

Coexistence of Indarctos and Amphimachairodus (Carnivora) in the Late Early Hemphillian of Florida, North America

Qigao Jiangzuo · Richard C. Hulbert Jr.

Summarized by Eric Kastelic, who is a geology major at The University of South Florida. Currently, he is a senior. Starting in Fall 2022, he will be pursuing graduate studies in hydrogeology focusing on groundwater recharge and once he earns his degree, he plans to work as a research hydrologist or become a research professor. When he’s not studying geology, he loves to go on walks with his friends and explore nature!

What data were used? ~ 7.5–6.5 million year old Indarctos fossils from the Withlacoochee River 4A Formation in Northern Florida, USA. These fossils were compared to previously collected specimens from elsewhere in the United States and China. 

Methods: This work descriptively compared ~ 7.5–6.5 million year old  Indarctos fossils form Northern Florida with corresponding Indarctos fossils from formations in Kansas, Texas, Oregon, California and Nevada. Additionally, fossils from Northern China were reviewed to connect a possible ancestral relationship.  

Results: This study investigated at least four Indarctos individuals found in the Withlacoochee River 4A Formation of Florida. As it is uncommon to find numerous individuals in one site, this fossil find marks one of the most comprehensive groupings of Indarctos fossils in in North America. These four individuals made it possible for the researchers to compare jaw, dental, neck, pelvic, and heel properties between the specimens at the formation and other Indarctos fossils worldwide. The similarities in dental characteristics between Indarctos of the Withlacoochee River 4A formation and I. oregonensis, a species of Indoarctos, paired with differences in slenderness of postcranial bones between the Florida specimens and I. oregonensis (skeleton excluding the skull) shows a at least two variations of postcranial bones in North America. What does this mean about the Florida Indoarctos? Is it a new species? This works makes no definite support or rejection of the Indarctos of the Withlacoochee River 4A Formation being a previously unknown species, but acknowledges the need for further research to determine this. 

 Photo of bear skull fossil from two differing areas with similar shape and size. The Indarctos skull fossils from the Withlacoochee River 4A in northern Florida is approximately 30 cm in length, yellow in color, has teeth with two prominent front teeth, and the piece of the skull between the top of the skull and nose is missing. The I. zdanskyi from Baode in North China is about 40 cm in length, white in color, has four prominent front teeth, and is missing the bone supporting the left side of the face.
Figure 1: Top, bottom, and side views of a Indarctos skull fossils from the Withlacoochee River 4A in northern Florida (A1-3) and a I. zdanskyi from Baode in north China (B1-3).

Why is this study important? This study shows a possible unique species of Indarctos that hasn’t previously been identified. Indarctos throughout North America show a differing type of bone robustness, despite not being geographically separated. This work documents that Indarctos may have ancestors in northern China, showing a possible movement to North America from Eurasia in the geologic past. This work, paired with fossils of other fauna (animals) and climatic data, may be able to show shifts in ecosystems as a driver in the migration of Indarctos.

The big picture: New fossil finds strengthen understandings of how organisms moved across the globe in geologic time. The information gained form comparing Indarctos fossils provides insight into how other mammals may have moved.

Citation: Jiangzuo, Qigao, and Richard C. Hulbert. “Coexistence of Indarctos and Amphimachairodus (Carnivora) in the Late Early Hemphillian of Florida, North America.” Journal of Mammalian Evolution 28.3 (2021): 707-728.