A recent discovery in North Dakota has revealed that a massive prehistoric predator, known as a mosasaur, may not have confined its hunting to the oceans. The fossilized tooth, estimated to be around 66 million years old, suggests that this formidable creature, which could grow up to 12 metres (40 feet) in length, may have also hunted in freshwater environments. Researchers from Uppsala University in Sweden made this significant finding, challenging previous assumptions about the mosasaur’s habitat.
The fossil was unearthed in the Hell Creek Formation and displayed characteristics indicative of exposure to river water. This evidence supports the idea that mosasaurs, traditionally viewed as marine reptiles, could inhabit freshwater environments. The study, published in the journal BMC Zoology, has led researchers to nickname this species the “King of the Riverside.”
Analysis of the tooth revealed chemical signatures consistent with a freshwater lifestyle. Variants of oxygen and strontium found within the fossil are typically associated with freshwater habitats. Researchers theorize that the area where the tooth was discovered may have once been a river connected to the ancient sea known as the Western Interior Seaway. Such a habitat would have allowed mosasaurs to prey on freshwater animals, expanding their ecological niche significantly.
Interestingly, the fossil tooth showed no signs of having been transported, suggesting that the mosasaur may have lived and died in the Hell Creek region. Prior to this finding, no other mosasaur teeth from this period had been identified in the area, making this discovery particularly noteworthy in the study of prehistoric life.
The findings also align with studies of older mosasaur teeth from the Western Interior Seaway, which indicate a shift from seawater to freshwater habitats over time. This suggests that declining salt levels in the region may have prompted mosasaurs to adapt to the changing environment, eventually venturing into river channels like those of Hell Creek.
Researchers noted, “This adaptation may indicate that large rivers of the Hell Creek Formation paleoenvironment could support large-bodied taxa, despite it being more likely for younger, smaller individuals to exploit these nearshore to riverine habitats.” This adaptability may have played a crucial role in the mosasaurs’ ability to thrive in diverse ecological niches during the Late Cretaceous period.
The implications of this discovery are profound, as they not only shed light on the lifestyle of these ancient creatures but also contribute to our understanding of prehistoric ecosystems. The research emphasizes the adaptability of mosasaurs and their capacity to navigate various environments, further enriching the narrative of life during the age of dinosaurs.
