Mosasaurus lived in the river: a finding in North Dakota changes the perception of giant reptiles.

According to ТСН: In North Dakota, usually known for its land dinosaurs, paleontologists made an impressive discovery – a fossilized tooth of a mosasaurus, a huge marine reptile from the Cretaceous period. This finding, discovered in river deposits, forced scientists to look at the lifestyle of these predators in a new light.

The Life of the Mosasaurus in a River Environment

Previously, mosasaurs were considered inhabitants of open oceans. However, the tooth found in 2022 along with remains of a tyrannosaurus, crocodile, and other land and freshwater animals did not fit traditional perceptions. New research showed that this mosasaurus did not just end up in the river - it lived there.

An international team of scientists, led by Uppsala University, conducted an analysis of the tooth enamel, which preserves chemical traces of the habitat. Isotopic analysis of oxygen, strontium, and carbon, performed by specialists at the Free University of Amsterdam, revealed signs typical for freshwater rather than marine environments.

In particular, increased proportions of the lighter oxygen isotope and strontium ratios typical for river systems were recorded in the tooth. Data on carbon also suggest a different diet: the mosasaurus likely did not dive deep and may have fed on prey carried by the current, including the carcasses of land dinosaurs.

Freshwater Ecosystems of Mosasaurs

Additional mosasaur teeth from nearby locations that are slightly older also demonstrate a freshwater isotopic signature. This suggests that at least some mosasaurs adapted to river ecosystems over the last millions of years before their extinction.

According to scientists, the creature could reach lengths of up to 11 meters and belonged to a group of prognathodon - powerful opportunistic predators. In the late Cretaceous, when the Western Interior Seaway gradually turned freshwater, such conditions could have opened new habitats for mosasaurs.

Researchers emphasize: the discovery does not negate the marine nature of mosasaurs in general but shows their ability to quickly adapt to changes. The river in present-day North Dakota about 66 million years ago was likely home to one of the largest predators of its time - far from the ocean where it was expected to be.

This finding represents an important step in studying the ecology of the Mesozoic era. By showing that mosasaurs could adapt to river conditions, scientists now have the opportunity to better understand their diversity and survival strategies in changing environments. Researching such extinct species helps not only in paleontology but can also influence the understanding of modern ecosystems.