Mosasaurus: Reptil Laut Seukuran Bus Hidup di Sungai & Air Tawar

For decades, the mosasaurus has been understood as a creature of the open ocean, a massive reptile dominating marine ecosystems millions of years ago. However, recent research is challenging that long-held belief, revealing a surprising adaptability in these ancient predators. A collaborative study, involving researchers from the Universitas Uppsala, Eastern West Virginia Community and Technical College, Vrije Universiteit Amsterdam, and the North Dakota Geological Survey, published December 12, 2025, in Springer Nature, indicates mosasaurs weren’t confined to saltwater environments.

Mosasaurus: A Predator of Immense Scale

Mosasaurus lived approximately 98 to 66 million years ago. These reptiles, belonging to the mosasauridae family, were characterized by their elongated bodies, powerful fins, and jaws lined with sharp teeth – features that made them formidable hunters. They reached impressive sizes, with some individuals growing up to 11 meters long, comparable to the length of a bus.

Did You Know? Fossil evidence suggests mosasaurs coexisted with Tyrannosaurus rex, with remains of both found in the same river deposits.

Freshwater Adaptation: A New Discovery

Traditionally, mosasaur fossils have been recovered from ancient marine deposits, reinforcing the idea of a strictly saltwater existence. However, the Universitas Uppsala team’s investigation uncovered mosasaurus teeth in North Dakota, United States, within riverbed sediments alongside fossils of Tyrannosaurus rex and crocodiles. Isotopic analysis of these teeth revealed a key difference.

“Isotop karbon pada gigi umumnya menunjukkan apa yang dimakan hewan tersebut. Banyak mosasaurus memiliki nilai ¹³C yang rendah karena mereka menyelam dalam-dalam. Namun, gigi mosasaurus yang ditemukan bersama gigi T. rex memiliki nilai ¹³C lebih tinggi dibandingkan semua mosasaurus,” explained Melanie During, a lead author of the study.

This higher carbon-13 value indicates the mosasaurus analyzed inhabited freshwater environments and likely preyed within these river systems. Researchers believe this adaptation occurred as inland seas dividing North America gradually transitioned to freshwater conditions near the time of the mosasaur’s extinction.

Expert Insight: This discovery highlights the remarkable plasticity of ancient species. The mosasaur’s ability to adapt to changing environmental conditions, shifting from saltwater to freshwater, demonstrates a resilience that challenges previous assumptions about these apex predators.

The analysis further suggests these freshwater mosasaurs may have even consumed dinosaurs that accidentally drowned. This adaptability echoes behaviors seen in modern animals, such as saltwater crocodiles that navigate both marine and freshwater habitats, and river dolphins that evolved from marine ancestors.

The findings suggest that, were mosasaurs still alive today, their size would position them as rivals to the largest marine predators, such as orcas and killer whales. Per Ahlberg, another author of the study, noted, “Ukuran hewan ini berarti bahwa ia akan menyaingi paus pembunuh terbesar, menjadikannya predator luar biasa yang akan ditemui di lingkungan sungai yang sebelumnya tidak terkait dengan reptil laut raksasa seperti itu.”

Frequently Asked Questions

What did mosasaurs eat?

Mosasaurus were apex predators that preyed on various marine animals. The recent research suggests some mosasaurs also consumed dinosaurs and hunted in freshwater environments.

How big did mosasaurs grow?

Mosasaurus could reach up to 11 meters in length, which is about the size of a bus.

When did mosasaurs live?

Mosasaurus lived approximately 98 to 66 million years ago.

Considering the mosasaur’s demonstrated adaptability, what other surprising behaviors or ecological roles might be uncovered in the fossil record?