The creature's internal organs, including its teeth and some of its intestines, have been preserved for tens of thousands of years.
Megalodon was the largest shark ever to have lived, potentially growing up to around 60 feet in length.
"Thalattosaurs were among the first groups of land-dwelling reptiles to readapt to life in the ocean," Neil Kelley, an author of the study from Vanderbilt University, said in a statement.
The 0.2-inch-long specimen was identified in amber from the Baltic Sea region in northern Europe.
The latest discovery comes four years after a similar find in the same region of Argentina.
Short-faced kangaroos are an entirely extinct group of marsupial herbivores that arose during the Miocene Epoch—around 23 to 5.3 million years ago—and diversified prolifically during Australia's Ice Age.
These creatures can grow to 800 pounds and 14 feet long.
Ichthyosaurs were large marine reptiles that roamed the seas during the age of the dinosaurs.
Behold these marvels of the sea.
Russian authorities found 24 teeth from a prehistoric sea predator that may have been related to the largest ever shark, in the baggage of a man set for China.
They are using different approaches to the de-extinction issue—and only one can be first.