The more than 200-year-old mystery of how the ancient plesiosaurs roamed the oceans appears to have been solved, and it turns out they swam like penguins.
Computer simulations were used to bring the four-limbed dinosaur to life, the results of which were published in PLOS Computational Biology today.
Little was known about the movement of the group of marine reptiles which were apex predators for around 135 million years during the time of the dinosaurs.
After trying thousands of different swimming motions, researchers from the Georgia Institute of Technology and Nottingham Natural History Museum found the most effective way was flapping the two front flippers in an underwater flight motion similar to a penguin.
The back flippers wouldn't have increased their forward speed, but were likely to be for stability and steering.
"Our results show that the front limbs provide the powerhouse for plesiosaur propulsion, while the hind limbs are more passive," palaeontologist Adam Smith says.
The authors say the mystery of how the plesiosaur used its unique body through the water had been debated since the first complete skeleton was described in 1824.
The plesiosaur was unlike any modern-day swimming animal.
The study says the same method can be used to understand the swimming motion of other prehistoric animals.