Pingusaurus

Pingusaurus is an extinct reptile part of the extinct archosaur family, pterosaurs. Its fossils were discovered in the east coast of South America and North America, where it likely lived on the shorelines, and lived in the Late Cretaceous from 70.1 millionnyears ago to 66 million years ago. Unlike most other pterosaurs, Pingusaurus was completely flightless and had a streamlined body, suggesting that it was semi-aquatic like a penguin, so while birds like hesperornids filled the niche similar to modern pinnipeds, pterosaurs like Pingusaurus filled the niche similar to modern penguins. It is unknown on what its form of locomotion on land was like when it was alive, but they certainly couldn't have walked like penguins as pterosaurs didn't have enough strength to keep their bodies up with their hind legs, so the Pingusaurus could have likely moved like a seal when on land. In the water, however, they probably moved very much like a modern day sea lion as their bones suggests. It is unknown why Pingusaurus became extinct suddenly.