Pleurodirans

Pleurodirans are a group of extinct turtles that belonged to the order Pleurodira, which is characterized by their unique neck retraction mechanism. Unlike modern turtles, which pull their necks straight back into their shells, pleurodirans retract their necks sideways, a feature that gives the order its name ("pleuro" refers to the side, and "dira" means direction). This adaptation is thought to have evolved as an evolutionary response to living in environments where a straight-necked retraction might be less effective, such as dense vegetation or aquatic habitats.

Pleurodirans first appeared during the Early Cretaceous period, around 125 million years ago, and persisted until the end of the Cretaceous, approximately 66 million years ago. Fossil evidence suggests they were widely distributed across Gondwana, the ancient supercontinent that included present-day South America, Africa, Antarctica, Australia, and India. Some of the most well-known pleurodiran genera include *Bothremys*, *Araripemys*, and *Plesiochelys*, with *Bothremys* being particularly diverse and abundant in Late Cretaceous deposits.

The skeletal structure of pleurodirans reveals several distinctive traits. Their shells were often more flattened and broader compared to modern turtles, which may have been an adaptation for swimming or navigating shallow waters. The limbs of pleurodirans were typically stout and paddle-like, indicating a strong aquatic lifestyle. Some species also exhibited specialized features, such as enlarged claws or modified shells, which may have been used for digging or defense.

The extinction of pleurodirans coincides with the Cretaceous-Paleogene (K-Pg) extinction event, which wiped out many other groups of reptiles, including non-avian dinosaurs. While the exact cause of their disappearance remains debated, factors such as climate change, oceanic anoxia, or competition with emerging groups like modern turtles may have played a role. Despite their extinction, pleurodirans left a lasting legacy, as their sideways-neck retraction mechanism persists in living pleurodiran species, such as the side-necked turtles of South America and Australia.