Sauropsida is the group that includes all modern reptiles and birds, along with their fossil ancestors like dinosaurs, pterosaurs, and marine reptiles. This lineage split from the one that led to mammals over 300 million years ago and has followed its own evolutionary path ever since.

Most Sauropsids have distinctive skulls with two holes behind each eye socket. These openings lighten the skull and make room for powerful jaw muscles. Turtles and some extinct forms lack these holes, but other traits confirm their place in the group.

Their skin is another key feature; it produces beta-keratin, a tough material that forms scales or feathers. Sauropsids also excrete waste as a dry paste instead of liquid urine, which helps conserve water - a useful trait for life on land.

Today, Sauropsids are everywhere: from lizards and crocodiles to sparrows and penguins, all part of this long and diverse lineage.