Hylonomus lyelli

Hylonomus, a genus of early reptile from the late Carboniferous period, is considered one of the first creatures to exhibit truly terrestrial adaptations, such as a fully amniotic egg, which allowed it to reproduce away from water, a crucial evolutionary step for life on land. Measuring only around 20 centimeters in length, Hylonomus likely lived in the dense, swampy forests of what is now North America, and its diet probably consisted of small arthropods and other invertebrates. Its anatomy, including elongated limbs and a relatively simple, lizard-like body structure, highlights its evolutionary position as a forerunner to more advanced reptiles, bridging the gap between amphibians and later, more evolved reptiles such as dinosaurs. The discovery of Hylonomus has provided valuable insights into the early development of amniotes, the group of vertebrates that includes reptiles, birds, and mammals.