archelosauria

Archelosauria is a clade of reptiles that includes turtles and their extinct relatives, and birds and their extinct relatives, the dinosaurs. This grouping is based on a variety of anatomical and genetic evidence that suggests a close evolutionary relationship between these seemingly disparate groups. The name Archelosauria is derived from the Greek words "archelo" meaning turtle and "sauros" meaning lizard or reptile.

Within Archelosauria, two major lineages are recognized. One is Testudines, which encompasses all living turtles and their extinct kin. This group is characterized by the presence of a bony or cartilaginous shell, which evolved independently in different lineages of reptiles. The other major lineage is Archosauria, which includes crocodilians, pterosaurs, and dinosaurs. Birds are the sole surviving lineage of dinosaurs. Key features uniting archosaurs include specific skull bone arrangements and often bipedal locomotion in their terrestrial forms.

The placement of turtles within Archelosauria has been a subject of debate for some time. Earlier classifications often placed turtles as a separate group, distinct from archosaurs. However, modern phylogenetic analyses, particularly those incorporating molecular data, have strongly supported their inclusion within this larger clade. This understanding has significantly reshaped our view of reptile evolution, highlighting a deep evolutionary connection between turtles and the lineage that gave rise to dinosaurs and birds. The study of archelosaurian relationships continues to provide insights into the diversification and evolutionary history of reptiles.