Final answer:
Archaeopteryx is recognized as a transition species from dinosaurs to birds, possessing both reptilian and avian features. It serves as evidence for the evolutionary link between these two groups.
Step-by-step explanation:
Archaeopteryx is widely considered a pivotal transition species that showcases characteristics intermediary between non-avian dinosaurs and birds. Originating from the Jurassic period, it displayed both reptilian traits, such as a jaw with teeth and a long bony tail, and avian characteristics, notably feathers modified for flight. While some classify Archaeopteryx as a bird, others view it within the dinosaur classification due to its mix of traits.
This debate underscores a broader understanding of evolutionary lineage, with overwhelming evidence suggesting that birds evolved within the clade Dinosauria, specifically from theropod dinosaurs. Archaeopteryx and its contemporary Xiaotingia were part of this evolutionary narrative, exhibiting features like a flow-through respiratory system akin to modern birds. Thus, Archaeopteryx serves as a line of evidence for the evolutionary connection between dinosaurs and birds.