Final answer:
The term "Currently Living Dinosaur" refers to birds, which are the modern relatives of theropod dinosaurs. Birds are the sole surviving lineage of the once-dominant dinosaurs, with Archaeopteryx being a key transitional fossil demonstrating bird-dinosaur relationships.
Step-by-step explanation:
When we talk about the term "Currently Living Dinosaur," we are referring to birds as the only living descendants of theropod dinosaurs. Dinosaurs, such as the mighty Tyrannosaurus rex, ruled during the Mesozoic era but faced extinction at the end of the Cretaceous period due to a catastrophic impact event known as the Cretaceous-Tertiary extinction, which took place 65 million years ago. While most of the dinosaur clades perished, it's fascinating that one lineage survived and flourished, leading to today's avian species.
The transition from dinosaurs to birds is exemplified by Archaeopteryx, a species from the Jurassic period with both dinosaur and bird features, such as cuplike thecodont teeth and flight feathers. Cladistics, a method of classifying organisms, places birds within the Dinosauria clade, thereby confirming their direct ancestral link to dinosaurs. Thus, when we observe birds today, we can appreciate them as modern representatives of the dinosaur lineage.