Final answer:
Paleontologists recognize the concept of a "missing link" as an outdated and misleading term because evolution is not linear but complex and branching. Evidence for mass extinctions and common ancestry, such as the iridium layer from the Cretaceous-Paleogene extinction event and fossils like Archaeopteryx, support the reality of extinct species. Claims of undiscovered living species ignore the substantial evidence of changes in the fossil record over time.
Step-by-step explanation:
The idea of the "missing link" is recognized as impossible by paleontologists due to the continuously evolving nature of species and the fragmented nature of the fossil record. The term "missing link" is considered outdated and misleading because it suggests that evolutionary history is a linear chain of beings directly leading from one species to the next, like links in a chain. However, evolution is far more complex and does not necessarily follow a direct path.
Mass extinctions, such as the one marked by the Cretaceous-Paleogene boundary, are identified by evidence like the global layer of iridium-enriched clay, sudden disappearance of numerous species, and geological features like the impact crater in the Yucatan Peninsula. When we consider fossils such as Archaeopteryx, which exhibits features of both reptiles and birds, they provide support for the evolutionary theory that modern species share a common ancestor.
It is an erroneous claim to argue that all thought-to-be-extinct fossils are simply undiscovered living species. The evidence from the fossil record, such as organismal forms that do not appear in more recent strata and the absence of certain species in ecosystems where they previously thrived, overwhelmingly supports the extinction of many organisms.