How many years has the rat species existed? - briefly
Rats first appeared in the fossil record during the Oligocene epoch, roughly 23 million years ago. Their lineage has persisted continuously to the present day.
How many years has the rat species existed? - in detail
Rats belong to the order Rodentia, which emerged shortly after the Cretaceous‑Paleogene extinction event. Fossil evidence places the origin of true rodents at approximately 56 million years ago (Mya). Within this order, the lineage that leads to modern rats diverged from other murine rodents during the late Miocene, about 7–10 Mya.
The genus Rattus—the taxonomic group that includes the brown rat (R. norvegicus) and the black rat (R. rattus)—first appears in the fossil record around 2 Mya. Molecular‑clock analyses, calibrated with these fossils, suggest that the common ancestor of extant Rattus species lived roughly 1.5 Mya. Consequently, the rat lineage, from its earliest recognizable members to present‑day species, has persisted for at least two million years.
Key milestones:
- ~56 Mya – Emergence of the order Rodentia.
- 7–10 Mya – Divergence of the murine branch that would give rise to rats.
- ~2 Mya – First fossil evidence of the genus Rattus.
- 1.5 Mya – Estimated age of the most recent common ancestor of living rat species.
Overall, rats as a distinct genus have existed for a minimum of two million years, while their broader rodent ancestry extends back over fifty million years.