When did rats appear on Earth? - briefly
The earliest known rat fossils date to the early Miocene, about 23 million years ago. Molecular data indicate that the genus Rattus itself diversified later, during the Pliocene.
When did rats appear on Earth? - in detail
Rats belong to the family Muridae, a branch of the muroid rodents that diversified during the Oligocene‑Miocene transition (approximately 23–15 million years ago). Fossil teeth attributed to early murines appear in Asian strata dated to about 12 million years ago, indicating the first murine ancestors occupied temperate forests of what is now eastern Asia.
The genus Rattus itself emerges later in the fossil record. The oldest confirmed Rattus specimens are dental remains from the Pliocene of Thailand, dated to roughly 3 million years ago. Molecular clock analyses, calibrated with these fossils, place the split between the brown rat (Rattus norvegicus) and the black rat (Rattus rattus) at 1.5–2 million years ago.
Key stages in the evolutionary timeline:
- ~12 Ma – Early murine teeth in Asian deposits; ancestors of modern rats evolve.
- ~3 Ma – First Rattus fossils appear in Southeast Asia.
- 1–2 Ma – Divergence of major Rattus lineages.
- ~10 ka – Expansion of Rattus species alongside human maritime trade; global distribution achieved.
Geographic origin is traced to the Indo‑Malayan region, where dense forest habitats supported the diversification of murids. Climatic fluctuations during the Pleistocene created corridors that allowed Rattus populations to spread across Eurasia. Human activity accelerated dispersal: rats boarded ships during the Neolithic, Bronze Age, and later commercial voyages, establishing populations on every continent except Antarctica.
The modern rat’s adaptability derives from a combination of omnivorous diet, high reproductive rate, and tolerance of varied environments. These traits, rooted in the lineage’s Miocene origins, explain the rapid colonization of anthropogenic habitats worldwide.