When did rats and mice appear? - briefly
Rats and mice belong to the Muridae family, whose fossil record begins in the early Oligocene, roughly 34 million years ago, and true murine species appear by the early Miocene, about 23 million years ago.
When did rats and mice appear? - in detail
Rats and mice belong to the family Muridae, which emerged during the Eocene epoch, roughly 40–50 million years ago. Fossil records indicate that the earliest members of the subfamily Murinae appeared in Asia, where warm climates and diverse habitats promoted rapid diversification.
The evolutionary sequence can be summarized as follows:
- Early Eocene (≈ 45 Ma): First murine-like teeth discovered in Asian strata, suggesting primitive forms of the group.
- Middle to Late Eocene (≈ 38–34 Ma): Appearance of definitive murine characteristics, such as the distinctive molar pattern and elongated rostrum.
- Oligocene (≈ 30–23 Ma): Expansion into Europe and Africa, evidenced by dental fossils that closely resemble modern Rattus and Mus genera.
- Miocene (≈ 23–5 Ma): Global dispersal facilitated by the formation of land bridges; early representatives of the genus Rattus appear in African and Asian deposits.
- Pliocene–Pleistocene (≈ 5 Ma–10 ka): Further radiation of species, with Mus musculus and Rattus norvegicus establishing widespread populations; human activity accelerates their range during the Holocene.
Molecular clock analyses corroborate the fossil data, estimating a common ancestor for contemporary rats and mice at about 12–15 million years ago. Genetic divergence between the two principal genera, Rattus and Mus, aligns with the late Miocene climatic fluctuations that created new ecological niches.
In summary, murine rodents originated in the early Eocene, diversified across continents through the Oligocene and Miocene, and reached their modern global distribution by the Pleistocene, with human influence intensifying their spread in recent millennia.