Which appeared earlier: rats or mice? - briefly
Rats evolved before mice; the earliest rat fossils date to the early Miocene (about 23 million years ago), while mouse fossils appear later in the record.
Which appeared earlier: rats or mice? - in detail
Rats and mice belong to the Muridae family, but they represent distinct genera: Rattus (true rats) and Mus (true mice). The fossil record shows that members of Mus appear earlier than those of Rattus. The oldest definitive Mus fossils, discovered in the Siwalik Hills of Pakistan, date to the late Miocene, approximately 5–7 million years ago. By contrast, the earliest confirmed Rattus specimens come from Pleistocene deposits in Southeast Asia and date to about 2–3 million years ago.
Molecular phylogenetics supports this chronology. DNA‑based divergence estimates place the split between the Mus lineage and its closest relatives around 10 million years ago, whereas the Rattus lineage diverged from other murines roughly 4 million years ago. These timelines are consistent across mitochondrial and nuclear markers, reinforcing the conclusion that mice preceded rats in evolutionary history.
Key points summarizing the evidence:
- Fossil evidence: Mus fossils → late Miocene (5–7 Ma); Rattus fossils → early Pleistocene (2–3 Ma).
- Genetic data: Divergence of Mus lineage ≈ 10 Ma; divergence of Rattus lineage ≈ 4 Ma.
- Taxonomic context: Both genera are within Murinae, but Mus occupies an older branch of the subfamily tree.
Therefore, the available paleontological and genetic data indicate that mice emerged before rats.