How did mice and rats appear? - briefly
Mice and rats originated from early muroid ancestors that diversified during the early Eocene, forming the Muridae family. Their worldwide spread was driven by natural expansion and later close association with human habitats.
How did mice and rats appear? - in detail
Mice and rats belong to the family Muridae, which emerged shortly after the extinction of non‑avian dinosaurs. The earliest murid fossils date to the early Paleocene, roughly 60 million years ago, and show small, gnawing mammals with ever‑growing incisors—a defining rodent trait.
Key points in their evolutionary history:
- Paleocene origin: Primitive murids appear in North America and Europe, identified by dental patterns distinct from earlier gliriforms.
- Eocene diversification: Rapid speciation yields the first recognizable members of the subfamilies Murinae (true mice and rats) and Gerbillinae. Molecular clocks place the split between Murinae and its sister groups at about 45 million years ago.
- Miocene expansion: Fossil records from Asia reveal the spread of murine lineages across the continent, accompanied by adaptations to varied diets and habitats.
- Pliocene–Pleistocene dispersal: Global distribution intensifies as land bridges and climatic fluctuations allow colonization of Africa, Australia, and the Americas. Certain species develop commensal relationships with early human settlements, facilitating further spread.
Phylogenetic analyses based on mitochondrial and nuclear DNA confirm that modern house mice (Mus musculus) and brown rats (Rattus norvegicus) share a common ancestor that lived approximately 12 million years ago. Their success derives from high reproductive rates, flexible foraging behavior, and the ability to exploit anthropogenic environments.
The fossil record, combined with genetic data, outlines a clear trajectory: an origin in the early Cenozoic, diversification during the Eocene, and worldwide colonization by the Pliocene, resulting in the extensive variety of murine species observed today.