From which ancestors did rats evolve? - briefly
Rats originated within the Murinae subfamily of the Muridae family, descending from early murine rodents that appeared in the late Oligocene‑early Miocene. These ancestral forms gave rise to the modern Rattus genus through successive diversification of murid lineages.
From which ancestors did rats evolve? - in detail
Rats belong to the family Muridae, subfamily Murinae, and their evolutionary lineage can be traced through a series of early rodent groups that appeared after the Cretaceous‑Paleogene extinction. The first true rodents emerged in the Late Paleocene (≈58 Ma) and displayed the characteristic ever‑growing incisors and a hystricognathous jaw. Early representatives such as Ischyromys and Paramys exhibit primitive dental patterns that later gave rise to the more derived muroid rodents.
The muroid superfamily, which includes mice, rats, hamsters and their relatives, first appears in the Oligocene (≈30 Ma). Within muroids, the Muridae family diverges from other lineages (e.g., Cricetidae) during the early Miocene (≈20 Ma). Fossil genera that illustrate this transition include:
- Protomys – early murid with mixed dental traits.
- Pseudocricetomys – shows the shift toward the murine molar pattern.
- Myomimus – exhibits the modern murine skull morphology.
- Rattus‑like forms from the late Miocene (≈10 Ma) that possess the definitive rat dental formula (1/1 incisors, 0/0 canines, 0/0 premolars, 3/3 molars).
Molecular phylogenies, calibrated with these fossils, estimate that the lineage leading to contemporary rats split from other murines roughly 12–15 Ma. Genetic markers (mitochondrial cytochrome b, nuclear IRBP) show a rapid radiation of the Rattus genus in the Pliocene, giving rise to species such as R. norvegicus and R. rattus.
In summary, rats evolved from early Paleocene rodents, progressed through Oligocene muroids, and acquired their distinctive murine features in the Miocene, with both fossil evidence and molecular data pinpointing the divergence of the modern rat lineage to the mid‑Miocene to early Pliocene.