The traditional age stages for eutherian mammals (infant, juvenile, adult, senile) can be difficult to apply in the fossil record. Based on the tooth eruption and wear of the cheek teeth we propose six ''individual dental age stages'' (IDAS) that can be applied to almost all fossil and extant mammalian dentitions. The six stages of IDAS cover the entire life span. Traditional terms can be correlated to the IDAS stages and thus redefined based on the dentition: IDAS 0-prenatal, IDAS 1-infant, IDAS 2-juvenile, IDAS 3-adult, IDAS 4-late adult, and IDAS 5-senile. Furthermore IDAS enables comparison between individuals, characterizing the mortality in monospecific populations, and even of entire communities composed of various species. The data obtained can be used for paleoecological interpretations. The varying duration of different stages in the IDAS pattern during the life history forms an additional way to characterize mammalian groups by development and wear of their dentition.

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Although Lagomorpha (rabbits, hares and pikas) have a long evolutionary history in Eurasia and Africa, including primitive genera of Eurasia historically considered assignable at the family level to Leporidae, the predecessors of modern rabbits were absent throughout this vast region for most of the Miocene until late in that epoch. During the early and middle Miocene, crown group Leporidae differentiated in North America, then dispersed to northern Asia in the late Miocene around 8 Ma (million years before present) and afterward. They then spread widely and apparently rapidly throughout Eurasia, reaching South Asia by 7.4 Ma and penetrating Africa about 7 Ma. The apparently abrupt introduction of Leporidae is a striking late Miocene event that we call the Leporid Datum. Perceived in terms of biochrons, the Leporid Datum includes localities in Europe and western Asia of late MN11 (Mammifères Néogènes system) age and younger, and precedes by less than one million years the Bahean‐Baodean land mammal age boundary in China. The late Miocene spread of Leporidae throughout Eurasia was a successful invasion in terms of the numerous occurrences and abundant fossils preserved. Where dating is sufficiently robust, the Leporid Datum is late Miocene, nowhere certainly more than ∼8 Ma. In contrast to this sudden and widespread invasion, rare older finds suggest two possible refinements to this scenario: stem lagomorphs close to modern Leporidae may have lingered into the middle Miocene of Eurasia, or an independent, unsuccessful leporid invasion from North America may have preceded the 8 Ma datum. The Leporid Datum marks an important palaeoecological event for the Old World and complements the significance of molecular dates for origins of modern genera.

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