We assigned ground squirrel specimens to an age class based

on eruption of lower cheek teeth; it was deemed to come from an adult if

all lower cheek teeth were fully erupted and from a juvenile if not.

Additionally, we divided specimens by the degree of wear of cheek teeth as an indirect proxy for age, allowing us to categorize specimens into 5 wear categories (1–5, from unworn to heavy wear). However placement into annual age cohorts (1 year old, 2 years old, and so on) based on tooth wear was compromised by substantial variation in rates of wear evidenced in a sample of S. richardsonii of precisely known age (n=25), particularly among yearlings, with males exhibiting greater rates of wear than females (see Fig 5 in Goodwin et al 2005).

You would have to determine how much these rats wear their teeth in your location, but you could have a general age class like:

juvenile (partially erupted molar)

young adult (wear 1-2)

old adult (wear 3-5)

Article Hibernation is recorded in lower incisors of Recent and foss...

Check out this article: Morris P. A review of mammalian age determination methods. (1972) Mammal Review 2(3): 69–104.

Many thanks to both of you!

See my paper

Freudenthal, M., E. Martín-Suárez & N. Bendala, 2002. Estimating age through tooth wear. A pilot study on tooth abrasion in Apodemus (Rodentia, Mammalia). --- Mammalia, 66,2: 275-284.