The age of the terrestrial clastics of the Derincay Formation that outcrop widely in the Mut region is controversial. In an attempt to resolve their age, small mammals have been collected at the locality Yapinti from the lacustrine mudstones in this formation. This assemblage contains Enginia cf. E. gertcheki, Cricetodon cf. C. kasapligili, Cricetodon aff. C. aliveriensis, Megacricetodon collongensis, Democricetodon sp., Karydomys n.sp., Eumyarion sp., Tamias sp. Gliridae gen. et sp. indet, Sayimys sp., Albertona n.sp., Galerix uenayae, Talpidae gen. et sp. indet, Oligosorex sp., Soricidae gen. et sp. indet. This association suggests an Early Miocene Age (MN3 to early MN4) which roughly correlates with the middle Burdigalian (+/-18 Ma). The Yapinti assemblage is of special interest because the continental deposits of the Derincay Formation that yielded the rodents are disconformably overlain by the marine Mut and Koselerli formations assigned to the late Burdigalian on the basis of planktonic Foraminifera, which is a first order correlation between continental and marine deposits.