Abstract:
A relatively complete fragmentary lower jaw of a late fetus of Mammuthus was first found in Western Siberia in the Late Pleistocene Krasnyi Yar locality (Tomsk Region, Russia). The extent to which the jaw was developed and morphological features, such as a well-developed compact bone layer in the symphysial region, the structure of the alveoli for the first and second tooth generations (dp2 and dp3), and the jaw measurements, show that the fetus is at about 14-16 months of prenatal development. A number of morphological features, i.e., the absence of symphysial suture, mental foramina, and nutrient canals and a large size of the dp2 alveoļi, distinguish this specimen from fetuses of M. primigenius, Elephas maximus, and Loxodonta africana. The measurements of the dp2 alveolus of the specimen from the Krasnyi Yar locality fall into the range of the dp 2 variation in M. trogontherii. Certain morphological features of this fetus give evidence for aberrative deviations in prenatal development. Other features indicate that certain skeletal characters typical of the late ontogenetic stages of early proboscideans were shifted to the earlier stages in late elephants of the mammoth-like group.
