The fauna of the Enspel (Westerwald) and the neighbouring Kä rlich (Neuwied basin) fossil deposits correspond to the Upper Oligocene Mammal Paleogene (MP) reference level 28 and 28-30, respectively. Basaltic flows and a trachyte tuff terminating and predating the fossil deposit sedimentation allow to numerically calibrate the MP reference levels by radioisotope dating. Laser fusion 40 Ar/ 39 Ar step heating on volcanic feldspars yield a time interval of 24.9-24.5 Ma for reference level MP28 at Enspel and a maximum age of 25.5 Ma for the time interval MP28-MP30 at Kä rlich. Interpolation between the time intervals determined for the Enspel reference level MP28 and the age of the global Oligocene/Miocene boundary of 24.0 ± 0.1 Ma taken from literature results in time intervals of 24.5-24.2 Ma and 24.2-23.9 Ma for the younger reference levels MP29 and MP30, respectively. These intervals of £ 0.4 m.y. for MP reference levels of the latest Oligocene are short relative to older Oligocene MP reference levels 21-27 between 34 and 25 Ma. Since subdivision into MP reference levels essentially is based on assemblages of mammal taxa and on evolutionary changes in tooth morphology of mammals short MP time intervals during the latest Oligocene indicate a rapid evolutionary change relative to the early Oligocene.

There is a general consensus that most of today's nonvenomous snakes are descendants of venomous snakes that lost their venomous capabilities secondarily. This implies that the evolutionary history of venomous snakes and their venom apparatus should be older than the current evidence from the fossil record. We compared some of the oldest-known fossil snake fangs from the Lower Miocene of Germany with those of modern viperids and elapids and found their morphology to be indistinguishable from the modern forms. The primary function of recent elapid and viperid snake fangs is to facilitate the extremely rapid, stab-like application of highly toxic venoms. Our findings therefore indicate that the other components of the venom-delivery system of Early Miocene vipers and elapids were also highly developed, and that these snakes used their venom in the same way as their modern relatives. Thus, the fossil record supports the view that snakes used their venoms to rapidly subdue prey long before the mid-Tertiary onset of the global environmental changes that seem to have supported the successful radiation of venomous snakes.

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