Above is the partial right dentary (lower jaw) of a western pipistrelle bat, Parastrellus hesperus. It’s shown in lateral view, with anterior to the left, and the black and white bars under it are each 1 mm wide; this is a tiny jaw! The single preserved tooth is the lower third molar. Below is medial view:
Pipistrelles are not a common component of the Diamond Valley Lake fauna, but their presence is not surprising. They are currently common throughout the southwest, especially in desert areas; we occasionally find them roosting on the museum buildings. While widespread, they are not particularly gregarious, and are usually found alone roosting in rock crevices during the day. Like many other bats, they are voracious predators of insects.
Pipistrelles are one of the numerous small animal species present in the DVL fauna that are still common in southern California today. They form an interesting contrast with the large animal fauna, which is almost completely different from what currently lives here.