Description of a new toothed mysticete from the Late Oligocene of San Juan de La Costa, B.C.S., Mexico

摘要

This paper describes a toothed mysticete that belongs to a basal family found in Oligocene sedimentary rocks deposited in the North Pacific Ocean. The material that is described here belongs in the Chattian stage of the Oligocene, and it was collected near Arroyo El Saladito from the San Juan Member in the El Cien Formation, Baja California Sur, Mexico. The sedimentary environment of this area has been interpreted to be a continental platform with nutrient-rich waters combined with anoxic conditions. Therefore, the specimens that have been found in the phosphorite layers lived in an environment of shallow coastal waters. The material described is a dentary fragment, a skull and fragments of the teeth. The new taxon is located within the Superfamily Aetiocetoidea due to the presence of functional teeth, which have a slightly globose shape with eight slightly triangular apices. Niparajacetus palmadentis presents a morphology that contrasts with other toothed whales. For example, it shows an elongated and wide skull in the posterior region with a triangular shape, and its estimated total length is 3.2-3.5 m.