Ectenotheriids

Ectenotheriids are an extinct family of small to medium-sized mammals that belonged to the order Multituberculata, a group that thrived during the Mesozoic and early Cenozoic eras. These animals are notable for their specialized dentition and adaptations, particularly in their cheek teeth, which featured multiple cusps arranged in complex patterns. Their name, derived from the Greek *ectenos* (meaning "comb-like") and *therion* (meaning "beast"), reflects the distinctive structure of their molars.

Ectenotheriids are primarily known from fossil records dating back to the Late Cretaceous period, around 70 to 66 million years ago, though some species may have persisted into the early Paleocene. They were widespread across what is now North America, with fossils discovered in regions such as Montana, Wyoming, and Alberta. These mammals were likely small, possibly rodent-like in size, and may have inhabited forested or wooded environments.

The dental morphology of ectenotheriids suggests they were herbivorous, feeding on soft plant material. Their molars had elongated, comb-like ridges that facilitated efficient grinding, a trait that may have allowed them to exploit a niche similar to modern-day rodents or lagomorphs. Unlike some other multituberculates, ectenotheriids lacked the extreme specialization seen in groups like the Taeniodonta, indicating a more generalized diet.

Fossil evidence of ectenotheriids is relatively limited compared to other multituberculates, but their unique dental adaptations provide insights into the evolutionary diversity of Mesozoic mammals. Their extinction coincides with the Cretaceous-Paleogene (K-Pg) mass extinction event, which wiped out many other species, including non-avian dinosaurs. While ectenotheriids did not survive beyond the early Cenozoic, their study contributes to understanding the ecological roles of small mammals during the late Mesozoic era.