Cladotherians

Cladotherians are an extinct group of mammals that lived during the Jurassic and Cretaceous periods. They are characterized by their highly specialized molar teeth, which possess a distinct tribosphenic pattern. This pattern, featuring a shearing crest and a crushing basin, is considered a crucial evolutionary innovation that allowed for a more varied diet in early mammals. The name "cladotherian" itself refers to this "branching" arrangement of cusps on their molars.

Fossil evidence suggests that cladotherians were relatively small, often shrew-like or rodent-like in size. Their limbs were adapted for terrestrial locomotion, though some may have been semi-arboreal. They are considered an important group in understanding the early diversification of mammals, as their tribosphenic molars are a precursor to the molar structure found in most modern placental mammals and marsupials.

The evolutionary significance of cladotherians lies in their role as a transitional form. While not direct ancestors of all modern mammals, they represent a lineage that developed key dental features that would be inherited and modified by subsequent mammalian groups. Their extinction, occurring before the end of the Cretaceous, likely coincided with the rise of more dominant mammalian groups that eventually diversified into the wide array of species we see today. Studying cladotherians helps paleontologists reconstruct the evolutionary tree of mammals and understand the ecological pressures that shaped early mammalian evolution.