How do extreme traits arise? Through inheritance. Generation after generation, individuals with an advantageous trait, or adaptation, will survive longer and produce more offspring, until most or even all members of the species possess it. Called natural selection, this important mechanism of evolution has sometimes produced remarkable characteristics.
Headgear: Used for defense, recognizing species, and mating, mammal headgear evolved into unusual forms that included multiple horns, antlers as wide as a car, or tusks that grew through the skull.
Super Teeth: While the teeth in a reptile’s mouth are all basically the same shape and size, a suite of teeth in a single mammal’s mouth can include a wide range of forms and functions for slicing, tearing, chomping, and grinding.
Big Brains: Mammals have brains that are larger than most members of other vertebrate groups. Mammal brains also have three unique features that help with information processing, the sense of smell, and spatial navigation.
Hair & Armor: Mammals use hair for insulation, wooing mates, and camouflage, and whiskers for navigating through dark, narrow spaces. Sometimes hair and skin even form body armor, claws, and quills for defense!
Tails: Many mammals have exuberantly long tails with a range of unusual uses—from swimming, to hanging, to balancing while hopping or running, to serving as a blanket.
Horned Rodent Ceratogaulus rhinocerus
One extinct group of rodents really did have horns, including the foot-long Ceratogaulus rhinoceros. Recent studies suggest that these burrowing animals foraged frequently for food above ground and evolved horns to protect themselves from predators.
Horns—the most common type of headgear—can be made from hair, teeth, or bone and arose independently in at least seven dramatically different groups of mammals. Each time, horns evolved in animals whose ancestors had no headgear at all.
Evolving big brains relative to body size distinguishes mammals from other vertebrates, and humans from all other mammals. Much of the increase occured in the cerebrum, the part of the brain largely associated with thought, memory, most senses, and information processing.
Mammal brains also typically share three unique features: a neocortex for increased information processing; a complex olfactory system that gives mammals perhaps the best sense of smell of all vertebrates; and a vermis—an expansion of the cerebellum that probably helps mammals maneuver through complex three-dimensional environments.