What characteristic uniquely identifies members of the Order Rodentia?
A single pair of continuously growing, self-sharpening incisors
Members of the Order Rodentia are defined explicitly by a specific dental structure necessary for their lifestyle of gnawing on various materials like bark, seeds, and nesting components. This defining characteristic is the presence of only one pair of incisors in both the upper and lower jaws. Crucially, these incisors grow continuously throughout the rodent's life. To maintain a functional biting surface and prevent overgrowth, the animal must constantly gnaw, which naturally self-sharpens the enamel on the front surface of these teeth. The other options describe broader taxonomic placements: possession of a notochord places an animal in Phylum Chordata; milk production and being warm-blooded define the Class Mammalia; and being heterotrophic and multicellular begins the classification at the broadest level, Kingdom Animalia.
