|An adult TBD (left), TBD (center), and TBD (right)|
Most alvonatal species give birth to substantially more developed precocial young, which are capable of movement from the moment of birth. As with placentals and marsupials, alvonatals are nourished within the placenta of an apex alvonatal until birth, and are partially-nursed and protected by mesa alvonatals until capable of digesting solid foods on their own. However, the vast majority of alvonatal newborns can see, hear, and move on their own from the moment of birth. Alvonatals represent the overwhelming majority of mammalian lifeforms residing on the planet of TBD, and most of the animal life imported to the other worlds inhabited by TBD are comprised of alvonatals.
The word alvonatal is derived from the Latin words alvus ("belly" or "stomach") and nātus ("born"), referring to the method of birth via the navel cavity.