TILLODONTIA  , a

group of mammals of uncertain position, typified by Tillotherium from the Middle Eocene of Wyoming, (From Marsh.) Skull of Tillotherium fodiens . (* nat. size.) and perhaps including Esthonyx from the Lower Eocene of the same district, and other genera from the same horizon in both North America and Europe . In Tillotherium the skull is decidedly rodent-like, with an elongated cranial and a short facial portion, and a small brain-cavity; the jugal bone occupying the middle of the zygomatic arch . The dentition, of which the formula is i., c . , p . , m. i, also approximates to the rodent type, the canines being minute and functionless, and the first pair of incisors large and chisel-like . On these and other grounds it has been suggested that Tillotherium (of which the greater part of the skeleton is known) indicates the ancestral form of the Rodentia . Professor Max Weber considers, however, that such a view has but little justification . Relationship with the Ungulata and Carnivera has also been suggested; if there be any with the latter, it must have been with the most primitive forms, as the plantigrade feet are furnished with five toes carrying long pointed claws . Possibly Platychoerops richardsoni, from the Lower Eocene London Clay, belongs to the group . (R .