Publication Date


Series Number



Mammals of metatherian-eutherian grade are represented in a collection recovered from a Wise County, Texas, locality of Lower Cretaceous (Albian) age. The form, or forms, are distinctly primitive as evidenced by the very small low protocones, large stylar cusps, and wide stylar shelf. The presence of well-developed and separate metacones at such an early date would seem to place Deltatheridium well off the evolutionary line of all later mammals except possibly zalambdodonts. The premolars contain both anterior and posterior cingulum cusps in addition to the protoconid and posterior accessory cusp. The lower molars have trigonids that are extremely compressed anteroposteriorly, and all but one have three talonid cusps. One lower molar apparently has but a single talonid cusp, the hypoconulid, and may have inferences as to the evolution of the therian talonid. A new family, Pappotheriidae, is proposed which in known parts has all of the prerequisites necessary to be in or near the ancestry of all later therians.