Eoconodon ("Triisodontidae," Mammalia) from the Early Paleocene (Puercan) of northeastern Montana, USA
The uppermost Hell Creek and Tullock Formations of Garfield and McCone Counties, northeastern Montana, have yielded large samples of earliest Paleocene (Puercan North American Land Mammal 'Age') local faunas. These are allocated to either the earliest Puercan (Pu1) interval zone or an undifferentiated Pu2/Pu3 interval zone of middle and/or late Puercan age. Eoconodon ("Triisodontidae") is absent from Pu1 local faunas of northeastern Montana, but is represented by two species (E. nidhoggi and E. hutchisoni, new species) in Pu2/Pu3 interval zone local faunas. Morphology of their cheek teeth, presence of Hunter-Schreger bands in their enamel, and relatively large mandibular horizontal ramus and symphysis (known only for E. hutchisoni, new species) are similar to those of mesonychians. These derived characters suggest that the species of Eoconodon included early eutherian experiments in evolution of large body size and a predatory mode of life.
Species of Eoconodon or a closely related sister group are not known from latest Cretaceous local faunas of the Western Interior. The oldest records of the genus are limited to the Pu1 Mantua Lentil local fauna in the Big Horn Basin and UW locality 91015 in the Ferris Formation, Wyoming. They provide support for the hypothesis that Eoconodon was an immigrant entering the Western Interior during the Pu1 interval zone. Samples of Pu2 and Pu3 local faunas document differentiation of the genus into three species known primarily from the San Juan Basin, New Mexico, and two other species currently known in local faunas of Montana and other northern localities.
KEY WORDS: Mammalia; "Triisodontidae;" Eoconodon; new species; Paleocene; Puercan; Montana, USA
PE Article Number:
Copyright: Society of
Vertebrate Paleontology November 2011
Submission: 15 June 2007. Acceptance: 25 February 2011