Alphadon halleyi

DESCRIPTION: Several lower molars from Clambank Hollow show morphological differences from teeth that can be assigned to A. praesagus. AMNH 77367 is significantly smaller (length 2.1 mm., fig. 13 U, V) than lower molars of A. praesagus. Its paraconid is a conical cusp and it is slightly medial to the metaconid. The metaconid is anteroposteriorly elongated, particularly at its base, and tapers toward the apex. The protoconid is taller than the metaconid and situated anterior to it. The talonid is deep and basined and the crista obliqua is oriented in the manner characteristic of Alphadon. The hypoconid is a well-developed cusp, and the hypoconulid is directed posteriorly and more separated from the entoconid than in most contemporary marsupials. The width of the talonid (1.2 mm.) is equal to that of the trigonid. A partial upper molar, AMNH 77370, is small enough to be included within A. halleyi (fig. 13 W). The width of the crown is 1.7 mm. and it is approximately equal to the estimated length. The stylar shelf anterior to stylar cusp C is broken. Stylar cusp D is well developed and larger than stylar cusp C. The metacone is as high as the paracone and separated from it by a narrow valley. Both conules are present, and the protocone is a low cusp. Alphadon halleyi is a possible ancestor to the Maestrichtian A. lulli.

DIAGNOSIS: Smaller than Alphadon praesagus but larger than A. lulli from the Lance Formation. Upper molars with stylar cusp D well developed and larger than stylar cusp C; metaconule and protoconule distinct, protocone low.

ETYMOLOGY: Named in honor of the Warren Halley family on whose ranch most of our prospecting was done.

HOLOTYPE: AMNH 77367, a lower molar. TYPE LOCALITY: Clambank Hollow, Chouteau County, Montana. KNOWN DISTRIBUTION: Judith River Formation, Montana.