Timothy H. Heaton
Department of Paleobiology, Smithsonian Institution, Washington, D.C. 20560
Over 1200 Leptomeryx dentaries have been recovered from a 136 m interval of section at Flagstaff Rim. Specimens from the lower 30 m are concentrated in three quarries; above 30 m they occur at all levels, but they become sparse above 116 m.
Material from above 30 m groups into two static lineages, one large and one small, with no size overlap. But below 30 m these two lineages become successively less distinct, until the sample from the lowest quarry comprises a single normally-distributed population with a coefficient of variation equivalent to that of each of the two lineages above 30 m.
Compared to the two lineages above 30 m, specimens from the lowest quarry are more similar in size to those of the smaller lineage but more similar in shape to those of the larger lineage. Multivariate statistical analyses provide no criteria for subdividing the lowest quarry sample into more than one species, while evidence for two coexisting lineages is conclusive at all other levels.
Leptomeryx from Flagstaff Rim may represent a case of sympatric speciation within a large population.