Relationship between floras of type Lance and Fort Union formations

Abstract

Despite its controversial nature in connection with Mesozoic-Cenozoic boundary problems, the flora of the Lance formation at its type locality has never been adequately studied or described. During the past two summers collections were made at nine localities in the type Lance Creek area of eastern Wyoming, under joint auspices of the Carnegie Institution of Washington and Princeton University. Combined with smaller collections from the same region, now in the United States National Museum, the flora at present comprises 74 species, of which eight are apparently new. More than 75 per cent of the species have previously been reported elsewhere. An overwhelming majority are found only in formations now regarded as of Upper Cretaceous age on the basis of both stratigraphy and paleontology. It is clearly shown that this flora has very little resemblance to the widespread and well-known Fort Union flora. There are only seven species in common between the two floras; one of these species is a long-ranging form, and two of the others are only questionably reported from the Fort Union. As work progresses it is becoming apparent that previously published reports of the similarity between the Lance and Fort Union floras are erroneous and were based mainly on inclusion in the Lance flora of species now known to have come from beds which overlie the true Lance. It is evident that the flora of the nondinosaur-bearing beds which have been generally regarded as upper Lance is of Fort Union aspect and has little in common with the flora of the underlying dinosaur-bearing beds of the true Lance.