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Fowler, 2006: SVP abstract

FOWLER, D.W. (2006), Terrestrial Late Cretaceous stratigraphy of North America and the utility of ceratopsids in biostratigraphy, Journal of Vertebrate Palaeontology 26(3, supp): 63A


A comprehensive stratigraphy is presented for the terrestrial Late Cretaceous units of North America . This combines published radiometric dates, magnetostratigraphy, and reviews ranges of known taxa, paying particular attention to ceratopsids.

While the stratigraphic relationships of Campanian strata are well constrained, the majority of the Maastrichtian is still largely unresolved. In the Campanian, integrity of the recently proposed Kirtlandian age is maintained. Uppermost deposits of the Two Medicine Fm, Montana , are demonstrated as early Kirtlandian in age. Purported north-south provinciality of dinosaurs is shown to be mostly an artefact of stratigraphic incongruence. Exceptions are two biogeographically distinct chasmosaurine lineages present in the Judithian, and the presence of sauropods in the south, but not the north during the Edmontonian. Contrary to much recent work, stratigraphy and new material tentatively supports a single anagenetic lineage for centrosaurines.

Most Late Cretaceous sauropod material from North America is attributed to Alamosaurus sanjuanensis and this has been used to infer stratigraphic relationships for Alamosaurus -bearing strata. There is little evidence to support this. The form taxon Alamosaurus is unknown before the Maastrichtian, but is otherwise shown to be stratigraphically uninformative. We should not expect all ceratopsids found in formations bearing Alamosaurus to be the same taxon. If the pattern of speciation seen in the Campanian is followed, it is likely that many more species of chasmosaurine remain to be discovered from 70.5-66Ma. Rapid stepwise acquisition of characters in ceratopsids suggests that careful analysis of ceratopsid taxonomy and distribution presents them as the best biostratigraphic markers to be used where radiometric dates are not available.