Mountain building triggered late cretaceous North American megaherbivore dinosaur radiation

Abstract

Prior studies of Mesozoic biodiversity document a diversity peak for dinosaur species in the Campanian stage of the Late Cretaceous, yet have failed to provide explicit causal mechanisms. We provide evidence that a marked increase in North American dinosaur biodiversity can be attributed to dynamic orogenic episodes within the Western Interior Basin (WIB). Detailed fossil occurrences document an association between the shift from Sevier-style, latitudinally arrayed basins to smaller Laramide-style, longitudinally arrayed basins and a well substantiated decreased geographic range/increased taxonomic diversity of megaherbivorous dinosaur species. Dispersal-vicariance analysis demonstrates that the nearly identical biogeographic histories of the megaherbivorous dinosaur clades Ceratopsidae and Hadrosauridae are attributable to rapid diversification events within restricted basins and that isolation events are contemporaneous with known tectonic activity in the region. SymmeTREE analysis indicates that megaherbivorous dinosaur clades exhibited significant variation in diversification rates throughout the Late Cretaceous. Phylogenetic divergence estimates of fossil clades offer a new lower boundary on Laramide surficial deformation that precedes estimates based on sedimentological data alone.

Figure 1. Paleogeographic maps of North America during the (A) late Campanian (∼75 Ma) and (B) late Maastrichtian (∼65 Ma).

The Sevier Orogenic Belt is the major mountain building system in western North America during the late Campanian, but note that by the latest Maastrichtian the Laramide Orogeny creates uplift structures further to the east. Maps courtesy of Ron Blakey, Colorado Plateau Geosystems.

Figure 2. Saurolophine hadrosaurid phylogeny from Prieto-Márquez with taxa time calibrated to known geologic occurrences.

Numbers in brackets indicate the midpoint of a geologic stage that a taxon is known to occur if that species does not have more constrained stratigraphic ages. Symbols on phylogenetic branches designate the inheritance of geographic distribution based on results from the DIVA analyses.

Figure 3. Chasmosaurine ceratopsid phylogeny from Sampson et al. [40] with taxa time calibrated to known geologic occurrences.

Numbers in brackets indicate the midpoint of a geologic stage that a taxon is known to occur if that species does not have more constrained stratigraphic ages. Symbols on phylogenetic branches designate the inheritance of geographic distribution based on results from the DIVA analyses. Note that Torosaurus and Triceratops both appeared on the Sampson et al. [40] phylogeny used in this study; and that in light of recent work documenting these taxa as congeneric [68], they remain as distinct genera within the present figure in order to maintain the original data integrity of the Sampson et al. [40] study, but are considered and discussed here as solely Triceratops.

Figure 4. Saurolophine range distribution throughout the Western Interior Basin during the Campanian (lower grey area) and Maastrichtian (upper white area).

To the right, paleogeographic maps of North America during the late Campanian (∼75 Ma) and late Maastrichtian (∼65 Ma). The sources for the geographic and stratigraphic position of the hadrosaurid species are as follows: Acristavus gagslarsoni , Brachylophosaurus Canadensis , Edmontosaurus annectens and E. regalis , Gryposaurus latidens , G. monumentensis , G. notabilis , Gryposaurus new species , Kritosaurus navajovius , , Maiasaura peeblesorum , Prosaurolophus maximus , , Sabinas OTU , , Saurolophus osborni , , and UTEP OTU , . Maps courtesy of Ron Blakey, Colorado Plateau Geosystems.

Figure 5. Time calibrated phylogeny of lambeosaurine hadrosaurids.

Data from Prieto-Márquez et al. .