Revised geochronology, correlation, and dinosaur stratigraphic ranges of the Santonian-Maastrichtian (Late Cretaceous) formations of the Western Interior of North America

Abstract

Interbasinal stratigraphic correlation provides the foundation for all consequent continental-scale geological and paleontological analyses. Correlation requires synthesis of lithostratigraphic, biostratigraphic and geochronologic data, and must be periodically updated to accord with advances in dating techniques, changing standards for radiometric dates, new stratigraphic concepts, hypotheses, fossil specimens, and field data. Outdated or incorrect correlation exposes geological and paleontological analyses to potential error. The current work presents a high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. 40Ar / 39Ar radiometric dates are newly recalibrated to both current standard and decay constant pairings. Revisions to the stratigraphic placement of most units are slight, but important changes are made to the proposed correlations of the Aguja and Javelina formations, Texas, and recalibration corrections in particular affect the relative age positions of the Belly River Group, Alberta; Judith River Formation, Montana; Kaiparowits Formation, Utah; and Fruitland and Kirtland formations, New Mexico. The stratigraphic ranges of selected clades of dinosaur species are plotted on the chronostratigraphic framework, with some clades comprising short-duration species that do not overlap stratigraphically with preceding or succeeding forms. This is the expected pattern that is produced by an anagenetic mode of evolution, suggesting that true branching (speciation) events were rare and may have geographic significance. The recent hypothesis of intracontinental latitudinal provinciality of dinosaurs is shown to be affected by previous stratigraphic miscorrelation. Rapid stepwise acquisition of display characters in many dinosaur clades, in particular chasmosaurine ceratopsids, suggests that they may be useful for high resolution biostratigraphy.

What factors influence our reconstructions of Morrison Formation sauropod diversity?

“…As demonstrated within the Hell Creek Formation, stratigraphy is an important consideration for diversity estimates (Horner and others, 2011;Scannella and others, 2014;Fowler, 2017). While Horner and Goodwin (2006) were able to show that Triceratops species diversity was a false artifact from ontogimorphs of two species, Scannella and others (2014) was able to refine this image by incorporating stratigraphic information.…”

“…The Late Cretaceous Hell Creek Formation represents a dinosaur-bearing formation that is historically well known and extensively studied, with similarly high dinosaur diversity to that of the Morrison Formation. However, over the past decade, ontogenetic and stratigraphic assessments (Horner and Goodwin, 2006Scannella and Fowler, 2009;Horner, 2010, 2011;Campione and Evans, 2011;Horner and others, 2011;Scannella and others, 2014;Goodwin and Evans, 2016;Fowler 2017;others, 2017, 2018) have reassessed the diver-sity, life development, and evolution of the Hell Creek Formation dinosaurs. These analyses alternatively suggest lower species richness.…”

A new tyrannosaurid (Dinosauria: Theropoda) from the Upper Cretaceous Menefee Formation of New Mexico

“…Two tyrannosaurids are now known from the lower Campanian of southern Laramidia, L. argestes from the Wahweap Formation of Utah ( Loewen et al, 2013 ) and Dynamoterror dynastes from the Allison Member of the Menefee Formation of New Mexico. However, diagnostic tyrannosaurid material is currently lacking from roughly contemporaneous units in northern Laramidia, such as the lower Two Medicine Formation and McClelland Ferry Member of the Judith River Formation of Montana, and the Deadhorse Coulee Member of the Milk River Formation, Foremost Formation, and lower Oldman Formation of Alberta ( Fowler, 2017 ). Furthermore, the early evolution and biogeography of Tyrannosaurinae in southern Laramidia remain enigmatic pending the discovery of additional tyrannosaurine material from the Menefee, Wahweap, and Kaiparowits formations.…”

“…Although exceptionally rich, the tyrannosaurid record from Laramidia is temporally restricted to between approximately 77.0 Ma ( Daspletosaurus torosus ( Currie, 2003 ; Carr et al, 2017 ; Fowler, 2017 )) and 66.0 Ma ( Tyrannosaurus rex ( Carr & Williamson, 2004 ; Holtz, 2004 )), obscuring the earlier evolution of the group. The recent discovery of a new tyrannosaurid, Lythronax argestes , from the Wahweap Formation of Utah ( Loewen et al, 2013 ), provided the first extensive morphological data for an early Campanian (∼80 Ma) tyrannosaurid from Laramidia.…”

Calibration, Coherence, and Consilience in Radiometric Measures of Geologic Time

“…Without recalibration, two argonargon dates (one obtained prior to 2012 and one obtained after) that should have identical ages in the Cambrian period, for example, will appear more than 3 million years apart. An inadequate appreciation of this problem of legacy dates has recently been noted in connection with a number of paleobiological studies of dinosaur evolution by Fowler (2017), who provides a recalibration table using the new Min et al decay constants and Kuiper et al mineral standard age for 200 key (pre-2012 measured) argon-argon dates during the Cretaceous period. As he notes, accounting for these changes in calibration can completely reverse some paleobiological conclusions, yet this fact has not been adequately appreciated by many researchers (Fowler 2017, p. 2).…”