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Abstract The spectacular fossil fauna and flora preserved in the Upper Cretaceous terrestrial strata of North America’s Western Interior Basin record an exceptional peak in the diversification of fossil vertebrates in the Campanian, which has been termed the ‘zenith of dinosaur diversity’. The wide latitudinal distribution of rocks and fossils that represent this episode, spanning from northern Mexico to the northern slopes of Alaska, provides a unique opportunity to gain insights into dinosaur paleoecology and to address outstanding questions regarding faunal provinciality in connection to paleogeography and climate. Whereas reliable basin-wide correlations are fundamental to investigations of this sort, three decades of radioisotope geochronology of various vintages and limited compatibility has complicated correlation of distant fossil-bearing successions and given rise to contradictory paleobiogeographic and evolutionary hypotheses. Here we present new U–Pb geochronology by the CA-ID-TIMS method for 16 stratigraphically well constrained bentonite beds, ranging in age from 82.419 ± 0.074 Ma to 73.496 ± 0.039 Ma (2σ internal uncertainties), and the resulting Bayesian age models for six key fossil-bearing formations over a 1600 km latitudinal distance from northwest New Mexico, USA to southern Alberta, Canada. Our high-resolution chronostratigraphic framework for the upper Campanian of the Western Interior Basin reveals that despite their contrasting depositional settings and basin evolution histories, significant age overlap exists between the main fossil-bearing intervals of the Kaiparowits Formation (southern Utah), Judith River Formation (central Montana), Two Medicine Formation (western Montana) and Dinosaur Park Formation (southern Alberta). Pending more extensive paleontologic collecting that would allow more rigorous faunal analyses, our results support a first-order connection between paleoecologic and fossil diversities and help overcome the chronostratigraphic ambiguities that have impeded the testing of proposed models of latitudinal provinciality of dinosaur taxa during the Campanian.
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A latest Paleocene mammal fauna from the Great Divide Basin in southern Wyoming and a revised biozonation of the Clarkforkian land mammal age
A new latest Paleocene mammal fauna from the Great Divide Basin in southern Wyoming is described and compared with fossil assemblages of similar age elsewhere in Wyoming. The Twelvemile Gulch local fauna is currently documented by 182 mammalian (127 identifiable) specimens from two localities representing 10 orders, 18 families, and 22 species of mammals, including Phenacolemur cavatus, new species. Several characteristic taxa indicate a Clarkforkian age, but some taxa that co-occur at Twelvemile Gulch show disjunct stratigraphic ranges in the well-documented stratigraphic sequence exposed in the Clarks Fork Basin of northern Wyoming. Anachronistic occurrences of Clarkforkian taxa in northern and southern Wyoming have now been documented repeatedly. These unexpected faunal associations likely reflect changing climates and associated taxon-specific range shifts across a latitudinal gradient in the Rocky Mountain Interior. The apparently asynchronous first and last appearances of certain taxa across this latitudinal gradient highlight the utility of immigrant clades over endemic taxa in biostratigraphy. A previous biozonation scheme for the Clarkforkian of the Clarks Fork Basin emphasized endemic Plesiadapis cookei and Copecion as index taxa for Clarkforkian biozones Cf-2 and Cf-3, respectively. However, the applicability of this zonation to Clarkforkian faunas from other parts of Wyoming has been problematic because Plesiadapis cookei occurs in all of them, despite substantial evidence for age disparity among these faunas. A revised biozonation for the Clarkforkian leverages first appearances of invasive Coryphodontidae and Miacidae to discriminate later Clarkforkian faunas including Twelvemile Gulch from earlier Clarkforkian faunas such as Big Multi Quarry.
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- Award ID(s):
- 2117299
- PAR ID:
- 10652564
- Publisher / Repository:
- Society for Vertebrate Paleontology
- Date Published:
- Journal Name:
- Journal of Vertebrate Paleontology
- Volume:
- 44
- Issue:
- 3
- ISSN:
- 0272-4634
- Page Range / eLocation ID:
- e2424139
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Journal Article:
- https://doi.org/10.1080/02724634.2024.2424139
