Early mammalian recovery after the end-Cretaceous mass extinction: A high-resolution view from McGuire Creek area, Montana, USA

Abstract

Changes in mammalian faunal composition and structure following the Cretaceous-Paleo gene mass extinction are central to understanding not only how terrestrial communities recovered from this ecological perturbation but also the evolution of archaic groups leading to extant mammalian clades. Here, we analyzed changes in mammalian local faunas during the earliest Paleogene biotic recovery on a small spatiotemporal scale. We compiled samples of mammals from four localities in the Hell Creek Formation and Tullock Member of the Fort Union Formation, in the McGuire Creek area, McCone County, Montana, USA, and placed these localities into a high-precision chronostratigraphic framework using 40 Ar/ 39 Ar tephra ages and magnetostratigraphy. Within this framework, we quantitatively compared faunal composition, heterogeneity, and richness among McGuire Creek local faunas and made broader comparisons to other earliest Paleogene faunas from throughout the Western Interior of North America. In the first ~320 k.y. of the recovery, mammalian local faunas at McGuire Creek, all of which can be placed in the Puercan 1 North American Land Mammal Age (NALMA) interval zone, underwent modest increases in taxonomic richness and heterogeneity, indicating the beginning of biotic recovery; however, no Mc-Guire Creek fauna reached fully recovered levels of taxonomic richness. Further, appearance of immigrant taxa such as Purgato-rius in younger McGuire Creek faunas demonstrates important compositional changes within the Pu1 of McGuire Creek. These results highlight the difficulties with describing the nuanced mammalian recovery process using the NALMA system and emphasize the increasing importance of high-precision dating, especially when comparing faunas across large geographic distances.

Constructing a Timescale of Biotic Recovery across the Cretaceous–Paleogene Boundary, Corral Bluffs, Denver Basin, Colorado

“…Opportunistic immigrant taxa spearheaded by archaic ungulates are common in the earliest Paleocene, possibly from refugia either to the north or south of the Western Interior (Lofgren et al, 2004;Wilson, 2014). Assemblages from the Hell Creek region of Montana indicate that recovery of mammal communities in this area took between 320 kyr to 1 myr with eutherian taxa taking 400 kyr to 1 myr to recover (Wilson, 2014;Smith et al, 2018). Lillegraven and Eberle (1999) noted that the eutherian faunas in the Ferris Formation of the Hanna Basin, the only locality currently where Pu1-3 are in direct superposition, do not show significant losses at the K-Pg but instead radiate to fill vacant niche space.…”

“…The Laramide synorgenic sediment sequence within the Denver Basin represents one of the best terrestrial records of the K-Pg boundary in the world with observed osmium and iridium anomalies, shocked quartz, extinction of flora and fauna, and a spike in abundance of fern spores that are commonly used as indicators of the boundary (Nichols and Fleming, 2002;Barclay, 2003;Raynolds and Johnson, 2003;Zaiss et al, 2014). Several important megafloral and vertebrate paleontological localities have been identified within the basin; however, the Denver Basin is relatively under-sampled in comparison to coeval sites in the San Juan Basin of New Mexico and Williston Basin of North Dakota and Montana (Archibald, 1982;Williamson, 1996;Clemens, 2002;Williamson et al, 2012;Wilson, 2013;Smith et al, 2018). There are 231…”

Diversity and dispersal trends following the latest-permian mass extinction

“…Other intervals with low CI values all fall within the plateau, and it ca n The results of this analysis are congruent with the finds from other studies. Rapid onset of recovery following the K-Pg extinction has also been observed in other analyses of Paleocene richness (Maas and Krause, 1994;Alroy, 1999Alroy, , 2000Wilson, 2013;Longrich et al, 2016), including studies that were able to incorporate the use of rarefaction to standardize for sampling (Wilson, 2014;Smith et al, 2018).…”

“…If the Deccan traps did play a role in the weakening of late Maastrichtian terrestrial ecosystems, then there exists no evidence of these effects continuing in the aftermath of the bollide impact. Even though the majority of the volume of Deccan basalts appear to have erupted following the Chicxulub impact (Keller et al, 2016;Sprain et al, 2018), and the apparent effects of this volcanism continued to be felt in marine ecosystems into the early Paleocene (Keller et al, 2009a), major climatic deviations and terrestrial ecological downturns (Wilson, 2013(Wilson, , 2014Longrich et al, 2016;Smith et al, 2018) are unknown from the rest of the eruption period (Chenet et al, 2007;Schoene et al, 2015). The apparent drop in diversity found in this study for the To1 interval post-dates the termination of Deccan volcanism (Keller et al, 2016).…”

“…Studies performed on geographically dispersed sections have demonstrated that K-Pg foram extinctions began prior to the Chicxulub impact, and that the bulk of foram extinctions post-date the impact by 100-300ka (Keller et al, 2009a(Keller et al, , 2009b(Keller et al, , 2013(Keller et al, , 2016. By the time of the foram mass die-off, estimated to coincide with Pu2 -Pu3 NALMA substages , the terrestrial recovery was already well-underway in North America and showing no signs of interruption (Wilson, 2013(Wilson, , 2014Smith et al, 2018). Changes to mammalian and salamander communities in North America during the very end of the Cretaceous have been interpreted as resulting from the deterioration of environmental conditions, likely stemming from the effects of Deccan volcanism (Wilson, 2005(Wilson, , 2014Wilson et al, 2014;Sprain et al, 2015Sprain et al, , 2018, although the bulk of terrestrial extinctions in North America coincide very closely with the bollide impact (Renne et al, 2013;Sprain et al, 2015Sprain et al, , 2018Clyde et al, 2016).…”