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.
Stagodontid marsupials were a common component of late Mesozoic vertebrate faunas of the Western Interior of North America and were among the largest mammals that coexisted with Late Cretaceous dinosaurs. Two genera have been described, Didelphodon and Eodelphis; three if Pariadens (?Stagodontidae) from the Cenomanian of Utah (Cifelli and Eaton, 1987) is included. The dental arcade of stagodontids is notable for the presence of bulbous premolars, each with a massive main cusp and a large accessory lobe. The most complete stagodontid material consists of a maxillary fragment and a few nearly complete dentaries referred to Didelphodon (see Clemens, 1968, 1973; Fox and Naylor, 1986). However, the configuration of the anterior upper dentition of Didelphodon and other stagodontids is uncertain because of the lack of specimens preserving this portion of the skull. Thus, based on isolated teeth, upper premolars of Didelphodon have been interpreted to have been oriented with their accessory lobes either on their labial (Clemens, 1966) or lingual (Clemens, 1968; Lillegraven, 1969; Archibald, 1982; Fox and Naylor, 1986) sides.
With the discovery and description of the Bug Creek faunas in 1965, it became necessary to reexamine the sequence of mammal ages (Lancian-Puercan) spanning the Cretaceous-Tertiary boundary. Bug Creek faunal assemblages have been viewed as being in part coeval with the Lancian assemblages or slightly younger. Because of the lack of Lancian sites above the Bug Creek-type sites and the discontinuous nature of the sediments preserving the latter type faunas, it appears that the Bug Creek faunas postdate Lancian faunas. Although the Bug Creek faunas cannot be well constrained biostratigraphically, the appearance of a number of new taxa and the continuation of these or closely related taxa into the Puercan is strong evidence for a biochronologic sequence of Lancian-Bug Creek-Puercan.When the faunal contents of Lancian, Bug Creek, and earliest Puercan (Pui) sites are scrutinized, it is clear that important faunal introductions occur with the commencement of Bug Creek assemblages. In contrast, between Bug Creek and earliest Puercan (Pui) assemblages there are very few major faunal introductions and thus more faunal continuity. Therefore, the definition and concept of the Puercan Land Mammal Age is modified, and the Bug Creek faunas are formally defined and characterized as the
Protungulatum/Peradectes
Interval-Zone (Puo) of the Puercan Land Mammal Age. The Protungulatum/Peradectes
Interval-Zone (Puo) postdates the (latest Cretaceous) Lancian Land Mammal Age and commences the (latest Cretaceous?-early Paleocene) Puercan Land Mammal Age. This interval-zone is defined as including faunas that occur during the time between the first appearance of the arctocyonid ungulate Protungulatum and the first appearance of the didelphid marsupial Peradectes.Certain biochronological criteria (first appearances and "cladochronology") within this interval-zone strengthen the view that the original sequence (from oldest to youngest) of Bug Creek Anthills, Bug Creek West, and Harbicht Hill is correct. Therefore, three informal biochrons are recognized, the Protungulatum/Mimatuta (bki), Mimatuta/Oxyprimus (bk 2 ), and Oxyprimus/Peradectes (bk 3 ) biochrons.Dinosaurs and Lancian mammals are found at all Puo localities. Although the possibility of reworking cannot be completely dismissed, the abundance of Lancian mammals and the nature of dinosaur material at certain Pu« sites suggest some temporal overlap. Similarly, the stratigraphie placement of palynological change and an iridium anomaly relative to Puo faunas remains equivocal.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.