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ABSTRACT The 'Age of Mammals' began in the Paleocene epoch, the 10 million year interval immediately following the Cretaceous-Palaeogene mass extinction. The apparently rapid shift in mammalian ecomorphs from small, largely insectivorous forms to many small-to-large-bodied, diverse taxa has driven a hypothesis that the end-Cretaceous heralded an adaptive radiation in placental mammal evolution. However, the affinities of most Paleocene mammals have remained unresolved, despite significant advances in understanding the relationships of the extant orders, hindering efforts to reconstruct robustly the origin and early evolution of placental mammals. Here we present the largest cladistic analysis of Paleocene placentals to date, from a data matrix including 177 taxa (130 of which are Palaeogene) and 680 morphological characters. We improve the resolution of the relationships of several enigmatic Paleocene clades, including families of 'condylarths'. Protungulatum is resolved as a stem eutherian, meaning that no crown-placental mammal unambiguously pre-dates the Cretaceous-Palaeogene boundary. Our results support an Atlantogenata-Boreoeutheria split at the root of crown Placentalia, the presence of phenacodontids as closest relatives of Perissodactyla, the validity of Euungulata, and the placement of Arctocyonidae close to Carnivora. Periptychidae and Pantodonta are resolved as sister taxa, Leptictida and Cimolestidae are found to be stem eutherians, and Hyopsodontidae is highly polyphyletic. The inclusion of Paleocene taxa in a placental phylogeny alters interpretations of relationships and key events in mammalian evolutionary history. Paleocene mammals are an essential source of data for understanding fully the biotic dynamics associated with the end-Cretaceous mass extinction. The relationships presented here mark a critical first step towards accurate reconstruction of this important interval in the evolution of the modern fauna. [ABSTRACT FROM AUTHOR]

A new arctocyonid ‘condylarth’,Sigynorum magnadivisusgen. et sp. nov., is described from a recently discovered earliest Paleocene (early Puercan) fauna from the China Butte Member of the Fort Union Formation in the Great Divide Basin, southern Wyoming. Based on a sample of 18 specimens (including 14 partial dentaries) whose combined dentitions represent the p2, p4 and m1–3, the new taxon appears most similar in size and molar morphology to the early Puercan arctocyonidOxyprimus erikseni, but differs in its p4 morphology. To examine the relationship betweenS. magnadivisusand other Puercan ‘condylarths’ from the Western Interior of North America, a phylogenetic analysis was performed, utilizing 23 taxa (including 21 ‘condylarth’ species and the outgroup taxaCimolestesandGypsonictops) and 73 dental characters. The resulting strict consensus tree of 248 steps confirms the close relationship betweenS. magnadivisusandO. erikseni. Interestingly, our phylogenetic analysis also suggests that Puercan Periptychidae is paraphyletic; the early Puercan periptychidsMimatuta morgoth, Mimatuta minuial, Maiorana noctilucaandAuraria urbanaappear more closely allied with arctocyonid and hyopsodontid taxa, while other Puercan periptychidsConacodonspp.,Ampliconus browni, Alticonus gazini, Oxyacodonspp. andMithrandir gillianusfall into a separate monophyletic clade. This analysis is among the first to focus on a large set of Puercan ‘condylarth’ taxa across geographically widespread localities, and, with the addition of the new species from the Great Divide Basin, suggests that diversity among early Puercan ‘condylarths’ is higher than previously recognized. http://zoobank.org/urn:lsid:zoobank.org:pub:4BF2E9D5-1803-43E9-82FF-EC4723203A87 [ABSTRACT FROM AUTHOR]

A previously undescribed tooth from the Muñani Formation at the Laguna Umayo locality, Peru, represents the new didolodontid Umayodus raimondi gen. et sp. nov., here diagnosed by the presence of a well developed metastylid and ectostylid, and a twinned hypoconulid. This taxon is closely related to the middle Paleocene genera Escribania and Raulvaccia from the locality of Punta Peligro in Patagonia, Argentina. Phylogenetic analysis here performed indicates that they constitute a monophyletic group within Didolodontidae, supported by five derived characters: the hypocone well developed and close to the protocone; the strongly concave precingulum; the contact between the postcristid and the entoconid; the contact of the crista pre-paraconular, precingulum and parastyle; and the mesiodistal enlargement of the m3 talonid. Their paleogeographic distribution fit with those of the actual Andean Region of the Austral Kingdom. The previously assumed Thanetian--Ypresian age assignment for the Laguna Umayo LU3 fauna is here reinforced by faunistic comparisons with the earliest Eocene Murgon fauna, in Australia, and the Itaboraian South American Land Mammal Age, represented from faunas of Patagonia, Argentina and São José de Itaboraí, Brazil. [ABSTRACT FROM AUTHOR]