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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]

Peligrochelys walshaegen. et sp. nov. is a new stem turtle closely related to the clade Meiolaniidae found in the Palaeocene levels of the Salamanca Formation (Maastrichtian–Danian) of central Patagonia, Chubut Province, Argentina. A phylogenetic analysis shows thatPeligrochelys walshaeforms a monophyletic group withMongolochelys efremovi, a clade that, in return, is the sister group of a clade formed byPatagoniaemys gasparinae,Otwayemys cunicularius,Kallokibotion bajazidiand Meiolaniidae. Meiolaniidae is recovered deeply nested in a monophyletic group (Meiolaniformes, new taxon name) dominated by Gondwanan taxa (e.g.Chubutemys copelloi,Patagoniaemys gasparinae,Otwayemys cuniculariusandPeligrochelys walshae), that also includes some notable Laurasian representatives (Mongolochelys efremoviandKallokibotion bajazidi). The biogeographic scenario presented here supports the hypothesis that this group of turtles may have originated as early as the Early Cretaceous in the South American part of Gondwana. The long ghost lineage that extends below this clade suggests that it may have originated any time between the Early Jurassic and the Early Cretaceous, implying a Pangaean or Gondwanan origin for the clade, respectively. The phylogenetic scenario presented here shows that at least two lineages (Peligrochelys walshaeand Meiolaniidae) of Meiolaniformes survived the K–P boundary extinction. Another interesting characteristic of meiolaniform turtles in the fossil record is their frequent association with another clade of strictly Gondwanan distribution, the pleurodiran clade Chelidae. This association is typically found in outcrops from the Early Cretaceous to the Eocene in central Patagonia, and in the Early Cretaceous and from the Miocene to the Pleistocene in Australia. [ABSTRACT FROM PUBLISHER]

Metatherian mammals were the most diverse mammalian clade in North America through the Late Cretaceous, but they underwent a severe extinction at the Cretaceous–Palaeogene (K-Pg) boundary. In order to clarify the origin of Palaeogene metatherians and the pattern of metatherian survivorship across the K-Pg boundary we conducted an inclusive species-level phylogenetic analysis of Cretaceous and early Palaeogene metatherian taxa. This analysis includes information from new Palaeocene specimens from south-western North America. Both the phylogenetic topology and information from new specimens support the validity of the genus Thylacodon and justify the recognition of a new species, T. montanensis. Thylacodon is closely related to Swaindelphys and Herpetotheriidae, which must have diverged by the latest Cretaceous due to its close relationship with late Campanian Ectocentrocristus. Pediomyidae and ‘Peradectidae sensu lato’ together comprise a major metatherian clade. Maastrichtidelphys, from the Late Cretaceous of the Netherlands, is the oldest member of ‘Peradectidae sensu lato’, indicating a Cretaceous origination for this group. Therefore, the major groups Herpetotheriidae and ‘Peradectidae sensu lato’, represented almost completely by Palaeocene taxa, must have originated in the Late Cretaceous. The lineages leading to these clades include at least four lineages that must have crossed the K-Pg boundary and therefore confirm that the K-Pg boundary marked a profound extinction event for metatherians and suggests that Palaeogene taxa originated from only a few clades of Cretaceous species, all of which were relatively minor or very rare components of known Cretaceous mammalian faunas. [ABSTRACT FROM PUBLISHER]