Craniodental Morphology and Systematics of a New Family of Hystricognathous Rodents (Gaudeamuridae) from the Late Eocene and Early Oligocene of Egypt

BACKGROUND: Gaudeamus is an enigmatic hystricognathous rodent that was, until recently, known solely from fragmentary material from early Oligocene sites in Egypt, Oman, and Libya. Gaudeamus' molars are similar to those of the extant cane rat Thryonomys, and multiple authorities have aligned Gaudeamus with Thryonomys to the exclusion of other living and extinct African hystricognaths; recent phylogenetic analyses have, however, also suggested affinities with South American caviomorphs or Old World porcupines (Hystricidae). METHODOLOGY/PRINCIPAL FINDINGS: Here we describe the oldest known remains of Gaudeamus, including largely complete but crushed crania and complete upper and lower dentitions. Unlike younger Gaudeamus species, the primitive species described here have relatively complex occlusal patterns, and retain a number of plesiomorphic features. Unconstrained parsimony analysis nests Gaudeamus and Hystrix within the South American caviomorph radiation, implying what we consider to be an implausible back-dispersal across the Atlantic Ocean to account for Gaudeamus' presence in the late Eocene of Africa. An analysis that was constrained to recover the biogeographically more plausible hypothesis of caviomorph monophyly does not place Gaudeamus as a stem caviomorph, but rather as a sister taxon of hystricids. CONCLUSIONS/SIGNIFICANCE: We place Gaudeamus species in a new family, Gaudeamuridae, and consider it likely that the group originated, diversified, and then went extinct over a geologically brief period of time during the latest Eocene and early Oligocene in Afro-Arabia. Gaudeamurids are the only known crown hystricognaths from Afro-Arabia that are likely to be aligned with non-phiomorph members of that clade, and as such provide additional support for an Afro-Arabian origin of advanced stem and basal crown members of Hystricognathi

Evolution of South American Paucituberculata (Metatheria: Marsupialia): adaptive radiation and climate changes at the Eocene- Oligocene boundary

The Eocene-Oligocene boundary (EOB) marks a period of remodeling in the metatherian faunas of South America. Paucituberculata was one of the groups that successfully diversified as the climate and environment conditions changed, and they became, during the first part of the Neogene, an important component of micromammal assemblages. Among paucituberculatans, the non-pichipilid palaeothentoids (NPP) has been recognized as the clade that diversified most widely in post-EOB times. Here we explore the evolutionary response of the NPP to the climatic-environmental changes around the EOB, by analysing the temporal patterns of disparity, taxonomic diversity and body mass in a phylogenetic context. To asses the magnitude of the NPP radiation comparisons based on these macroevolutionary parameters were done with its sister-group Pichipilidae, and its next closest relative, the Caenolestidae. In all considered parameters, NPP reached values significantly higher than the remaining paucituberculatans clades. From its initial diversification in the middle Eocene, taxonomic diversity increased through time, but it was decoupled from disparity across the EOB, and from the late Oligocene to early Miocene. The Oligocene emerges as the key period in NPP evolution, which is evidenced by a significant and concordant expansion of disparity and taxonomic diversity, suggesting evolution into empty ecospace.Facultad de Ciencias Naturales y Muse