The first North American Propterodon (Hyaenodonta: Hyaenodontidae), a new species from the late Uintan of Utah

New data on the mammalian fauna from the late middle Eocene (MP 15-16) of Mazaterón (Soria, Spain): The youngest presence of the genus Prodissopsalis (Hyaenodonta, Hyaenodontidae) in Europe

The Hyaenodonta were the most diverse carnivorous mammals in the European Eocene and were classically divided into three subfamilies: Sinopaninae, Arfianinae, and Proviverrinae, with this latter being the most successful of the three, as it exhibited a much larger geographic and temporal range. This classification is currently abandoned, as cladistic analyses of Hyaenodonta showed that several of these groups were paraphyletic. In any case, the former "proviverrines" were European endemic hyaenodontids which occupied the niche of small to medium-sized predators from the Ypresian (MP7) to the Priabonian (MP19). Recent phylogenetic proposals recognize the "Eurotherium clade" including this latter genus, besides Cartierodon and Prodissopsalis. A single species is known for Prodissopsalis, Prodissopsalis eocaenicus, previously recorded in European fossil sites of MP 12 to MP 14; nevertheless, the new material studied here, a mandible of a subadult individual from the late Middle Eocene (Bartonian, MP 15-16) site of La Solana (Mazaterón, Soria, Spain) constitutes a new species of Prodissopsalis and the youngest record of this genus up to now, extending its chronological range and remarking the shelter role of the northwestern region of the Iberian Peninsula during the Middle and Late Eocene. The new species, Prodissopsalis jimenezi provides new data not only on the eruption sequence of the genus, but also on the evolution of its dental adaptations, as the new species exhibits a more trenchant, hypercarnivorous dentition in comparison to the more primitive species P. eocaenicus, which would point toward a refining of the hunting abilities of this hyaenodont during the Middle Eocene.

A new small hyaenodon (Hyaenodonta: Hyaenodontinae) from the Eocene Lingbao Basin, Henan Province, China

In this article, the discovery of Hyaenodon lingbaoensis, a new species of small Hyaenodontinae, is reported from the Middle Eocene Chuankou Formation in the Lingbao Basin of Henan province, China. The specimen is represented by a partial maxilla which preserves two deciduous premolars (DP3, DP4) and one molar (M1). The taxon can be assigned to Hyaenodon based on a "T-shaped" DP3; a small and low protocone on DP3-M1; and a buccolingually compressed and long metastylar blade on DP4-M1. The new taxon represents a basal Hyaenodon because it is more pleiomorphic than later members in having a M1 with a more developed paraconule and metaconule, a more enlarged protocone and less fused paracone and metacone. This finding casts new light on the early evolution of Hyaenodon and supports its Asian origin. Additionally, its deciduous and permanent premolars are described and new evidence regarding their replacement patterns of Asian Hyaenodon is provided.

A macroevolutionary pathway to megaherbivory

Several scenarios have been proposed to explain rapid net size increases in some early Cenozoic mammalian lineages: sustained and gradual directional change, successive occupation of adaptive zones associated with progressively larger body sizes, and nondirectional evolution associated with branching events in combination with higher diversification potential of the larger lineages. We test these hypotheses in brontotheres, which are among the first radiations of mammals that consistently evolved multitonne sizes. Body-mass evolution in brontotheres mainly occurred during speciation and had no preferential direction. Long-term directional change stemmed from the higher survival of larger lineages in less-saturated herbivore guilds. Our study emphasizes the role of differential species proliferation in explaining the long-term phenotypic trends observed in the fossil record, which are more than an accumulation of steady microevolutionary changes.

Diegoaelurus, a new machaeroidine (Oxyaenidae) from the Santiago Formation (late Uintan) of southern California and the relationships of Machaeroidinae, the oldest group of sabertooth mammals

Machaeroidinae is a taxonomically small clade of early and middle Eocene carnivorous mammals that includes the earliest known saber-toothed mammalian carnivores. Machaeroidine diversity is low, with only a handful of species described from North America and Asia. Here we report a new genus and species of machaeroidine, Diegoaelurus vanvalkenburghae, established on the basis of a nearly complete dentary with most of the dentition from the late Uintan (middle Eocene) portion of the Santiago Formation of southern California. The new taxon is the youngest known machaeroidine and provides the first evidence for the presence of multiple machaeroidine lineages, as it differs substantially from Apataelurus kayi, the only near-contemporaneous member of the group. Phylogenetic analysis indicates that Diegoaelurus is the sister taxon of Apataelurus, while older species are recovered as a monophyletic Machaeroides. Both phylogenetic results are relatively weakly supported. The new taxon extends the record of machaeroidines to the end of the Uintan, potentially tying machaeroidine extinction to the faunal turnover spanning the middle to late Eocene transition in North America.