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The Eocene–Oligocene transition (EOT) represents a period of global environmental changes particularly marked in Europe and coincides with a dramatic biotic turnover. Here, using an exceptional fossil preservation, we document and analyse the diversity dynamics of a mammal clade, Cainotherioidea (Artiodactyla), that survived the EOT and radiated rapidly immediately after. We infer their diversification history from Quercy Konzentrat– Lagerstätte (south-west France) at the species level using Bayesian birth–death models. We show that cainotherioid diversity fluctuated through time, with extinction events at the EOT and in the late Oligocene, and a major speciation burst in the early Oligocene. The latter is in line with our finding that cainotherioids had a high morphological adaptability following environmental changes throughout the EOT, which probably played a key role in the survival and evolutionary success of this clade in the aftermath. Speciation is positively associated with temperature and continental fragmentation in a time-continuous way, while extinction seems to synchronize with environmental change in a punctuated way. Withinclade interactions negatively affected the cainotherioid diversification, while inter-clade competition might explain their final decline during the late Oligocene. Our results provide a detailed dynamic picture of the evolutionary history of a mammal clade in a context of global change. [ABSTRACT FROM AUTHOR]

We present new anatomical details about the bony labyrinth of Protungulatum based on micro CT-scan investigation of an isolated petrosal bone retrieved at the Puercan locality of Bug Creek Anthills and referred to Protungulatum sp. The exceptional state of preservation of the specimen allowed us to reconstruct the very fine details of the inside of the petrosal bone, including the bony labyrinth, the innervation of the vestibule and the innervation and vasculature of the cochlea. Estimation of the auditory capability of Protungulatum based on cochlear morphology indicate that Protungulatum was specialized for high-frequency hearing, with estimated low frequency limits above 1 KHz. Comparisons with Late Cretaceous non-placental eutherians and with early Tertiary pan-euungulates indicate that the bony labyrinth of Protungulatum is closer in general morphology to Mesozoic forms (low coiling and low aspect ratio of the cochlea, posterior orientation of the common crus, dorsal outpocketing of the cochlear fossula), and shares only a few characters with pan-euungulate and euungulate taxa. Interestingly, the bony labyrinth of Protungulatum also shares some morphological features with South American notoungulates and litopterns recently described from Itaboraí, Brazil. These new observations provide new morphological features of potential phylogenetic interest. [ABSTRACT FROM AUTHOR]

Among Artiodactylamorpha, dichobunoids are some of the oldest fossil species that have been associated with Artiodactyla, the crown clade that includes hippopotamids, camelids, suoids, ruminants, and cetaceans. These important fossil species are known from early Eocene rocks of North America, Europe, and Asia, but their phylogenetic position has yet to be well resolved. Before generating such a phylogeny, it is first critical to document all of the anatomy of known dichobunoid fossils. Here we use CT scans to describe previously undescribed anatomy of the petrosal bone, a complex part of the mammalian skull that contains many variable and phylogenetically informative features. Results show that these extinct species share a number of features that are not documented in modern species including a lateral process of the epitympanic wing constituting the medial border of the piriform fenestra, and a tegmen tympani foramen that may have given passage to the ramus superior of the stapedial artery. Future comprehensive phylogenetic studies may show that many of these characters are plesiomophic for Artiodactylamopha. Some species ( Diacodexis, Homacodon and ? Helohyus) exhibit a dorsolateral exposure of the mastoid region of the petrosal on the temporal part of the cranium. This uncommon feature has, to our knowledge, not been reported in another euungulate group. [ABSTRACT FROM AUTHOR]

The morphology of the petrosal is often employed in mammalian systematics, yet this bone has not been described in detail for a comparative sample of extinct members of Suoidea (the clade encompassing pigs, peccaries and their extinct relatives), a total clade that represents one of the major divisions within Artiodactyla. Here, the petrosal osteology of fossil Suoidea ranging from their early representatives (Late Eocene) up to Late Miocene is described. A sample of petrosal specimens documenting eight genera from the four suoid families (Suidae, Tayassuidae, Sanitheriidae and Palaeochoeridae) has been collected fromin situmechanical preparation, CT-based reconstruction or identification of isolated petrosals. The diagnostic significance of petrosal characters for suoid systematics is assessed by the inclusion of the new petrosals data in a phylogenetic analysis. As in other mammal groups, petrosal characters are shown to be of primary phylogenetic interest. The monophyly of the included families and subfamilies shown by craniodental and postcranial characters is supported by petrosal characters, and the problematic New World suoidPerchoerusis interpreted as the first offshoot of the Suoidea clade. This work allows definition of Suoidea on the basis of petrosal morphological characters and reveals the shaping over time of the peculiar petrosal morphology observed in extant suoids, notably the drastic reduction of the mastoid of this ‘amastoidean’ group, convergently present in hippos. [ABSTRACT FROM PUBLISHER]

We provide the first detailed description of the inner ear of the oldest artiodactyl, Diacodexis, based on a three-dimensional reconstruction extracted from computed tomography imagery of a skull of Diacodexis ilicis of earliest Wasatchian age (ca. 55 Ma). This description provides new anatomical data for the earliest artiodactyls, and reveals that the bony labyrinth of Diacodexis differs greatly from that of modern artiodactyls described so far. The bony labyrinth of Diacodexis presents a weakly coiled cochlea (720 °), a secondary common crus, a dorsal extension of the anterior semicircular canal more pronounced than that of the posterior one, and a small angle between the basal turn of the bony cochlear canal and the lateral semicircular canal. This suite of characters also occurs in basal eutherian mammals. Diacodexis strongly resembles small living tragulid ruminants in its overall body shape and hindlimb proportions. Comparison of the bony labyrinth of Diacodexis to that of the tragulid Moschiola meminna (Indian mouse deer) reveals great morphological difference in cochlear shape and semicircular canal disposition. The shape of the cochlea suggests that Diacodexis was a high-frequency hearing specialist, with a high low-frequency hearing limit (543 Hz at 60 dB). By comparison, the estimated low-frequency limit of Moschiola meminna is much lower (186.0 Hz at 60 dB). We also assess the locomotor agility of Diacodexis based on measurements of the semicircular canals. Locomotor agility estimates for Diacodexis range between 3.62 and 3.93, and suggest a degree of agility compatible with a nimble, fast running to jumping animal. These results are congruent with the postcranial functional analysis for this extinct taxon. [ABSTRACT FROM AUTHOR]

Raoellidae are small fossil cetartiodactyls closely related to the Cetacea. Until now undisputable raoellid remains were reported only from the early Middle Eocene of the Indian Subcontinent, although this Indo-Pakistani endemism has been challenged by several recent works describing potential raoellids from Mongolia, Myanmar and China. In this contribution we address the question of raoellid taxonomic content and definition, through a revision of the dental features of the family. This work, which includes a revision of the putative raoellid material from outside Indo-Pakistan, is primarily based on a re-examination of ‘suoid’ specimens from Shanghuang (Middle Eocene, coastal China). Our results indicate that the Shanghuang material both substantiates the youngest and easternmost occurrence of Raoellidae and represents the only unquestionable record of raoellids outside the Indian Subcontinent at present. This significantly extends the geographical and chronological range of the family. The occurrence of a raoellid species in the Middle Eocene of coastal China implies that raoellids dispersed from the Indian Subcontinent to eastern Asia during Early or Middle Eocene time. This tempers classical hypotheses of Middle Eocene Indian endemism and eastern Asian provincialism. [ABSTRACT FROM PUBLISHER]