Maëva Judith Orliac

The land-to-water transition of cetacean mammals is a case study illustrating morphological transformation over time. The earliest cetaceans, still able to walk on land, document spectacular transitional states of their skull and body, allowing a step-by-step reconstruction of their adaptations to the aquatic environment. However, their highly derived carnivorous teeth appear abruptly in the fossil record and the earliest evolutionary history of their dentition remain poorly understood. Here we describe the most basal representative of Cetacea, Kalakocetus aurorae gen. et sp. nov., from the Eocene of India. Its unprecedented dental morphology bridges the gap between the shearing molars of early carnivorous cetaceans and the crushing molars of their closest terrestrial relatives. Functional analyses point to a carnivorous diet implying shearing movement of the jaw and a loss of crushing function of the third molar. The intermediate morphology of K. aurorae gen. et sp. nov. provides the missing element critical to the understanding of the emergence of the carnivorous dental pattern of cetaceans. Its basal position in the cetacean tree sheds new light on cetacean origins and dental evolution.

South American marsupials are widely dominated by opossums and their kin today. Nevertheless, metatherian high-level taxonomic diversity was much higher before Pleistocene times. Here, we describe two new species and a new genus documenting the extinct order Polydolopimorphia, based on extensive material from Eocene–Oligocene localities of Peruvian Amazonia. Wamradolops telloi Stutz sp. nov. and Pozodolops manuelorum Stutz gen. et sp. nov. are morphologically close to the early Oligocene Wamradolops tsullodon Goin & Candela, 2004 from the same area. Parsimony analyses performed here strongly suggest that these three taxa document a new early-diverging clade of Polydolopimorphia, Wamradolopidae Stutz fam. nov., restricted to tropical–equatorial lowlands and falling outside the suborders Bonapartheriiformes and Polydolopiformes. These phylogenetic affinities further point to a Palaeocene–early Eocene ghost lineage for Wamradolopidae Stutz fam. nov., most probably at low latitudes of South America. Dental dimensions suggest that representatives of Wamradolopidae Stutz fam. nov. were extremely small, with estimated body masses ranging from 3 to 55 g. With cranial dimensions comparable to those of the living long-tailed planigale and Etruscan shrew, Wamradolops telloi Stutz sp. nov. is among the smallest mammals ever described.

The present 3D dataset contains 3D models of new material from the middle Eocene of the Upper Subathu Formation in the Kalakot area (India), documenting the anterior dentition of the raoellid Indohyus indirae. Raoellidae are closely related to stem cetaceans and bring crucial information to understand the earliest phase of land to water transition in Cetacea.

The present 3D dataset contains 3D models of the endocranial cast of the raoellid Khirtharia inflata retrieved from the middle Eocene of the Upper Subathu Formation in the Kalakot area (India). Raoellidae are closely related to stem cetaceans and bring crucial information to understand the earliest phase of land to water transition in Cetacea.

Introduction: Raoellidae are small artiodactyls retrieved from the middle Eocene of Asia (ca. -47 Ma) and closely related to stem Cetacea. Morphological observations of their endocranial structures allow for outlining some of the early steps of the evolutionary history of the cetacean brain. The external features of the brain and associated sinuses of Raoellidae are so far only documented by the virtual reconstruction of the endocast based on specimens of the species Indohyus indirae. These specimens are however too deformed to fully access the external morphology, surface area, and volume measurements of the brain. Methods: We bring here new elements to the picture of the raoellid brain by an investigation of the internal structures of an exceptionally well-preserved cranium collected from the Kalakot area (Jammu and Kashmir, India) referred to the species Khirtharia inflata. Micro-CT scan investigation and virtual reconstruction of the endocast and associated sinuses of this specimen provide crucial additional data about the morphological diversity within Raoellidae as well as reliable linear, surfaces, and volumes measurements, allowing for quantitative studies. Results: We show that, like I. indirae, the brain of K. inflata exhibits a mosaic of features observed in earliest artiodactyls: a small neocortex with simple folding pattern, widely exposed midbrain, and relatively long cerebellum. But, like Indohyus, the brain of Khirtharia shows unique derived characters also observed in stem cetaceans: narrow elongated olfactory bulbs and peduncles, posterior location of the braincase in the cranium, and complex network of blood vessels around the cerebellum. The volume of the brain relative to body mass of K. inflata is markedly small when compared to other early artiodactyls. Conclusion: We show here that cetaceans that nowadays have the second biggest brain after humans derive from a group of animals that had a lower-than-average expected brain size. This is probably a side effect of the adaptation to aquatic life. Conversely, this very small brain size relative to body mass might be another line of evidence supporting the aquatic habits in raoellids.