Quentin Martinez

Capacités olfactives et thermorégulatrices des petits mammifères terrestres : une étude des turbines nasales: La plupart des tétrapodes actuels, possède dans leur cavité nasale, des rouleaux osseux que l'on appelle les turbines (= turbinaux). Parmi eux, les mammifères ont en moyenne les turbines les plus développées et, qui sont généralement divisées en deux catégories : les turbines respiratoires et olfactives. Les turbines respiratoires participent à la conservation de la chaleur et de l'humidité alors que les turbines olfactives interviennent dans les processus de détection des odeurs. Malgré quelques études chez les primates, Carnivora, chauves-souris, lagomorphes ainsi que chez les rongeurs, notre compréhension globale des pressions de sélection affectant les turbines reste incomplète. Cette thèse avait pour objectif de caractériser les facteurs évolutifs expliquant la grande diversité anatomique, morphologique mais également de taille et de complexité des turbines. A l’aide d’une technologie d’imagerie non destructive, la tomographie à rayons X (= micro-CT), nous avons généré un jeu de données sans précédent sur les turbines de rongeurs et les petits mammifères terrestres. Ainsi, nous avons pu tester statistiquement des hypothèses évolutives en lien avec l'écologie (p. ex. régime alimentaire ou milieu de vie), la convergence (= acquisition indépendante d’un caractère dans des lignées non directement apparentées) ou les compromis évolutifs (p. ex. conflits entre deux structures anatomiques pour l’espace dans la cavité nasale).Ce manuscrit de thèse, tente de réaliser une révision non exhaustive sur l’état du domaine de l’étude de l’olfaction et aborde brièvement la question de la conservation et de l’humidité. A la lumière de nos travaux, nous discutons des limites méthodologiques et conceptuelles de ces domaines d’étude ainsi que les difficultés liées à l’étude de l’olfaction. En effet, l’olfaction peut être abordée par différentes approches méthodologiques (p. ex. morphologie, histologie, génomique) et via différents proxies anatomiques (p. ex. turbines, bulbe olfactif, organe voméronasal). Dans ce contexte, nous avons entrepris des travaux intégratifs allant de l’étude de différents organes olfactifs à l’immuno-histochimie et en passant par la transcriptomique.

Pachyostosis, the increase in volume of bones, has been documented in a myriad of tetrapods that secondarily adapted to the aquatic environment. However, this convergent trait has hitherto only been quantified in complete ribs and long bones. Here we present a methodology designed to quantify the degree of pachyostosis in ribs and vertebrae, both for complete and fragmentary skeletal elements. Using surface models, we measured volumes of costal and vertebral regions and standardized them using size proxies to devise a pachyostosis index. Sirenians are used as a case study, given the disparity of pachyostosis degrees that have already been documented in the clade, especially in their ribs. The new methodology can detect this disparity and further demonstrates that pachyostosis also affects their vertebrae. Milder cases of pachyostosis, such as in the extant Dugong dugon, are likely secondary specializations to a specific lifestyle. The craniocaudal distribution of the pachyostosis index values is also potentially helpful to further distinguish finer lifestyle differences. This new method has the potential to clarify the causes of the disparity in pachyostosis degrees observed in the fossil record of sirenians, and it may also prove valuable in broader, non-mammalian contexts.

Olfaction is a critical sense for tetrapods, playing a key role in survival and reproduction by aiding in food detection, predator avoidance, and social interactions. Olfactory performance has been experimentally tested in only a few taxa, so comparative analyses rely on anatomical and genomic proxies. Among anatomical proxies, the olfactory bulb endocast is widely used, particularly in extinct species, where it is often the only preserved proxy and can be reconstructed even in million-year-old fossils. While the functional significance of chemoreceptor genes has received attention, the extent to which the olfactory bulb endocast correlates with genomic proxies remains unclear. Using brain endocasts across all mammalian orders, we investigated the relationship between the absolute (absOB) and relative (relatOB) volumes of the olfactory bulb endocast and the number of intact chemoreceptor genes. While no clear correlations were found between absOB and the genomic proxies tested, we identified a significant correlation between relatOB and the total number of combined intact chemoreceptor genes (CombChemo), primarily driven by olfactory receptor genes (OR). Leveraging this correlation, and aiming to infer olfactory capabilities in taxa for which only the skull is available, we estimated OR numbers for three mammalian orders lacking genomic data, as well as for five extinct mammals. Building on studies that have established a link between intact OR and olfactory sensitivity and discrimination, we conclude that relatOB enables inference of olfactory capabilities in mammals. This provides a basis to investigate sensory evolution and opens perspectives for interpreting paleoecology and behavior of extinct mammals.

The mammalian nasal cavity houses complex turbinals and laminae that conserve heat and moisture and mediate olfaction. Despite renewed interest driven by CT technology, some mammals remain scarcely studied, especially from developmental perspectives. This is true for pangolins, hypothesized to possess unique turbinals due to their elongated rostrum and possible olfactory adaptations for a specialized diet. Their turbinal complexity makes it difficult to establish hypotheses of homology with other mammals. Foetal anatomy and ontogenetic changes in the nasal capsule, therefore, provide key insights for assessing turbinal homology. Using diceCT, we reconstructed the foetal nasal capsules of Manis pentadactyla and M. javanica, and examined adults representing seven pangolin species, to clarify homology. By mapping turbinal and lamina traits on to a molecular phylogeny, we propose an evolutionary scenario for the morphology. Maxilloturbinals differ between Asian pangolins (double-scrolled folds) and African pangolins (a double scroll with a small caudal branch). Ethmoturbinal complexity also varies: in all pangolins, ethmoturbinal I comprises rostral (pars anterior) and caudal (pars posterior) portions, with lineage-specific degrees of subsequent fusion. These observations support two possible evolutionary pathways for the ethmoturbinal I: (i) complete separation into distinct pars; (ii) initial separation followed by secondary fusion in some lineages.

Do caecilians retain some degree of vision? Navarrete Méndez et al. (2025) used an integrative approach to show that the long-wavelength-sensitive (LWS) opsin gene is present and that retinal morphology remains intact across all eight caecilian families investigated. This finding suggests that caecilians maintain some visual capacity, likely enabling day–night or color discrimination. More broadly, this study highlights key aspects of sensory adaptation in subterranean tetrapods.

Turbinal bones in mammals, due to their roles in thermoregulation and olfaction, are effective indicators for studying ecological habits. Hypothetically, larger respiratory turbinals aid in heat and moisture retention, particularly in challenging environments like those at high elevations. The Andes, with its diverse landscapes and high biodiversity, provides an ideal environment for such studies. Among Andean endemics, the genus Thomasomys—mostly restricted to montane forests and páramos—exhibits high species diversity and adaptability across elevational gradients, making it an ideal candidate for exploring the relationship between ecological niches, habitat selection, and turbinal morphology. Using 3D CT scans of Thomasomys turbinal bones, our study aims to understand the interplay between turbinal surface area and environmental factors (elevation and bioclimatic variables). Our findings reveal consistent turbinal morphological features among Thomasomys species, showing: (i) positive allometric relationships with skull length; (ii) an absence of evolutionary trade-offs between the nasoturbinals and maxilloturbinals and between respiratory and olfactory turbinals; (iii) influence of elevation on the turbinal surface area with lower-elevation species having comparatively smaller turbinal surface areas than higher-elevation species; and (iv) that bioclimatic variables show significant correlations with the proportion of respiratory and olfactory turbinals. Therefore, our results align with the general hypothesis that large respiratory turbinals may help in coping with harsh environmental conditions. However, the relation between elevation and olfactory turbinal surface areas remains puzzling. Various other ecological confounding factors appear to be present and are discussed. Overall, this study sheds light on the complex adaptations of turbinal bones and their interactions with environmental factors, contributing to our understanding of mammalian ecomorphology in montane forest habitats.

Extant whales, dolphins, and porpoises result from a major macroevolutionary lifestyle transition that transformed land-dwelling cetaceans into fully aquatic species. This involved significant changes in sensory systems. The increase in brain size relative to body size (encephalization quotient) is an outstanding feature of modern cetaceans, especially toothed whales. Conversely, olfactory capabilities are assumed to have diminished along this transition, with airborne olfaction becoming less relevant. The extent and timing of olfactory reduction remain obscure due to challenges in accessing well-preserved fossil endocranial anatomy. This study shows that early cetaceans had already evolved an increased encephalization quotient, and that their olfactory apparatus was likely not yet under selective pressure leading to its reduction. We demonstrate this through an analysis of the extinct whale, Protocetus atavus, a member of the middle Eocene semiaquatic cetacean group Protocetidae. We provide the first documentation of its endocranial anatomy using high-resolution computed tomography and compare it to other early cetaceans as well as extant mammals. We conclude that cetaceans increased their brain size earlier than previously thought, while relying on a well-developed olfactory system at a time when they were still partly terrestrial.

The present 3D Dataset contains the 3D models of Protocetus atavus described and figured in the following publication:

Shrews are among the most speciose of mammalian clades, but their evolutionary history is poorly understood. Their fossil record is fragmentary and even the anatomy of living groups is not well documented. Here, we incorporate the oldest, most complete fossil shrew yet known into the first phylogenetic analysis of the group to include molecular, morphological and temporal data. Our study reveals previously unknown diversity among total- and crown-group soricids. This includes a novel element of the mammalian skeleton: a robust, needle-like sesamoid extending cranially from the second thoracic neural arch in Myosoricini, comparable in length to these species' humeri. Additionally, ‘red-toothed’ shrews have an unusually elongate basicranium, and ‘white-toothed’ shrews probably evolved from a common ancestor with dental pigmentation. The fossil Domnina and crown soricids have a double-jaw articulation and incomplete zygomatic arch, but unlike nearly all crown species, Domnina has open vomeronasal canals and a tympanic process of the basisphenoid. Domnina and other heterosoricids are phylogenetically outside crown Soricidae. The oldest, well-supported total-group soricoids are North American, not Asian, and Soricidae probably originated during the Palaeocene or early Eocene. The diverse mammalian genus Crocidura originated and began to diversify during the Miocene.