Yohan Pochat-Cottilloux

Les crocodiliens actuels sont des organismes semi-aquatiques, mais au long de leur évolution, les crocodylomorphes se sont adaptés à différents milieux de vie et ont survécu à de nombreuses crises biologiques. Le mode de vie de ces formes a été déduit de leur anatomie postcrânienne, de leur dentition et de la forme de leur crâne. Par exemple, les crocodylomorphes terrestres présentent souvent une morphologie altirostrale (c'est-à-dire un rostre élevé dorsoventralement). Dans cette thèse, les adaptations à un mode de vie terrestre de plusieurs de ces clades sont examinées de plus près avec les questions suivantes à l'esprit : existe-t-il d'autres indices pouvant être utilisés pour évaluer le mode de vie terrestre de ces organismes ? Comment la terrestrialité est-elle apparue et a-t-elle évolué chez les crocodylomorphes ? La morphologie altirostrale est-elle toujours liée à ce mode de vie ? Tout d'abord, une revue des différentes adaptations non semi-aquatiques dans le registre fossile des crocodylomorphes est proposée et je confirme qu'un mode de vie terrestre est la condition ancestrale du groupe, avec des adaptations ultérieures à l'environnement semi-aquatique et aquatique. Afin de proposer une étude évolutive à grande échelle, les relations phylogénétiques des différents taxons doivent d'abord être comprises le mieux possible. En conséquence, je montre ensuite à travers une revue de la littérature qu'aucune des hypothèses phylogénétiques concernant les relations de certains clades de notosuchiens ne peut être privilégiée, et que cette question bénéficierait de l'ajout d'autres données (postcrânien, structures internes). Une première publication porte sur le statut phylogénétique et taxonomique d'Hamadasuchus, un peirosauridé du Crétacé du Maroc. De nouveaux spécimens permettent d'amender la diagnose d'Hamadasuchus rebouli, la seule espèce de ce genre et de réduire son contenu taxonomique. Un second manuscrit soumis présente de nouveaux spécimens d'atoposauridés du Crétacé de Thaïlande, permettant d'ériger le nouveau taxon Varanosuchus sakonnakhonensis. Ce taxon est adapté à un mode de vie semi-terrestre. L'étude et la reconstruction des structures internes des organismes disparus, par le biais d'analyses tomodensitométriques, constituent un moyen d'évaluer la paléoécologie de ces organismes. L'étude de Zulmasuchus (Sebecidae), Hamadasuchus (Peirosauridae) et Varanosuchus (Atoposauridae) permet de déduire leur mode de vie (respectivement terrestre et semi-terrestre). Un accent particulier est mis sur le signal ontogénétique, phylogénétique et écologique de l'oreille interne, par le biais d'une étude de géométrie morphométrique 3D sur un vaste ensemble de données de taxons existants et éteints. La forme de cette structure est fortement liée à l'ontogénie et minimalement à la phylogénie, mais pas à l'écologie. Un deuxième indicateur est ensuite étudié, à savoir la composition isotopique des tissus du squelette. Les études multi-isotopiques d’éléments indépendants permettent de comprendre le mode de vie et les habitudes alimentaires des organismes disparus, ainsi que leurs relations trophiques et de proposer une reconstruction paléoenvironnementale. Plusieurs faunes du Paléogène d'Amérique du Sud, d'Afrique et d'Europe sont étudiées et confirment que les sébécidés étaient déjà des prédateurs au sommet de la chaîne alimentaire au lendemain de la transition Crétacé-Paléogène et tout au long de cette période. En outre, l'enregistrement géochimique de la dentine par échantillonnage sérié pourrait également être une approche intéressante, en particulier pour détecter des changements écologiques sur une courte période (c'est-à-dire le temps de développement des dents), comme le montrent les mesures effectuées sur des spécimens existants. Enfin, l'histologie des ostéodermes de certains crocodylomorphes est présentée et représente une perspective intéressante pour de futures études, tant internes qu'externes.

Modern trionychids (Testudines, Cryptodira) have a pan‐tropical distribution, but their range encompassed Central Europe during the Miocene. However, their true Neogene northernmost limit is uncertain because of limited Miocene exposures in the northern half of Europe, including Poland. Here, we address this problem, describing the first Polish remains from this family, coming from three new Middle Miocene vertebrate localities. The material includes isolated shell fragments and an incomplete skull, studied using computed tomography. Through a detailed review of the variation of cranial characters in extant and extinct trionychids, as well as considering the already existing occurrences of the family in the Miocene of Europe, we propose a tentative assignment for this last specimen to Trionyx cf. vindobonensis . This is somehow unexpected since the geographically closest diagnostic records of the family from the Early Miocene of Czechia belong to Rafetus . These new occurrences hint toward an environment still suitable for thermophilic organisms between the Mid‐Miocene Climatic Optimum and Late Miocene “washhouse” climate in the northern part of Central Europe.

The endosseous labyrinths are associated with several functions, including hearing and spatial orientation. Throughout their evolutionary history, crocodylomorphs have thrived in diverse environments, and the morphology of their endosseous labyrinths has been suggested as a proxy for inferring their lifestyle. However, the relationships between the shape of their endosseous labyrinths and ontogenetic and phylogenetic factors are difficult to interpret and have rarely been investigated in depth previously, particularly in terms of dataset size. Here, we present the most complete dataset to date on the endosseous labyrinths of extant crocodylians, including 111 specimens covering 22 species of different ontogenetic status (from hatchlings to adults). Using 3D geometric morphometrics, we show that allometry constitutes a major contributor of the shape variation of the crocodylian endosseous labyrinths and that the development of this structure is likely linked to the braincase conformation, in all extant genera. We also find a moderate phylogenetic signal, but only without considering the size effect, so it could not be translated into relevant discrete morphological characters. Based on these results, we discuss several remaining problems that prevent the inclusion of fossil forms with highly divergent lifestyles to study how ecological differences shaped the endosseous labyrinths of crocodylomorphs.

Crocodylomorphs constitute a clade of archosaurs that have thrived since the Mesozoic until today and have survived numerous major biological crises. Contrary to historic belief, their semiaquatic extant representatives (crocodylians) are not living fossils, and, during their evolutionary history, crocodylomorphs have evolved to live in a variety of environments. This review aims to summarize the non‐semiaquatic adaptations (i.e., either terrestrial or fully aquatic) of different groups from different periods, highlighting how exactly those different lifestyles are inferred for those animals, with regard to their geographic and temporal distribution and phylogenetic relationships. The ancestral condition for Crocodylomorpha seems to have been a terrestrial lifestyle, linked with several morphological adaptations such as an altirostral skull, long limbs allowing a fully erect posture and a specialized dentition for diets based on land. However, some members of this clade, such as thalattosuchians and dyrosaurids display adaptations for an opposite, aquatic lifestyle, interestingly inferred from the same type of morphological observations. Finally, new techniques for inferring the paleobiology of those extinct animals have been put forward in the last decade, appearing as a complementary approach to traditional morphological descriptions and comparisons. Such is the case of paleoneuroanatomical (CT scan data), histological, and geochemical studies.

The holotype of Hamadasuchus rebouli Buffetaut 1994 from the Kem Kem beds of Morocco (Late Albian-Cenomanian) consists of a left dentary which is limited, fragmentary and reconstructed in some areas. To aid in assessing if the original diagnosis can be considered as valid, the specimen was CT scanned for the first time. This is especially important to resolve the taxonomic status of certain specimens that have been assigned to Hamadasuchus rebouli since then. The reconstructed structures in this contribution are in agreement with the original description, notably in terms of alveolar count; thus the original diagnosis of this taxon remains valid and some specimens are not referable to H. rebouli anymore.

The origin of modern crocodylians is rooted in the Cretaceous, but their evolutionary history is obscure because the relationships of outgroups and transitional forms are poorly resolved. Here, we describe a new form, Varanosuchus sakonnakhonensis gen. nov., sp. nov., from the Early Cretaceous of Thailand that fills an evolutionary gap between Paralligatoridae and Atoposauridae, two derived neosuchian lineages with previously unsettled phylogenetic relationships. Three individuals, including a complete skull and associated postcranial remains, allow for a detailed description and phylogenetic analysis. The new taxon is distinguished from all other crocodylomorphs by an association of features, including a narrow altirostral morphology, a dorsal part of the postorbital with an anterolaterally facing edge, a depression on the posterolateral surface of the maxilla, and fully pterygoid-bound choanae. A phylogenetic analysis confirms the monophyly and taxonomic content of Atoposauridae and Paralligatoridae, and we underline the difficulty in reaching a robust definition of Eusuchia. Furthermore, we put forward further arguments related to the putative terrestrial ecology with semi-aquatic affinities of atoposaurids based on their altirostral snout morphology and osteoderm ornamentation.

The present 3D Dataset contains the 3D models analyzed in

Voay robustus, the extinct Malagasy “horned” crocodile, was originally considered to be the only crocodylian representative in Madagascar during most part of the Holocene. However, Malagasy crocodylian remains have had confused taxonomic attributions and recent studies have underlined that Crocodylus and Voay populations coexisted on the island for at least 7500 years. Here, we describe the inner braincase anatomy of Voay robustus using x‐ray computed tomography on four specimens, to provide new anatomical information that distinguishes Voay from Crocodylus, especially features of the brain endocast and the paratympanic sinuses. Geometric morphometric analyses are performed on 3D models of the internal organs to compare statistically Voay with a subset of extant Crocodylidae. Following these comparisons, we build an endocranial morphological matrix to discuss the proposed phylogenetic affinities of Voay with Osteolaeminae from an endocranial point of view. Additionally, we discuss the use of internal characters in systematic studies and find that they can have a major impact on morphological analyses. Finally, new radiocarbon data on Voay and subfossil Crocodylus specimens are recovered between 2010 and 2750 cal BP, which confirm the cohabitation of the two species in the same area for a long period of time. We thus assess several extinction scenarios, and propose a slightly different ecology of Voay compared to Crocodylus, which could have allowed habitat partitioning on the island. Our approach complements information obtained from previous molecular and morphological phylogenies, as well as previous radiocarbon dating, together revealing past diversity and faunal turnovers in Madagascar.

We describe the endocranial structures of Hamadasuchus, a peirosaurid crocodylomorph from the late Albian‐Cenomanian Kem Kem group of Morocco. The cranial endocast, associated nerves and arteries, endosseous labyrinths, and cranial pneumatization, as well as the bones of the braincase of a new specimen, are reconstructed and compared with extant and fossil crocodylomorphs, which represent different lifestyles. Cranial bones of this specimen are identified as belonging to Hamadasuchus, with close affinities with Rukwasuchus yajabalijekundu, another peirosaurid from the ‘middle’ Cretaceous of Tanzania. The endocranial structures are comparable to those of R. yajabalijekundu but also to baurusuchids and sebecids (sebecosuchians). Paleobiological traits of Hamadasuchus, such as alert head posture, ecology, and behavior are explored for the first time, using quantitative metrics. The expanded but narrow semi‐circular canals and enlarged pneumatization of the skull of Hamadasuchus are linked to a terrestrial lifestyle. Continuing work on the neuroanatomy of supposedly terrestrial crocodylomorphs needs to be broadened to other groups and will allow to characterize whether some internal structures are affected by the lifestyle of these organisms.