Neuroanatomy and pneumaticity of the extinct Malagasy "horned" crocodile Voay robustus and its implications for crocodylid phylogeny and palaeoecology.

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.

Inferring odontocete life history traits in dentine using a multiproxy approach (δ15 N, δ44/42 Ca and trace elements).

RATIONALE: Understanding the interactions between marine mammals and their environment is critical for ecological and conservation purposes. Odontocetes offer a continuous record of their life history from birth as recorded in annual increments of their tooth dentine. Because dentine is not remodeled and contains collagen, nitrogen stable isotope compositions (δ15 N) reflect nursing and weaning events, life history traits that would otherwise be impossible to retrieve in such elusive marine animals. Yet, capturing the magnitude and temporal changes in these events is constrained by tooth size and sampling resolution. Moreover, historical and fossil specimens undergo collagen decay, hence the need to develop the measurements of other proxies. METHODS: Here, we present a multiproxy approach to investigate the use of Ca isotope compositions (δ44/42 Ca) in relation to δ15 N and laser ablation profiles for different trace metal (Ba, Mg, Sr, Zn) concentrations across the dentine of a single individual of the common bottlenose dolphin Tursiops truncatus. RESULTS: To help interpret the dentine data, we provide milk elemental compositions and δ44/42 Ca values for two odontocete individuals. We discuss the observed changes in δ44/42 Ca across the dentine as potential markers of birth, weaning interval, incidental ingestion of seawater, trophic level and physiology. Incidental ingestion of seawater during nursing induces a positive offset in δ44/42 Ca values recorded in the early formed dentine. CONCLUSIONS: Life history parameters of individual marine mammals are extremely difficult to retrieve due to limitations in observing specimens in the wild and the methodology presented here offers new ecological and paleoecological perspectives.

Description and phylogenetic relationships of a new species of Torvoneustes (Crocodylomorpha, Thalattosuchia) from the Kimmeridgian of Switzerland.

Metriorhynchids are marine crocodylomorphs found across Jurassic and Lower Cretaceous deposits of Europe and Central and South America. Despite being one of the oldest fossil families named in paleontology, the phylogenetic relationships within Metriorhynchidae have been subject to many revisions over the past 15 years. Herein, we describe a new metriorhynchid from the Kimmeridgian of Porrentruy, Switzerland. The material consists of a relatively complete, disarticulated skeleton preserving pieces of the skull, including the frontal, prefrontals, right postorbital, nasals, maxillae, right premaxillae and nearly the entire mandible, and many remains of the axial and appendicular skeleton such as cervical, dorsal, and caudal vertebrae, ribs, the left ischium, the right femur, and the right fibula. This new specimen is referred to the new species Torvoneustes jurensis sp. nov. as part of the large-bodied macrophagous tribe Geosaurini. Torvoneustes jurensis presents a unique combination of cranial and dental characters including a smooth cranium, a unique frontal shape, acute ziphodont teeth, an enamel ornamentation made of numerous apicobasal ridges shifting to small ridges forming an anastomosed pattern toward the apex of the crown and an enamel ornamentation touching the carina. The description of this new species allows to take a new look at the currently proposed evolutionary trends within the genus Torvoneustes and provides new information on the evolution of this clade.

The neuroanatomy and pneumaticity of Hamadasuchus (Crocodylomorpha, Peirosauridae) from the Cretaceous of Morocco and its paleoecological significance for altirostral forms.

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.

Ontogenetic variability of the intertympanic sinus distinguishes lineages within Crocodylia.

The phylogenetic relationships within crown Crocodylia remain contentious due to conflicts between molecular and morphological hypotheses. However, morphology-based datasets are mostly constructed on external characters, overlooking internal structures. Here, we use 3D geometric morphometrics to study the shape of the intertympanic sinus system in crown crocodylians during ontogeny, in order to assess its significance in a taxonomic context. Intertympanic sinus shape was found to be highly correlated with size and modulated by cranial shape during development. Still, adult sinus morphology distinguishes specimens at the family, genus and species level. We observe a clear distinction between Alligatoridae and Longirostres, a separation of different Crocodylus species and the subfossil Malagasy genus Voay, and a distinction between the Tomistoma and Gavialis lineages. Our approach is independent of molecular methods but concurs with the molecular topologies. Therefore, sinus characters could add significantly to morphological datasets, offering an alternative viewpoint to resolve problems in crocodylian relationships.

A survey of osteoderm histology and ornamentation among Crocodylomorpha: A new proxy to infer lifestyle?

Osteoderms of eight extant and extinct species of crocodylomorphs are studied histologically and morphologically. Most osteoderms display the typical "crocodilian" structure with a woven-fibered matrix surrounded by an upper and a lower parallel fibered matrix. The dorsal ornamentation of those specimens consists of a pit-and-ridge structure, with corresponding remodeling mechanisms. However, an osteoderm of Iberosuchus, studied here for the first time, differs in being nearly devoid of ornamentation; moreover, it shows strong bundles of straight Sharpey's fibers perpendicular to the surface in its lateral and dorsal walls, along with a rough plywood-like structure in its basal plate. This suggests that this osteoderm was more deeply anchored within the dermis than the other osteoderms studied hitherto. This peculiar structure might have been linked to a terrestrial ecology and a specific thermoregulation strategy. Some other notosuchians in our sample do not exhibit ornamentation on their osteoderms, as opposed to neosuchians. Considering current interpretations of osteoderm function(s) in crocodilians, our observations are discussed in reference to possible ecophysiological peculiarities of Notosuchia in general, and Iberosuchus in particular.

Exploring diet shifts and ecology in modern sharks using calcium isotopes and trace metal records of their teeth.

Sharks occupy all living environments of the marine realm as well as some freshwater systems. They display varied and flexible feeding behaviours, but understanding their diet remains challenging due to their elusive ecology and the invasiveness of stomach content analyses in regard of their threatened status. As a potential alternative, we discuss the variability in δ44/42 Ca values recorded in the tooth enamel of size-graded individuals belonging to three species of large sharks with distinct diets (Isurus oxyrinchus, Hexanchus griseus and Carcharodon carcharias). The preliminary results highlight shifts in diet linked to ontogeny (I. oxyrinchus and H. griseus) and spatial distribution (C. carcharias) characterizing feeding behaviour in these species at individual and population level. These outcomes agree with the results of traditional stomach analyses supporting that nontraditional stable isotopes thus represent new perspectives for the study of modern and extinct shark ecology. In addition, for the first time, the Sr/Ca elemental ratios measured in H. griseus reflect sexual differences that could be interpreted in terms of spatial segregation or physiological heterogeneities.

The neuroanatomy of Zulmasuchus querejazus (Crocodylomorpha, Sebecidae) and its implications for the paleoecology of sebecosuchians.

The endocranial structures of the sebecid crocodylomorph Zulmasuchus querejazus (MHNC 6672) from the Lower Paleocene of Bolivia are described in this article. Using computed tomography scanning, the cranial endocast, associated nerves and arteries, endosseous labyrinths, and cranial pneumatization are reconstructed and compared with those of extant and fossil crocodylomorphs, representative of different ecomorphological adaptations. Z. querejazus exhibits an unusual flexure of the brain, pericerebral spines, semicircular canals with a narrow diameter, as well as enlarged pharyngotympanic sinuses. First, those structures allow to estimate the alert head posture and hearing capabilities of Zulmasuchus. Then, functional comparisons are proposed between this purportedly terrestrial taxon, semi-aquatic, and aquatic forms (extant crocodylians, thalattosuchians, and dyrosaurids). The narrow diameter of the semicircular canals but expanded morphology of the endosseous labyrinths and the enlarged pneumatization of the skull compared to other forms indeed tend to indicate a terrestrial lifestyle for Zulmasuchus. Our results highlight the need to gather new data, especially from altirostral forms in order to further our understanding of the evolution of endocranial structures in crocodylomorphs with different ecomorphological adaptations.

Lactation and gestation controls on calcium isotopic compositions in a mammalian model.

Lactation and gestation are among the physiological events that trigger the most intense changes in body calcium (Ca) fluxes. Along with the composition of the animal 2021 diet, these events are suspected to impact the Ca isotopic composition of Ca body reservoirs but their dynamics are poorly understood. In this study, we monitored a group of domestic sows across a full reproduction cycle. We collected tissues and fluids (blood, urine, milk, colostrum, umbilical blood, adult and piglet bones) at different steps of gestation and lactation, and analyzed their Ca isotopic compositions (i.e. δ44/42Ca) by means of multi-collector inductively coupled plasma mass spectrometry. Among other results, we report the first observations of Ca isotopic fractionation between maternal and umbilical blood (Δ44/42Caumbilical blood-sow blood = -0.18 ± 0.11‰, n = 3). Our data also highlight that gestation and lactation periods are characterized by small diet-bone Ca isotopic offsets (Δ44/42Cabone-diet = -0.28 ± 0.11‰, n = 3), with 44Ca-enriched blood compositions during nursing (Δ44/42Canursing blood-gestation blood = $+ 0.42{\rm{\,\,}}_{ - 0.12}^{ + 0.11}$‰, n = 3). Under the light of an up-to-date mammalian box model, we explored different scenarios of gestation and lactation Ca fluxes experienced by a sow-like animal. These simulations suggest that gestation changes on body δ44/42Ca values may result from the intensification of Ca absorption by the animal, whereas the production of 44Ca-depleted milk is the main driver for the 44Ca enrichment in blood during lactation. In addition, our results also support that bone mineralization could be associated with a more restricted Ca isotopic fractionation than previously envisioned. Together, these results refine the framework of Ca isotope applications, notably regarding the monitoring of human bone balance and the study of species and ecosystems from the present and the past.

Isotopic calcium biogeochemistry of MIS 5 fossil vertebrate bones: application to the study of the dietary reconstruction of Regourdou 1 Neandertal fossil.

The calcium isotopic composition (δ44/42Ca) of bone and tooth enamel can be used for dietary reconstructions of extant and extinct mammals. In natural conditions, the δ44/42Ca value of bone and teeth varies according to dietary intake with a constant isotopic offset of about -0.6‰. Owing to the poor conservation of collagen, carbon (C), and nitrogen (N) isotopic compositions of the Regourdou Mousterian site (MIS 5, Dordogne, France) previously failed to provide any paleodietary information. Therefore, to reconstruct the trophic chain, we have measured calcium (Ca) isotopes from fossil bone samples of the fauna from the Regourdou site, as well as from three bone samples of the Regourdou 1 Neandertal specimen. The results show a taxon-dependent patterning of the Ca isotopic compositions: herbivores generally have higher δ44/42Ca values than carnivores. All the δ44/42Ca values of Regourdou 1 are low (<-1.6‰), placing this specimen amid carnivores. Using a bone-muscle Ca isotopic offset determined on extant animals, we further show that the δ44/42Ca value of the Regourdou 1 diet, and that of most carnivores, cannot be accounted for by the consumption of meat only, as plants and meat have indistinguishable δ44/42Ca values. Mass balance calculations indicate that the low δ44/42Ca values of the Neandertal's carnivorous diet are explained by the ingestion of bone marrow containing as little as 1% trabecular bone. Our results show that the Regourdou 1 Neanderthal consumed a mixture of various herbivorous prey, as well as trabecular bone, which probably occurred when marrow was ingested, by accident or intentionally.

Isotopic systematics point to wild origin of mummified birds in Ancient Egypt.

Millions of mummified birds serving for religious purpose have been discovered from archeological sites along the Nile Valley of Egypt, in majority ibises. Whether these birds were industrially raised or massively hunted is a matter of heavy debate as it would have a significant impact on the economy related to their supply and cult, and if hunted it would have represented an ecological burden on the birds populations. Here we have measured and analysed the stable oxygen, carbon and radiogenic strontium isotope compositions as well as calcium and barium content of bones along with the stable carbon, nitrogen and sulfur isotope composition of feathers from 20 mummified ibises and birds of prey recovered from various archeological sites of Ancient Egypt. If these migratory birds were locally bred, their stable oxygen, radiogenic strontium and stable sulfur isotopic compositions would be similar to that of coexisting Egyptians, and their stable carbon, nitrogen and oxygen isotope variance would be close, or lower than that of Egyptians. On one hand, isotopic values show that ibises ingested food from the Nile valley but with a higher isotopic scattering than observed for the diet of ancient Egyptians. On the other hand, birds of prey have exotic isotopic values compatible with their migratory behaviour. We therefore propose that most mummified ibises and all the birds of prey analysed here were wild animals hunted for religious practice.

Calcium isotopic ecology of Turkana Basin hominins.

Diet is a major driver of hominin evolution, but most of the geochemical evidence relies on carbon isotopes (δ13C). Here, we report enamel stable calcium isotope (δ44/42Ca) values against δ13C values for several hominins and co-existing primates in the Turkana Basin area, circa 4 to 2 Ma. Australopithecus anamensis clusters with mammal browsers, Kenyanthropus platyops is distinct from A. anamensis in foraging into more open environments and the coexisting Theropithecus brumpti encompasses both the grazer and omnivore/carnivore domains. Early Homo is remarkable for its wide distribution in δ44/42Ca values, possibly reflecting omnivorous and opportunistic preferences. Paranthropus boisei is uniquely distributed in the δ13C versus δ44/42Ca iso-space being distinct from all other hominins from the Turkana Basin area as well as from the co-existing Theropithecus oswaldi. Several hypotheses are explored to discuss the unique δ44/42Ca values of Paranthropus boisei including significant differences observed with δ44/42Ca values recently reported for P. robustus from South Africa, questioning the monophyly of this genus.

Thermophysiologies of Jurassic marine crocodylomorphs inferred from the oxygen isotope composition of their tooth apatite.

Teleosauridae and Metriorhynchidae were thalattosuchian crocodylomorph clades that secondarily adapted to marine life and coexisted during the Middle to Late Jurassic. While teleosaurid diversity collapsed at the end of the Jurassic, most likely as a result of a global cooling of the oceans and associated marine regressions, metriorhynchid diversity was largely unaffected, although the fossil record of Thalattosuchia is poor in the Cretaceous. In order to investigate the possible differences in thermophysiologies between these two thalattosuchian lineages, we analysed stable oxygen isotope compositions (expressed as δ18O values) of tooth apatite from metriorhynchid and teleosaurid specimens. We then compared them with the δ18O values of coexisting endo-homeothermic ichthyosaurs and plesiosaurs, as well as ecto-poikilothermic chondrichthyans and osteichthyans. The distribution of δ18O values suggests that both teleosaurids and metriorhynchids had body temperatures intermediate between those of typical ecto-poikilothermic vertebrates and warm-blooded ichthyosaurs and plesiosaurs, metriorhynchids being slightly warmer than teleosaurids. We propose that metriorhynchids were able to raise their body temperature above that of the ambient environment by metabolic heat production, as endotherms do, but could not maintain a constant body temperature compared with fully homeothermic ichthyosaurs and plesiosaurs. Teleosaurids, on the other hand, may have raised their body temperature by mouth-gape basking, as modern crocodylians do, and benefited from the thermal inertia of their large body mass to maintain their body temperature above the ambient one. Endothermy in metriorhynchids might have been a by-product of their ecological adaptations to active pelagic hunting, and it probably allowed them to survive the global cooling of the Late Jurassic, thus explaining the selective extinction affecting Thalattosuchia at the Jurassic-Cretaceous boundary. This article is part of the theme issue 'Vertebrate palaeophysiology'.

Calcium isotopic patterns in enamel reflect different nursing behaviors among South African early hominins.

Nursing is pivotal in the social and biological evolution of hominins, but to date, early-life behavior among hominin lineages is a matter of debate. The calcium isotopic compositions (δ44/42Ca) of tooth enamel can provide dietary information on this period. Here, we measure the δ44/42Ca values in spatially located microsized regions in tooth enamel of 37 South African hominins to reconstruct early-life dietary-specific variability in Australopithecus africanus, Paranthropus robustus, and early Homo. Very low δ44/42Ca values (<-1.4‰), indicative of milk consumption, are measured in early Homo but not in A. africanus and P. robustus. In these latter taxa, transitional or adult nonmilk foods must have been provided in substantial quantities relative to breast milk rapidly after birth. The results suggest that early Homo have continued a predominantly breast milk-based nursing period for longer than A. africanus and P. robustus and have consequently more prolonged interbirth interval.

Assessing human weaning practices with calcium isotopes in tooth enamel.

Weaning practices differ among great apes and likely diverged during the course of human evolution, but behavioral inference from the fossil record is hampered by a lack of unambiguous biomarkers. Here, we show that early-life dietary transitions are recorded in human deciduous tooth enamel as marked variations in Ca isotope ratios (δ44/42Ca). Using a sequential microsampling method along the enamel growth axis, we collected more than 150 enamel microsamples from 51 deciduous teeth of 12 different modern human individuals of known dietary histories, as well as nine enamel samples from permanent third molars. We measured and reconstructed the evolution of 44Ca/42Ca ratios in enamel from in utero development to first months of postnatal development. We show that the observed variations of δ44/42Ca record a transition from placental nutrition to an adult-like diet and that Ca isotopes reflect the duration of the breastfeeding period experienced by each infant. Typically, the δ44/42Ca values of individuals briefly or not breastfed show a systematic increase during the first 5-10 mo, whereas individuals with long breastfeeding histories display no measurable variation in δ44/42Ca of enamel formed during this time. The use of Ca isotope analysis in tooth enamel allows microsampling and offers an independent approach to tackle challenging questions related to past population dynamics and evolution of weaning practices in hominins.

Calcium Isotopic Evidence for Vulnerable Marine Ecosystem Structure Prior to the K/Pg Extinction.

The collapse of marine ecosystems during the end-Cretaceous mass extinction involved the base of the food chain [1] up to ubiquitous vertebrate apex predators [2-5]. Large marine reptiles became suddenly extinct at the Cretaceous-Paleogene (K/Pg) boundary, whereas other contemporaneous groups such as bothremydid turtles or dyrosaurid crocodylomorphs, although affected at the familial, genus, or species level, survived into post-crisis environments of the Paleocene [5-9] and could have found refuge in freshwater habitats [10-12]. A recent hypothesis proposes that the extinction of plesiosaurians and mosasaurids could have been caused by an important drop in sea level [13]. Mosasaurids are unusually diverse and locally abundant in the Maastrichtian phosphatic deposits of Morocco, and with large sharks and one species of elasmosaurid plesiosaurian recognized so far, contribute to an overabundance of apex predators [3, 7, 14, 15]. For this reason, high local diversity of marine reptiles exhibiting different body masses and a wealth of tooth morphologies hints at complex trophic interactions within this latest Cretaceous marine ecosystem. Using calcium isotopes, we investigated the trophic structure of this extinct assemblage. Our results are consistent with a calcium isotope pattern observed in modern marine ecosystems and show that plesiosaurians and mosasaurids indiscriminately fall in the tertiary piscivore group. This suggests that marine reptile apex predators relied onto a single dietary calcium source, compatible with the vulnerable wasp-waist food webs of the modern world [16]. This inferred peculiar ecosystem structure may help explain plesiosaurian and mosasaurid extinction following the end-Cretaceous biological crisis.

Magnesium stable isotope ecology using mammal tooth enamel.

Geochemical inferences on ancient diet using bone and enamel apatite rely mainly on carbon isotope ratios (δ(13)C) and to a lesser extent on strontium/calcium (Sr/Ca) and barium/calcium (Ba/Ca) elemental ratios. Recent developments in nontraditional stable isotopes provide an unprecedented opportunity to use additional paleodietary proxies to disentangle complex diets such as omnivory. Of particular relevance for paleodietary reconstruction are metals present in large quantity in bone and enamel apatite, providing that biologically mediated fractionation processes are constrained. Calcium isotope ratios (δ(44)Ca) meet these criteria but exhibit complex ecological patterning. Stable magnesium isotope ratios (δ(26)Mg) also meet these criteria but a comprehensive understanding of its variability awaits new isotopic data. Here, 11 extant mammal species of known ecology from a single locality in equatorial Africa were sampled for tooth enamel and, together with vegetation and feces, analyzed for δ(26)Mg, δ(13)C, Sr/Ca, and Ba/Ca ratios. The results demonstrate that δ(26)Mg incorporated in tooth enamel becomes heavier from strict herbivores to omnivores/faunivores. Using data from experimentally raised sheep, we suggest that this (26)Mg enrichment up the trophic chain is due to a (26)Mg enrichment in muscle relative to bone. Notably, it is possible to distinguish omnivores from herbivores, using δ(26)Mg coupled to Ba/Ca ratios. The potential effects of metabolic and dietary changes on the enamel δ(26)Mg composition remain to be explored but, in the future, multiproxy approaches would permit a substantial refinement of dietary behaviors or enable accurate trophic reconstruction despite specimen-limited sampling, as is often the case for fossil assemblages.

Ichthyosaurs from the French Rhaetian indicate a severe turnover across the Triassic-Jurassic boundary.

Mesozoic marine reptiles went through a severe turnover near the end of the Triassic. Notably, an important extinction event affected ichthyosaurs, sweeping a large part of the group. This crisis is, however, obscured by an extremely poor fossil record and is regarded as protracted over the entire Norian-earliest Jurassic interval, for the lack of a more precise scenario. The iconic whale-sized shastasaurid ichthyosaurs are regarded as early victims of this turnover, disappearing by the middle Norian. Here we evaluate the pattern of this turnover among ichthyosaurs by analysing the faunal record of two Rhaetian localities. One locality is Autun, eastern France; we rediscovered in this material the holotypes or partial 'type' series of Rachitrema pellati, Actiosaurus gaudryi, Ichthyosaurus rheticus, Ichthyosaurus carinatus and Plesiosaurus bibractensis; a revised taxonomic scheme is proposed. The second assemblage comes from a new locality: Cuers, southeastern France. Both these assemblages provide several lines of evidence for the presence of shastasaurid-like ichthyosaurs in the Rhaetian of Europe. These occurrences suggest that both the demise of shastasaurids and the sudden radiation of neoichthyosaurians occurred within a short time window; this turnover appears not only more abrupt but also more complex than previously postulated and adds a new facet of the end-Triassic mass extinction.

Sea surface temperature contributes to marine crocodylomorph evolution.

During the Mesozoic and Cenozoic, four distinct crocodylomorph lineages colonized the marine environment. They were conspicuously absent from high latitudes, which in the Mesozoic were occupied by warm-blooded ichthyosaurs and plesiosaurs. Despite a relatively well-constrained stratigraphic distribution, the varying diversities of marine crocodylomorphs are poorly understood, because their extinctions neither coincided with any major biological crises nor with the advent of potential competitors. Here we test the potential link between their evolutionary history in terms of taxic diversity and two abiotic factors, sea level variations and sea surface temperatures (SST). Excluding Metriorhynchoidea, which may have had a peculiar ecology, significant correlations obtained between generic diversity and estimated Tethyan SST suggest that water temperature was a driver of marine crocodylomorph diversity. Being most probably ectothermic reptiles, these lineages colonized the marine realm and diversified during warm periods, then declined or became extinct during cold intervals.