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Crocodilians grow slowly and have low metabolic rates similar to other living reptiles, but palaeohistology indicates that they evolved from an ancestor with higher growth rates. 1 , 2 , 3 , 4 , 5 It remains unclear when slow growth appeared in the clade due to the sparse data on key divergences among early Mesozoic members of their stem lineage. We present new osteohistological data from a broad sample of early crocodylomorphs, evaluated in a phylogenetic context alongside other pseudosuchians. We find that the transition to slow-growing bone types during mid-late ontogeny occurred around the origin of Crocodylomorpha during the Late Triassic. Earlier-diverging pseudosuchians had high maximum growth rates, as indicated by the presence of woven bone during middle and (sometimes) late ontogeny. 6 , 7 , 8 , 9 Large-bodied pseudosuchians in particular exhibit some of the fastest-growing bone types, giving evidence for prolonged, rapid growth. By contrast, early-branching crocodylomorphs, including a new large-bodied taxon, had slow maximum rates of bone deposition, as evidenced by the presence of predominantly parallel-fibered or lamellar bone tissue during middle-late ontogeny. Late Triassic crocodylomorphs show skeletal anatomy consistent with "active" terrestrial habits, 10 , 11 , 12 and their slow growth rates reject hypotheses linking this transition with sedentary, semiaquatic lifestyles or sprawling posture. Faster-growing pseudosuchian lineages go extinct in the Triassic, whereas slow-growing crocodylomorphs do not. This contrasts with the Jurassic radiation of fast-growing dinosaurs on the bird-stem lineage, 13 suggesting that the End-Triassic mass extinction initiated a divergent distribution of growth strategies that persist in present-day archosaurs., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The ascendancy of dinosaurs to become dominant components of terrestrial ecosystems was a pivotal event in the history of life, yet the drivers of their early evolution and biodiversity are poorly understood. 1 , 2 , 3 During their early diversification in the Late Triassic, dinosaurs were initially rare and geographically restricted, only attaining wider distributions and greater abundance following the end-Triassic mass extinction event. 4 , 5 , 6 This pattern is consistent with an opportunistic expansion model, initiated by the extinction of co-occurring groups such as aetosaurs, rauisuchians, and therapsids. 4 , 7 , 8 However, this pattern could instead be a response to changes in global climatic distributions through the Triassic to Jurassic transition, especially given the increasing evidence that climate played a key role in constraining Triassic dinosaur distributions. 7 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 Here, we test this hypothesis and elucidate how climate influenced early dinosaur distribution by quantitatively examining changes in dinosaur and tetrapod "climatic niche space" across the Triassic-Jurassic boundary. Statistical analyses show that Late Triassic sauropodomorph dinosaurs occupied a more restricted climatic niche space than other tetrapods and dinosaurs, being excluded from the hottest, low-latitude climate zones. A subsequent, earliest Jurassic expansion of sauropodomorph geographic distribution is linked to the expansion of their preferred climatic conditions. Evolutionary model-fitting analyses provide evidence for an important evolutionary shift from cooler to warmer climatic niches during the origin of Sauropoda. These results are consistent with the hypothesis that global abundance of sauropodomorph dinosaurs was facilitated by climatic change and provide support for the key role of climate in the ascendancy of dinosaurs., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Sauropod dinosaurs include the largest land animals to have walked the earth, mostly weighing 10-70 tons (e.g., Sander et al. 1 and Carballido et al. 2 ). Osteohistology suggests that derived physiological traits evolved near the origin of sauropod gigantism, including both rapid and uninterrupted growth from juvenile to adult with little developmental plasticity. 1 , 3 , 4 This differs from the slower, seasonally interrupted growth of their direct ancestors, as evident in most non-sauropodan sauropodomorphs, which also show developmental plasticity in some groups. Accelerated but seasonally interrupted growth is present in Lessemsauridae, the sister clade to Sauropoda, which also attained giant adult body sizes (>10 tons). 5 These observations suggest a correlation between giant size and accelerated growth. However, testing this evolutionary connection has been limited by the incomplete understanding of the growth patterns in some of the closest non-giant relatives of sauropods. We present the osteohistology of two such taxa, Aardonyx celestae and Sefapanosaurus zatronensis. Both exhibit highly vascularized woven-parallel complexes, with fibrolamellar complexes during early to mid-ontogeny, containing regular growth marks. These observations provide strong evidence for rapid but seasonally interrupted growth with limited developmental plasticity (indicated by the regular spacing of growth marks). Combined with our review of early branching sauropodomorph osteohistology, these results show that highly accelerated growth rates originated among smaller, non-sauropodan sauropodomorphs weighing 1 to 2 tons but preceded the origins of giant size (>10 tons). Therefore, the capacity for rapid bone tissue formation, a derived aspect of rapid growth seen in sauropods, did not evolve specifically to enable giant body sizes but may have been a prerequisite for them., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The fossil record is the primary source of information on how biodiversity has varied in deep time, providing unique insight on the long-term dynamics of diversification and their drivers. However, interpretations of fossil record diversity patterns have been much debated, with a traditional focus on global diversity through time. Problems arise because the fossil record is spatially and temporally patchy, so 'global' diversity estimates actually represent the summed diversity across a set of geographically and environmentally distinct regions that vary substantially in number and identity through time. Furthermore, a focus on global diversity lumps the signal of ecological drivers at local and regional scales with the signal of global-scale processes, including variation in the distribution of environments and in provincialism (the extent of subdivision into distinct biogeographic regions). These signals cannot be untangled by studying global diversity measures alone. These conceptual and empirical concerns necessitate a shift away from the study of 'biodiversity through time' and towards the study of 'biodiversity across time and space'. Spatially explicit investigations, including analyses of local- and regional-scale datasets, are central to achieving this and allow analysis of geographic scale, location and the environmental parameters directly experienced by organisms. So far, research in this area has revealed the stability of species richness variation among environments through time, and the potential climatic and Earth-system drivers of changing biodiversity. Ultimately, this research program promises to address key questions regarding the assembly of biodiversity, and the contributions of local-, regional- and global-scale processes to the diversification of life on Earth., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Adaptive radiations are hypothesized as a generating mechanism for much of the morphological diversity of extant species. 1-7 The Cenozoic radiation of placental mammals, the foundational example of this concept, 8 , 9 gave rise to much of the morphological disparity of extant mammals, and is generally attributed to relaxed evolutionary constraints following the extinction of non-avian dinosaurs. 10-13 However, study of this and other radiations has focused on variation in evolutionary rates, 4 , 5 , 7 , 14 leaving the extent to which relaxation of constraints enabled the origin of novel phenotypes less well characterized. 15-17 We evaluate constraints on morphological evolution among mammaliaforms (mammals and their closest relatives) using a new method that quantifies the capacity of evolutionary change to generate phenotypic novelty. We find that Mesozoic crown-group therians, which include the ancestors of placental mammals, were significantly more constrained than other mammaliaforms. Relaxation of these constraints occurred in the mid-Paleocene, post-dating the extinction of non-avian dinosaurs at the K/Pg boundary, instead coinciding with important environmental shifts and with declining ecomorphological diversity in non-theriimorph mammaliaforms. This relaxation occurred even in small-bodied Cenozoic mammals weighing <100 g, which are unlikely to have competed with dinosaurs. Instead, our findings support a more complex model whereby Mesozoic crown therian evolution was in part constrained by co-occurrence with disparate mammaliaforms, as well as by the presence of dinosaurs, within-lineage incumbency effects, and environmental factors. Our results demonstrate that variation in evolutionary constraints can occur independently of variation in evolutionary rate, and that both make important contributions to the understanding of adaptive radiations., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Living archosaurs (birds and crocodylians) have disparate locomotor strategies that evolved since their divergence ∼250 mya. Little is known about the early evolution of the sensory structures that are coupled with these changes, mostly due to limited sampling of early fossils on key stem lineages. In particular, the morphology of the semicircular canals (SCCs) of the endosseous labyrinth has a long-hypothesized relationship with locomotion. Here, we analyze SCC shapes and sizes of living and extinct archosaurs encompassing diverse locomotor habits, including bipedal, semi-aquatic, and flying taxa. We test form-function hypotheses of the SCCs and chronicle their evolution during deep archosaurian divergences. We find that SCC shape is statistically associated with both flight and bipedalism. However, this shape variation is small and is more likely explained by changes in braincase geometry than by locomotor changes. We demonstrate high disparity of both shape and size among stem-archosaurs and a deep divergence of SCC morphologies at the bird-crocodylian split. Stem-crocodylians exhibit diverse morphologies, including aspects also present in birds and distinct from other reptiles. Therefore, extant crocodylian SCC morphologies do not reflect retention of a "primitive" reptilian condition. Key aspects of bird SCC morphology that hitherto were interpreted as flight related, including large SCC size and enhanced sensitivity, appeared early on the bird stem-lineage in non-flying dinosaur precursors. Taken together, our results indicate a deep divergence of SCC traits at the bird-crocodylian split and that living archosaurs evolved from an early radiation with high sensory diversity. VIDEO ABSTRACT., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Plant-eating dinosaurs evolved varied feeding strategies. A new study demonstrates convergent evolution of their skulls and teeth towards two distinct functional optima, one resembling advanced mammalian herbivory and the other echoing herbivory in birds and other reptiles., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Crocodylians are carnivores, but their extinct relatives had wider-ranging diets. A new study shows that herbivory evolved often in these animals, and that their teeth rivalled those of mammals in terms of complexity., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Sauropod dinosaurs were dominant, bulk-browsing herbivores for 130 million years of the Mesozoic, attaining gigantic body masses in excess of 60 metric tons [1, 2]. A columnar-limbed, quadrupedal posture enabled these giant body sizes [3], but the nature of the transition from bipedal sauropodomorph ancestors to derived quadrupeds remains contentious [4-6]. We describe a gigantic, new sauropodomorph from the earliest Jurassic of South Africa weighing 12 metric tons and representing a phylogenetically independent origin of sauropod-like body size in a non-sauropod. Osteohistological evidence shows that this specimen was an adult of maximum size and approximately 14 years old at death. Ledumahadi mafube gen. et sp. nov. shows that gigantic body sizes were possible in early sauropodomorphs, which were habitual quadrupeds but lacked the derived, columnar limb postures of sauropods. We use data from this new taxon and a discriminant analysis of tetrapod limb measurements to study postural evolution in sauropodomorphs. Our results show that quadrupedality appeared by the mid-Late Triassic (Norian), well outside of Sauropoda. Secondary reversion to bipedality occurred in some lineages phylogenetically close to Sauropoda, indicating early experimentation in locomotory styles. Morphofunctional observations support the hypothesis that partially flexed (rather than columnar) limbs characterized Ledumahadi and other early-branching quadrupedal sauropodomorphs. Patterns of locomotory and body-size evolution show that quadrupedality allowed Triassic sauropodomorphs to achieve body sizes of at least 3.8 metric tons. Ledumahadi's Early Jurassic age shows that maximum body mass in sauropodomorph dinosaurs was either unaffected or rapidly rebounded after the end-Triassic extinction event., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Highly specialized animals are often difficult to place phylogenetically. The Late Cretaceous members of Alvarezsauria represent such an example, having been posited as members of various theropod lineages, including birds [1-11]. A 70-million-year ghost lineage exists between them and the Late Jurassic putative alvarezsaurian Haplocheirus [12], which preserves so few derived features that its membership in Alvarezsauria has recently been questioned [13]. If Haplocheirus is indeed an alvarezsaurian, then the 70-million-year gap between Haplocheirus and other alvarezsaurians represents the longest temporal hiatus within the fossil record of any theropod subgroup [14]. Here we report two new alvarezsaurians from the Early Cretaceous of Western China that document successive, transitional stages in alvarezsaurian evolution. They provide further support for Haplocheirus as an alvarezsaurian and for alvarezsaurians as basal maniraptorans. Furthermore, they suggest that the early biogeographic history of the Alvarezsauria involved dispersals from Asia to other continents. The new specimens are temporally, morphologically, and functionally intermediate between Haplocheirus and other known alvarezsaurians and provide a striking example of the evolutionary transition from a typical theropod forelimb configuration (i.e., the relatively long arm and three-digit grasping hand of typical tetanuran form in early-branching alvarezsaurians) to a highly specialized one (i.e., the highly modified and shortened arm and one-digit digging hand of Late Cretaceous parvicursorines such as Linhenykus [1, 15]). Comprehensive analyses incorporating data from these new finds show that the specialized alvarezsaurian forelimb morphology evolved slowly and in a mosaic fashion during the Cretaceous., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Sauropterygia, a successful clade of marine reptiles abundant in aquatic ecosystems of the Mesozoic, inhabited nearshore to pelagic habitats over >180 million years of evolutionary history [1]. Aquatic vertebrates experience strong buoyancy forces that allow movement in a three-dimensional environment, resulting in structural convergences such as flippers and fish-like bauplans [2, 3], as well as convergences in the sensory systems. We used computed tomographic scans of 19 sauropterygian species to determine how the transition to pelagic lifestyles influenced the evolution of the endosseous labyrinth, which houses the vestibular sensory organ of balance and orientation [4]. Semicircular canal geometries underwent distinct changes during the transition from nearshore Triassic sauropterygians to the later, pelagic plesiosaurs. Triassic sauropterygians have dorsoventrally compact, anteroposteriorly elongate labyrinths, resembling those of crocodylians. In contrast, plesiosaurs have compact, bulbous labyrinths, sharing some features with those of sea turtles. Differences in relative labyrinth size among sauropterygians correspond to locomotory differences: bottom-walking [5, 6] placodonts have proportionally larger labyrinths than actively swimming taxa (i.e., all other sauropterygians). Furthermore, independent evolutionary origins of short-necked, large-headed "pliosauromorph" body proportions among plesiosaurs coincide with reductions of labyrinth size, paralleling the evolutionary history of cetaceans [7]. Sauropterygian labyrinth evolution is therefore correlated closely with both locomotory style and body proportions, and these changes are consistent with isolated observations made previously in other marine tetrapods. Our study presents the first virtual reconstructions of plesiosaur endosseous labyrinths and the first large-scale, quantitative study detailing the effects of increasingly aquatic lifestyles on labyrinth morphology among marine reptiles., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Plesiosaurs were the longest-surviving group of secondarily marine tetrapods, comparable in diversity to today's cetaceans. During their long evolutionary history, which spanned the Jurassic and the Cretaceous (201 to 66 Ma), plesiosaurs repeatedly evolved long- and short-necked body plans [1, 2]. Despite this postcranial plasticity, short-necked plesiosaur clades have traditionally been regarded as being highly constrained to persistent and clearly distinct ecological niches: advanced members of Pliosauridae (ranging from the Middle Jurassic to the early Late Cretaceous) have been characterized as apex predators [2-5], whereas members of the distantly related clade Polycotylidae (middle to Late Cretaceous) were thought to have been fast-swimming piscivores [1, 5-7]. We report a new, highly unusual pliosaurid from the Early Cretaceous of Russia that shows close convergence with the cranial structure of polycotylids: Luskhan itilensis gen. et sp. nov. Using novel cladistic and ecomorphological data, we show that pliosaurids iteratively evolved polycotylid-like cranial morphologies from the Early Jurassic until the Early Cretaceous. This underscores the ecological diversity of derived pliosaurids and reveals a more complex evolutionary history than their iconic representation as gigantic apex predators of Mesozoic marine ecosystems suggests. Collectively, these data demonstrate an even higher degree of morphological plasticity and convergence in the evolution of plesiosaurs than previously thought and suggest the existence of an optimal ecomorphology for short-necked piscivorous plesiosaurs through time and across phylogeny., (Copyright © 2017 Elsevier Ltd. All rights reserved.)