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An exploration into the world of dinosaurs, presented by paleontologist Armin Schmitt. Through firsthand experiences and groundbreaking research, Schmitt delves into the lives of these ancient creatures, showcasing global excavations and remarkable discoveries. While familiar favorites like Tyrannosaurus rex make appearances, Schmitt also addresses intriguing questions, such as the excavation process, the survival of birds during extinction events, the evolution of paleontology since the Bone Wars era, and parallels between past climate changes and contemporary environmental challenges.

For 130 years, dinosaurs have been divided into two distinct clades—Ornithischia and Saurischia. Here we present a hypothesis for the phylogenetic relationships of the major dinosaurian groups that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study has found a sister-group relationship between Ornithischia and Theropoda (united in the new clade Ornithoscelida), with Sauropodomorpha and Herrerasauridae (as the redefined Saurischia) forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests that hypercarnivory was acquired independently in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as notable convergences between theropods and early ornithischians. Analysis of a wide range of dinosaurs and dinosauromorphs recovers a sister-taxon relationship between Ornithischia and Theropoda, calling for the redefinition of all the major clades within Dinosauria and the revival of the clade Ornithoscelida. Redefining dinosaur diversification (BARON 21700, Bio Article, Henry Gee) For decades, dinosaurs have been divided into two universally accepted groups: the Saurischia, including the carnivorous theropods such as Tyrannosaurus rex and the giant sauropods such as Diplodocus , and the Ornithschia, including the ornithopods such as Iguanodon and armored dinosaurs such as Triceratops and Stegosaurus . However, approaches to dinosaur phylogeny may have taken these two groups for granted. A new hypothesis that includes neglected early ornithischians proposes a radical realignment in which sauropods are grouped with the early, carnivorous herrerasaurs, while ornithischians are grouped with theropods. If this new view of the dinosaur evolutionary tree is confirmed, not only will diagrams of dinosaur diversification require an overhaul, but museum displays the world over will have to be rearranged.

Large-scale adaptive radiations might explain the runaway success of a minority of extant vertebrate clades. This hypothesis predicts, among other things, rapid rates of morphological evolution during the early history of major groups, as lineages invade disparate ecological niches. However, few studies of adaptive radiation have included deep time data, so the links between extant diversity and major extinct radiations are unclear. The intensively studied Mesozoic dinosaur record provides a model system for such investigation, representing an ecologically diverse group that dominated terrestrial ecosystems for 170 million years. Furthermore, with 10,000 species, extant dinosaurs (birds) are the most speciose living tetrapod clade. We assembled composite trees of 614-622 Mesozoic dinosaurs/birds, and a comprehensive body mass dataset using the scaling relationship of limb bone robustness. Maximum-likelihood modelling and the node height test reveal rapid evolutionary rates and a predominance of rapid shifts among size classes in early (Triassic) dinosaurs. This indicates an early burst niche-filling pattern and contrasts with previous studies that favoured gradualistic rates. Subsequently, rates declined in most lineages, which rarely exploited new ecological niches. However, feathered maniraptoran dinosaurs (including Mesozoic birds) sustained rapid evolution from at least the Middle Jurassic, suggesting that these taxa evaded the effects of niche saturation. This indicates that a long evolutionary history of continuing ecological innovation paved the way for a second great radiation of dinosaurs, in birds. We therefore demonstrate links between the predominantly extinct deep time adaptive radiation of non-avian dinosaurs and the phenomenal diversification of birds, via continuing rapid rates of evolution along the phylogenetic stem lineage. This raises the possibility that the uneven distribution of biodiversity results not just from large-scale extrapolation of the process of adaptive radiation in a few extant clades, but also from the maintenance of evolvability on vast time scales across the history of life, in key lineages.

Dinosaurs diversified in two steps during the Triassic. They originated about 245 Ma, during the recovery from the Permian-Triassic mass extinction, and then remained insignificant until they exploded in diversity and ecological importance during the Late Triassic. Hitherto, this Late Triassic explosion was poorly constrained and poorly dated. Here we provide evidence that it followed the Carnian Pluvial Episode (CPE), dated to 234–232 Ma, a time when climates switched from arid to humid and back to arid again. Our evidence comes from a combined analysis of skeletal evidence and footprint occurrences, and especially from the exquisitely dated ichnofaunas of the Italian Dolomites. These provide evidence of tetrapod faunal compositions through the Carnian and Norian, and show that dinosaur footprints appear exactly at the time of the CPE. We argue then that dinosaurs diversified explosively in the mid Carnian, at a time of major climate and floral change and the extinction of key herbivores, which the dinosaurs opportunistically replaced. Dinosaurs originated ~245 million years ago (mya) but did not diversify until some time in the Late Triassic. Here, Bernardi and colleagues synthesize palaeontological and dated stratigraphic evidence to show that dinosaur diversification followed the Carnian Pluvial Episode 234–232 mya.

In recent decades, intensive research on non-avian dinosaurs has strongly suggested that these animals were restricted to terrestrial environments 1 . Historical proposals that some groups, such as sauropods and hadrosaurs, lived in aquatic environments 2 , 3 were abandoned decades ago 4 , 5 – 6 . It has recently been argued that at least some of the spinosaurids—an unusual group of large-bodied theropods of the Cretaceous era—were semi-aquatic 7 , 8 , but this idea has been challenged on anatomical, biomechanical and taphonomic grounds, and remains controversial 9 , 10 – 11 . Here we present unambiguous evidence for an aquatic propulsive structure in a dinosaur, the giant theropod Spinosaurus aegyptiacus 7 , 12 . This dinosaur has a tail with an unexpected and unique shape that consists of extremely tall neural spines and elongate chevrons, which forms a large, flexible fin-like organ capable of extensive lateral excursion. Using a robotic flapping apparatus to measure undulatory forces in physical models of different tail shapes, we show that the tail shape of Spinosaurus produces greater thrust and efficiency in water than the tail shapes of terrestrial dinosaurs and that these measures of performance are more comparable to those of extant aquatic vertebrates that use vertically expanded tails to generate forward propulsion while swimming. These results are consistent with the suite of adaptations for an aquatic lifestyle and piscivorous diet that have previously been documented for Spinosaurus 7 , 13 , 14 . Although developed to a lesser degree, aquatic adaptations are also found in other members of the spinosaurid clade 15 , 16 , which had a near-global distribution and a stratigraphic range of more than 50 million years 14 , pointing to a substantial invasion of aquatic environments by dinosaurs. Discovery that the giant theropod dinosaur Spinosaurus has a large flexible tail indicates that it was primarily aquatic and swam in a similar manner to extant tail-propelled aquatic vertebrates.

The archosaur species Teleocrater rhadinus , part of the new clade Aphanosauria, is an example of the earliest divergence of the avian stem lineage (Avemetatarsalia), the lineage that contains dinosaurs (including birds). Earliest avian archosaur The early history of the bird-line archosaurs, a group including dinosaurs, birds and pterosaurs, but excluding crocodilians, is not well defined. This is due in part to a fragmentary fossil record, but the distinctive morphology of pterosaurs has also obscured their ancestry. Sterling Nesbitt and colleagues describe a new species, Teleocraterrhadinus , from the Middle Triassic of Tanzania, that represents the most primitive known member of the bird-line archosaurs. Teleocrater provides the best guide so far to the ancestral bird-line condition. It was a lightly built, quadrupedal carnivore, so more like a crocodile than the small bipeds often depicted at this point in archosaur evolution. These are long-awaited findings on Teleocrater , which was undergoing study by the late Alan Charig of the Natural History Museum in London, and remained unpublished on his death in 1997. The relationship between dinosaurs and other reptiles is well established 1 , 2 , 3 , 4 , but the sequence of acquisition of dinosaurian features has been obscured by the scarcity of fossils with transitional morphologies. The closest extinct relatives of dinosaurs either have highly derived morphologies 5 , 6 , 7 or are known from poorly preserved 8 , 9 or incomplete material 10 , 11 . Here we describe one of the stratigraphically lowest and phylogenetically earliest members of the avian stem lineage (Avemetatarsalia), Teleocrater rhadinus gen. et sp. nov., from the Middle Triassic epoch. The anatomy of T. rhadinus provides key information that unites several enigmatic taxa from across Pangaea into a previously unrecognized clade, Aphanosauria. This clade is the sister taxon of Ornithodira (pterosaurs and birds) and shortens the ghost lineage inferred at the base of Avemetatarsalia. We demonstrate that several anatomical features long thought to characterize Dinosauria and dinosauriforms evolved much earlier, soon after the bird–crocodylian split, and that the earliest avemetatarsalians retained the crocodylian-like ankle morphology and hindlimb proportions of stem archosaurs and early pseudosuchians. Early avemetatarsalians were substantially more species-rich, widely geographically distributed and morphologically diverse than previously recognized. Moreover, several early dinosauromorphs that were previously used as models to understand dinosaur origins may represent specialized forms rather than the ancestral avemetatarsalian morphology.

Were dinosaurs ectotherms or fast-metabolizing endotherms whose activities were unconstrained by temperature? To date, some of the strongest evidence for endothermy comes from the rapid growth rates derived from the analysis of fossil bones. However, these studies are constrained by a lack of comparative data and an appropriate energetic framework. Here we compile data on ontogenetic growth for extant and fossil vertebrates, including all major dinosaur clades. Using a metabolic scaling approach, we find that growth and metabolic rates follow theoretical predictions across clades, although some groups deviate. Moreover, when the effects of size and temperature are considered, dinosaur metabolic rates were intermediate to those of endotherms and ectotherms and closest to those of extant mesotherms. Our results suggest that the modern dichotomy of endothermic versus ectothermic is overly simplistic.

Pterosaurs were the first vertebrates to evolve powered flight 1 and comprised one of the main evolutionary radiations in terrestrial ecosystems of the Mesozoic era (approximately 252–66 million years ago), but their origin has remained an unresolved enigma in palaeontology since the nineteenth century 2 – 4 . These flying reptiles have been hypothesized to be the close relatives of a wide variety of reptilian clades, including dinosaur relatives 2 – 8 , and there is still a major morphological gap between those forms and the oldest, unambiguous pterosaurs from the Upper Triassic series. Here, using recent discoveries of well-preserved cranial remains, microcomputed tomography scans of fragile skull bones (jaws, skull roofs and braincases) and reliably associated postcrania, we demonstrate that lagerpetids—a group of cursorial, non-volant dinosaur precursors—are the sister group of pterosaurs, sharing numerous synapomorphies across the entire skeleton. This finding substantially shortens the temporal and morphological gap between the oldest pterosaurs and their closest relatives and simultaneously strengthens the evidence that pterosaurs belong to the avian line of archosaurs. Neuroanatomical features related to the enhanced sensory abilities of pterosaurs 9 are already present in lagerpetids, which indicates that these features evolved before flight. Our evidence illuminates the first steps of the assembly of the pterosaur body plan, whose conquest of aerial space represents a remarkable morphofunctional innovation in vertebrate evolution. Lagerpetids, bipedal archosaurs that are thought to be related to dinosaurs, are instead a sister group to pterosaurs, and although they have no obvious flight adaptations they share numerous synapomorphies with pterosaurs across the entire skeleton.

To provide context for the diversification of archosaurs—the group that includes crocodilians, dinosaurs, and birds—we generated draft genomes of three crocodilians: Alligator mississippiensis (the American alligator), Crocodylus porosus (the saltwater crocodile), and Gavialis gangeticus (the Indian gharial). We observed an exceptionally slow rate of genome evolution within crocodilians at all levels, including nucleotide substitutions, indels, transposable element content and movement, gene family evolution, and chromosomal synteny. When placed within the context of related taxa including birds and turtles, this suggests that the common ancestor of all of these taxa also exhibited slow genome evolution and that the comparatively rapid evolution is derived in birds. The data also provided the opportunity to analyze heterozygosity in crocodilians, which indicates a likely reduction in population size for all three taxa through the Pleistocene. Finally, these data combined with newly published bird genomes allowed us to reconstruct the partial genome of the common ancestor of archosaurs, thereby providing a tool to investigate the genetic starting material of crocodilians, birds, and dinosaurs.