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      A mid-Cretaceous embryonic-to-neonate snake in amber from Myanmar

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          The first known fossil baby snake (Late Cretaceous amber, Myanmar) shows that some ancient snakes lived in marginal marine forests.


          We present the first known fossilized snake embryo/neonate preserved in early Late Cretaceous (Early Cenomanian) amber from Myanmar, which at the time, was an island arc including terranes from Austral Gondwana. This unique and very tiny snake fossil is an articulated postcranial skeleton, which includes posterior precloacal, cloacal, and caudal vertebrae, and details of squamation and body shape; a second specimen preserves a fragment of shed skin interpreted as a snake. Important details of skeletal ontogeny, including the stage at which snake zygosphene-zygantral joints began to form along with the neural arch lamina, are preserved. The vertebrae show similarities to those of fossil Gondwanan snakes, suggesting a dispersal route of Gondwanan faunas to Laurasia. Finally, the new species is the first Mesozoic snake to be found in a forested environment, indicating greater ecological diversity among early snakes than previously thought.

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          The evolution of dinosaurs.

          The ascendancy of dinosaurs on land near the close of the Triassic now appears to have been as accidental and opportunistic as their demise and replacement by therian mammals at the end of the Cretaceous. The dinosaurian radiation, launched by 1-meter-long bipeds, was slower in tempo and more restricted in adaptive scope than that of therian mammals. A notable exception was the evolution of birds from small-bodied predatory dinosaurs, which involved a dramatic decrease in body size. Recurring phylogenetic trends among dinosaurs include, to the contrary, increase in body size. There is no evidence for co-evolution between predators and prey or between herbivores and flowering plants. As the major land masses drifted apart, dinosaurian biogeography was molded more by regional extinction and intercontinental dispersal than by the breakup sequence of Pangaea.
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            Fossiliferous Cretaceous Amber from Myanmar (Burma): Its Rediscovery, Biotic Diversity, and Paleontological Significance

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              Structural Extremes in a Cretaceous Dinosaur

              Fossils of the Early Cretaceous dinosaur, Nigersaurus taqueti, document for the first time the cranial anatomy of a rebbachisaurid sauropod. Its extreme adaptations for herbivory at ground-level challenge current hypotheses regarding feeding function and feeding strategy among diplodocoids, the larger clade of sauropods that includes Nigersaurus. We used high resolution computed tomography, stereolithography, and standard molding and casting techniques to reassemble the extremely fragile skull. Computed tomography also allowed us to render the first endocast for a sauropod preserving portions of the olfactory bulbs, cerebrum and inner ear, the latter permitting us to establish habitual head posture. To elucidate evidence of tooth wear and tooth replacement rate, we used photographic-casting techniques and crown thin sections, respectively. To reconstruct its 9-meter postcranial skeleton, we combined and size-adjusted multiple partial skeletons. Finally, we used maximum parsimony algorithms on character data to obtain the best estimate of phylogenetic relationships among diplodocoid sauropods. Nigersaurus taqueti shows extreme adaptations for a dinosaurian herbivore including a skull of extremely light construction, tooth batteries located at the distal end of the jaws, tooth replacement as fast as one per month, an expanded muzzle that faces directly toward the ground, and hollow presacral vertebral centra with more air sac space than bone by volume. A cranial endocast provides the first reasonably complete view of a sauropod brain including its small olfactory bulbs and cerebrum. Skeletal and dental evidence suggests that Nigersaurus was a ground-level herbivore that gathered and sliced relatively soft vegetation, the culmination of a low-browsing feeding strategy first established among diplodocoids during the Jurassic.

                Author and article information

                Sci Adv
                Sci Adv
                Science Advances
                American Association for the Advancement of Science
                July 2018
                18 July 2018
                : 4
                : 7
                [1 ]State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China.
                [2 ]School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China.
                [3 ]Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
                [4 ]Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
                [5 ]Department of Anatomy, Midwestern University, Glendale, AZ 85308, USA.
                [6 ]South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia.
                [7 ]College of Science and Engineering, Flinders University, Adelaide, South Australia, Australia.
                [8 ]Royal Saskatchewan Museum, Regina, Saskatchewan S4P 4W7, Canada.
                [9 ]Biology Department, University of Regina, Regina, Saskatchewan S4S 0A2, Canada.
                [10 ]Paleo-diary Museum of Natural History, Beijing 100097, China.
                [11 ]Beijing Forestry University, Beijing 100083, China.
                Author notes
                [* ]Corresponding author. Email: mw.caldwell@ 123456ualberta.ca
                Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

                Funded by: doi http://dx.doi.org/10.13039/100006363, National Geographic Society;
                Award ID: EC0768-15
                Funded by: doi http://dx.doi.org/10.13039/501100000038, Natural Sciences and Engineering Research Council of Canada;
                Award ID: 23458
                Funded by: doi http://dx.doi.org/10.13039/501100002367, Chinese Academy of Sciences;
                Award ID: YZ201211
                Funded by: Fundamental Research Funds for the Central Universities;
                Award ID: 2652017215
                Funded by: National Science Fund of China;
                Award ID: 41772008, 41790455, 31672345
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