Fossils explained 54
نویسنده
چکیده
Plesiosaurs may be divided into two general morphotypes, based on body shape. ‘Pliosauromorphs’ have a large head and a short neck—traditionally thought to be pliosaurs, while ‘plesiosauromorphs’ have a small head and long neck, and have been seen as plesiosauroids. This is in fact an oversimplification, and today, detailed analysis and investigations of plesiosaur anatomy suggest that these morphotypes actually evolved independently many times—such that there are short-necked plesiosauroids and long-necked pliosaurs. This confusing state of affairs is illustrated by the convergence of morphologies seen in the shortnecked Family Polycotylidae. Historically, this group was classified as pliosaurs, yet recent analyses indicate that it may be an offshoot of the Plesiosauroidea, with their short necks acquired independently. Despite this variation in the head and neck of plesiosaurs, the gross morphology of the rest of the body is widely considered to have been conservative throughout the evolution of the group, with all plesiosaurs having four flippers, a short body, and a short tail (Fig. 1). Plesiosaurs vary in size from 1.5 m (e.g., Thalassiodracon from the Lower Jurassic) to 15 m long giants (e.g., Pliosaurus from the Middle Jurassic). IsoPlesiosaurs
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Sedimentary Facies, Architectural Elements and Trace Fossils of Kashkan Formation, Folded Zagros Zone in SW Iran
The Kashkan Formation (Paleocene to Middle Eocene), consists of conglomerate, sandstone, and siltstone in the Zagros Folded zone, southwest Iran. Type of the sedimentary facies, architectural elements and trace fossils show that Kashkan deposits were formed in a low sinuosity braided stream system, with north to south flow direction. The formation displays coarsening-upward succession reflects ...
متن کاملAppendix 1 List of fossils, described as new by Senowbari-Daryan et al. from the Permian and Mesozoic of Iran
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The University of Kansas Paleontological Contributions
5 Interspecific relationships 48 INTRODUCTION 5 Predation 49 Location and geologic setting 5 Competition 50 Previous work 7 Commensalism 50 Approaches and study objectives 7 DEPOSITIONAL ENVIRONMENT AND Vertebrate paleontology 8 PALEOECOLOGIC SYNTHESIS 50 Paleobotany 8 Climate and paleogeography 50 Stratigraphy and correlation 8 Succession of the ancient communities 51 Acknowledgments 12 Summar...
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The problem of intermediates in the fossil record has been frequently discussed ever since Darwin. The extent of 'gaps' (missing transitional stages) has been used to argue against gradual evolution from a common ancestor. Traditionally, gaps have often been explained by the improbability of fossilization and the discontinuous selection of found fossils. Here we take an analytical approach and ...
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