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[dinosaur] Thalattosuchian braincase + snake-like squamates + amniote tooth implantation + more




Ben Creisler


Some recent non-dino papers, some with free pdfs:

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Free pdf:

Yanina Herrera, Juan MartÃn Leardi & Marta S. FernÃndez (2018)
Braincase and endocranial anatomy of two thalattosuchian crocodylomorphs and their relevance in understanding their adaptations to the marine environment.
PeerJ 6:e5686
Free pdf:



Thalattosuchians are a group of Mesozoic crocodylomorphs known from aquatic deposits of the Early Jurassic-Early Cretaceous that comprises two main lineages of almost exclusively marine forms, Teleosauridae and Metriorhynchoidea. Teleosaurids were found in shallow marine, brackish and freshwater deposits, and have been characterized as semiaquatic near-shore forms, whereas metriorhynchids are a lineage of fully pelagic forms, supported by a large set of morphological characters of the skull and postcranial anatomy. Recent contributions on Thalattosuchia have been focused on the study of the endocranial anatomy. This newly available information provides novel evidence to suggest adaptations on the neuroanatomy, senses organs, vasculature, and behavioral evolution of these crocodylomorphs. However, is still not clear if the major morphological differences between teleosaurids and metriorhynchids were also mirrored by changes in the braincase and endocranial anatomy. Based on X-ray CT scanning and digital endocast reconstructions we describe the braincase and endocranial anatomy of two well-preserved specimens of Thalattosuchia, the semiaquatic teleosaurid Steneosaurus bollensis and the pelagic metriorhynchid Cricosaurus araucanensis. We propose that some morphological traits, such as: an enlarged foramen for the internal carotid artery, a carotid foramen ventral to the occipital condyle, a single CN XII foramen, absence of brain flexures, well-developed cephalic vascular system, lack of subtympanic foramina and the reduction of the paratympanic sinus system, are distinctive features of Thalattosuchia. It has been previously suggested that the enlarged foramen for the internal carotid artery, the absence of brain flexures, and the hypertrophied cephalic vascular system were synapomorphies of Metriorhynchidae; however, new information revealed that all of these features were already established at the base of Thalattosuchia and might have been exapted later on their evolutionary history. Also, we recognized some differences within Thalattosuchia that previously have not been received attention or even were overlooked (e.g., circular/bilobate trigeminal foramen, single/double CN XII foramen, separation of the cranioquadrate canal from the external otic aperture, absence/presence of lateral pharyngeal foramen). The functional significances of these traits are still unclear. Extending the sampling to other Thalattosuchia will help to test the timing of acquisition and distribution of these morphological modifications among the whole lineage. Also comparison with extant marine tetrapods (including physiological information) will be crucial to understand if some (and/or which) of the morphological peculiarities of thalattosuchian braincases are products of directional natural selection resulting in a fully adaptation to a nektonic life style.

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Dean R. Lomax (2018)
Hidden sea dragons--discovering new species of Jurassic ichthyosaurs in museum collections.
Geology Today 34(6): 236-240

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Ichthyosaurs were a highly successful group of marine reptiles that first appeared in the Early Triassic, around 248 million years ago, and became extinct about 90 million years ago, in the Late Cretaceous. They are often referred to as âswimming dinosaursâ, but they are not dinosaurs. They were fully aquatic marine tetrapods that lived in the seas, whilst their more famous counterparts, the dinosaurs, roamed the land (Fig. 1). They achieved a worldâwide distribution, and well over a hundred species are known, with thousands of specimens having been found. Ichthyosaurs evolved similar body plans to sharks, dolphins and whales, and are great examples of convergent evolution.



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Jonathan D. Radley & Robert A. Coram (2018)
Warwick sandstone: a window onto Middle Triassic life and landscapes.
Geology Today 34(6): 230-235


The town of Warwick in central England, UK is built on Middle Triassic sandstone of alluvial origin. The sandstone beds were once extensively quarried for building stone, which is seen in many of the townâs older buildings. The quarries yielded fossilized remains of reptiles and amphibians, providing a glimpse of recovering life in the aftermath of the endâPermian mass extinction. Study of sedimentary structures preserved within the sandstones has allowed reconstruction of the Pangean rivers and their floodplains, influenced by a hot, semiâarid climate.

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Philip J. Bergmann & Gen Morinaga (2018)
The convergent evolution of snakeâlike forms by divergent evolutionary pathways in squamate reptiles.
Evolution (advance online publication)

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Convergent evolution of phenotypes is considered evidence that evolution is deterministic. Establishing if such convergent phenotypes arose through convergent evolutionary pathways is a stronger test of determinism. We studied the evolution of snakeâlike body shapes in six clades of lizards, each containing species ranging from shortâbodied and pentadactyl to longâbodied and limbless. We tested whether body shapes that evolved in each clade were convergent, and whether clades evolved snakeâlike body shapes following convergent evolutionary pathways. Our analyses showed that indeed species with the same numbers of digits in each clade evolved convergent body shapes. We then compared evolutionary pathways among clades by considering patterns of evolutionary integration and shape of relationship among body parts, patterns of vertebral evolution, and models of digit evolution. We found that all clades elongated their bodies through the addition, not elongation, of vertebrae, and had similar patterns of integration. However, patterns of integration, the body parts that were related by a linear or a threshold model, and patterns of digit evolution differed among clades. These results showed that clades followed different evolutionary pathways. This suggests an important role of historical contingency as opposed to determinism in the convergent evolution of snakeâlike body shapes.

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Martin G. Lockley, Lida Xing & Xu Xing (2018)
The "lost" holotype of Laiyangpus liuiYoung 1960 (Lower Cretaceous, Shandong Province, China) is found: implications for trackmaker identification, ichnotaxonomy and interpretation of turtle tracks.
Cretaceous Research (advance online publication)

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The vertebrate track Liayangpus liui, from the Lower Cretaceous of Shandong Province in China has been the subject of misunderstanding and misinterpretation since it was discovered and named in 1960, and reposited in the Institute of Vertebrate Paleontology and Paleoanthropology collections in Beijing. It was initially misinterpreted as evidence of a coelurosaurian (non-avian theropod) trackmaker supposedly showing evidence of tridactyl manus and tetradactyl pes. This discredited conclusion was influenced by erroneous 1930s interpretations in the European literature, of tracks later shown to be of turtle affinity. A half century later, when morphologically disparate avian and non-avian theropod tracks were reported from the type locality, it was suggested that the ichnites were most likely crocodilian swim tracks. However, at that date (2010), and for some time previously, the type specimen was believed lost, and in at least one instance the label Laiyangpus had been applied to quite different theropod track specimens in the collections. With the discovery of turtle swim tracks at several Early Cretaceous sites in China, it was suspected, and later (2015) stated that the tracks were likely attributable to turtles. This, inference was confirmed when the holotype was rediscovered and examined in detail, revealing that Laiyangpus liui is sufficiently similar, morphologically, to Chelonipus to be considered a subjective senior synonym. We therefore propose transferring L. liui to Chelonipus liui, comb. nov. which is diagnostic of tracks attributable to turtles.


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Free pdf:

Thomas J. C. Bertin, BÃatrice Thivichon-Prince, Aaron R. H. LeBlanc, Michael W. Caldwell and Laurent Viriot (2018)
Current Perspectives on Tooth Implantation, Attachment, and Replacement in Amniota.
Frontiers in Physiology 9: 1630ÂÂ
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Teeth and dentitions contain many morphological characters which give them a particularly important weight in comparative anatomy, systematics, physiology and ecology. As teeth are organs that contain the hardest mineralized tissues vertebrates can produce, their fossil remains are abundant and the study of their anatomy in fossil specimens is of major importance in evolutionary biology. Comparative anatomy has long favored studies of dental characters rather than features associated with tooth attachment and implantation. Here we review a large part of the historical and modern work on the attachment, implantation and replacement of teeth in Amniota. We propose synthetic definitions or redefinitions of most commonly used terms, some of which have led to confusion and conflation of terminology. In particular, there has long been much conflation between dental implantation that strictly concerns the geometrical aspects of the tooth-bone interface, and the nature of the dental attachment, which mostly concerns the histological features occurring at this interface. A second aim of this work was to evaluate the diversity of tooth attachment, implantation and replacement in extant and extinct amniotes in order to derive hypothetical evolutionary trends in these different dental traits over time. Continuous dental replacement prevails within amniotes, replacement being drastically modified only in Mammalia and when dental implantation is acrodont. By comparison, dental implantation frequently and rapidly changes at various taxonomic scales and is often homoplastic. This contrasts with the conservatism in the identity of the tooth attachment tissues (cementum, periodontal ligament, and alveolar bone), which were already present in the earliest known amniotes. Because the study of dental attachment requires invasive histological investigations, this trait is least documented and therefore its evolutionary history is currently poorly understood. Finally, it is essential to go on collecting data from all groups of amniotes in order to better understand and consequently better define dental characters.


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Amy C. Henrici, Peter Druschke, Richard P. Hilton & Joshua W. Bonde (2018)
Redescription and phylogenetic reassessment of the enigmatic anuran Eorubeta nevadensis (Amphibia) based on new specimens from ?latest CretaceousâPaleocene beds of the Sheep Pass Formation, Nevada.
Journal of Vertebrate Paleontology e1510413Â (advance online publication)
DOI: 10.1080/02724634.2018.1508027


Eorubeta nevadensis was originally based on a poorly preserved specimen from a well core in Member B of the Late CretaceousâEocene Sheep Pass Formation, White Pine County, Nevada. Originally thought to be a member of Leptodactylidae, E. nevadensis was later determined to have uncertain affinities with other anurans. Additional specimens of E. nevadensis recently collected from the outcrop from Members B and C of the Sheep Pass Formation in the Sheep Pass Canyon area, White Pine County, fill many gaps in knowledge about this poorly understood anuran. The new information allows for the first time a phylogenetic analysis of Eorubeta using parsimony. This analysis places E. nevadensis as the sister taxon of Acosmanura. Eorubeta nevadensis was originally reported as early Eocene but is now considered to be ?latest CretaceousâPaleocene, based on invertebrates and pollen. Thus, although it is uncertain if E. nevadensis spans the CretaceousâPaleogene boundary, it was at least part of the recovery fauna. The anuran fossil record from this time interval in North America is based on very fragmentary material of mostly uncertain relationships, making E. nevadensis the only nearly complete, well-preserved anuran fossil known. Eorubeta nevadensis, one of the larger fossil anurans recorded, is remarkable for being the only fossil anuran documented from a high-elevation environment, which has been compared to the modern Puna-Altiplano or the Tibetan Plateau.


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David Millward, Sarah J. Davies, Peter J. Brand, Michael A. E. Browne, Carys E. Bennett, Timothy I. Kearsey, Janet E. Sherwin and John E. A. Marshall (2018)Â
Palaeogeography of tropical seasonal coastal wetlands in northern Britain during the early Mississippian Romer's Gap.
Earth and Environmental Science Transactions of The Royal Society of Edinburgh (advance online publication)



The lower Mississippian Ballagan Formation of northern Britain is one of only two successions worldwide to yield the earliest known tetrapods with terrestrial capability following the end-Devonian mass extinction event. Studies of the sedimentary environments and habitats in which these beasts lived have been an integral part of a major research project into how, why and under what circumstances this profound step in the evolution of life on Earth occurred. Here, a new palaeogeographic map is constructed from outcrop data integrated with new and archived borehole material. The map shows the extent of a very low-relief coastal wetland developed along the tropical southern continental margin of Laurussia. Coastal floodplains in the Midland Valley and Tweed basins were separated from the marginal marine seaway of the NorthumberlandâSolway Basin to the south by an archipelago of more elevated areas. A complex mosaic of sedimentary environments was juxtaposed, and included fresh and brackish to saline and hypersaline lakes, a diverse suite of floodplain palaeosols and a persistent fluvial system in the east of the region. The strongly seasonal climate led to the formation of evaporite deposits alternating with flooding events, both meteoric and marine. Storm surges drove marine floods from the SW into both the western Midland Valley and NorthumberlandâSolway Basin; marine water also flooded into the Tweed Basin and Tayside in the east. The Ballagan Formation is a rare example in the geological record of a tropical, seasonal coastal wetland that contains abundant, small-scale evaporite deposits. The diverse sedimentary environments and palaeosol types indicate a network of different terrestrial and aquatic habitats in which the tetrapods lived.

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Lorenzo Alibardi (2018)
Perspective: Appendage regeneration in amphibians and some reptiles derived from specific evolutionary histories.
Journal of Experimental Zoology Part B: Molecular and Developmental Evolution (advance online publication)

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Some hypotheses on the evolution of regeneration in amphibians and reptiles are presented. Amphibian regeneration is derived from metamorphosis present in sarcopterygian fish and amphibians of the DevonianâCarboniferous. The genetic ability to rebuild organs during metamorphosis was maintained in form of "regeneration" in urodele and anuran tadpoles. Amphibian regeneration may be a consequence of the transition from an aquatic to a terrestrial environment through the evolution of a developmental program for the tadpole stage and replacements of adult organs controlled by the endocrine and immune system. Following metamorphosis, the regeneration program for terrestrial anurans and amniotes was lost or modified, whereas the immune system involved in selfâintegrity and microbial protection became in charge of regeneration that was replaced by scarring. Among amniotes only lizards regenerate an organ as large and complex as the tail. It is hypothesized that in Permian captorhinids and in Triassic lizards (eosuchians) a regenerative blastema evolved in relation to autotomy, a unique phenomenon present in these reptiles that enhanced survival against the larger predators of the PermianâMesozoic. Appendage regeneration in amphibians and lizards occurs after the migration of activated mesenchymal and epidermal cells in the wounded areas to form soft and hyaluronateârich blastemas. Autotomy and production of high hyaluronate levels allows high hydration and immunosuppression, favoring regeneration. It is suggested that a way for regenerative medicine to induce limb regeneration in humans is to develop medical procedures to recreate soft blastemas that can grow, a long and difficult process because it counteracts mammalian evolution toward scarring.

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