Ben Creisler
Some recent non-dino papers:
Ecology and biomechanics play central roles in the generation of phenotypic diversity. When unrelated taxa invade a similar ecological niche, biomechanical demands can drive convergent morphological transformations. Thus, identifying and examining convergence helps to elucidate the key catalysts of phenotypic change. Gliding mammals are often presented as a classic case of convergent evolution because they independently evolved in numerous clades, each possessing patagia ('wing' membranes) that generate lift during gliding. We use phylogenetic comparative methods to test whether the skeletal morphologies of the six clades of extant gliding mammals demonstrate convergence. Our results indicate that glider skeletons are convergent, with glider groups consistently evolving proportionally longer, more gracile limbs than arborealists, likely to increase patagial surface area. Nonetheless, we interpret gliders to represent incomplete convergence because (i) evolutionary modelâfitting analyses do not indicate strong selective pressures for glider trait optima, (ii) the three marsupial glider groups diverge rather than converge, and (iii) the gliding groups remain separated in morphospace (rather than converging on a single morphotype), which is reflected by an unexpectedly high level of morphological disparity. That glider skeletons are morphologically diverse is further demonstrated by fossil gliders from the Mesozoic Era, which possess unique skeletal characteristics that are absent in extant gliders. Glider morphologies may be strongly influenced by factors such as body size and attachment location of patagia on the forelimb, which can vary among clades. Thus, convergence in gliders appears to be driven by a simple lengthening of the limbs, whereas additional skeletal traits reflect nuances of the gliding apparatus that are distinct among different evolutionary lineages. Our unexpected results add to growing evidence that incomplete convergence is prevalent in vertebrate clades, even among classic cases of convergence, and they highlight the importance of examining formâfunction relationships in light of phylogeny, biomechanics, and the fossil record.
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Free pdf:
SÃrgio Ferreira-Cardoso, Pierre-Henri Fabre, Benoit de Thoisy, FrÃdÃric Delsuc & Lionel Hautier (2020)
Comparative masticatory myology in anteaters and its implications for interpreting morphological convergence in myrmecophagous placentals.
PeerJ 8:e9690
doi:
https://doi.org/10.7717/peerj.9690https://peerj.com/articles/9690/Background
Ecological adaptations of mammals are reflected in the morphological diversity of their feeding apparatus, which includes differences in tooth crown morphologies, variation in snout size, or changes in muscles of the feeding apparatus. The adaptability of their feeding apparatus allowed them to optimize resource exploitation in a wide range of habitats. The combination of computer-assisted X-ray microtomography (Â-CT) with contrast-enhancing staining protocols has bolstered the reconstruction of three-dimensional (3D) models of muscles. This new approach allows for accurate descriptions of muscular anatomy, as well as the quick measurement of muscle volumes and fiber orientation. Ant- and termite-eating (myrmecophagy) represents a case of extreme feeding specialization, which is usually accompanied by tooth reduction or complete tooth loss, snout elongation, acquisition of a long vermiform tongue, and loss of the zygomatic arch. Many of these traits evolved independently in distantly-related mammalian lineages. Previous reports on South American anteaters (Vermilingua) have shown major changes in the masticatory, intermandibular, and lingual muscular apparatus. These changes have been related to a functional shift in the role of upper and lower jaws in the evolutionary context of their complete loss of teeth and masticatory ability.
Methods
We used an iodine staining solution (I2KI) to perform contrast-enhanced Â-CT scanning on heads of the pygmy (Cyclopes didactylus), collared (Tamandua tetradactyla) and giant (Myrmecophaga tridactyla) anteaters. We reconstructed the musculature of the feeding apparatus of the three extant anteater genera using 3D reconstructions complemented with classical dissections of the specimens. We performed a description of the musculature of the feeding apparatus in the two morphologically divergent vermilinguan families (Myrmecophagidae and Cyclopedidae) and compared it to the association of morphological features found in other myrmecophagous placentals.
Results
We found that pygmy anteaters (Cyclopes) present a relatively larger and architecturally complex temporal musculature than that of collared (Tamandua) and giant (Myrmecophaga) anteaters, but shows a reduced masseter musculature, including the loss of the deep masseter. The loss of this muscle concurs with the loss of the jugal bone in Cyclopedidae. We show that anteaters, pangolins, and aardvarks present distinct anatomies despite morphological and ecological convergences.
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Highlights
Depositional paleoenvironment of the Tartaruguito site is characterized.
Geochemical characterization of Bauruemys elegans from Presidente Prudente Formation.
Substitution by fluorine in bone apatite might improve fossil preservation.
Powder X-Ray Diffraction and Infrared Spectroscopy to enlighten fossil diagenesis.
Abstract
The Tartaruguito outcrop (Pirapozinho municipality, Presidente Prudente Formation, Bauru Basin) has been considered a Fossil-LagerstÃtte due to its exceptional fossil quality and large number of fossils recovered. Despite its historical and paleontological importance, a geochemical composition study of the fossils from this site and their sedimentary matrixes has never been performed. Here, we have analyzed fossil turtle shell fragments and their respective sedimentary matrixes collected at Tartaruguito through Powder X-Ray Diffraction and Infrared Spectroscopy techniques, to determine their geochemical composition and obtain clues regarding the fossil diagenesis processes. The analyses showed that the fossil remains of the side-necked turtle Bauruemys elegans from the Tartaruguito locality are mainly composed of calcite (CaCO3) and hydroxyapatite partially substituted by fluorine (Ca10(PO4)6(OH)2-xFx). The sedimentary matrixes are mostly composed of quartz (SiO2) and calcite, with secondary amounts of feldspar. The presence of calcite on both, fossil and rocky matrix, might indicate that the fossil diagenesis process that occurred at the Tartaruguito locality was permineralization by calcite, especially considering the absence of quartz on the bones of the fossil specimens. Furthermore, the presence of a fluor-hydroxyapatite solid-solution might be a plausible explanation for the quality of fossils recovered in Tartaruguito, due to the better stability of fluorapatite when compared to hydroxyapatite.
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This review elaborates the idea that organ regeneration derives from specific evolutionary histories of vertebrates. Regenerative ability depends on genomic regulation of genes specific to the lifeâcycles that have differentially evolved in anamniotes and amniotes. In aquatic environments, where fish and amphibians live, one or multiple metamorphic transitions occur before the adult stage is reached. Each transition involves the destruction and remodeling of larval organs that are replaced with adult organs. After organ injury or loss in adult anamniotes, regeneration uses similar genes and developmental process than those operating during larval growth and metamorphosis. Therefore, the broad presence of regenerative capability across anamniotes is possible because generating new organs is included in their life history at metamorphic stages. Soft hyaluronateârich regenerative blastemas grow in submersed or in hydrated environments, that is, essential conditions for regeneration, like during development. In adult anamniotes, the ability to regenerate different organs decreases in comparison to larval stages and becomes limited during aging. Comparisons of genes activated during metamorphosis and regeneration in anamniotes identify key genes unique to these processes, and include thyroid, wnt and nonâcoding RNAs developmental pathways. In the terrestrial environment, some genes or developmental pathways for metamorphic transitions were lost during amniote evolution, determining loss of regeneration. Among amniotes, the formation of soft and hydrated blastemas only occurs in lizards, a morphogenetic process that evolved favoring their survival through tail autotomy, leading to a massive although imperfect regeneration of the tail. Deciphering genes activity during lizard tail regeneration would address future attempts to recreate in other amniotes regenerative blastemas that grow into variably completed organs.
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Jason S. Anderson, Diane Scott & Robert R. Reisz (2020)
The anatomy of the dermatocranium and mandible of Cacops aspidephorus Williston, 1910 (Temnospondyli: Dissorophidae), from the Lower Permian of Texas.
Journal of Vertebrate Paleontology Article: e1776720
doi:
https://doi.org/10.1080/02724634.2020.1776720 https://www.tandfonline.com/doi/abs/10.1080/02724634.2020.1776720For the first time, the cranial suture pattern for the type species of Cacops, C. aspidephorus, is described in detail. A majority of sutures, including the lower jaw, the skull roof, and the palate, are now known in detail, although details are still lacking for the posterior skull table. Notable new information about C. aspidephorus includes the presence of a lateral exposure of the palatine (LEP), a lateral exposure of the ectopterygoid (LEE) that fuses with the jugal with growth, and a subtympanic flange composed mostly of the supratemporal. Cacops aspidephorus is very similar to C. morrisi, but differences, including a fully closed otic notch in C. aspidephorus, are sufficient to maintain both as distinct species. Uniquely, C. aspidephorus shows palatal dentition of the same size as the marginal dentition, but it remains to be seen whether this is a widespread feature or ontogenetically transient. These new data will finally permit the inclusion of this iconic taxon, described over 100 years ago, into larger-scale phylogenies of dissorophoid and temnospondyl relationships.
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Dinosaur-related climate stuff:
We reconstruct the late Maastrichtian Koryak (North-East of Russia) Arctic environment.
The Kakanaut Formation flora is a mix of advanced dicots and relictual gymnosperms.
CLAMP analysis yields a year-round temperate humid maritime climate.
This climate was experienced by the latest known breeding colony of polar dinosaurs.
Abstract
We describe fossil plant assemblages from the late Maastrichtian Kakanaut Formation of the Koryak Upland, North-East of Russia, which represent a high (75oN) palaeolatitude flora. The flora contains about 40 species, including liverworts, horsetails, ferns, cycadophytes, ginkgos, conifers and angiosperms. Angiosperms and conifers predominate and, unusually, the flora contains typical Cretaceous taxa admixed with elements that are more characteristic of the Paleocene. Reconstruction of the palaeoclimate in the Kakanaut area was made using the Climate Leaf Analysis Multivariate Program (CLAMP) employing a recently developed calibration that yields 23 different climate variables. Analysis was made based on 21 morphotypes of woody dicotyledonous plants from the Kakanaut flora. The analysis indicated a mean annual temperature of 12.2âÂâ2.0âÂC, a warmest month mean temperature of 20.6âÂâ2.5âÂC, a coldest month mean temperature of 4.8âÂâ3.2âÂC. The growing season lasted approximately 7âmonths, during which there was almost 1âm of precipitation. This and other indicators (relative humidity, vapour pressure deficit and potential evapotranspiration) all suggest a year-round humid regime. The winter temperatures suggest occasional mild frosts in this near sea level setting, so that at higher elevations freezing conditions would have been more persistent. These results throw new light on the living and breeding conditions of diverse latest Cretaceous Arctic dinosaur populations as represented by numerous skeletal and egg remains associated with the plants.
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