F. Clarac, F. Goussard, L. Teresi, Vde. Buffrénil, & V. Sansalone (2017)
Do the ornamented osteoderms influence the heat conduction through the skin? A finite element analysis in Crocodylomorpha.
Journal of Thermal Biology (advance online publication)
An original FEA model is proposed to calculate the influence of the ornamented osteoderms on the heat conduction through the crocodylians’ skin.
The heat conduction through the osteoderms is neither modified by the presence of an apical ornamentation nor by the variation of inner porosity.
The presence of a post-cranial dermal ossification does not significantly impact the skin’s global conduction.
In order to assess the implication of the crocodylomorph ornamented osteoderms on the skin conduction during basking, we have performed three dimensional modeling and finite element analyses on a sample which includes both extant dry bones and well-preserved fossils tracing back to the Early Jurassic. In purpose to reveal the possible implication of the superficial ornamentation on the osteoderm heat conduction, we repeated the simulation on an equivalent set of smoothed 3D-modeled osteoderms. The comparison of the results evidenced that the presence of the apical sculpture has no significant impact on the osteoderm global conduction. Furthermore, as we also aimed to assess the influence of the inner bone porosity on the osteoderm conduction, we modified the heat equation parameters so that the 3D-modeled osteoderms successively score the compact and the cancellous bone properties (i.e. mass density, heat capacity, thermal conductivity and thermal diffusivity). Finally, we repeated the analyses using the soft-dermis properties which lead to outline that neither the degree of porosity nor the presence of the osteoderms (in itself) significantly modifies the heat conduction through the crocodylomorph skin. Consequently, as hypothesized by previous authors, if the dermal shield happens to be involved into heat capture during basking for crocodylians, this process must mainly rely on a convective effect based on the osteoderm relative degree of vascularization. This last assumption could thus explain why the crocodylians which produce little metabolic heat would carry an entire vascularized osteoderm shield.
Junya Watanabe (2017)
Quantitative discrimination of flightlessness in fossil Anatidae from skeletal proportions.
The Auk 134(3):672-695
Flight ability has been lost many times in the family Anatidae (ducks, geese, swans, and allies), and this provides unique insights into the morphological and ecological evolution of the family. Although ∼15 fossil anatids have been reported to be flightless or possibly so, there has not been an established criterion that is widely applicable to assessing flight ability in fossil anatids. In this study, discriminant rules for the presence–absence of flight ability were constructed by linear discriminant analysis (LDA) based on 7 skeletal measurements in 93 modern anatids in order to set a basis for the inference of flight ability in fossil anatids. Model selection for LDA was conducted by a high-dimensional modification of Akaike's Information Criterion, and selected models discriminated the volant and flightless groups with only one misclassification (Tachyeres patachonicus). Flight abilities of fossil anatids were assessed by the constructed rules, supplemented by resampling experiments that were designed to assess the uncertainty in estimating skeletal proportions of fossil anatids in the absence of associated skeletons. The flightless condition was strongly supported for Cnemiornis spp., Branta rhuax, Hawaiian moa-nalos, Chenonetta finschi, Anas chathamica, Chendytes spp., Shiriyanetta hasegawai, Cayaoa bruneti, and the “Annaka Short-winged Swan,” whereas the volant condition was supported for Mergus milleneri and Bambolinetta lignitifila. Results were ambiguous for Branta hylobadistes and Anas marecula. The constructed rules can easily be applied to new observations in the future, although limitations in the inference of ecological traits in fossil species from morphological measurements, including the risk of extrapolations, should be appreciated.
Diomedavus knapptonensis, n. gen. et sp.
Gerald Mayr and James L. Goedert (2017)
Oligocene and Miocene albatross fossils from Washington State (USA) and the evolutionary history of North Pacific Diomedeidae.
The Auk 134(3): 659-671
Albatross fossils have been collected from the late Oligocene Lincoln Creek Formation and the early/middle Miocene Astoria Formation near the townsite of Knappton, Pacific County, Washington (USA). The albatross from the Lincoln Creek Formation, Diomedavus knapptonensis, n. gen. et sp., is smaller than all extant albatrosses and represents the oldest published fossil albatross from the North Pacific Basin. Diomedavus knapptonensis is clearly distinguished from extant albatrosses in several osteological features; some are likely plesiomorphic, supporting a phylogenetic position outside the crown group. The unusual shape of the deltopectoral crest of the humerus suggests that D. knapptonensis also differed from extant albatrosses in its flight performance. A partial skeleton from the Astoria Formation likely represents another new albatross species; however, it is not named because there is no overlap with the skeletal elements of other fossil Diomedeidae. This species, here informally termed the “Astoria Formation albatross,” also identified as a stem group representative of the Diomedeidae, differs from extant species in subtle features of the leg bones. Therefore, stem group albatrosses inhabited the North Pacific Basin before the emergence of the taxon Phoebastria, which includes extant North Pacific albatrosses. Cenozoic albatrosses were widely distributed in the Northern Hemisphere and the complex biogeographic history of the Diomedeidae may have been shaped by changes in global marine or atmospheric circulation systems and the loss of safe breeding grounds.
Adriana Cecilia Mancuso, Elena Previtera, Cecilia Andrea Benavente & Santiago Hernandez Del Pino (2017)
Evidence of bacterial decay and early diagenesis in a partially articulated tetrapod from the Triassic Chañares Formation.
PALAIOS 32 (6)
The vertebrate fauna from the lower Carnian Chañares Formation of Argentina is dominated by well-preserved small- and medium-bodied archosauriforms and therapsids. Here we report the discovery of a non-mammalian therapsid dicynodont (of greater than 20 cm skull length) that was found partially articulated within the floodplain deposit. Taphonomic analysis of this specimen reveals details of its paleobiology and taphonomic history, including the cause of death, exposure to predation and/or scavenging, subsequent subaerial decay, and final entombment. The specimen studied also allowed for the documentation of the activity of micro-organisms involved in decay processes during the biostratinomic stage (soft tissue decomposition on surface) and diagenetic stages (anaerobic decay). Our results indicate that despite bones being found in concretions the formation of calcareous concretions is not required for bone preservation. Consequently, this study highlights the role of volcanic ash in promoting bone preservation.
Stephen M. Gatesy & Peter L. Falkingham (2017)
Neither bones nor feet: track morphological variation and 'preservation quality.'
Journal of Vertebrate Paleontology Article: e1314298.
As purely sedimentary structures, fossil footprints are all about shape. Correctly interpreting the significance of their surface topography requires understanding the sources of morphological variation. Differences among specimens are most frequently attributed to either taxonomy (trackmaker) or to preservation quality. ‘Well-preserved’ tracks are judged more similar to pedal anatomy than ‘poorly preserved’ ones, but such broad-brush characterizations confound two separate episodes in a track's history. Current evaluations of track quality fail to distinguish among behavioral, formational, intravolumetric, and postformational sources of variation. On the basis of analogy with body fossils, we recommend restricting assessments of track preservation quality to modifications that take place only after a track is created. Ichnologists need to try to parse the relative influence of factors affecting disparity, but we currently lack an adequate vocabulary to describe the overall shapes and specific features of formational variants.
Ryan T. Tucker, Eric M. Roberts, Vikie Darlington & Steven W. Salisbury (2017)
Investigating the stratigraphy and palaeoenvironments for a suite of newly discovered mid-Cretaceous vertebrate fossil-localities in the Winton Formation, Queensland, Australia.
Sedimentary Geology (advance online publication)
The Winton Formation of central Queensland is recognized as a quintessential source of mid-Cretaceous terrestrial faunas and floras in Australia. However, sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited. The intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved Winton Formation in the Eromanga Basin, including Isisford, Lark Quarry, and Bladensburg National Park. Twenty-three facies and six repeated facies associations were documented, indicating a mosaic of marginal marine to inland alluvial depositional environments. These developed synchronously with the final regression of the Eromanga Seaway from central Australia during the late Albian-early Turonian. Investigations of regional- and local-scale structural features and outcrop, core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin. Significant palaeoenvironmental differences exist between the lower and upper portions of the preserved Winton Formation, warranting informal subdivisions; a lower tidally influenced fluvial-deltaic member and an upper inland alluvial member. This work further demonstrates that the Isisford fauna is part of the lower member of the preserved Winton Formation; whereas, fossil localities around Winton, including Lark Quarry and Bladensburg National Park, are part of the upper member of the Winton Formation. These results permit a more meaningful framework for both regional and global comparisons of the Winton flora and fauna.
Posted in earlier form on the DML, now free:
Jungang Peng, Jianguo Li, Wenben Li, Sam M. Slater, Huaicheng Zhu & Vivi Vajda (2017)
The Triassic to Early Jurassic palynological record of the Tarim Basin, China.
Palaeobiodiversity and Palaeoenvironments (advance online publication)
The Tarim Basin, located in northwestern China, is an important oil-bearing region, and the extensive non-marine Mesozoic successions make this a key location for understanding environmental changes through the Triassic and Jurassic. Palynological analyses on samples from Lunnan-1 and Tazhong-1 drill cores from the northern and central part of the Tarim Basin reveal well-preserved spore–pollen assemblages. Five palynological assemblages, i.e. Tarim Triassic 1 (TT1)–Tarim Triassic 4 (TT4) and Tarim Jurassic 1 (TJ1), spanning the Early Triassic to Early Jurassic were identified based on compositional changes, which are supported by ordination of samples using non-metric multidimensional scaling (NMDS). The Early Triassic assemblages possess abundant bryophytes and Densoisporites spp.-producers, which potentially represent a recovery succession following the end-Permian event. The Late Triassic spore–pollen assemblages are more similar to those of the North China Palynofloral Province compared to the South China Province. Based on our phytogeographic analysis, we propose that the western section of the boundary between the North and South China palynofloras should be placed at the southern margin of the Tarim Basin.