Ryan N. Felice, Joseph A. Tobias, Alex L. Pigot and Anjali Goswami (2019)
Dietary niche and the evolution of cranial morphology in birds.
Proceedings of the Royal Society B: Biological Sciences 286(1897): 20182677
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Cranial morphology in birds is thought to be shaped by adaptive evolution for foraging performance. This understanding of ecomorphological evolution is supported by observations of avian island radiations, such as Darwin's finches, which display rapid evolution of skull shape in response to food resource availability and a strong fit between cranial phenotype and trophic ecology. However, a recent analysis of larger clades has suggested that diet is not necessarily a primary driver of cranial shape and that phylogeny and allometry are more significant factors in skull evolution. We use phenome-scale morphometric data across the breadth of extant bird diversity to test the influence of diet and foraging behaviour in shaping cranial evolution. We demonstrate that these trophic characters are significant but very weak predictors of cranial form at this scale. However, dietary groups exhibit significantly different rates of morphological evolution across multiple cranial regions. Granivores and nectarivores exhibit the highest rates of evolution in the face and cranial vault, whereas terrestrial carnivores evolve the slowest. The basisphenoid, occipital, and jaw joint regions have less extreme differences among dietary groups. These patterns demonstrate that dietary niche shapes the tempo and mode of phenotypic evolution in deep time, despite a weaker than expected formâfunction relationship across large clades.
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Zachary S. Morris, Kent A. Vliet, Arhat Abzhanov and Stephanie E. Pierce (2019)
Heterochronic shifts and conserved embryonic shape underlie crocodylian craniofacial disparity and convergence.
Proceedings of the Royal Society B: Biological Sciences 286(1897): 20182389
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The distinctive anatomy of the crocodylian skull is intimately linked with dietary ecology, resulting in repeated convergence on blunt- and slender-snouted ecomorphs. These evolutionary shifts depend upon modifications of the developmental processes which direct growth and morphogenesis. Here we examine the evolution of cranial ontogenetic trajectories to shed light on the mechanisms underlying convergent snout evolution. We use geometric morphometrics to quantify skeletogenesis in an evolutionary context and reconstruct ancestral patterns of ontogenetic allometry to understand the developmental drivers of craniofacial diversity within Crocodylia. Our analyses uncovered a conserved embryonic region of morphospace (CER) shared by all non-gavialid crocodylians regardless of their eventual adult ecomorph. This observation suggests the presence of conserved developmental processes during early development (before Ferguson stage 20) across most of Crocodylia. Ancestral state reconstruction of ontogenetic trajectories revealed heterochrony, developmental constraint, and developmental systems drift have all played essential roles in the evolution of ecomorphs. Based on these observations, we conclude that two separate, but interconnected, developmental programmes controlling craniofacial morphogenesis and growth enabled the evolutionary plasticity of skull shape in crocodylians.
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Michael W. Maisch & Andreas T. Matzke (2019)Â
Anthodon? haughtoni (V. HUENE, 1944), a pareiasaurid (Parareptilia: Pareiasauria) from the Late Permian Usili Formation of Kingori, Ruhuhu Basin, Tanzania.
Neues Jahrbuch fÃr Geologie und PalÃontologie - Abhandlungen 291(2): 197-204
The pareiasaur Anthodon ? haughtoni (v. Huene, 1944), known only from an incomplete postcranium comprising part of the dorsal vertebral column and associated osteoderms, is redescribed. It is shown that it represents a valid taxon that can be diagnosed based on autapomorphies of osteoderm morphology. There are two rows of parasagittal osteoderms and at least one row of lateral osteoderms. Unpaired sagittal osteoderms are absent. The lateral osteoderms are rhombic and very extensive mediolaterally. The very distinctive osteodermal armour which is unlike other known pareiasaurs does not allow to refer the specimen to Anthodon, nor can it be dismissed as a nomen dubium as suggested by previous studies. Nonetheless, it appears premature to base a new genus on such scanty material. As it most closely resembles a referred specimen of Pareiasaurus serridens among known pareiasaurids, it is tentatively identified as Pareiasaurus (?) haughtoni, pending the discovery of more complete material. There is thus no record of the genus Anthodon from the Ruhuhu Basin of south-western Tanzania.
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T. M. Cullen, F. J. Longstaffe, U. G. Wortmann, M. B. Goodwin, L. Huang and D. C. Evans (2019)
Stable isotopic characterization of a coastal floodplain forest community: a case study for isotopic reconstruction of Mesozoic vertebrate assemblages.
Royal Society Open Science 6(2): 181210
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Stable isotopes are powerful tools for elucidating ecological trends in extant vertebrate communities, though their application to Mesozoic ecosystems is complicated by a lack of extant isotope data from comparable environments/ecosystems (e.g. coastal floodplain forest environments, lacking significant C4 plant components). We sampled 20 taxa across a broad phylogenetic, body size, and physiological scope from the Atchafalaya River Basin of Louisiana as an environmental analogue to the Late Cretaceous coastal floodplains of North America. Samples were analysed for stable carbon, oxygen and nitrogen isotope compositions from bioapatite and keratin tissues to test the degree of ecological resolution that can be determined in a system with similar environmental conditions, and using similar constraints, as those in many Mesozoic assemblages. Isotopic results suggest a broad overlap in resource use among taxa and considerable terrestrialâaquatic interchange, highlighting the challenges of ecological interpretation in C3 systems, particularly when lacking observational data for comparison. We also propose a modified oxygen isotope-temperature equation that uses mean endotherm and mean ectotherm isotope data to more precisely predict temperature when compared with measured Atchafalaya River water data. These results provide a critical isotopic baseline for coastal floodplain forests, and act as a framework for future studies of Mesozoic palaeoecology.
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John E. A. Marshall, Emma J. Reeves, Carys E. Bennett, Sarah J. Davies, Timothy I. Kearsey, David Millward, Timothy R. Smithson & Michael A. E. Browne (2019)
Reinterpreting the age of the uppermost 'Old Red Sandstone' and Early Carboniferous in Scotland.
Earth and Environmental Science Transactions of The Royal Society of Edinburgh (advance online publication)
In Scotland, the base of the Ballagan Formation has traditionally been placed at the first grey mudstone within a contiguous Late Devonian to Carboniferous succession. This convention places the DevonianâCarboniferous boundary within the Old Red Sandstone (ORS) Kinnesswood Formation. The consequences of this placement are that tetrapods from the Ballagan Formation were dated as late Tournaisian in age and that the ranges of typically Devonian fish found in the Kinnesswood Formation continued into the Carboniferous. The Pease Bay specimen of the fish Remigolepis is from the Kinnesswood Formation. Comparisons with its range in Greenland, calibrated against spores, show it was Famennian in age. Detailed palynological sampling at Burnmouth from the base of the Ballagan Formation proves that the early Tournaisian spore zones (VI and HD plus Cl 1) are present. The Schopfites species that occurs through most of the succession is Schopfites delicatus rather than Schopfites claviger. The latter species defines the late Tournaisian CM spore zone. The first spore assemblage that has been found in Upper âORS' strata underlying the Ballagan Formation (Preston, Whiteadder Water), contains Retispora lepidophyta and is from the early latest Famennian LL spore zone. The spore samples are interbedded with volcaniclastic debris, which shows that the Kelso Volcanic Formation is, in part, early latest Famennian in age. These findings demonstrate that the Ballagan Formation includes most of the Tournaisian with the DevonianâCarboniferous boundary positioned close to the top of the Kinnesswood Formation. The Stage 6 calcrete at Pease Bay can be correlated to the equivalent section at Carham, showing that it represents a time gap equivalent to the latest Famennian glaciation(s). Importantly, some of the recently described Ballagan Formation tetrapods are older than previously dated and now fill the key early part of Romer's Gap.
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