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[dinosaur] Macrocnemus + Permian timescale + Geiseltaliellus scales + more

Ben Creisler

Some recent non-dino papers that may be of interest:

This one is only in abstract form for now, full paper in open access to come later:

Vivien P. Jaquier, Nicholas C. Fraser, Heinz Furrer and Torsten M. Scheyer (2017)
Osteology of a new specimen of Macrocnemus aff. M. fuyuanensis (Archosauromorpha, Protorosauria) from the Middle Triassic of Europe: potential implications for species recognition and paleogeography of tanystropheid protorosaurs.
Frontiers in Earth Science (advance abstract)
doi: 10.3389/feart.2017.00091

Over the past two decades, a wealth of marine and terrestrial reptiles, including protorosaurian archosauromorphs, has been described from Triassic shales and limestone layers in southern China. Recovered from the eastern margin of the Tethys Ocean, these forms often show remarkable similarities to taxa that were previously known and described from Europe, i.e., the western Tethyan margin. One protorosaurian that is known from the western and the eastern Tethyan province is the genus Macrocnemus, with currently three recognized species: 1) M. bassanii from the Middle Triassic Besano Formation and Meride Limestone (late Anisian â early Ladinian), UNESCO World Heritage Site Monte San Giorgio, Ticino, Switzerland; 2) M. obristi from the Prosanto Formation (early Ladinian) of the Ducan area, Grisons, Switzerland; and 3) M. fuyuanensis from the Falang Formation (Ladinian), Yunnan Province, southern China. Recently a new specimen, PIMUZ T 1559, from the upper Besano Formation at Meride, Ticino, Switzerland, was prepared, revealing a disarticulated skeleton which includes most of the cranium and lower jaw, pre-caudal vertebral column and ribs, the forelimbs, and girdle elements. Unambiguously assignable to the genus Macrocnemus, it evinces particularly gracile elongated cervical ribs, as well as a humerus/radius ratio that is comparable only to that of M. fuyuanensis from southern China. Based on this feature we tentatively recognize the new specimen as M. aff. fuyuanensis from Europe. The position and exquisite preservation of the clavicle and interclavicle in this specimen allows a revision of the shoulder girdle of Macrocnemus when articulated, which also has implications for closely related protorosaurian taxa, such as the long-necked Tanystropheus. Furthermore, differences in the shape and morphology of the interclavicle including pointed wing-like lateral processes and a short, fusiform caudal process represent rare discrete characters that allow separation of the specimens of M. bassanii from the new specimen of M. aff. fuyuanensis.


Damien EsquerrÃ, Emma Sherratt & J. Scott Keogh (2017)

Evolution of extreme ontogenetic allometric diversity and heterochrony in pythons, a clade of giant and dwarf snakes.

Evolution (advance online publication)

DOI: 10.1111/evo.13382




Ontogenetic allometry, how species change with size through their lives, and heterochony, a decoupling between shape, size and age, are major contributors to biological diversity. However, macro-evolutionary allometric and heterochronic trends remain poorly understood because previous studies have focused on small groups of closely related species. Here we focus on testing hypotheses about the evolution of allometry and how allometry and heterochrony drive morphological diversification at the level of an entire species-rich and diverse clade. Pythons are a useful system due to their remarkably diverse and well-adapted phenotypes and extreme size disparity. We collected detailed phenotype data on 40 of the 44 species of python from 1,191 specimens. We used a suite of analyses to test for shifts in allometric trajectories that modify morphological diversity. Heterochrony is the main driver of initial divergence within python clades, and shifts in the slopes of allometric trajectories make exploration of novel phenotypes possible later in divergence history. We found that allometric coefficients are highly evolvable and there is an association between ontogenetic allometry and ecology, suggesting that allometry is both labile and adaptive rather than a constraint on possible phenotypes.



Free pdf:

K. T. Smith (2017)

The squamation of the Eocene stem-basilisk Geiseltaliellus maarius (Squamata: Iguanidae: Corytophaninae) from Messel, Germany.

SALAMANDRA 53(4): 519â530



An exceptional new specimen of the stem-basilisk Geiseltaliellus maarius from the middle Eocene of Messel, Germany, preserves details of the squamation of this extinct species. The dorsum and extremities were covered by small, rhomoidal scales, about 0.2 mm in size in most places; somewhat larger scales were present on the lower extremities and on the head. Scales of the venter were arranged in transverse rows, unlike in extant Polychrus and Laemanctus. There is some evidence that the scales on the extremities possessed keels, as in extant basilisks and Polychrus. Keratin appears to be preserved in places. The âOberhÃutchenâ is nearly featureless, probably the result of postmortem microbial decomposition; scale organs were not observed. Overall, the body of G. maarius possessed a fine, homogeneous squamation most similar to Basiliscus. Possible sexual dimorphism in the form of the parietal crest raises the prospect of a projecting median keel composed of skin in male G. maarius, although direct evidence on this point is currently lacking. The squamation of the tail is discussed in light of the pseudoautotomy shown by this species.


Jahandar Ramezani and Samuel A. Bowring (2017)
Advances in numerical calibration of the Permian timescale based on radioisotopic geochronology.
Geological Society of London Special Publication SP450: The Permian Timescale (advance online publication)
doi: https://doi.org/10.1144/SP450.17

Radioisotopic age determinations targeted at key stratigraphic successions worldwide continue to refine the geological timescale with increasing precision and accuracy and to unravel the tempo of global geological, palaeoclimatic and palaeobiotic processes that have shaped our planet. The last decade has witnessed significant progress in the calibration of the Permian Period through integrated stratigraphic, palaeontological and high-precision geochronological investigations. These studies have largely focused on the Cisuralian and Lopingian stages, particularly the end-Permian mass extinction, whereas much of the Guadalupian and its associated events remain inadequately calibrated. A compilation of the high-precision UâPb geochronology generated in the past ten years yields ages of 298.92Â0.19 Ma for the onset of the Permian, 293.52Â0.17 Ma for the base-Sakmarian, 290.10Â0.14 Ma for the base-Artinskian, 272.95Â0.11 Ma for the CisuralianâGuadalupian boundary, 265.22Â0.34 Ma for the base-Capitanian, 254.14Â0.12 Ma for the base-Changhsingian and 251.90Â0.10 Ma for the PermianâTriassic boundary. Extension of modern astrochronological methods to the Palaeozoic Era presents new opportunities for broader stratigraphic correlations and enhanced calibration of the Permian timescale.

Supplementary material: Table S1 (UâPb data) is available at https://doi.org/10.6084/m9.figshare.c.3917425


Free pdf:

(Nyasasaurus is used as an example.)

Joseph E. O'Reilly, Mark N. Puttick, Davide Pisani and Philip C. J. Donoghue (2017)

Probabilistic methods surpass parsimony when assessing clade support in phylogenetic analyses of discrete morphological data.

Palaeontology (advance online publication)

DOI: 10.1111/pala.12330



Fossil taxa are critical to inferences of historical diversity and the origins of modern biodiversity, but realizing their evolutionary significance is contingent on restoring fossil species to their correct position within the tree of life. For most fossil species, morphology is the only source of data for phylogenetic inference; this has traditionally been analysed using parsimony, the predominance of which is currently challenged by the development of probabilistic models that achieve greater phylogenetic accuracy. Here, based on simulated and empirical datasets, we explore the relative efficacy of competing phylogenetic methods in terms of clade support. We characterize clade support using bootstrapping for parsimony and Maximum Likelihood, and intrinsic Bayesian posterior probabilities, collapsing branches that exhibit less than 50% support. Ignoring node support, Bayesian inference is the most accurate method in estimating the tree used to simulate the data. After assessing clade support, Bayesian and Maximum Likelihood exhibit comparable levels of accuracy, and parsimony remains the least accurate method. However, Maximum Likelihood is less precise than Bayesian phylogeny estimation, and Bayesian inference recaptures more correct nodes with higher support compared to all other methods, including Maximum Likelihood. We assess the effects of these findings on empirical phylogenies. Our results indicate probabilistic methods should be favoured over parsimony.


Natalia Artemieva, Joanna Morgan & Expedition 364 Science Party (2017)

Quantifying the Release of Climate-Active Gases by Large Meteorite Impacts With a Case Study of Chicxulub.

Geophysical Research Letters (advance online publication)

DOI: 10.1002/2017GL074879Â


Potentially hazardous asteroids and comets have hit Earth throughout its history, with catastrophic consequences in the case of the Chicxulub impact. Here we reexamine one of the mechanisms that allow an impact to have a global effectâthe release of climate-active gases from sedimentary rocks. We use the SOVA hydrocode and model ejected materials for a sufficient time after impact to quantify the volume of gases that reach high enough altitudes (> 25 km) to have global consequences. We vary impact angle, sediment thickness and porosity, water depth, and shock pressure for devolatilization and present the results in a dimensionless form so that the released gases can be estimated for any impact into a sedimentary target. Using new constraints on the Chicxulub impact angle and target composition, we estimate that 325 Â 130 Gt of sulfur and 425 Â 160 Gt CO2 were ejected and produced severe changes to the global climate.


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