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[dinosaur] Polar dinosaurs + Cretaceous climate + how Draco lizard fly + more

Ben Creisler

Some recent papers on different topics (some dino) that may be of interest:

Zeev Lewy (2016)
Dinosaur demise in light of their alleged perennial polar residency.
International Journal of Earth Sciences (advance online publication)
DOI: 10.1007/s00531-016-1426-9

The end-Cretaceous biological crisis is represented by the demise of the non-avian dinosaurs. However, most crucial biologically was the elimination of the photosynthesizing marine phyto- and zooplankton forming the base of the marine food chain. Their abrupt demise attests to sunlight screening darkening the atmosphere for a few years. Alvarez et al. (Science 208:1095–1108, 1980. doi:10.1126/science.208.44) noticed in deep marine end-Cretaceous sediments an anomalous rise in the chemical element iridium (Ir), which is rare on planet Earth and thus suggests an extraterrestrial origin through an impact of a large asteroid. This impact would have ejected enormous quantities of particles and aerosols, shading the solar illumination as attested to by the elimination of the marine photosynthesizing plankton. Such a dark period must have affected life on land. The apparent cold-blooded non-avian dinosaurs, which were used to living in open terrains to absorb the solar illumination, became inactive during the dark period and were incapable of withstanding predators. This was in contrast to cold-blooded crocodilians, turtles and lizards that could hide in refuge sites on land and in the water. Dinosaur relics discovered in Cretaceous Polar Regions were attributed to perennial residents, surviving the nearly half-year-long dark winter despite their ability to leave. The polar concentrations of disarticulated dinosaur bones were suggested as having resulted from a catastrophic burial of a population by floods. However, this should have fossilized complete skeletons. Alternatively, herds of dinosaurs living in high latitudes might have been sexually driven to spend the half year of continuously illuminated polar summer for mating rather than for nourishment, in which the lower latitudes provided as well. The aggressive mating competitions would have left victims among the rivals and of young ones incidentally trampled over, all being consumed and their skeletons disarticulated. Accordingly, the alleged ‘polar dinosaurs’ do not challenge the logical conclusion that the non-avian dinosaurs were cold-blooded, as a result of which they became inactive and subjected to predation during the end-Cretaceous dark period.


William W. Hay (2016)
Toward understanding Cretaceous climate—An updated review.
Science China Earth Sciences (advance online publication)
DOI: 10.1007/s11430-016-0095-9

New data and ideas are changing our view of conditions during the Cretaceous. Paleotopography of the continents was lower than originally thought, eliminating the ‘cold continental interior paradox’ of fossils of plants that could not tolerate freezing occurring in regions indicated by climate models to be well below freezing in winter. The controversy over the height of Cretaceous sea levels has been resolved by knowledge of the effects of passage of the subducted slab of the Farallon Plate beneath the North American crust. The cause of shorter term sea level changes of the order of 30 to 50 meters is not because of growth and decay of ice sheets, but more likely the filling and release of water from groundwater reservoirs and lakes although there may have been some ice in the Early and latest Cretaceous. Carbon dioxide was not the only significant greenhouse gas; methane contributed significantly to the warmer climate. Suggestions of very warm tropical ocean temperatures (>40°C) have implications for the nature of plant life on land limited by Rubisco activase. The land surfaces were much wetter than has been thought, with meandering rivers and many oxbow lakes providing habitat for large dinosaurs. A major rethinking of the nature of conditions on a warmer Earth is underway, and a new suite of paleoclimate simulations for the Cretaceous is needed.


Free pdf:

Marcelo R. Sánchez‑Villagra and Ingmar Werneburg (2016)
Mammalian organogenesis in deep time: tools for teaching and outreach
Evolution: Education and Outreach 9:11
DOI: 10.1186/s12052-016-0062-y

Mammals constitute a rich subject of study on evolution and development and provide model organisms for experimental investigations. They can serve to illustrate how ontogeny and phylogeny can be studied together and how the reconstruction of ancestors of our own evolutionary lineage can be approached. Likewise, mammals can be used to promote 'tree thinking' and can provide an organismal appreciation of evolutionary changes. This subject is suitable for the classroom and to the public at large given the interest and familiarity of people with mammals and their closest relatives. We present a simple exercise in which embryonic development is presented as a transformative process that can be observed, compared, and analyzed. In addition, we provide and discuss a freely available animation on organogenesis and life history evolution in mammals. An evolutionary tree can be the best tool to order and understand those transformations for different species. A simple exercise introduces the subject of changes in developmental timing or heterochrony and its importance in evolution. The developmental perspective is relevant in teaching and outreach efforts for the understanding of evolutionary theory today.


Free pdf:

J. Maximilian Dehling (2016)
How lizards fly: A novel type of wing in animals.
bioRxiv (preprints)
doi: http://dx.doi.org/10.1101/086496

Flying lizards of the genus Draco are famous for their gliding ability, using an aerofoil formed by winglike patagial membranes and supported by elongated thoracic ribs. It has remained unknown, however, how the lizards manoeuvre during flight. Here, I show that the patagium is deliberately grasped and controlled by the forelimbs while airborne. This type of composite wing is unique inasmuch as the lift-generating and the controlling units are formed independently by different parts of the body and are connected to each other only for the duration of the flight. The major advantage for the lizards is that the forelimbs keep their entire movement range and functionality for climbing and running when they are not used as the controlling unit of the wing. These findings not only shed a new light on the flight of Draco lizards but also have implications for the interpretation of gliding performance in fossil species.




Christian Foth & Walter G. Joyce (2016)
Slow and steady: the evolution of cranial disparity in fossil and recent turtles
Proceedings of the Royal Society B 2016 283 20161881
DOI: 10.1098/rspb.2016.1881

Turtles (Testudinata) are a diverse group of amniotes that have a rich fossil record that extends back to the Late Triassic, but little is known about global patterns of disparity through time. We here investigate the cranial disparity of 172 representatives of the turtle lineage and their ancestors grouped into 20 time bins ranging from the Late Triassic until the Recent using two-dimensional geometric morphometrics. Three evolutionary phases are apparent in all three anatomical views investigated. In the first phase, disparity increases gradually from the Late Triassic to the Palaeogene with only a minor perturbation at the K/T extinct event. Although global warming may have influenced this increase, we find the Mesozoic fragmentation of Pangaea to be a more plausible factor. Following its maximum, disparity decreases strongly towards the Miocene, only to recover partially towards the Recent. The marked collapse in disparity is likely a result of habitat destruction caused by global drying, combined with the homogenization of global turtle faunas that resulted from increased transcontinental dispersal in the Tertiary. The disparity minimum in the Miocene is likely an artefact of poor sampling.


Pedro S. R. Romano (2016)
The tale of the headless turtle.
Zootaxa 4200(2): 
DOI: http://dx.doi.org/10.11646/zootaxa.4200.2.7

Pelomedusoides is the most diverse clade of side-necked turtles and there is an extensive fossil record (de Broin, 1988; Lapparent de Broin, 2000; Gaffney et al., 2006, 2011) that dates back at least to the Barremian (Lower Cretaceous) (Romano et al., 2014). Its large fossil record evidences a greater diversity in the past, particularly at the end of the Mesozoic, and exhibits a good sampling of species that are represented by skull material (Gaffney et al., 2006, 2011). As a consequence, the most complete and recent phylogenetic hypotheses for this clade (e.g. Romano et al., 2014; Cadena, 2015) are based on matrices comprising a great amount of cranial characters derived largely from Gaffney et al. (2006, 2011). In addition, it is well established that shell characters show a lot of phenotypic plasticity, even in the fossil species (Romano, 2008; Gaffney et al., 2006, 2011). In most cases it consequently is not justified to rely on “diagnostic features” of poorly informative shell-only material for describing a new species. Because of that, most authors remark new morphotypes in the literature when such aberrant specimens are recovered, but do not make any nomenclatural act by proposing a new yet poorly supported species (e.g. Romano et al., 2013; Ferreira & Langer, 2013; Menegazzo et al., 2015). Unfortunately, such a supposedly new bothremydid turtle (Pleurodira: Bothremydidae) from the Early Paleocene of Brazil was recently described based on poorly diagnostic remains (Carvalho et al., 2016; hereafter CGB, for the authors initials) and a correction of this unfounded nomenclatural act is required. In addition I present some comments on shell only material from Brazil in order to guide splitter-taxonomists to stop describing poorly preserved fossil specimens as new species.


Sarah W. Keenan (2016)

From bone to fossil: A review of the diagenesis of bioapatite.

American Mineralogist  101 (9): 1943-1951

DOI: 10.2138/am-2016-5737



The preservation of bone or bioapatite over geologic time has presented paleobiologists with longstanding and formidable questions. Namely, to elucidate the mechanisms, processes, rates, and depositional conditions responsible for the formation of a fossil from a once living tissue. Approaches integrating geochemistry, mineralogy, physics, hydrology, sedimentology, and taphonomy have all furthered insights into fossilization, but several fundamental gaps still remain. Notably, our limited understanding of: (1) the timing of processes during diagenesis (e.g., early and/or late), (2) the rate of bioapatite transformation into thermodynamically more stable phases, (3) the controls imparted by depositional environment, and (4) the role of (micro)biology in determining the fate of bone bioapatite (dissolution or preservation). The versatility of fossil bioapatite to provide information on the biology of extinct vertebrates rests on our ability to identify and characterize the changes that occurred to bioapatite during diagenesis. This review will evaluate our current understanding of bioapatite diagenesis and fossilization, focusing on the biogeochemical transformations that occur during diagenesis to the mineral and organic components of bone (excluding teeth and enamel), the analytical approaches applied to evaluate fossilization processes, and outline some suggestions for future promising directions.