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[dinosaur] Ichthyosaurs + metoposaurid feeding + Iberosuchus bone histology





Ben Creisler
bcreisler@gmail.com


Some recent non-dino items:



Traci Watson (2017)
How giant marine reptiles terrorized the ancient seas.
Nature 543: 603–607 (30 March 2017) 
doi:10.1038/543603a
http://www.nature.com/news/how-giant-marine-reptiles-terrorized-the-ancient-seas-1.21722

Free pdf

http://www.nature.com/polopoly_fs/7.43294!/file/543603a.pdf


Ichthyosaurs were some of the largest and most mysterious predators to ever prowl the oceans. Now they are giving up their secrets.

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Note that the reconstructions of Ophthalmosaurus and other icthyosaurs depict the eye with a fully exposed sclerotic ring area under a rounded lens--an old mistake that keeps getting repeated in paleoart (as a "malmeme"?). Undoubtedly only the iris and pupil would have been visible under a protruding cornea, with the rest of eye protected in tissue, as in all modern animals (except humans)...


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Josep Fortuny, Jordi Marcé-Nogué and Dorota Konietzko-Meier (2017)
Feeding biomechanics of Late Triassic metoposaurids (Amphibia: Temnospondyli): a 3D finite element analysis approach.
Journal of Anatomy (advance online publication)
DOI: 10.1111/joa.12605
http://onlinelibrary.wiley.com/doi/10.1111/joa.12605/full


The Late Triassic freshwater ecosystems were occupied by different tetrapod groups including large-sized anamniotes, such as metoposaurids. Most members of this group of temnospondyls acquired gigantic sizes (up to 5 m long) with a nearly worldwide distribution. The paleoecology of metoposaurids is controversial; they have been historically considered passive, bottom-dwelling animals, waiting for prey on the bottom of rivers and lakes, or they have been suggested to be active mid-water feeders. The present study aims to expand upon the paleoecological interpretations of these animals using 3D finite element analyses (FEA). Skulls from two taxa, Metoposaurus krasiejowensis, a gigantic taxon from Europe, and Apachesaurus gregorii, a non-gigantic taxon from North America, were analyzed under different biomechanical scenarios. Both 3D models of the skulls were scaled to allow comparisons between them and reveal that the general stress distribution pattern found in both taxa is clearly similar in all scenarios. In light of our results, both previous hypotheses about the paleoecology of these animals can be partly merged: metoposaurids probably were ambush and active predators, but not the top predators of these aquatic environments. The FEA results demonstrate that they were particularly efficient at bilateral biting, and together with their characteristically anteropositioned orbits, optimal for an ambush strategy. Nonetheless, the results also show that these animals were capable of lateral strikes of the head, suggesting active hunting of prey. Regarding the important skull size differences between the taxa analyzed, our results suggest that the size reduction in the North American taxon could be related to drastic environmental changes or the increase of competitors. The size reduction might have helped them expand into new ecological niches, but they likely remained fully aquatic, as are all other metoposaurids.


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Jorge Cubo, Meike Köhler and Vivian de Buffrenil (2017)

Bone histology of Iberosuchus macrodon (Sebecosuchia, Crocodylomorpha).

Lethaia (advance online publication)

DOI: 10.1111/let.12203

http://onlinelibrary.wiley.com/doi/10.1111/let.12203/full




 

Iberosuchus macrodon is a Cenozoic crocodyliform interpreted as a terrestrial, cursorial form. To assess whether this adaptation was accompanied by a high growth rate and an elevated resting metabolic rate (two features commonly attributed to several terrestrial Triassic Crocodylomorpha based on histology), we studied bone histology in the femora of two specimens attributed to I. macrodon. Beyond this question is the broader problem of the possible survival to the Cretaceous-Palaeogene extinction event of tachymetabolic sauropsids other than birds. At mid-diaphysis, bone cortices in Iberosuchus are made of a parallel-fibred tissue that turns locally to true lamellar bone. Cortical vascularization consists of simple longitudinal canals forming a network of medium density. The spacing pattern of conspicuous lines of arrested growth suggests asymptotic growth for Iberosuchus. This general histological structure prevails also in the metaphyseal region of the bones. It is basically similar to that encountered in certain large lizards adapted to active predation, the Varanidae and the Teidae. In one of the two Iberosuchus femora, however, an intracortical meniscus made of a tissue displaying a global radial architecture occurs in the region of the fourth trochanter. Histologically, the latter can be interpreted either as compacted spongiosa or as a fibro-lamellar complex with a gross radial orientation, a tissue corresponding to fast periosteal apposition. These observations suggest that Iberosuchus basically had a slow, cyclical growth indicative of an ecto-poikilothermic, lizard-like, resting metabolic rate. However, it might also have retained a limited capacity for fast periosteal accretion in relation to local morphogenetic requirements as, for instance, the development of crests or trochanters.