quarta-feira, 12 de março de 2014

Nova informação sobre Henkelotherium guimarotae da Mina da Guimarota (Leiria)

Figuration by Gerard Ciavatti

Deixamos aqui mais um resumo apresentado no encontro anual da Society of Vertebrate Paleotology que teve como objectivo o estudo do esqueleto pós-cranial de Henkelotherium guimarotaese. Kai Jäger e colaboradores da Universidade de Boon (Alemanha) e Chicago (EUA), com a utilização de novas tecnologias (e.g. CT scan), reveem a morfologia anatómica do mamífero Henkelotherium guimarotae proveniente dos sedimentos do Kimmeridgiano (Jurássico Superior) da Mina da Guimarota em Leiria. Este encontro teve lugar na cidade americana de Los Angeles no passado mês de Novembro. 

"The dryolestoid Henkelotherium guimarotae from the Late Jurassic of the Guimarota coal mine in Portugal is represented by a largely complete postcranial skeleton and fragmentary skull. Although the postcranium has been described earlier, several details could not be examined previously because they were hidden in the plastic matrix to which the skeleton was transferred during preparation. Here we used x-ray computed tomography (—CT) and virtual image rendering (Avizo) to further study the postcranium of Henkelotherium. Some previously inaccessible features of the articulated bones and unexposed bone elements are described. Contrary to earlier description, Henkelotherium shows a plesiomorphic condition like Dryolestes leiriensis in having individual radial and ulnar condyles on the anterior aspect of the distal humerus. Only an incipient trochlea is present on the posterior aspect of the humerus, with the ulnar condyle spiraling posteriorly to some extent. The scapula is also more plesiomorphic than previously assumed with a laterally flared rim on the posterior border of the scapula. In this regard it is similar to the scapula of such symmetrodontans as Zhangheotherium but more derived than symmetrodontans in having a larger supraspinous fossa. The previously unknown interclavicle and several unfused sternal elements have now been recognized through CT scans. The ratio of the sum of the lengths of the proximal and intermediate phalanges divided by the metatarsal length of digit ray 3 of the completely preserved left foot is 153.8%. This exceeds ratios of extant primates as well as terrestrial Mesozoic mammals. The caudal vertebrae show a length/width ratio similar to those of extant arboreal mammals without grasping tails. Several additional characters of hind limb and pelvis (e.g., the absence of a parafibular process, a slender femur with a long neck, slightly asymetrical distal femoral condyles) suggest a more derived posture, closer to that of Didelphisthan extant monotremes. Our new study has corroborated a previous hypothesis that Henkelotherium had an arboreal lifestyle."

Jäger, K., Luo, Z., Martin, T. CT Scaning and 3D image analyses of the postcranial skeleton of Henkelotherium guimarotae (Cladotheria, Mammalia) from the Late Jurassic of Portugal and its locomotor adaptations. Journal of Vertebrate Paleontology, Program and Abstracts, 2013, 147.

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