13/10/2010
Agência FAPESP – Alguns dinossauros eram ainda maiores do que se achava. Um novo estudo concluiu que a cartilagem que conectava os ossos dos gigantes répteis era bem espessa, o que poderia acrescentar até mais de um décimo em sua altura.
A descoberta, publicada na revista de acesso aberto PLoS ONE, da Public Library of Science, tem implicações também em estudos futuros sobre a postura e a dinâmica de movimentos dos dinossauros.
Estudo indica que cartilagens dos dinossauros eram espessas o suficiente para acrescentar até mais de um décimo na altura dos gigantes pré-históricos (divulgação)
Casey Holliday, professor de anatomia na Escola de Medicina da Universidade do Missouri, nos Estados Unidos, e colegas compararam registros fósseis com a análise dos membros de parentes vivos dos extintos répteis pré-históricos.
“As extremidades de muitos dos ossos longos dos dinossauros, entre eles os ossos da perna, como fêmur e tíbia, são arredondadas, rígidas e não dispunham de estruturas importantes responsáveis pela articulação, como os côndilos, que são projeções ósseas”, disse o cientista.
“Isso indica que cartilagens muito espessas ocuparam os lugares dessas estruturas, formando as juntas. Essas partes, somadas, adicionavam uma altura significativa em algumas espécies de dinossauros”, completou.
De acordo com o cientista, o estudo fornece novos dados para ajudar a entender como e por que répteis e mamíferos construíram suas juntas com tamanha diversidade nas quantidades de osso e de cartilagem.
Holliday e colegas conduziram a pesquisa com avestruzes e jacarés, considerados alguns dos animais vivos mais próximos dos dinossauros, cujos membros são formados por de 6% a 10% de cartilagem. Foram analisados fósseis de tiranossauros, alossauros, braquiossauros e tricerátops.
Os cientistas obtiveram um “fator de correção de cartilagem” para determinar que o tiranossauro, por exemplo, era apenas um pouco maior do que se estimava. Mas o tricerátops e o braquiossauro podem ter sido mais de 10% mais altos. A diferença em altura, no caso do braquiossauro, seria de mais de 30 centímetros.
O artigo Cartilaginous Epiphyses in Extant Archosaurs and Their Implications for Reconstructing Limb Function in Dinosaurs
(doi:10.1371/journal.pone.0013120), de Casey Holliday e outros, pode ser lido em www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013120.
+++++
Cartilaginous Epiphyses in Extant Archosaurs and Their Implications for Reconstructing Limb Function in Dinosaurs
Casey M. Holliday1*, Ryan C. Ridgely2, Jayc C. Sedlmayr3,Lawrence M. Witmer2
1 Department of Pathology and Anatomical Sciences, School of Medicine, University of Missouri, Columbia, Missouri, United States of America, 2Department of Biomedical Sciences, College of Osteopathic Medicine, Ohio University, Athens, Ohio, United States of America, 3 Department of Cell Biology and Anatomy, School of Medicine, Louisiana State University - New Orleans, New Orleans, Louisiana, United States of America
Abstract
Extinct archosaurs, including many non-avian dinosaurs, exhibit relatively simply shaped condylar regions in their appendicular bones, suggesting potentially large amounts of unpreserved epiphyseal (articular) cartilage. This “lost anatomy” is often underappreciated such that the ends of bones are typically considered to be the joint surfaces, potentially having a major impact on functional interpretation. Extant alligators and birds were used to establish an objective basis for inferences about cartilaginous articular structures in such extinct archosaur clades as non-avian dinosaurs. Limb elements of alligators, ostriches, and other birds were dissected, disarticulated, and defleshed. Lengths and condylar shapes of elements with intact epiphyses were measured. Limbs were subsequently completely skeletonized and the measurements repeated. Removal of cartilaginous condylar regions resulted in statistically significant changes in element length and condylar breadth. Moreover, there was marked loss of those cartilaginous structures responsible for joint architecture and congruence. Compared to alligators, birds showed less dramatic, but still significant changes. Condylar morphologies of dinosaur limb bones suggest that most non-coelurosaurian clades possessed large cartilaginous epiphyses that relied on the maintenance of vascular channels that are otherwise eliminated early in ontogeny in smaller-bodied tetrapods. A sensitivity analysis using cartilage correction factors (CCFs) obtained from extant taxa indicates that whereas the presence of cartilaginous epiphyses only moderately increases estimates of dinosaur height and speed, it has important implications for our ability to infer joint morphology, posture, and the complicated functional movements in the limbs of many extinct archosaurs. Evidence suggests that the sizes of sauropod epiphyseal cartilages surpassed those of alligators, which account for at least 10% of hindlimb length. These data suggest that large cartilaginous epiphyses were widely distributed among non-avian archosaurs and must be considered when making inferences about locomotor functional morphology in fossil taxa.
Citation: Holliday CM, Ridgely RC, Sedlmayr JC, Witmer LM (2010) Cartilaginous Epiphyses in Extant Archosaurs and Their Implications for Reconstructing Limb Function in Dinosaurs. PLoS ONE 5(9): e13120. doi:10.1371/journal.pone.0013120
Editor: Andrew Allen Farke, Raymond M. Alf Museum of Paleontology, United States of America
Received: July 12, 2010; Accepted: September 6, 2010; Published: September 30, 2010
Copyright: © 2010 Holliday et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: Funding was provided by National Science Foundation (NSF) DDIG 0407735 (to L.M.W and C.M.H.) and NSF IBN-9601174, IBN-0343744, IOB-0517257 (to L.M.W.) as well as Ohio University Departments of Biological and Biomedical Sciences, Ohio University College of Osteopathic Medicine, and University of Missouri Department of Pathology and Anatomical Sciences. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: hollidayca@missouri.edu
+++++
