Biomechanics is the study of the structures, motions and mechanical properties of natural organisms. It is applied in different fields to develop new instruments or devices, such as engineering, medical applications, veterinary, etc... An example is the study of the walking abilities of geckos, which brought the scientists to look at the fingers of these lovely reptiles. The fingers are covered with microscopic hairs, or spatulae, each of these hairs generates adhesion force, and the sum of all the microscopic adhesion forces is more than the weight of the animal, allowing it to climb upside down on our ceilings. This application is being developed to produce gloves able to make a man climb on the glass.
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| Here is a photograph of a gecko on a glass. |
In palaeontology the biomechanics is mainly used to estimate the forces acting on the bones while the animal was alive, with the aim to reconstruct its ecological niche and as method of comparison. Biomechanics is mainly based on Finite Element Analyses. FEA is a computer process that allows the simulation of the application of a force over a 3D model of an object. The model of the bones, in the case of palaeontology, is divided into microscopic cubes then it is imported into the software. The division in cubes is necessary to allow the computer to perform simple calculations. For each cube of the model, there are six vectorial equations per instant of the simulation, and each model is composed of thousands, or even millions, of cubes. The entire process could take weeks of simulations. The output of the simulation is the stress under which the object is subjected by the force applied. When the stress surpasses the value of resistance of the material of the object, the object breaks. This entire process saves lots of costs, since different simulations can be run on the same object virtually breaking it infinite times. The use of computer simulations in palaeontology is the only way to estimate these forces, since the original material components of the bones have been replaced during fossilization, in fact, if we would use a real fossil to perform the analyses we would obtain results coinciding with the properties of the rocks which compose the fossil, with no real meaning.
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| Simulation of an oscillation of a beam. The brighter the color the major deformation is affecting the beam |
Why should we be interested in breaking sauropod dinosaur bones?
Sauropoda is a clade of dinosaurs that evolved during the Late Triassic, surviving to the latest Cretaceous, being among the most successful animal that ever inhabited Earth. Sauropod dinosaurs are one of the most intriguing and famous dinosaurs, characterized by their long neck, tails, and enormous bodies. These animals have achieved the largest dimensions among terrestrial vertebrates (Curry & Wilson, 2005). Only a few animals have achieved dimensions comparable to little/medium-sized sauropods: some species of hadrosaurid (duck-billed) dinosaurs and a handful of species of mammals. A comparable size nowadays would be an airliner of middle dimensions, and still, the masses of airliners would be smaller than the ones of some species of sauropod dinosaurs.
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| Estimated masses of a moose, an elephant a Tyrannosaurus rex, and different sauropod dinosaurs compared to a Boeing airliner. |
Sauropod remains have been found in every continent and they reached the greatest diversity during the Late Jurassic, when different lineages were sharing the same environments. Despite at first sight the sauropod dinosaurs may seem all similar, sharing the elongated neck, tail and round bodies supported by columnar limbs, their shapes changed a lot during their evolution and created different lineages. The most diverse group and the longest to survive have been the Titanosauria, a group of sauropod dinosaurs that evolved from the Macronaria, during the Late Jurassic and survived to the end of the Mesozoic. This group of animals has achieved the largest dimensions among terrestrial vertebrates, with estimated masses more than 50 tonnes. The Macronaria, from which descends all the titanosaurian sauropods, includes one of the most famous dinosaur: Brachiosaurus. These taxa of sauropod dinosaurs are estimated to have maintained the neck in an inclined position, between 30° and 45°. Among Macronaria have been found also the smallest sauropod dinosaurs, like Europasaurus holgeri Sander et al., 2006, a relative of Brachiosaurus that inhabited Europe during the Late Jurassic, and the littlest sauropod known, Majarosaurus dacus (von Nopcsa, 1915), an insular dwarf titanosaur that inhabited Europe during the Late Cretaceous, that is estimated to weigh around 900kg as an adult. Though the most famous group of sauropod dinosaurs may be considered the family of Diplodocidae, with Diplodocus and the renowned Brontosaurus. This family was most diverse during the Late Jurassic, but went extinct during the Early Cretaceous. The neck of these animals shows different adaptations compared to other sauropods, and it is estimated that the neck was held in a near-horizontal position, parallel to the ground, opposite to an elongated tail. The tail was elongated, counting up to 82 elements, and a joint study of engineers and paleontologists (Myrvhold & Currie, 1997) showed that the tail was able to reach supersonic speeds, hypothesizing the use as defensive weapon or sound maker device.
These animals are extremely fascinating, having survived for more than 150 million years, being subjected to the pressure of natural selection and evolved in the largest terrestrial animals as well as evolved in insular dwarf forms. We, as a team, are interested to investigate how their skeleton was able to sustain such large bodies, and how the shape of the bones may have helped them be so successful in their evolutionary history.
References:
Curry Rogers, K., Ericsson, G.M., 2005. Sauropod histology. In: Curry Rogers, K.A.,Wilson, J.A. (Eds.), The Sauropods, Evolution and Paleobiology. University of California Press, Berkeley, pp. 303–326.
Lacovara, K., Lamanna, M., Ibiricu, L. et al. A Gigantic, Exceptionally Complete Titanosaurian Sauropod Dinosaur from Southern Patagonia, Argentina. Sci Rep 4, 6196 (2015). https://doi.org/10.1038/srep06196
Myhrvold, N., & Currie, P. (1997). Supersonic sauropods? Tail dynamics in the diplodocids. Paleobiology, 23(4), 393-409. doi:10.1017/S0094837300019801
Sander, P., Mateus, O., Laven, T. et al. (2006). Bone histology indicates insular dwarfism in a new Late Jurassic sauropod dinosaur. Nature 441, 739–741. https://doi.org/10.1038/nature04633
Nopcsa, F (1915). "Die Dinosaurier der siebenburgischen Landesteile Ungarns". Ungar. Geol. Reichsanst. 23: 1–26.
Photographs sources:
https://upload.wikimedia.org/wikipedia/en/1/14/Gecko_on_window.jpg
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