Los esqueletos de dinosaurios completos y articulados con cuello y cola largos, exhiben una postura en la cual la cabeza y el cuello se curvan sobre la espalda del animal. Esta postura, que aparece en el Archaeopteryx, ha fascinado a los paleontólogos por más de 150 años. Se denomina en lenguaje coloquial “postura del ciclista” o en lenguaje científico “postura opistótona”. Esta última definición proviene de uno de los síntomas más conocidos del tétanos, tanto en humanos como en animales y suele ser el resultado de una deficiencia vitamínica, del envenenamiento o de daños en el cerebelo.
Un síndrome similar se empezó a discutir para los vertebrados fósiles hace 100 años, pero no logró una general aceptación hasta que en 2007 la “hipótesis opistótona” fue planteada de nuevo y recibió mucha atención por parte del público y la comunidad científica. Ahora, cinco años después, los científicos han re-evaluado la hipótesis, por medio del examen de uno de sus iconos emblemáticos el dinosaurio bípedo Compsognathus longipes del "Archipiélago Solnhofen" (Alemania), un dinosaurio terrestre de hace 150 millones de años que fue atrapado en una fosa inundada en una laguna tropical.
Según los investigadores, la postura opistótona se preserva cuando el vertebrado terrestre queda embebido en agua inmediatamente después de su muerte sin que haya un transporte sustancial del cuerpo. Se hicieron experimentos con cuellos de gallina sumergidos en agua, que se arquearon espontáneamente más de 90º, aumentando incluso el ángulo a lo largo de los meses. Una cuidadosa preparación y disección demostró que el ligamento que conecta las vértebras por su cara superior Ligamentum elasticum era el responsable del curvamiento de los cuellos en las gallinas.
Los investigadores concluyen que "un potente Ligamentum elasticum era esencial para todos los dinaosurios de cuello y cola largos. Les ayudaba a ahorrar energía en su forma de vida terrestre. Tras su muerte, y sumergidos en agua, la energía almacenada a lo largo de las vértebras, era lo bastante fuerte como para doblar la espina dorsal hacia atrás, tanto más cuanto más y más músculos y otras partes blandas del esqueleto se iban deteriorando". Por tanto la biomecánica y no la agonía es la que rige la extraña postura pot mortem de un esqueleto en un fosa inundada”.
More or less complete and articulated skeletons of dinosaurs with a long neck and tail often exhibit a body posture in which the head and neck are recurved over the back of the animal. This posture, also known from Archaeopteryx, has been fascinating paleontologists for more than 150 years. It was called "bicycle pose" when talking with a wink, or "opisthotonic posture" in a more oppressive way of speaking. The latter alludes to an accessory symptom of tetanus, well known in human and veterinarian medicine, and usually, is the result of vitamin deficiency, poisoning or damage to the cerebellum.
A syndrome like that was discussed for the first time about 100 years ago for some vertebrate fossils, but the acceptance was low until 2007, when the "opisthotonus hypothesis" was newly posted and received much attention in the public and the scientific community. Now, five years later, the scientists have re-evaluated the hypothesis" and examined one of its icons, the famous bipedal dinosaur Compsognathus longipes from the "Solnhofen Archipelago" (Germany) a 150-millions-years-old land-living dinosaur which was embedded in a watery grave of a tropical lagoon.
According to the researchers the opisthotonic posture in a fossil requires that the terrestrial vertebrates must have been embedded immediately after death without substantial transport. Experiments were carried out with chicken necks, immersed in water that spontaneously arched backwards for more than 90° increasing the angle during some months after. Thorough preparation and dissection combined with testing revealed that a ligament connecting the vertebrae at their upper side, called the Ligamentum elasticum, was responsible for the recurved necks in the chickens.
"A strong Ligamentum elasticum was essential for all long necked dinosaurs with a long tail, helped them saving energy in their terrestrial mode of life. Following their death, at which they were immersed in water, the stored energy along the vertebra was strong enough to arch back the spine, increasingly so as more and more muscles and other soft parts were decaying" conclude the researchers. Therefore, biomechanics is ruling the postmortem weird posture of a carcass in a watery grave, not death throes.
Tomado de/taken from AlphaGalileo
Publicación científica/Research paper
Re-evaluating Moodie’s Opisthotonic-Posture Hypothesis in Fossil Vertebrates Part I: Reptiles—the taphonomy of the bipedal dinosaurs Compsognathus longipes and Juravenator starki from the Solnhofen Archipelago (Jurassic, Germany)
Achim G. Reisdorf and Michael Wuttke
doi: 10.1007/s12549-011-0068-y
Abstract
More or less complete and articulated skeletons of fossil air-breathing vertebrates with a long neck and tail often exhibit a body posture in which the head and neck are recurved over the back of the animal. Additionally, the tail is typically drawn over the body, while the limbs have a rigid appearance. In palaeontological literature, this “opisthotonic posture” of such fossils still requires a causal interpretation in an etiological context. According to this hypothesis, there is a presumption of a cerebral disorder generating perimortem muscle spasms that are preserved by rapid burial or other sequestration of a skeleton in the fossil record. We re-evaluate this “opisthotonic posture hypothesis” by analysing the non-avian theropods Compsognathus longipes and Juravenator starki from the famous South Franconian plattenkalks of the Upper Jurassic Solnhofen Archipelago. Decay experiments with the extant domestic fowl Gallus gallus L. and analysis of the theropods’ constructional morphological constraints reveal that the opisthotonic posture is not a peri- but a postmortem phenomenon. By analysing the timeline of decomposition, it is possible to recognise different stages of decay, depending on the varying decay resistance of soft tissues. Adipocere formation must have blocked further decay until embedding was completed by minimal sedimentation. Analyses of the palaeoenvironment of the basins of the Solnhofen Archipelago show that the conditions of deposition of individual basins cannot be considered to be similar, even inside the same time frame. Therefore, a generalised approach of looking at the depositional setting must be excluded. Assumptions by Faux and Padian (2007) that the accepted palaeoenvironmental reconstruction of the Solnhofen Fossillagerstätte has to be questioned in the light of the opisthotonic posture hypothesis enforce the need for a review of palaeoecological factors of the Franconian Plattenkalks from a taphonomic perspective.
