school energy&environment

Stories of daily living

The study of fossils, organisms that died millions of years ago, sometimes offers incredible surprises with the discovery of organisms struck by death during their daily activities. These findings are extremely precious for the reconstruction of the way of life, they offer us the possibility to observe, in a surprisingly vivid manner, some scenes of daily living, at times cruel, at times gentle and moving. In a cave in Mount Generoso, near the frontier between Italy and Switzerland, near Chiasso, a cave was discovered in which a group of cave-bears had hibernated : it is possible to see the “nests” these large animals had dug in order to be more comfortable and also traces of predation on their “room-mates” that had died during the winter, or perhaps due to a too deep sleep, small skeletons of cubs that perhaps had died at the time of their birth, which took place, as for modern-day bears, during the winter sleep. Nests and eggs of reptiles, have sometimes been found near to each other, to testify a kind of nursery, at times near the skeletons of cubs. The presence, that is still not completely confirmed, of adult individuals near the nests, shows that also large reptiles dedicated parental care to their offspring. In Holzmaden, in Germany, a perfectly preserved skeleton of a female ichthyosaurus (Stenopterygius) carrying embryos was found, and she was surrounded by other cubs who had already been born: an unlucky prehistoric mother who died giving birth to her cubs. In the Gobi desert a specimen of Baluchiterium was discovered, a mammal that was over 5 m tall of the Oligocene Epoch: from its position, standing on its legs, it is supposed that it must have fallen into a thick muddy deposit from which it tried to free itself in vain. At Rancho La Brea, near Los Angeles in California, during the Pliocene Epoch there were tar lakes in which numerous animals got trapped, probably as they fled from some predator. From the black mass today, perfectly preserved skeletons of sabre toothed tigers (Smilodon, the gruff Diego in the computer-animated film “Ice Age”) and gigantic quaternary elephants from North America, Archidiskodon imperator, have emerged. In Bereskova, in Siberia, a perfectly preserved mammoth was found trapped in the frozen ground, between its teeth there were traces of his last meal – 25,000 years ago the animal had fallen into a crevasse in the ice and remained trapped within, due to the severe fractures caused by its fall. On the shell of a Placenticeras ammonite, of the Cretaceous Period, traces of the teeth of a large sea predator, the Mosasaurus, were found. Evidently ammonites were one of their favourite foods, in fact, in the stomach of these enormous sea reptiles numerous remains of these cephalopods have been found. The Eocene deposit of Mount Bolca, near Verona, is famous for the splendid fish specimens. These instead, tell the story of a terrible catastrophe, an eruption that heated the water of an internal lagoon near a coral barrier, causing the sudden death of thousands of organisms. One of the latest discoveries of these scenes of life of the past was brought to us, a few months ago, from China. In sediments dating back 130 million years, the skeleton of a mammal was found, the Rapenomamus robustus, the size approximately of a big cat, about sixty centimetres long, weighing approximately 7 kg , in whose stomach, the skeleton of about 13 cm of a Psittacosaurus dinosaur cub was found. The Psittacosaurus dinosaur was a herbivorous dinosaur, about two metres long when fully grown, with a robust beak, similar to that of a parrot. The well-fed and full up predator was surprised by a volcanic eruption that covered it with ashes together with its small victim. Besides being a proof of life, these fossils show an ecological picture that is very different from the former theories that were hypothesized. It had always been believed in fact that the mammals in the entire Mesozoic Era had been timid and shy, always escaping the terrible predator reptiles (some have hypothesized that our innate fear of snakes derives from this ancestral memory…). However this finding proves that predators were to be found also among mammals. The discovery, near an even larger relative, the Rapenomamus giganteus, that weighed about twice its weight and presumably had similar predatory habits, indicates that competition with mammals was not always to the disadvantage of the latter. Paleontology, therefore, even though it is a study of the organisms of the past, enables us to reconstruct scenarios of natural environments with their inhabitants, their struggle for life and their habits in a clear and at times surprising manner. Each one of these scenarios then fit into the large complex puzzle of the history of life on the Earth, enabling us, with every new discovery, to understand our planet better.