Dark circles are typical in bone tissue - that is, the line of suspended growth - have been completely symptom cold-blooded dinosaurs, as previously thought, but the common denominator in all the major bone structure lizards, and some mammals, say scientists.
Since the discovery of the earliest fossils of the 19th century. Dinosaurs were considered cold-blooded reptiles, for whose normal existence were needed daily high temperatures that the animal would not give for a night of "cool." New discoveries of the 20th century have questioned this theory - scientists have found the remains of dinosaurs that lived in the polar latitudes, the rate of bone growth most of the species of large herbivorous sauropod dinosaurs, the hypothesis of their cold-blooded did not match.
With the head of a group of paleontologists Meike Keller, Autonomous University of Barcelona, has put into question one of the main arguments in favor of some of the ancient reptiles are cold-blooded - typical dark rings in the bones of dinosaurs, which are extremely rare in the remains of mammals.
As the researchers explain, the dark part of the bone indicate the period of slower growth of the organism, as well as reducing the rate of metabolism. Scientists believe that a large number of laps in the remains of dinosaurs indicates it is on their cold-blooded - ancient reptiles regulate their body temperature could not during cold snaps or winter, so the growth of their bones slowed periodically. It fitted in well with the fact that the annual layers similar to those found in the bones were other cold-blooded creatures - amphibians, fish and reptiles.
Keller and colleagues have questioned the validity of this hypothesis and comparing the structure of the bones of modern ruminant animals and dinosaurs, check it. Paleontologists have collected samples for this type of ruminant bones of 41 animals that live in tropical and equatorial parts of Africa, but also in parts of Europe with arctic and temperate climates.
It turned out that these lines are suspended growth also occurred in the bones of almost all studied ruminant mammals - from dwarf antelope in 3.2 pounds of weight and to the western giant eland (African antelope) in the 900 pound weight. Moreover, the annual growth rings in their bones were present in all climate zones with the same probability.
According to the researchers, their appearance is due to some adverse environmental conditions during periods when one or the other formed bone. In most cases, they turned out to be extraordinary or seasonal drought lowers the nutritional value of plants - the main source of energy especially for ruminants. The body of any animal adapts to a reduction in available resources and thus stops the growth, and as a result there is a bone in the dark ring.
It is believed Keller with her colleagues, their opening completely refute the possibility of using a suspended line growth as the main argument in favor of the hypothesis of ancient cold-blooded reptiles.