Math   Science   Chemistry   Economics   Biology   News   Search

> The Evolution of Turtles Issue: 2009-3 Section: Math




The first reptiles appeared in the Paleozoic era, probably in the Carboniferous period (345 million years ago), from a group of primitive amphibians that had already left the liquid element. These beings had a stumpy body with a strong skeleton (the skull was composed from few thick bones, without openings). They stirred the water with their body and their tail, partially crawling with the abdomen.

The anatomical structure that characterizes them is one of the most important examples of adaptation and the probable cause of their evolutionary success. In fact, many groups of reptiles and vertebrates disappeared from the evolutionary climax around 65 million years ago, perhaps because of a geological or climatic contortion, due to the detachment of the first terrestrial plates from the Pangea that has resulted in the current form of the continents. The elevated biological specialization of the reptiles, that until then had been their point of strength made them particularly vulnerable both from the point of view of the adaptation to the new climate and to the consequent changes of feeding. It was necessary to all the biological organisms to race to the shelter choosing some sources of food alternatives, or to suit for the new environmental conditions. It was almost impossible to carry out such a mechanism, so only a few specialized organisms trophically independent could overcome such evolutionary barriers. As a result they became the ‘gentlemen’ mammals of the earth, tearing its scepter from the reptiles. These reptiles abdicating the predatory diet and passing in great majority to a vegetarian or omnivorous diet, additionally to the development of a thick caress, reached some ideal conditions that favored their survival.

The reptiles have suffered an initiated prodigious evolution in the Carboniferous period, around 280 million years ago, when a group of amphibians left the swamps and the marshes assuming aquatic habits less and less and eventualy becoming earthlings. In fact, the swamps were the ideal habitat for a great number of species, increasing the food competition. The abandonment of the water probably provoked the development of the first eggs with hull, an essential footstep to assure the development of the embryo and to protect it from dehydration. Another characteristic of the eggs, the membranes’ amnios, chorion and allantoide, made turtles the winners of the evolutionary battle. Today turtles are classified in two principal categories: the Cryptodira and the Pleurodira based on the position of attack of some skull muscles. In 1970 the palaeontologist Eugene Gaffney conducted the first systematic study on the evolution of these reptiles and claimed that found fossils whose formation goes to 150 million years back, almost all belonged to one of the two classes. A few years later, the study conducted by Juliana Sterly, in Argentina, on a hull and a skull fossils recently found in the Latin country, discovered that they didn't belong to the Cryptodira, but instead to the Pleurodira. The found sample that dated between 160- 140 million years ago, was identified with the name of Condorchelys antiqua.

This was a further evidence in favor of the hypothesis that these first two groups would be younger than 60 million years, compared to what was believed a little time ago.

If this hypothesis is correct, the modern turtle would have needed much less time to evolve than till now held.