Insects and other invertebrates are preserved in a fossil state by a series of events that resulted burial in a suitable medium. Immediate burial for all the insect retains necessary; otherwise the body is softened and fall all its parts, often leaving only the wings. These break down more slowly and therefore can be stored on less favorable terms, why many specimens of fossilized insects consist only of the wings. Furthermore, fossil insects are not found in many sites or locations as most other arthropods.
They have found fossils of insects in about 150 locations around the world. Among the most important may be considered, Commentry, in the central part of France, where they were deposited in a lake of fresh water, in the Carboniferous period (300 million years approx.) Thousands of specimens that are more or less well preserved and are considered by some to be the oldest known insect. Another site of considerable importance is the limestone of Elmo, in the state of Kansas, USA., Where they have found so far about 10,000 aquatic insects and crutáceos admirably well preserved. The litigráfica Bavarian limestone and others like them, distributed mainly in Europe, have been invaluable to researchers material, but no deposit exceeds the wonderful wealth Baltic amber, in the coasts of Germany, to which the material will be referred for being insects more contemporary age.
Actually the first geological evidence of the origin of insects is still uncertain; They found a few fragments of small arthropods on a quartz Devonian (above the Carboniferous, 300 million years approx.) and a group of scientists classified them as Thysanura, small wingless insects body naked and often covered with scales, without a marked metamorphosis, but his true identity is dubious even when more is known of them. The same is true for three other fossils of the first Carboniferous period, consisting of some wings found in Czechoslovakia and Germany; the only thing that can be deduced is that then existed flying insects with well-developed wings.
From the next period (50 million years) onwards the entomofauna is much better known; it is already very advanced and includes several groups with analogies to some current orders of insects.
Carboniferous insects were gathered by the American paleontologist, Samuel Hubbard, in a large group called "Palaeodictiopteros", which has some similarities with the current Orthoptera (cockroaches, locusts and crickets); these ancient insects were medium and to our knowledge, all representatives had a pair of membranous lobes on the first thoracic segment, considered as indicators of the origin of functional wings. Unfortunately the metamorphic stages of them are known.
Other contemporaries of these giant dragonflies were the genre "Titanophasma" long and slender abdomen and narrow, membranous wings, almost as large as the above; Sorry no metamorfósicos states in any of the two groups, but were supposed to aquatic and simple metamorphosis. As at that time had still not appeared birds, nor any flying vertebrate, perhaps it was they who dominated the air undisturbed by any other animal.
Million years after the appearance of the first insect, when passed the Permian period (215 million years) various types of biting lice a few millimeters in length and some types of bugs and Neuroptera were already represented. Furthermore, also an odd order current like insects beetles, with well-developed wings, but most closely related to crickets, called "Protelytroptero" important for its complete metamorphosis type appears here.
Already in the Mesozoic era, the giant reptiles, entomofauna changed markedly, and none of the extinct orders survived after the insect started this período.entre representatives this time have certain Australian species related to crickets, they possessed in stridulatory wings great apparatus; This is the first record of producing sound of insects.
As at this time had not appeared birds, and other vertebrates that would produce ordinary animal sounds, you may estridulantes these insects and their relatives were the noisiest creatures of that time. And henceforth the insect fauna is very similar to modern, but still appear increasingly more families. In fact, the appearance of this fauna is so modern that if we see a collection of these specimens, stuck with pins in the usual manner, would not seem to us very different from our current collections, except that there would be no flower visitors like bees and bumblebees, because flowering plants appeared only in the following period, the Cretaceous (120 million years).
Although tertiary insects do not contribute to our knowledge of the evolution of the insect fauna as the most archaic, we report on the geographical distribution of families and genera, and allow us to secure gender and comparisons with existing species. To this period belong the numerous fossil insects amber Batic (so far 150,000 species have been collected approx.) Consisting of tiny crystalline sarcophagi within which ancient insects are in perfect conservación.El material is itself the fossilized resin an extinct species of pine (Pinitis succinifera), whose extensive geographic distribution encompassing northern regions of Europe; many insects and other vertebrates that inhabit these forests, were trapped in the resin of trees frequented; then the resin crystallized, fell to the ground froze, and was then swept away to the shores of the Baltic Sea, where they can now be found these incredible insect jewels. The Dr.Morton Weler, who has dedicated himself to the study of insects Baltic amber has managed to distinguish 43 genera of ants, of which 24 exist today. Moreover, he found that the social habits of these were as organized as those of the existing, with its castes, its workers and even in association with aphids; as this occurred approximately 60 million years ago., before the time of occurrence of most of the families of mammals that exist today, it is clear that the social organization of ants is far older than ours.
Of all the primitive insects we know today six different orders, all extinct thousands of years ago, except the group of blattidos (cockroaches), insects that have persisted over long geological periods without them being noticed an appreciable difference between primitive and species present; The small difference lies mainly in the arrangement of the ribs of the wings and possibly the size of the animal, as all fossil cockroach abundantísimos found are relatively medium proportions and none surpasses in size to some of our current tropical species .
A detailed study of the origin of insects reveals certain structural progressive changes through all geological periods; although this is still a matter of controversy among researchers, evidence indicates the important steps in the evolution of these animals have enough.
Morphological studies of existing insects prove that their first predecessors were apterous (wingless) as current Thisanura "silverfish" that are occasionally found in the libraries and shady sites. The appearance of the wings, side flaps likely modification was without a doubt the most significant change in the evolutionary line of insects.
Primitive flying insects could not flex the wings in position. The second important evolutionary step was the development of a joint that allowed them to collect their wings over the abdomen when not flying; the acquisition of this mechanism made slippery and given facilities to hide among the stones, rocks and plant detritus.
The third important evolutionary change was to achieve a more complete metamorphosis guy larval and nymph stages. Since then, they have not operated such major changes.
The insect fauna of our times is but a small part of all who lived 350 million years ago and survived all that time without undergoing changes as marked as in other living beings, but have adapted beautifully to support the full range of conditions on earth, and hopefully they have acquired specializations and adaptations that we do not fully understand. The degree of development of insects is extremely variable and difficult to measure by human standards. It is well known by all that many species of ants, bees and termites social trends, show a high degree of efficiency in their laborious constructions, moved by some inexplicable force defined as instinct, if not by powers of reason and intelligence.
Much remains to investigate the phylogenetic evolution of insects. While it is true that biology-aided with the discovery of 14- carbon has made considerable progress chronological. The fossils of many insects that lived in distant geological periods many millions of years of human era, are eloquent witnesses of the many vicissitudes through which they passed on incompatible media for any other animal species.
To reconsider and recognize the chronological priority of insects in relation to us, that is, all that long time elapsed before the appearance of man on earth, which witnessed, is in the eye of the biologist, in a sense, shameful our childhood in the table of geologic periods.
Notes on the origin of insects by Dr. Alvaro Jose Negrett. F.
INSECTS. Copyright 1963, Unites States Department of Agriculture-Washinton DC
NATURAL HISTORY. Geology - (Paleontology). Institute Gallach, Sixth Edition-Barcelona
Eduardo Hernández Pacheco. Fossils and fossilization.
THE INSECTS. Collection of Nature Life in Spanish-Offset Multicolor, SA 1968 Mexico-DF