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Beetles are of the insect order called Coleoptera. They have inhabited our planet Earth for an extremely long time. The earliest known beetle fossils date to the Permian period (291.5-253 million years ago). A.G. Ponomarenko mentions some important points about Permian beetles in this excerpt of a report titled Paleontologicial Discoveries of Beetles. The essay was published by the Palaeontological Institute, RAS in March 2003. Ponomarenko says:
"Beetles appear on pages of the geological record in the Permian Period nearly 300 mya. We cannot succeed in the study of the very origin of beetles. No transitional forms between them and other insects with a complete metamorphosis are known. Apart from that the study of early stages of the evolution of beetles is hampered because of the two groups that are not related but are very similar to beetles in the structure of elytra of insects - Protelytroptera and some cockroaches. The most ancient discoveries of beetles are indicated for the deposits of the Asselian layer of Niedermoschel locality in the vicinity of Mainz, Germany (Addresses of localities are given in the list of localities of fossil beetles), of the most ancient layer of the Permian, in Germany (Huerschemeyer, 1999). But neither the drawings nor descriptions of those have been made yet, so that their true nature remains unknown. The most ancient described beetles come from deposits of the next Sakmarian layer (sometime an even younger Artinian (Artinskian) layer is indicated) of Boskovice graben in eastern Czechia. Discoveries of beetles there are quite numerous and diverse. They have been described in 8 genera of the family Tshcardocoleidae."
[Note - The Permian period was 291.5 - 253.4 million years ago. The Sakmarian (288.5 - 283 million years ago) and the Artinian or Artinskian (283 - 277 million years ago) were subperiods of the Permian.]
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Ponomarenko points out that the venation (arrangement of veins) pattern of their cellular elytra (wing structure) resembles that of forewings of ancient insects called megalopterans. But he also mentions that In other structural characteristics, they are more similar to modern beetles. For example, the prothorax (anterior part of the thorax) is moveable. [Note - The prothorax has the first pair of legs.]
Other similarities that Ponomarenko mentions are:
highly developed cryptosternic metathorax (hind part of thorax)
[Note - The thorax is the middle part of the body of an insect.]
transversal posterior coxae incorporated in the thorax
[Note - The coxae is the first segment of the leg of an insect or other arthropod.]
schlerotized (hardened) basal sternites (sternites on the bottom) of abdomen and apical ones (ones on the top of the body) drawn inside
[Note - The ovipositor is the tube with which female insects lay eggs.]
The main difference between them and later beetles is that the elytra reaches far behind the apex is not able to fold. These beetles are especially similar to the Cupedidae family of recent beetles.
Older beetle fossils have been found in the deposits of the Asselian ( 291.5 - 288.5 million years ago) layer of Niedermoschel near Mainz, Germany. However, drawings of them have not been made, nor have they been described in published paleontological writings. [Note - The Asselian was the first subperiod of the Permian.]
By the end of the Permian period, the elytra (structure of wings) had evolved to a point that it was very much like the beetles of today. Their forewings were converted into a light and strong double-layer formation. The upper surface of it was formed by dilated veins, dislodged cells to empty narrow columns called columellae. These changes are obvious in late Permian beetles. There are two ways in which this process takes place. In one line of beetles, the cupedoids ((beetles resembling the later Cupidae) veins of pre-elytrons (what evolved into wing structures) are organized into a mechanically perfect lattice structure and veins replace the cells, converting fields of the wing structure into punctuated wings.
In another beetle lineage, the replacement in schisophroids occurs quickly. It is on the basis of little specialized venation.
Ponomarenko states an important point about a mutation of size that the Permian beetles had at the end of the Permian period. Beetles became 2 to 3 times smaller than before. Beetles became mostly aquatic; few terrestrial beetles remained. However, beetles would eventually return to the land. I will discuss that in future postings.
At this stage, beetles had spread to most parts of the world. Late Permian beetle fossils have been discovered in North America, Europe, Asia, Brazil, South Africa, and Australia.

Neal Robbins

P.S. Beetles are of the kingdom Animalia, the phylum Arthropoda, and the class Insecta. As I mentioned, the order of beetles is Coleoptera. I will not go into a listing of the suborders, families, genera, and species. However, I will mention this. Over 300,000 species of beetles have been described. There are more species of beetles than of any other members of the animal kingdom.

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Fossil - Subfossil Beetles

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