Living beetles and their grubs are the largest taxon of organisms; they make up 40 percent of all insects. Adult beetles are characterized by having two sets of wings; the forewings are armored to cover and protect the rear pair. Beetles generally are flat insects with a hard exoskeleton and jaws designed for biting and chewing.
Most winged insects can be diagnosed by examining the telltale vein pattern of their forewings. This presents a problem with beetles because these insects replaced their forewings with an armored shell. As a result, the fossil record of beetles, although extensive, is sometimes difficult for paleontologists to interpret. Fortunately, the exoskeleton and armor plating of a beetle often is decorated with pits or sculpted surfaces; this gives researchers visible patterns that can be used to compare and associate extinct forms of these creatures.
Ancestors of the beetles appeared in the Early Permian fossil record of Chekarda, in the Ural Mountains of Russia, and in the Czech Republic. The veined forewings of those protobeetles had not yet been completely transformed into an armor shield; instead, the forewing consisted of a long, narrow, leathery shield that was longer than the abdomen. The veins of the forewings made up a distinct pattern of tiny square cells arranged in parallel rows along the insect's length. More fossils of early beetles are found in Late Permian deposits across the supercontinent Pangaea: Specimens have been found in present-day Africa, Australia, Europe, and
Asia. These specimens show some reduction in the leathery, pitted forewings seen in Early Permian examples. The first true beetles, whose veined forewings had been replaced by hardened, veinless forms, lived in the Late Triassic. It is likely that the true beetles first appeared earlier in the Triassic Period, but the fossil record of insects from the Early Triassic has not yet provided evidence of any such transitional forms.
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