Humans may think they rule the world, but it’s beetles that really dominate it. In The Book of Beetles, editor Patrice Bouchard goes in-depth about these creatures that make up a quarter of the world’s animals. With 400,000 known species, these insects are about as abundant as they are interesting. This excerpt, which discusses the evolution of beetles and how they’ve adapted to changes around them in the past millions of years, is from the section “Evolution and Diversity.”
Evolution and Diversity of Beetles
The remains of the ancient beetle-like “Protocoleoptera” and true beetles are abundant in the fossil record, mostly as impressions in sedimentary rock or entombed in petrified tree sap called amber. Fossil Protocoleoptera are known from the Lower Permian rocks of eastern Europe, dating back about 280 million years. The insects were flattened, probably occupied tight spaces under loose bark, resembled the modern insect order of Megaloptera (alderflies, dobsonflies, and fishflies), and likely included precursors to several modern holometabolous insect orders. Protocoleopteran elytra had distinct ribbing and sculpturing resembling that of species in the extant family Cupedidae, but were less regularly sculptured and extended beyond the abdomen. Modern Coleoptera replaced the protocoleopterans by the Late Triassic (240–220 million years ago), when all four of today’s beetle suborders were present. Based on fossil evidence from Europe and Central Asia, the evolutionary lineages of all of the modern Coleoptera were established by the Jurassic (210–145 million years ago).
Amber secreted by conifers during the Jurassic suggests that these ancient trees were already under attack by wood-boring insects similar to modern bark beetles (Curculionidae). At least 60 beetle families have been found preserved in amber, most of which are attributable to tribes and genera that still occur to this day. Amber deposits with fossil intrusions formed in tropical forests and other ancient habitats are poorly represented in the fossil record.
Most fossil beetles from the Quaternary period (1.6–0.5 million years ago) are identical to modern beetles. Their remains are not fossilized, but instead were preserved among permanently frozen detritus, water-lain sediments, prehistoric dung middens, or asphalt seeps.
Mostly small and compact, beetles are well equipped to exploit most terrestrial and freshwater habitats. Beetles owe much of their success to the possession of elytra, allowing the effective concealment of soft membranes that are exposed in other insect groups. Whether beetles live on land or in the water, their elytra protect them from abrasion, desiccation, parasites, and predators. Between the elytra and abdomen is the subelytral cavity, an important adaptive feature used by both terrestrial and aquatic beetles. For example, desert species use the subelytral space to insulate the body from sudden changes in temperature and to prevent dessication, while some aquatic beetles use this space to capture and store oxygen in order to breathe under water. The ability of many beetles to fly also increases their chances to avoid predators, find food, locate mates, and colonize new microhabitats.
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This excerpt has been reprinted with permission from The Book of Beetles, edited by Patrice Bouchard and published by The University of Chicago Press, 2014.