| Palæos: |  |
Insecta |
| INVERTEBRATES | Coleoptera |
| Page Back | Unit Home | Page Next | Page Up | Unit Up | Cladogram |
| Palæos: | |
Insecta |
| INVERTEBRATES | Coleoptera |
| Page Back | Unit Home | Page Next | Page Up | Unit Up | Cladogram |
Asked by a theologian what could be inferred about the mind of the Creator from a study of His works, the British scientist J.B.S. Haldane dryly replied, "an inordinate fondness for beetles."
The beetles are the largest single order of insects. There are over a 360 000 known species, but probably several million more not known. In size they range from 0.25 to 0.3 mm (featherwing beetles - family Ptiliidae) to over 150 cm for the giant Goliath and Hercules beetles (Scarabaeidae), which in size are the largest living species of insects. Although the majority of species are herbivores, there are also others that are predators, fungivores, or are parasites. They inhabit every terrestrial ecosystem on earth, from rainforest canopies to alpine mountains, from lakes and rivers to hot dry deserts.
The term Coleoptera - from koleos - sheath, and pteron - wing - refers to the nature of the front pair of wings, which have metamorphosed into a hard protective casing for the rear (flight) pair. These are referred to as elytra. Among all the insects only beetles have these specialized fore-wings. There are other more technical ways to define what a beetle is, but I leave it to the enthusiastic web-surfer to pursue the necessary links.
The unique elytra may well be the reason for the beetles success. By protecting the delicate hind wings and the dorsal (upper) surface of the abdomen, they allow the beetle to exploit narrow passages such as, leaf litter and under bark which are rich in food and yet at the same time safe from predators.
Four suborders are recognized. These are each 
quite distinct, and authorities still disagree as to the actual relationships
between them. It is likely that if we were talking about vertebrates rather than insects, each suborder would be
awarded ordinal status.
Archostemata would
seem to be the earliest lineage, from which the other types evolved.
This group contains several families of beetles, most associated with wood..Archostemata
page
Adephaga includes
ground beetles, tiger beetles, predacious diving beetles, and whirligig
(aquatic) beetles. Most forms are predators. Adephaga
page
Polyphaga
is by far the largest suborder, containing 85% of the known species, including
rove beetles, scarabs, stag beetles, metallic wood-boring beetles, click
beetles, fireflies, blister beetles, mealworms, ladybirds, leaf beetles,
longhorn beetles, and weevils. Mostly herbivores. Polyphaga
page
Myxophaga is a small
suborder, containing less than 100 known species of small or tiny size,
mostly associated with aquatic habitats, drift material, or interstitial
habitats among sand grains.
Myxophaga
page
The Coleoptera date from the Permian period. Several Permain specimens are known from Russia
and Australia. As these two landmasses were at the time on opposite
ends of Pangea
it can be assumed that beetles very early attained world-wide distribution.
Four superfamilies are known from the Permian elytra, Cupedoidea, still
with remnants of venation (see photo on left for a recent member of the
family Cupedidae), Curculiopsidae, with rows of tubercles, Schizocoleridae,
with a single longitudinal groove, and Permosynidae, with striae (fine longitudinal
lines) (the latter three families are extinct).
The four living suborders of beetles diverged from one another in the Permian and early Triassic. These quickly diversified, and hundreds of species are known from the Mesozoic, and thousands from the Cenozoic. this however is only a tiny fraction of the millions of species of beetles that lived, evolved, and died throughout prehistoric time but never became preserved as fossils.
 |
Links | |
Insects |
