The scenario depicting the reduction and elimination of limbs on the insect abdomen may be paralleled by the history of the evolution of the number of insect wings. All modern winged insects bear two pairs of wings: forewings on the second thoracic segment and hindwings on the third thoracic segment. The invention of wings was a major event in the evolution of insects, catalyzing their radiation and domination of terrestrial habitats.
Insect wings are thought to have evolved only once, early in the insect lineage (the origin of insect wings will be discussed in more detail in Chapter 6). The insect fossil record suggests that, in the primitive state, wing-like structures formed on all of the trunk segments. Fossils of early insects from the Carboniferous (circa 325 Ma) include aquatic larval forms with seg-mentally iterated, wing-like projections that may have played a functional role in respiration. More recent fossilized mayfly nymphs had larger wing-like structures on thoracic segments
Ubx Dll, limb formation
Díptera (fruit flies)
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