The Fossil Record of Insect Diversity and Disparity
The fossil record of insects documents a high proportion of modern higher-level taxa (67% for families), although this capture rate drops off considerably for lower-level taxa. This record is Lagerstatten-driven, and is deployed by complementary, parallel body- and trace-fossil components that reveal a wealth of taxonomic and ecological detail. A family-level analysis of this record shows that past insect diversity is governed by low origination and extinction rates, both decreasing toward the Recent. This feature, in addition to prolonged taxal durations, has conferred on insects significant immunity from extinction. Nevertheless, the most profound event in insect history, the end-Permian extinction, decimated the Paleozoic Insect Fauna but allowed survival of lineages that gave rise to the Modern Insect Fauna of the Mesozoic and Cenozoic. Past insect ecomorphologic disparity can be documented as feeding attributes from the trace- and body-fossil records. Three such attributes are assessed in the insect fossil record: mouthpart class, functional feeding group, and dietary guild, which collectively are divided into 74 distinctive categories. A plot of durations of these categories discloses a distinct trend of ecomorphologic disparity peaking considerably earlier than taxonomic diversity, indicating that taxonomic diversification eventually partitioned earlier-created, major ecological roles. Entry into each of these categories has occurred iteratively and convergently between and within the Paleozoic and Modern Insect Faunas. Insect history is divided into five phases. Inidially there was (1) colonization of land in the earliest terrestrial ecosystems, followed by (2) taxic radiation and ecological penetration of plant tissues by numerous clades during the Late Carboniferous and Permian, a process that was curtailed by (3) the terminal Permian extinction. The (4) subsequent emergence of the Modern Insect Fauna in the Triassic and its rebound during the mid-Mesozoic was driven by ecological expansion into freshwater ecosystems, emergence of the parasitoid guild, and recolonization of new seed-plant lineages by phytophagous holometabolans. This process continued as (5) modern associations were established as Cretaceous angiosperms became dominant and mid-Cenozoic temperate grasslands expanded. These data indicate that insect success is attributable to intricate, multiplicative, and probably extinction-buffered associations with other organisms, especially vascular plants.
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