Biogeography of Therevidae
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Biogeography deals with the distribution of taxa around the planet in space and time, and the factors influencing this distribution. It includes understanding how modes of dispersal have affected which taxa are cosmopolitan (found worldwide), which are endemic (only found in limited regions), and which have disjunct (widely separated) distributions that may be explained by larger processes such as plate tectonics (changing position of landmasses over geologic time due to shifting of the earth’s plates), landscape and climatic features that provide opportunities and corridors of dispersal, and catastropic changes to an environment, such as volcanic eruptions. Combining the evidence from biogeography and that of genetic relationships among taxa through phylogenetic studies of their "family tree," scientists are able to make hypotheses about the when, how, and why taxonomic groups are distributed as we find them today or in the fossil record.
In the present time, therevids have been found in all of the biogeographic regions (Afrotropical, Australasian, Nearctic, Neotropical, Palearctic, Oceanian, and Oriental) except the Antarctic. The family is thought to have arisen in the Jurassic when the continents had coalesced into the supercontinent of Pangea, about 200 million years ago. Fossil evidence indicates that both the Therevidae and its sister family, Scenopenidae had already differentiated by the Upper Jurassic. This is consistent with the likely Triassic origin of the Brachycera and rise of other asiloids in the Jurassic (Gaimari and Irwin 2000).
Read more about biogeography:
New York University biogeography website
University of British Columbia: Explore the World's Biomes
UCMP: Plate Tectonics and Continental Drift
Link for Pangea: Paleomap Project