by John Terbot
Gondwana, the ancient supercontinent consisting of most current landmasses in the Southern hemisphere, is the geographic origin of parrots. This is a diverse order of birds comprised of 3 families, 88 genera, and 386 species (http://www.zoonomen.net/avtax/psit.html). They are currently present on most Southern-hemisphere landmasses (aside from
To appreciate the speciation of parrots, and other Gondwandan organisms (those originating in the Southern hemisphere), an understanding of the separation of Gondwana due to plate tectonics is needed. For brevity, modern names for landmasses will be used, however it is important to remember that over geological time the coastlines and amount of emergent land varies. Gondwana (South America, Africa,
Nestor notabilis, one of the endemic parrots found on
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The first lineage of parrots to diverge was Strigopidae, a family found only in
The Australian split from Antarctica around 40 Ma corresponds with a major divergence in parrots between mostly Australasian and Indo-Malaysian taxa and those from neotropical and afrotropical regions. The neotropical, Arini, and afrotropical, Psittacini, lineages separated from each other around the Eocene-Oligocene boundary, indicating a relation to the rapid cooling of this time (Cox 2000) and a potential origin from an Antarctic population that was pushed North by expanding ice sheets (Schweizer et al. 2011).
Other parrots found on the African continent, genus Agrapornis, likely represent further dispersal from
These Westward dispersal events of parrots occurred around the time that the modern geographic placement of
Head of a lory, note the brush-tipped tongue that allows for the use of nectar. ?xml:namespace>
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Along with this rapid divergence and dispersal of parrots, an ecological divergence also occurred that would lead to the group known as lories. As demonstrated by their brush-tipped tongues, a dietary shift occurred leading to a use of nectar as a food source. This novel food source has led to an extremely rapid speciation (approximately 53 species) considering their divergence from other parrots occurred as recently as the middle Miocene (Schweizer et al. 2011).
This comprehensive explanation of the distribution and divergence of parrots serves to illustrate two large trends in macro-evolutionary studies. The first is that when viewed with other bird taxa, it becomes clear that birds were co-existent with dinosaurs and diverged into major taxa (e.g., parrots) prior to the late Cretaceous even that led to the extinction of dinosaurs. As well, it illustrates well the importance of multiple theories to explain the diversity of species. Vicariance, climate change induced dispersal, trans-oceanic dispersal, and ecological changes must all be used to accurately describe and explain the observed molecular phylogenies.
Cox CB (2000) Plate tectonics, seaways and climate in the historical biogeography of mammals. Memórias do Instituto Oswaldo Cruz, 95, 509–516.
Hedges SB (2001) Afrotheria: Plate tectonics meets genomics. Proceedings of the
Schweizer M, Seehausen O, Hertwig ST (2011) Macroevolutionary patterns in the diversification of parrots: effects of climate change, geological events and key innovations. Journal of Biogeography, 38, 2176-2194.
Waters JM, Craw D (2006). Goodbye Gondwana?
Molecular phylogenetics and evolution. 09/2009;
Vicariance is thought to have played a major role in the evolution of modern parrots. However, as the relationships especially of the African taxa remained mostly unresolved, it has been difficult to... [more]Vicariance is thought to have played a major role in the evolution of modern parrots. However, as the relationships especially of the African taxa remained mostly unresolved, it has been difficult to draw firm conclusions about the roles of dispersal and vicariance. Our analyses using the broadest taxon sampling of old world parrots ever based on 3219 bp of three nuclear genes revealed well-resolved and congruent phylogenetic hypotheses. Agapornis of Africa and Madagascar was found to be the sister group to Loriculus of Australasia and Indo-Malayasia and together they clustered with the Australasian Loriinae, Cyclopsittacini and Melopsittacus. Poicephalus and Psittacus from mainland Africa formed the sister group of the Neotropical Arini and Coracopsis from Madagascar and adjacent islands may be the closest relative of Psittrichas from New Guinea. These biogeographic relationships are best explained by independent colonization of the African continent via trans-oceanic dispersal from Australasia and Antarctica in the Paleogene following what may have been vicariance events in the late Cretaceous and/or early Paleogene. Our data support a taxon pulse model for the diversification of parrots whereby trans-oceanic dispersal played a more important role than previously thought and was the prerequisite for range expansion into new continents.