Flying primate hypothesis
In evolutionary biology, the flying primate hypothesis posits that megabats, a subgroup of Chiroptera (also known as flying foxes), form an evolutionary sister group of primates. The hypothesis began with Carl Linnaeus, and was again advanced by J.D. Smith in 1980. It was proposed in its modern form by Australian neuroscientist Jack Pettigrew in 1986 after he discovered that the connections between the retina and the superior colliculus (a region of the midbrain) in the megabat Pteropus were organized in the same way found in primates, and different from all other mammals. This was followed up by a longer study published in 1989, in which this was supported by the analysis of many other brain and body characteristics. Pettigrew suggested that flying foxes, colugos, and primates were all descendants of the same group of early arboreal mammals. The megabat flight and the colugo gliding could be both seen as locomotory adaptations to a life high above the ground.
The flying primate hypothesis met resistance from many zoologists. Its biggest challenges were not centered on the argument that megabats and primates are evolutionarily related, which reflects earlier ideas (such as the grouping of primates, tree shrews, colugos, and bats under the same taxonomic group, the Superorder Archonta). Rather, many biologists resisted the implication that megabats and microbats (or echolocating bats) formed distinct branches of mammalian evolution, with flight having evolved twice. This implication was borne out of the fact that microbats do not resemble primates in any of the neural characteristics studied by Pettigrew, instead resembling primitive mammals such as Insectivora in these respects. The advanced brain characters demonstrated in Pteropus could not, therefore, be generalized to imply that all bats are similar to primates.
Soon after Pettigrew's study, work on another genus of megabat (Rousettus) disputed the existence of an advanced pattern of connections between the retina and the superior colliculus. However, this conclusion was later criticised on methodological grounds. Later studies have sought further evidence of unique characteristics linking the megabat and primate brains. These studies have had limited success in identifying unique links between megabats and present-day primates, instead concluding that the megabat brain has characteristics that may resemble those likely to have existed in primitive primate brains. Nonetheless, modern neuroanatomical studies have repeatedly supported the existence of very significant differences between the brains of megabats and microbats, which is one of the anchors of the "flying primate" hypothesis.
The implication that bats are diphyletic has been fiercely disputed by many zoologists, not only based on the unlikelihood that wings would have evolved twice in mammals, but also on biochemical studies of molecular evolution, which indicate that bats are monophyletic. However, other studies have disputed the validity of these conclusions. In particular, it has been argued that phylogenies based solely on DNA data can be subject to an artifact named the "base-compositional bias"  Further studies did not find base-compositional bias sufficient to discount support for the monophyly of bats.
- Pettigrew JD, Maseko BC, Manger PR (April 2008). "Primate-like retinotectal decussation in an echolocating megabat, Rousettus aegyptiacus". Neuroscience 153 (1): 226–31. doi:10.1016/j.neuroscience.2008.02.019. PMID 18367343.
- Pettigrew JD (1986). "Flying primates? Megabats have the advanced pathway from eye to midbrain". Science 231 (4743): 1304–1346. doi:10.1126/science.3945827. PMID 3945827.
- Pettigrew JD, Jamieson BG, Robson SK, Hall LS, McAnally KI, Cooper HM (1989). "Phylogenetic relations between microbats, megabats and primates (Mammalia: Chiroptera and Primates)". Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 325 (1229): 489–559. doi:10.1098/rstb.1989.0102.
- Springer, Ms; Teeling, Ec; Madsen, O; Stanhope, Mj; De, Jong, Ww (May 2001). "Integrated fossil and molecular data reconstruct bat echolocation" (Free full text). Proceedings of the National Academy of Sciences of the United States of America 98 (11): 6241–6. doi:10.1073/pnas.111551998. PMC 33452. PMID 11353869.
- "Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation". Nature. 2008-02-14. doi:10.1038/nature06549. Retrieved 2008-07-03.
- Teeling, Ec; Springer, Ms; Madsen, O; Bates, P; O'Brien, Sj; Murphy, Wj (January 2005). "A molecular phylogeny for bats illuminates biogeography and the fossil record". Science 307 (5709): 580–4. doi:10.1126/science.1105113. PMID 15681385.
- Eick, Gn; Jacobs, Ds; Matthee, Ca (September 2005). "A nuclear DNA phylogenetic perspective on the evolution of echolocation and historical biogeography of extant bats (chiroptera)" (Free full text). Molecular Biology and Evolution 22 (9): 1869–86. doi:10.1093/molbev/msi180. PMID 15930153.
- Thiele A, Vogelsang M, Hoffmann KP (1991). "Pattern of retinotectal projection in the megachiropteran bat Rousettus aegyptiacus". Journal of Comparative Neurology 314 (4): 671–683. doi:10.1002/cne.903140404. PMID 1816270.
- Rosa MG, Schmid LM (1994). "Topography and extent of visual-field representation in the superior colliculus of the megachiropteran Pteropus". Visual Neuroscience 11 (6): 1037–1057. doi:10.1017/S0952523800006878. PMID 7841115.
- Ichida JM, Rosa MG, Casagrande VA (2000). "Does the visual system of the flying fox resemble that of primates? The distribution of calcium-binding proteins in the primary visual pathway of Pteropus poliocephalus". Journal of Comparative Neurology 417 (1): 73–87. doi:10.1002/(SICI)1096-9861(20000131)417:1<73::AID-CNE6>3.0.CO;2-C. PMID 10660889.
- Maseko BC, Manger PR (2007). "Distribution and morphology of cholinergic, catecholaminergic and serotonergic neurons in the brain of Schreiber's long-fingered bat, Miniopterus schreibersii". Journal of Chemical Neuroanatomy 34 (3–4): 80–94. doi:10.1016/j.jchemneu.2007.05.004. PMID 17560075.
- Maseko BC, Bourne JA, Manger PR (2007). "Distribution and morphology of cholinergic, putative catecholaminergic and serotonergic neurons in the brain of the Egyptian rousette flying fox, Rousettus aegyptiacus". Journal of Chemical Neuroanatomy 34 (3–4): 108–127. doi:10.1016/j.jchemneu.2007.05.006. PMID 17624722.
- Mindell DP, Dick CW, Baker RJ (1991). "Phylogenetic relationships among megabats, microbats, and primates". Proceedings of the National Academy of Sciences of the USA 88 (22): 10322–10326. doi:10.1073/pnas.88.22.10322. PMC 52920. PMID 1658803.
- Stanhope MJ, Czelusniak J, Si JS, Nickerson J, Goodman M (1992). "A molecular perspective on mammalian evolution from the gene encoding interphotoreceptor retinoid binding protein, with convincing evidence for bat monophyly". Molecular Phylogenetics and Evolution 1 (2): 148–146. doi:10.1016/1055-7903(92)90026-D. PMID 1342928.
- Hutcheon JM, Kirsch JA, Pettigrew JD (1998). "Base-compositional biases and the bat problem. III. The questions of microchiropteran monophyly". Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 353 (1368): 607–617. doi:10.1098/rstb.1998.0229. PMC 1692242. PMID 9602535.