Flying primates: crashed, or crashed through?

Abstract

Abstract The flying primate hypothesis originated from the finding that megabats shared a number of advanced visual pathway characters with primates that were not found in any other mammalian order, nor in microbats. This hypothesis indicates that primates, colugos and megabats share a common ancestor with each other more recent than any shared with microbats. The hypothesis has found increasing support from other sources of evidence. Examples reviewed here include further derived brain features, both visual and non-visual, immunological studies of serum proteins with monoclonal antibodies and analysis of restriction sites and protein sequences (globins and cx-crystallin). DNA sequence data, while supporting the colugo-primate association, have been used to reject a primate-megabat connection, even though the total evidence for a colugo-megabat link is better than the generally accepted evidence for a colugo-primate link, and even though DNA sequence data and protein sequence data on the same genes give conflicting phylogenies. A resolution to this conflict is suggested by a bias in all the published DNA sequence data on bats. The shared substitutions claimed in support of bat monophyly are mostly of adenine (A) or thymine (T), in the same direction as the bias that exists in the overall base composition of DNA from metabolically-active, volant organisms. If the AT content of DNA is taken into account by using the NZ algorithm, the much-vaunted claims for bat monophyly based on DNA sequences are not supported. It is more parsimonious to assume that the AT bias responsible for the claimed association arose independently in the two lines of flying mammals.