Meeting Abstract

28.1  Friday, Jan. 4  Did bat ancestors glide? A phylogenetic approach PADIAN, K.*; DIAL, K.P.; Univ. of California, Berkeley; Univ. of Montana, Missoula kpadian@berkeley.edu

The predominant biological view of the evolution of flight is that it is preceded phylogenetically by a gliding stage. Support for this hypothesis has mainly rested on what is presumed to be “easier” or “necessary” based on models. The hypothesis can be empirically tested by examining the comparative phylogenetic positions of gliders and flyers. The three known clades of living and extinct vertebrate flyers are far removed from the 15 known clades of living and extinct gliders. The problem is particularly acute with bats, which are far removed from all eight clades of mammalian gliders, and are nested within a clade that contains only terrestrial and fossorial forms. We used phylogenetic analyses of major clades of bats, and the extinct chiropteran outgroups of crown-group bats, to assess ancestral states for ecological characters related to locomotion, echolocation, diet, and habitat. The ancestor of crown-group bats likely was insectivorous, echolocated as most bats do, could climb quadrupedally, and had poor terrestrial locomotory skills; the ancestral habitat is difficult to determine. Inferences about stem-group bats involve character states of fossil bats. Flight phylogenetically preceded advanced echolocation; the most basal stem-bats could climb, but their habitats are difficult to specify. No outgroups to bats are or apparently were bipedal; thus the forelimbs of bats could only be freed to evolve powered flight if standard quadrupedal locomotion was modified. Ontogeny also speaks against gliding in bat precursors. Bat wings develop by hypertrophy of the manus and chiropatagium (the thrust-producing part of the wing), not the medial part of the wing (brachiopatagium) that produces lift in gliding.