Fig. 8

Proliferation model depicting extended development (peramorphosis) regulating facial length. We summarize key phases of craniofacial development between the short-faced C. perspicillata, the shorter face of A. jamaicensis, and the longer face of G. soricina at CS16 (early), CS17 (mid), and CS18 (late). The overall window of proliferation is the same duration of time between species. The colored regions of the midface represent cell proliferation and relate to aspects of facial development. In phyllostomid evolution, compared to the ancestor, skull shape is changed through heterochrony by increasing the rate of growth (acceleration) in fruit bats and by extending the duration of growth (hypermorphosis) in nectar bats. At the cellular level, the facial development is shown to undergo three phases of cellular division: early (green), mid (yellow), and late (red). Early divisions may relate to neural crest cells (NCC) during mesenchymal condensations (green) that give rise to pre-cartilage and pre-bone progenitors (yellow) and mature into cartilage and bone progenitors (yellow/red). Cartilage and bone cells proliferate and mature with a terminal division (red). With acceleration, elevated growth rate in committed progenitors (yellow) may trigger terminal divisions to occur (red) at an earlier time, which can then led to a shorter or truncated face. With hypermorphosis, constant growth rate (yellow) may relate to an extension in progenitor proliferation (delay in terminal division), which gives the face more time to grow and leads to a longer face. The figure is