More howler monkey lovin'

John Hawks follows up the monkey hybridization story, providing some important ecological context:

[T]he primary difference between the two species is cold tolerance: A. pigra can and does live at higher altitudes than A. palliata, ranging high enough that it must tolerate freezing temperatures
…
Larger monkeys with larger, more complex molars, differences in throat anatomy, and greater cold tolerance, in contrast to a smaller, more cosmopolitan species, with the opportunity for gene flow during interglacials. They sound like Neanderhowlers.