Tails or thumbs?

Last year, Gutsick Gibbon linked Bo Xia et al. Or, as it were: sans tail.

We learn about the Loris. This is an anciently-diverged primate which has lost its tail. Like an ape. Yet the loris is not an ape.

GG mooted an ancient tradeoff between a swift branch-runner and jumper, which requires a tail for balance; and a larger, slower brachiator. The brachiator has two paths open: to go all-in on the tail as a fifth limb, or to invest in grip-strength. The New World went for prehensile tails; in the Old World, we apes increased the opposable thumb. The New World lost the thumb and the Old World lost the tail. Pace Bo Xia, who had involved losing the tail in the transition to a non-arboreal lifestyle.

The gene is TBXT. This appears also in Manx cats and, last year, they tweaked it for mice.

I take it that Chicxulub and South America's general latitudinal conservatism since then (compare, India) had allowed a persistent Amazon, until those Old World primates from Portugal showed up.

At stake here is the route to sentience. Obviously the Old World can scale: because we apes were able to get physically bigger, compared to monkeys. The New World can, too; not as apes, but as prehensile-tail monkeys.

BACKDATE 5/15