Two questions about Myrmecophaga tridactyla

[james_davis_nicoll]

First





Just how bright are they? That head sure looks small.

Second, wouldn't they be even cooler and more able to resist predators if they weighed a ton or so? I'm looking at you, genetic engineers with no particular system of ethics.

(blame the dragon's tales, although it doesn't take much to make me muse about replacing lost megafauna like terror birds or velociraptors in F16s pachyderms, with new and improved versions)

Comments

[carloshasanax.livejournal.com]

Not eager per se, but a) the explanation, while plausible sounding, is very hand-wavey, and b) the literature already reports them to be strongly clustered in phylogenetic groups.

E.g., from McNab and Eisenberg, "Many of the species with the largest brains relative to the mass standard are arboreal, most notably xenarthrans, carnivores, primates, and tree squirrels."

The primates and the carnivores are already known to have their own allometric series which might be confounding the arboreal effect. Tree squirrels, I don't know. But arboreal xenarthrans -- they're sloths! Like you said, it's really hard to argue that they have a larger brain than predicted because of their enhanced three-dimensional mobility.

So you have two orders where developmental allometric differences might be confounding matters, one order where the standard explanation makes little sense, and tree squirrels.

(Eisenberg did look within smaller phylogenetic groupings for evidence of the arboreal-brain size connection -- it's in his possum paper referred to in McNab and Eisenberg -- and while he found a relationship, it was hard to disentangle from other factors.)

So it's an Occam's razor sort of thing.

[luna-the-cat.livejournal.com]

But you have to start somewhere, and some hand-wavy just-so stories make a more logical starting hypothesis than others.

Here's a question for you: were tree sloths always so slow?