Plant materials are surprisingly inefficient calorie sources in a paleolithic environment. The majority of the natural "flora-mass" is bark and leaves, neither of which are easily digestible by humans. Protein and fat (animals) were the preferred sources of energy, and tubers, fruits, berries, nuts and seeds would provide more nutrition than greens in a food-scarce situation.

That being said, there are certain types of monkeys who ingest certain leaves and plants for their medicinal properties, a habit that early humans may have also developed.

I know a guy who flies supplies into the backcountry of Alaska in the spring, as soon as the weather allows. He says out of all the goodies he brings, the first thing everyone goes for are the greens. I know they aren't paleolithic, but they have been surviving all winter on fresh and canned meats and dry goods. I think paleo man probably grazed throughout the day on fruits and vegs when they were around, and when he couldn't catch enough meat.

Did we eat a ton of roughage? We aren't gorillas, and our digestive systems weren't designed to eat tons of it, but we do have an omnivore's digestive system, so plant matter likely was a significant part of our diet.

As pointed out by others, plant matter tends to be lower in calories than animal products. But there's obviously more to nutrition than calories. Plants, per calorie, have more nutrition than do meat products. But arguably, you can't easily eat the same number of calories of plants than you can of animals. Luckily, you don't need to eat a ton of plants to get a significant amount of nutrition.

Many would have eaten substantial fiber from minimally processed vegetable matter. Some may have intentionally gathered greens. This practice probably varied widely.

I don't think so. All " roughage " does it scar the lining of the intestines which can lead to insufficient nutritional utilization. Think about it. Rub lard on your leg for minutes than rub greens and roughage? Roughage causes scarring and irritation. Imagine how this happens every day to your delicate intestines which are soft and smooth. I can't eat fiber. It just doesn't work. There is no point. Fat and animals is where it is at!!