Evidence of diets that were exclusively vegetarian

Question

What evidence, provided by archaeological anthropology, is there in regards to diets that were exclusively vegetarian by choice from Ancient history (4th millennium BC) to Classical antiquity (5th century AD)? Have there been any studies to double-check historical accounts of vegetarianism against archeological records for the same people(s)?

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The inspiration for this question spawned from the following articles.

Did Roman Soldiers Eat Meat?

We've been led to think that ancient Romans were mainly vegetarian

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R.W. Davies and "The Roman Military Diet"
By N.S. Gill, About.com Guide

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Humans are naturally plant-eaters

A fair look at the evidence shows that humans are optimized for eating mostly or exclusively plant foods, according to the best evidence of our bodies. 

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By Michael Bluejay  "Humans are naturally plant-eaters"
June 2002 • Updated May 2012 (michaelbluejay.com)

Answer 1

It is quite possible to examine diet through archeological means (composition of bones and teeth). However, I don't know that anybody has done a systematic study of such records with an eye towards looking for vegetarianism.

The one piece of similar information I am aware of is that teeth of hunter-gatherers are often discernible at a glance, due to the relative lack of cavities, due to their diets being far lower in carbohydrates. That's a grain issue, not a meat issue though.

If vegetarians were archeologically found, I'd think it would be nearly impossible to tell if it were by choice rather than lack of opportunity. We do know, based on tool sets, that some hominid cultures weren't slaughtering large game. That doesn't mean they weren't eating fish or snails though.

On a macro-genetic scale we do know the following:

• Our closest relative in the animal kingdom is the Chimpanzee. Based on common traits, it would be reasonable to assume that our common ancestor (about 6 million years ago) was a creature that was omnivorous, including eating insects (perhaps occasionally with the help of crude tools), and occasional organized hunting parties for bigger game. Chimps (and hunter-gatherer humans) do all that today.

• Around 2 million years ago there were multiple hominid species living, including Paranthropus Robustus and Homo Habilis. Panthropus was a big bruiser, resembling an ambulatory gorilla. While there's some debate about his diet, he does appear to have been specialized for plant eating. He had bigger molars, and bigger jaw muscles to deal with all the extra plant chewing. Habilis on the other hand, was a tool-using omnivore who probably would eat pretty much anything consumable he could get hold of. The Panthropus line died out, while the Homo line eventually evolved into Homo Sapiens.

• Large scale cultivation of grains didn't happen until about 10,000 years ago. Skeletons of farming people are instantly recognizable for the dental damage caused by all those carbohydrates. This is still the case today, which indicates 10,000 years has not been enough time to evolve teeth better suited to this diet. One thing we can say is that our species was clearly not designed for the carbohydrate-heavy diet most people have been eating for the last 10,000 years.

So as far as the "optimization" of our bodies for our diet goes, you will probably need to look at our diet further back than 10,000 years ago. As recently as 2 million years ago, people (Genus Homo) were clearly the hominid species designed to be flexible omnivores.

Answer 2

An archaeological evidence I think could be impossible: if they analyze the content of the digestive system like they did with Ötzi,even if they can find some bodies like this preserved under some special conditions, will be evidence for a few days of diet. If they analyze some lack of nutrients in the bones that lack might be also due to some other factors, not to mention the fact that there are no evidences whatsoever that vegetarian diets cause nutrients deficiency in the bones. Think of it as how hard is analyzing the doping of the sportsmen in the present, if they would try to analyze diet just by blood samples and with this state of the art technology on living bodies is almost impossible. To extrapolate what would be to do that to 2500 years old bodies and make conclusions for large groups of people and you find that it is impossible.

Jains I guess can be easily considered as the ancient vegans. Most of the sources I read sustain with textual evidence this extreme vegetarianism. Also there is a lot of influence of Jainism over the Hinduism and Buddhist mentioned in the literature.

Take this books for example of how strict the diet can become for Jains:

Although Jains are permitted to eat plant foods, which involves taking the life of one-sensed immobile beings, Jains recognize that fewer plants are killed if humans eat plants directly rather than feeding them to animals that humans then consume. Animals raised for meat consume more protein than they produce. So the standard Jain diet not only seeks to eliminate violence to animals but also has the effect of minimizing the amount of plants necessary to feed humans. Jains recognize that meat-based agriculture is an ecological disaster, and a central tenet of Jain philosophy involves the obligation of humans to minimize their adverse impact on the environment. Jains maintain that all sentient beings have equal inherent value as living beings. The proscription against violence against all sentient beings has strong support in Jain scriptures and widely accepted secondary literature. For example, the Akaranga Sutra, states that "all breathing, existing, living, sentient creatures should not be slain, nor treated with violence, nor abused, nor tormented, nor driven...

Also according to Wikipedia aproximatly same period might have other candidates:

"Pythagorean diet" was a common name for the abstention from eating meat and fish, until the coining of "vegetarian" in the 19th century.