Snakes, Birds and evolutionary failure

Not much is known about the evolution of snakes seeing that their skeletons are so fragile and doesn't fossilize very well. We do however know enough to confidently say that snakes evolved from the Diapsids group. (Assuming that the 3 evolutionary groups of reptiles is true: Anapsids = modern turtles, Synapsids = modern mammals, Diapsids = modern lizards and snakes and most probably birds.)

All three groups evolved to include herbivores, omnivores and carnivores (i.e. predators). Taking all of this in account, and also the theory that at one stage (after dinosaurs went extinct) birds "ruled the earth" because they had the advantage of flight. Birds had the opportunity to rule the earth, so to speak. It is also safe to say that most of the earlier birds were predators.

But somewhere along the lines most birds evolved to be herbivores (a wide variety from Folivore, Frugivore, Graminivore, Granivore, Nectarivore, Palynivore, Xylophagy). The reason for this, according to Darwinian evolution, is off course the lack of food supplies.

When we look at snakes, however, they are all - with no exception - carnivores. We can even look at the broader spectrum of reptiles and include the Crocodilia order which is also strictly predatorily.

The question is now, why would some species - snakes and other selected reptiles - be stuck in carnivore mode? Did they always have abundant food? Wouldn't it be easier to be a herbivore, seeing that your food isn't running away from you all the time? One can understand that a species doesn't need to evolve if it is relatively successful, such as with Crocodilia. But snakes are not as strong a species as the mighty croc/gator. Yet, it shows no interest in plant material, whereas the rest of the world's species have diversified in all directions.

My question is not directed at a creationism vs. evolution debate, but at a possible scientific reason as to why such a vast species as snakes would not include a single herbivore?

I think the answer is fairly simple. Snakes are generally highly adapted and specialized ambush predators. Because of their body layout/design they are basically stuck in their niche. Certain evolutionary branches are dead ends so to speak. For example, herbivores have complex digestive systems complete with symbiotic bacteria so that they can get the most out of their "low energy fuel", plants. Where as something not as specialized as a snake, say a rat for example, might be able to switch to eating only plant matter if the need arises, and then perhaps evolve to exclusively feed on plant matter, should the supply of meat dry up, a snake would not be able to get any useful energy from plant matter, due to its specialized digestive system being geared for meat. They would just starve if no animals were available for food.

I think this may be true of all carnivores that have lost all ability to cope with plant matter. They have hit an evolutionary dead-end, and this is often why species go extinct. They simply can't adapt to a new way of life.

reply to post by C.H.U.D.


All excellent points of explanation!

But take for example the panda bear and the koala bear (not to be confused with the drop bear ). The panda needs to spend the whole day eating bamboo, simply because the nutritional value in bamboo is so low. The same goes for Koalas and Eucalyptus. It is a safe bet to say that at least the panda was a predator at one stage and had to resort to plant material when their prey disappeared? Surely at one stage their digestive tracks could not cope with plant material?

Perhaps this is where the suggestion of "an evolutionary dead-end" comes into play? May that be a reason why both these species are/were near extinction? Would they have become extinct anyway if humans were taken out of the equation?

And what about the "ridiculous" evolutionary development as seen with mosquitoes, where the female is omnivorous and the male herbivorous. Should there be no blood for her to feed on, she will survive, but won't be able to produce eggs.


[edit on 10-7-2008 by Gemwolf]

I think that with pandas, they were probably evolved from an omnivorous ancestor. Most bears are omnivorous. Pandas have teeth that were obviously designed for killing prey/tearing meat, so I think there is little doubt their ancestors ate meat in the past. I don't think it's safe to say that they were forced to move to a vegetarian diet. They may just have found that plants were an easier option, and since little else eats bamboo they evolved to exploit this food source.

Specialization is a risky path to take. By specializing in a particular food source, you effectively limit your options, and if that particular food source runs into problems then you end up in trouble. That is why may species are endangered, and also because man disrupts their natural habitats.

Of course, man is not the only cause of extinctions. Nature is a fluid thing, and sometimes one species gets the upper hand on another, resulting in the extinction of the species that can no longer effectively compete.

In the case of the panda, they are endangered because their habitat has been fragmented by man, and they need large ranges in order to survive, and there are very few left now. So I think it's safe to say that the panda would not be endangered if it were not for man.

Other cases would have to be taken on their own individual merits, but in general I think man's interference is the cause of the majority of species becoming extinct/endangered. In many cases, the relationships between organisms in a food web are very fragile anyway, and it may only take a little push by man for the balance to be upset and for at least one species involved to suffer.

Interesting fact about mosquitoes there (I did not know that females were omnivorous). I agree, it does seem to be a strange way of doing things, but it does seem to work for the mosquito! Despite massive attempts by man to eradicate it ('___' spraying campaigns, and covering all standing water with oil to prevent the larval stage from emerging and becoming adults), they are thriving!

So despite this strangeness in their feeding habits, mossies have made a rather shrewd evolutionary move it seems. They have specialized feeding habits, but at the same time can survive on a number of food sources, so they have left their options open enough that they are not heading into an evolutionary dead end - at least not yet anyway!