Eyes

[Stefan-A]

I am not so sure about that. I was under the impression that colubrids and vipers are the "newer" snakes and that the intricate varieties of venom (whether lethal or not) are the "cutting edge" of snake evolution.

Fossil record indicate boids to be among the oldest snakes (with their vestigial hips and spurs). I would think (don't quote me on that) death by constriction may go way back!

Steve

The evolution of the snake from lizards, which also have the gene as you mentioned (meaning that venom actually predates snakes) to a more subterranean lifestyle would suggest that constriction probably wasn't the first method and it certainly wouldn't be a practical one under those conditions. Venom on the other hand would be. Constriction probably wouldn't have been a solution until the snakes started to return to the surface.

But you are definitely right about boids coming early and viperids etc. being a more recent "invention".

[Zephyr]

I also recall there being venom glands in monitors, hinting and ancestor to snakes...

[Steven@HumboldtHerps]

Snake evolution: This conundrum has been locked in debate for many years.
The current argument that snakes evolved from lizards still holds the most ground. But which lizards?

For a while some theorists actually believed that the extinct line of aquatic reptiles known as the mososaurs were the predecessors to the serpentine form. While it sounds good, and mososaurs like the plesiosaur did have elongated serpentine forms, the whole "snakes crawling out of the sea" thing just didn't cut the cake. One might think that sea snakes might have been the orginal snakes, but DNA tells us they are relatively new arrivals on the evolutionary scene. It also does not explain the process of why suspected "live-bearers" such as mososaurs would revert to the egg-laying process that so many snakes today endure.

Going backwards down the snake family tree all the way to primitive boas, sunbeam snakes, and the likes, we may find ourselves looking at something more like skinks, varanids, or anguids. Here we find long, lanky bodies and tails (many), the presence of forked tongues in some families, the evidence of limb reduction (skinks and anguids). Anguids include the legless lizards and the glass lizards (all limbless). We should also not forget that mysterious group of squamates (Remember: the order Squamata includes both snakes and lizards and...): the amphisbaenians! Look these funky sand swimmers up, and you may totally start imagining how things way back when underwent numerous trial and error "experiments". Ha! Another reminder: You don't lose your legs because you need to... Evolution doesn't work that way. You lose your legs because you're a mutant compared to the norm, and the mutation did not affect you ability to survive, and you passed the trait on.... Even if the new trait helps you perhaps survive better than your normal homies, evolution is still an accidental occurrence!

One could surmise that skinks be left out of the list of suspects, simply because they lack the venom genes we have been talking about, and that they are along a separate (older?) lineage of lizards.

Really, look at some pics of some amphisbaenians. Some have front stubs (limbs), and some have hind stubs!

Here is the way I like to paint the picture (and it sure didn't happen overnight; probably took a long time....). Let say you belong to a group of lizards who somehow adapted to a more fossorial (underground) lifestyle. With each subsequent generation you have very subtle mutations whereby you, as a species, slowly change physiology. If you start chasing rodents, worms, or other subterranean prey, legs will get in the way. The serpentine or worm shape is just perfect for an underground lifestyle. With each evolutionary "mistake for the better" you are becoming ruler of the underground niche. Are there any other potential mutations that, in the long run, can serve you better for this lifestyle? Of course there are! You don't need external ear openings. Since you have become elongated, why do you need two lungs side by side? Gosh darn! San keeps getting in under your eyelids; don't need them either; an eye scale works better! And then there are the eyes.... It is very likely that retinal regression occurred in these lizard-snakes - Who needs eyes if you are in complete darkness, and you have a tongue that smells better than most animals?! In regards to the eyes, I believe that the blueprint for a functional eye may have gone dormant and then re-invented itself.

So how do you explain going from above-ground seeing serpentine lizard to fossorial blind lizard-snake to once again above-ground seeing snake? (Remember, their are primitive blind snakes alive today!)

Think apocalypse! We have had numerous extinction level events in Earth's amazing history (too many years for most humans to imagine - We are so small in our scope of time!). Many of these disasters (meteors, comets, super-volcanoes, mega methane burps, glaciation, global warming, etc.) may have left alive only species who were adapted to a more fossorial lifestyle. Say the earth went dark for a while; say the earth's surface was severely pummeled; maybe the underground denizens were better off. Who's to say that when the environment changed (or "got better") some of the burrowers didn't poke their heads out of some holes to smell the sunshine?!

Uh, oh... I have to get off the computer...

Talk to you all soon...

Steve

[Steven@HumboldtHerps]

The evolution of the snake from lizards, which also have the gene as you mentioned (meaning that venom actually predates snakes) to a more subterranean lifestyle would suggest that constriction probably wasn't the first method and it certainly wouldn't be a practical one under those conditions. Venom on the other hand would be. Constriction probably wouldn't have been a solution until the snakes started to return to the surface.

But you are definitely right about boids coming early and viperids etc. being a more recent "invention".

I stand corrected. Thanks Stefan. Makes complete sense.

[adamanteus]

Of course Heloderma have venom glands. I think the recognised ancestors of snakes were early 'skink-like' lizards, which adapted to a subterrainian lifestyle. I have no idea which came first... venom or constriction.... I've never really thought about it... but I will now.

[Stefan-A]

I stand corrected. Thanks Stefan. Makes complete sense.

I may yet stand corrected myself, but at the moment, it seems to me that early snakes wouldn't have been much better at constriction than their lizard ancestors, which may or may not have had the ability to produce venoms.

[Zephyr]

I'm going to say venom came first. :P

[adamanteus]

Maybe not relevent.... but what springs to my mind is certain snakes (such as Pituophis) which are known constrict their prey underground (in burrows) by pressing the animal against the side of it's tunnel. Obviously Pituophis are pretty successful constrictors above ground too.

[Stefan-A]

I'm going to say venom came first. :P

You better not. Say that venom may have come first.

[Zephyr]

Well, we'll never really know for sure until Back to the Future becomes a reality. :P