Fossils Reveal Anacondas Have Been Giants for Over 12 Million Years

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Cause your nervous system knows what a snake is but doesn't know what a picture is?

I've always found this interesting because nothing about the appearance of a snake has ever bothered me, unsettled me, or made me fearful. They actually look very neat to me, and the tiny snakes I've had the fortune of holding were very fun to feel slithering about in my hands.

Cockroaches on the hand, not scary at all, but I feel disgusted by them.

And large spiders, extremely scary to me, instant fear response.

There is the theory that a substantive percentage of people have dangerous prenatal experiences with their umbilical chord, as the source of their fear of snakes, and that it can be resolved later in life with regressive therapy. See e.g. ”Womb Surround” by Ray Castellino.

I'm not unsettled by them.

There is no age gating on this content.

Ah, so buns means movement.

This comment seems to be generating downvotes, but I find the questions fascinating. It is a stretch to say the fossil record rules out any evolutionary changes to anacondas. However, if anacondas represent another form of so-called "living fossils" [0], it is interesting to think about what makes them resistant to the change that seems to occur as a matter of course in many other organisms?

0. https://en.wikipedia.org/wiki/Living_fossil

We can't observe these ancient snakes or sharks actually living, so we can only make assumptions based on their morphology. And morphology certainly constraints and suggests behavior, and so we can make some assumptions here.

That being said if the question is "why have we not seen significant morphological changes" - there are a few ways to think about this.

First is that we would be blind to many types of morphological evolution. For example, if an isolated sub population of snakes or sharks started shrinking due to isolated environmental pressures, we would be unlikely to see this, but also if we fixate on the "largest anaconda", then we would filter out all "smaller snakes".

Second, the way we talk about "not evolving", especially for sharks is probably misleading. When we say sharks haven't changed, we mean to say that the shark body plan hasn't significantly changed. And this makes sense - they have a very efficient body plan for being a hunter in the see. We have "proof" of the suitable-ness since dolphins and other whales have converged onto a very similar body plan. Conversely, there are plenty of extinct sharks with body features that seem totally bizarre (https://www.fieldmuseum.org/blog/four-fossil-sharks-are-cool...).

Finally, especially in the context of "the largest" - the largest animals that can exist in a given environment is.... environmentally constrained, especially for land animals. The largest anaconda is likely near the largest sizes that the local environment to support, and so something larger appear is unlikely, without drastic environmental changes.

They've reached a local maximum.

anaconda is a package manager for python