What caused the Cambrian Explosion?


#1

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#2

whoever it was, they’re on a watchlist now.


#3

I recall reading an interesting idea, that maybe the Cambrian explosion wasn’t an explosion at all. Rather than a huge variety of critters suddenly evolving, maybe this is just the date when they evolved hard parts. If there was great variety before that, it might not leave fossils behind. Also, when one predator develops teeth, pretty much everybody needs a shell or they’re dinner, so sudden parallel evolution makes sense.


#4

I remember finding out from Prof. Alan V. Morgan at the University of Waterloo that you could make an entire career out of identifying beetle penises.


#5

I’m going to adopt this as my go-to line whenever there’s a prolonged silence at social get-together’s.


#6

Most paleontologists view Peter Ward as a hack. He’s prone to making up stories to explain why this or that trait evolved or exists. This is the same thing which makes people dislike evolutionary psychology.

Thing is, we don’t know what caused the Cambrian explosion, and we never will. No one was there, no one saw. The best we can say is “this is what we think happened and here’s why we think it.”


#7

That has been my theory as well. And I think it is the most logical. Especially when it comes to an arthropod type creature, take away the shell and what do you have, soft squishy things that lived in the ocean.

I think it stands to reason there could have been a lot variety of life already, but until something triggered them to grow a hard shell then they didn’t leave evidence of it. It also stands to reason things started out very small. Look now at a drop of sea water and all the crazy zoo plankton and the like. I think that was the type of creatures that all began evolving. And again, remember when they say explosion we are still talking a hundred million years or so.

As for WHY it happened - I think it was time. I think life had evolved enough of the base parts for things to take on new, radical forms. Sort of one you add enough heat, water will boil.


#8

Interesting fellow.

At the very least, I’d recommend a good copy editor. Some of those sentences were extremely hard to parse.


#9

There now seems to be much more to it than that, though. We have soft Cambrian fossils from the Burgess shale, Chengjiang, and Emu Bay. There is a lot to suggest phyla like annelids and mollusks were just recently diverged from one another, and many of the peculiar forms appear to be other groups between them.

We also have soft fossils from the late Precambrian in the form of the Vendian biota. Most of them are hard to interpret, but it would be very hard to say they are all the later animals without shells. There is genuinely a huge amount of development in the dozens of millions of years that make up the early Cambrian.

I think size is an interesting question. Most of the fossils we do have from this time period are on the scale of modern worms and bugs, and they cover a lot of the animal tree of life, so I expect that’s where most of the original development was happening.

I’d be surprised if many phyla originated from microscopic plankton; it now looks like nearly all bilaterally symmetrical animals had coelomate ancestors, with a complete body cavity, and in those tinier groups that cavity is nearly always reduced or absent. But that is the case for the arthropods themselves, and their relatives like tardigrades and nematodes do tend to be too small too see.


#10

Haven’t paid much attention to him since taking two quarters of paleontology from him years ago, but I always enjoyed his classes. Good lecturer and a civil person to boot.


#12

Time itself doesn’t provide the push to evolve, you must have something else to provide the selective pressure, and that something was probably the first appearance of sight. At first very primitive sight, say an improvement in the ability to sense heat, but in the kingdom of the blind it could provide an enormous advantage for either a grazer or predator. So other species start developing that heat-sight and gradually develop true optical sight Even species that remain blind can’t avoid this pressure, they must evolve the tools to defend themselves or end up as a trilobite’s lunch. So once there is sight it also starts making evolutionary sense to develop a whole new set of features that would have been inefficient, even useless in a blind world.


#13

Monolith.


#14

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