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Crabs evolved at least five times from separate groups of crustaceans (2021)

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Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#131

Post by sopooneo »

ckw wrote: post #123

Something related I wonder about: consider seals, sea lions, elephant seals, walruses and whales. In those species are we seeing the process of the convergent evolution of a land occupying species toward a purely oceanic going whale form species, where the boundary between land and sea represents a transitional niche which can be occupied only by evolutionarily unstable forms? So that if you could see a sort of extre…

As far as I can tell, there is some degree of convergent evolution, with current sea mammal all coming from three separate earth-to-sea ancestors. There’s the seal, sea lion, walrus line. The whale, dolphin line. And finally the humble sea cow / manatee line.

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#132

Post by Zuider »

sopooneo wrote: post #131
ckw wrote: post #123

Something related I wonder about: consider seals, sea lions, elephant seals, walruses and whales. In those species are we seeing the process of the convergent evolution of a land occupying species toward a purely oceanic going whale form species, where the boundary between land and sea represents a transitional niche which can be occupied only by evolutionarily unstable forms? So that if you could see a sort of extre…

As far as I can tell, there is some degree of convergent evolution, with current sea mammal all coming from three separate earth-to-sea ancestors. There’s the seal, sea lion, walrus line. The whale, dolphin line. And finally the humble sea cow / manatee line.

In that scheme, otters, and possibly beavers, might represent the beginning of the process. The ancestors of the whale looked like furry alligators.

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#133

Post by Zuider »

version_five wrote: post #21
samatman wrote: post #15

Even more wild to me is that saber-toothed cat-like predators evolved seven separate times: https://en.wikipedia.org/wiki/Saber-toothed_predator

There was a recent article on here about how species that looked alike were not necessarily related and is was more common to have physically dissimilar but geographically close species that were evolutionary relatives. One of the points was that convergent evolution was more common than people thought. These stories appear to support the convergent evolution assertion

Eyes evolved independently in six different phyla. Compound, lensed, eyes are even found in brainless box-jellyfish, which helps them negotiate the mangrove swamps where they live.

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#134

Post by Zuider »

throwaway742 wrote: post #70
gibolt wrote: post #17

Earlier quoted context omitted.

The teeth are already there. A few gradually longer ones makes obvious sense to be a better predator, giving them an evolutionary advantage.

Then why aren't they still around? Why don't they evolve again?

They may wekk evolve again, given the right circumstances. Giganticism in both predator and prey is a response to plentiful food. It happened with both dinosaurs and mammals. By the same token, animals respond by evolving into smaller forms in food sparse environments. On the Indonesian island of Flores, both hominids and elephants became tiny.

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#135

Post by graycat »

mirekrusin wrote: post #113
graycat wrote: post #80

Earlier quoted context omitted.

My understanding is that eggs and no-eggs are not as different as might be expected. After all, the no-eggs still have eggs but, just, don't lay the eggs or let us make French toast, custards, or omelets! Maybe a key issue would be the amazing placenta. But maybe the egg animals are not so far from having a placenta because they still DO have to be willing to accept the male sperm without killing it, and part of what…

Yes, that's different subject on how egg, roe and womb is really the same kind of thing. What was striking to me was how far in ancestry chain you have to go back with rhinos to meet common ancestor with egg-lying triceratops - this ancestor will not look like any of them, however they did meet from completely divergent dna to be so look alike, crazy.

Yup, maybe that looking alike is called convergence. Apparently a big instance is eyes, apparently developed several times with surprisingly close to the same design.

Pigs, rhinos, hippos, ..., triceratops all look much the same to me!

Hmm ...? Would the real test of sameness be to see if they make similar BBQ???

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#136

Post by adgjlsfhk1 »

animal_spirits wrote: post #40
kjeetgill wrote: post #14

Eons did a great piece on this recently: https://youtu.be/wvfR3XLXPvw One of the things I love about the way Eons cover topics is how they don't just focus on what we know, but also how we know, who figured things out, and what we got wrong along the way. Can't endorse their style of science journalism enough.

PBS has been putting out such great content in the last 5 years. Really impressive and highly overlooked

it's a shame they killed "infinite series" it was one of the best math YouTube channels out there

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#137

Post by mirekrusin »

namaria wrote: post #124
mirekrusin wrote: post #61

Earlier quoted context omitted.

I wasn't aware of that some time ago, it's a fascinating insight. I got a lightbulb (going wtf/dark actually!) when watching cartoon or something with triceratops. They looked so much like rhinos. But had eggs. I had trouble reconciling it with evolution. They were so far ancestor-wise but so close physically-looking wise. Convergent evolution is very interesting. It suggests aliens may not be that different from us…

Considering how little time humans (or any kind of primates) have had on this planet, our overall design doesn't seem super stable. I would bet on crab-like aliens.

Didn't we have monkey- vs octopus- vs rat- like game where monkey- won the race?

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#138

Post by dredmorbius »

mirekrusin wrote: post #137
namaria wrote: post #124

Earlier quoted context omitted.

Considering how little time humans (or any kind of primates) have had on this planet, our overall design doesn't seem super stable. I would bet on crab-like aliens.

Didn't we have monkey- vs octopus- vs rat- like game where monkey- won the race?

Corvids have entered the chat.

I'd argue that rats are exceptionally close to humans (both are mammals). Similarly other potential candidates: raccoons, bear, possibly dolphins or other cetaceans.

Insect, plant, or colonial intelligences would be interesting.

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