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Acanthodiian/shark missing link
Topic Started: Mar 17 2017, 07:45 AM (490 Views)
heliosphoros
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http://www.sci-news.com/paleontology/sharks-acanthodians-04706.html
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Furka
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To be honest, dealing with the "ancestor" of sharks, which are well known for being very ancient animals, gives me a strange feeling.
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babehunter1324
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At this point I'm surprissed when a long held theory about cladistics turns out to be right all along.
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magpiealamode
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No good hero is a one-trick phony.

We just talked about this in class the other day. I'll have to tell my professor.
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heliosphoros
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Furka
Mar 17 2017, 08:30 AM
To be honest, dealing with the "ancestor" of sharks, which are well known for being very ancient animals, gives me a strange feeling.

The idea that sharks are living fossils falls apart when most modern shark groups don't predate the Cretaceous
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magpiealamode
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No good hero is a one-trick phony.

Isn't "living fossil" kind of a subjective term? I mean, considering that our own noble species has only been around for about 200,000 years give or take, being around mostly unchanged for 66 million years could qualify something as a living fossil, no?
But I do understand what you're getting at, when I saw my first Cladoselache I was a bit let down. But considering that it looks kinda like a frilled shark if they were from the Lamnidae, even that is a testament to the effectiveness of the shark body plan. Apparently, losing their bone was a good way to go. A lot of politicians today seem to agree.
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stargatedalek
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I'm not slow! That's just my moe!

Unless you take the term living fossil literally, in which case everything is a living fossil. So yah, stupid AF term.
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magpiealamode
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No good hero is a one-trick phony.

Well I don't think it's meant be taken literally. Honestly when I think "living fossil," I immediately think of coelacanths, which were known exclusively to science from fossils, until they were discovered alive. It makes sense then, but sure, it's a bit of cutesy phrase. Anyway, I'm getting off-topic.
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the dark phoenix
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King of wonderlandia

magpiealamode
Mar 17 2017, 01:03 PM
Apparently, losing their bone was a good way to go. A lot of politicians today seem to agree.


Laughing aside, this is pretty neat. With the exception of sharks with fin spines like the port jackson, isn't their teeth the only bony thing on them now? Acanthodians still had some bone but they were getting there.

Also I read that Acanthodians had a lot of freshwater species. How come not a lot of sharks today prefer the swamp or river? I know there is Glyphis and the oh so famous Bull shark but why no others?
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heliosphoros
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There are many freshwater rays, and several freshwater "regular" sharks have existed across the Cretaceous and Cenozoic.

My guess is that otherwise niches in those environments are taken by actinopterygians, which do have an edge in having swim bladders, which can act as lungs in poorly oxygenated waters.
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the dark phoenix
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King of wonderlandia

I was aware of the multiple ray species. I was unaware of freshwater species earlier in time outside of Xenacanthida.

Don't we have sharks that blow themselves up to wedge themselves in areas? Couldn't what they use be used as a false lung? But I get how the bony fish have a edge.
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Furka
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Unlikely, since from what I remember sand tigers store the air in their stomach, which isn't exactly an organ evolved to absorb oxygen from neither water or air.
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the dark phoenix
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King of wonderlandia

I thought it was a wells shark or some sort of Bamboo shark.
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magpiealamode
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No good hero is a one-trick phony.

Same thing. They store air in their stomach. They don't have anything resembling a lung or a swim bladder.
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