Could Hallucigenia be the echinoderm missing link?


#1

(Yes, taking a break from saving the world stuff)

For those who don't know, Wikipedia has a great primer.

So, you'll notice a lot of weird issues with how many legs they have, right? Now look at the fossils. . . closely!

Those aren't 'stubby legs' on the one end. Those are discs with spines only sticking out on one side!

Imagine a creature that isn't a Sea Urchin yet. It has pentaradial symmetry and flexible, starfish like skin (which is what we see fossilized) It has evolved semi-hard spines that stick out from seven rings of support structures around their body.

There's some variance in this, because they actually walk primarily on five rows of tiny tube feet, though some also have more flexible, less spiny projections they use for support. They also may use these tube feet to feed, collecting detritus from the ocean floor or plucking them out of the water and carrying them to it's mouth. We're not seeing the tube feet, because they don't fossilize

This creature specialized over time. Some began to connect the seven discs into a more solid support structure and specialized in sediment feeding, they tipped over so that their mouth was now right by their food.

From there some evolved an internal shell to support fiercer spines, again starting with those seven pentaradial rings, but eventually with a 'more the merrier' philosophy, they became the urchins.


Some of them opted to maintain some flexibility and speed and moved their rows of tube feet closer to the ground with a thornier protective layer on top, they began to evolve chemical defenses as well (or hallucigenia had started us down that path long ago) and adopted a more predatory lifestyle. The sea stars.


Some of the urchins decided to dig and became sand dollars.


And some of the rest mixed it up and became brittle stars, and so on.

Meanwhile, another branch went for flexibility from the get-go, they maintained that pentaradial symmetry and seven rows of support structures and became the sea cucumbers while evolving other. . . more creative defenses, They kept the seven rows of support structures, you can still see it today in the sea pig and many others, though after all this time rings have been lost by some and others have adopted other modes of locomotion

http://www.realmonstrosities.com/2011/07/sea-cucumber.html


Meanwhile, we have some odd mixes that start to make sense, like Xyoplax

Maybe this is what hallucigenia larvae looked like, too they sure look like baby starfish, and now we know they're related!


Then we have our suspension feeding tall skinny urchins, a logical step now, right?

As is the old Sphaeraster

See? I bet we got all that awesomeness from lil' old hallucigenia.

And those are totally discs!

HUGE credit to Joseph Jameson-Gould over at Realmonstrosities.com by inspiring the thought and enhancing it!

(Edit: To add. . )


And that also makes these guys start to make more sense. .


And these delightful critters

http://www.realmonstrosities.com/2012/04/basket-star.html


As do these guys!


And yet another fun hybrid


And a lot of the weirder old fossils, which suddenly make sense as variants on a theme!


#2

That the echinoderms show a fundamental unity in design doesn't really have to do with picking Hallucigenia as a starting point - and in fact that specific kind can't be for all of them, since there are already others from the Burgess Shale era, like Gogia, which aren't particularly similar to it.

Suggesting that Hallucigenia might belong with them is an interesting idea, but one which seems to be mostly justified by how ambiguous the squished fossils are. Something that is definitely less ambiguous is Orstenotubulus, for which there is some degree of a three-dimensional reconstruction (pdf). This fits in very well with the lobopods, other animals with paired stubby legs represented by modern onychophores, and I think Hallucigenia seems closer to it than it does to any of the older echinoderms.


#3

Actually, my big concern is that they just aren't considered. They certainly do share a large number of morphological elements when you connect the various echinoderms together.

Not that that's the ONLY way, but when you add in the fact that we've got two rows of distinct spines on top and nothing that resembles 'two rows of legs' it should point at least somewhat in the direction of pentaradial symmetry, true? I'm thinking the creature's design has already been framed.

Not that I don't love my velvet worms, or any of the other theories, but this is the first one that FELT right to me.


#4

Considering modern echinoderms together doesn't work very well - you have to consider what you'd be likely to find in a single ancient echinoderm, which you are doing to some extent, but sort of ignoring fossils from the time. And projections with a superficial resemblance to pentaradial symmetry isn't a great link on its own :

But note I'm not bringing up a comparison to velvet worms in general, but specifically to Orstenotubulus. That's known in enough detail that a relationship to other lobopods is much more likely than echinoderms, and it has spines like Hallucigenia, making it a pretty good connection between those two. Your mileage may vary, but that seems much more right to me.


#5

Oh yeah, I know about the lobopod connection. This isn't just a casual thought. The connection to Hallucigenia has ALWAYS seemed really dicey to me

These are fossils that don't give us much information, there's no obvious head, no real anatomy, nothing. The connection to the Onychophora and the lobopods has always been based on the same level of morphological evidence that I hit the echinoderms from.

Also, just to be clear, there's also plenty of room for a stem group of echinoderms too . . . I just had fun with the missing link angle, and we don't really have a good tree of life for the old echinoderms, either. The sea cucumbers in particular are a bit soft (heh),

Meanwhile, it's not like there's anything that discounts the echinoderm path as far as I've identified . . . again, this is a fossil they had upside down until a few years ago. We've overframed with fossils before (anomalocarus, anyone?)

Now, if we had something solid connecting to any other branch then that'd be awesome, but I'm not finding it, I haven't even found any evidence as to which end is which, have you? I'm not even sure the reconstructions are viable


#6

...I take it, then, you either
a) disagree with something in the paper I provided that relates Orstenotubulus to the lobopods on definitely a somewhat deeper level of morphology than you were looking at; or

b) you don't think it provides any insights on Hallucigenia, despite both sharing paired spines and stub feet, the same features you were using to relate it to a purely hypothetical echinoderm quite different from contemporaries.

Because saying there's no more solid connection without any such comment really makes it feel like the link counter is telling the truth, and you simply didn't look at the one I offered you. I mean, I'm not saying it counts as certain, but it's not purely speculative either.


#7

Sure that's not a Goa'uld fossil?


#8

I actually am saying that I don't think EITHER is a terribly solid connection, and all options should be on the table until we've got something better.

I think there's no indication of paired 'stub feet' in hallucigenia, and that's one of the biggest problems with it.

So, it could be that those aren't feet' at all, but something in between semi-flexible structures and discs, and may not even represent a mode of locomotion. That might be a concept that's too heavily framed.

Meanwhile, we've got very little on the echinoderm tree of life. As I mentioned, while the Crinoid side appears to give us something to go on, but same can't be said for the rest, especially Sea Cucumbers, which are actually what I'm seeing just as much supporting evidence for despite them being entirely unmentioned.

I'm not saying 'they're not worms with feet', there's not enough information to discount that, what I AM saying is that this is an option I can find nothing discounting the echinoderms. So they should also be considered as a possibility and at least we should expand the box and get something that actually excludes them before doing so.

I do think the echinoderms may be stronger, especially given the 'legs' issue (which is, at the least, a really weird coincidence, don't you think?). at the least breaking the context is likely useful, is it not?


#9

Now that's clearly a chordate, I'd hesitate to go much further without a complete skeleton. Those 'non-ribs' in the rear half(?) don't have any analogues that I'm aware of, despite that being an obvious vertebrate spinal column.

Isn't it amazing how all space aliens have such eerily similar skeletal structures to our own? wink


#10

As Wikipedia points out: Most palaeontologists would now tell you that your first photo is upside down, and that the species was a relative of modern arthropods.


#11

Yes, and the decision was quite recent and based upon information that does not apply only to the arthropod branch.

As mentioned, it very well could be a lobopod, but there's nothing useful I can find one way or another that discounts an echinoderm angle, and there DOES at least seem to be a little support.

We don't have much to go on with the little bugger to make a FIRM classification, but why discount an unexplored or only partially explored option?


#12

Mostly: We, here, are not competent to explore this idea properly. If you're serious, bring it before the community of experts and/or hit the research journals to see if it's already been considered and what the outcome thereof was. (I'd bet dollars to donuts that it has been looked at and that there's a good, well documented, summary of the analysis available if you ask practitioners rather than laymen.)

If it turns out that there isn't a previous discussion, great -- those are still the people you're going to have to get involved in analyzing whether your insight holds water or is simply all wet.

You've got a thesis. Now you need testable hypotheses which will support or refute it, and you need to perform those tests. Until you take it to that stage, it's all handwaving and hope and guesswork.


#13

And people wonder why so little gets done in this world.

It's like the rest of the world has turned into a macrocosm of bureaucracy in the private-public partnership.

A quick 'I don't know, but here's somebody who brings a level of experience that offers something a quick mind and the internet cannot provide' would suffice in the place of...

-- I haven't taken this seriously,
-- I see this specific problem based upon a source that you of course may have missed, does that enhance things?' or
-- 'Wow, yeah, that's kind of odd now that you bring enough . . . the thing was always considered a arthropod.

Sorry, That was a bit snarky, I just wonder how many things does a person have to be right about before people take their 'stupid questions' seriously. It's been a source of frustration for thirty years at least and it seems to be peaking recently.


#14

If you want it to be taken seriously, start by taking it seriously yourself. The proposal looks vaguely plausible on paper to this semi-informed layman, based on the extremely limited amount of data you've provided, but most of us don't have the background to evaluate it properly.

I think it's an interesting enough thought to be worth checking on; that is "taking it seriously". I suspect you're going to be disappointed, but I'd be delighted to see you gather the evidence and expert opinions to prove me wrong. So go do that. Please.

Getting the idea is where the process starts. Now you need to take it the rest of the way, or it's storytelling rather than science.


#15

Yeah, and that's never going to happen, It's a tiny idea in the grand scheme of things. Maybe in some odd point in the future it'll be worth pursuing. That doesn't, however, mean there's a fundamental flaw. . .if there is it's hidden behind a paywall somewhere.

I was hoping to get to a few clever questions (like 'oh! But hold on, while the Sea Pig does indeed have pentaradial symmetry it actually DOES have two pairs of legs on the bottom, and only two sets of spines on the top, how does that work?', which would've been a great observation!). That would've added a second mind to the process and helped enhance my knowledge.


#16

Hold up, what are you faulting here? People not taking your idea seriously, or people taking it seriously enough to try discussing it with you? Because contrary to what you imply here, bringing up problems and evidence you haven't mentioned is serious discussion. If you aren't so much as willing to look at a paper someone else thinks is pertinent, and it sure seems like you didn't, what did you hope to gain by bringing it up on a discussion board?

If you want to forward your idea to experts, it's easy enough to do that on your own. There are lots of papers for free on-line, and many of the others can be accessed from libraries. Even abstracts usually list contacting authors, and in my experience many of them are happy to discuss their work with anyone interested. Some even spontaneously give out copies of what they've written, which is a great way to learn more about a subject, or refer you to people who know still more than themselves.

Of course, I've usually come at them as someone wanting to learn more, instead of convinced they've been right enough times that they should never be questioned. Because enhancing knowledge doesn't just mean adding details to an idea, it also means giving possible criticisms, and while interesting this idea is not at all so spectacular none will come up. Even Newton and Darwin had to put up with that, and it ultimately made their theories better.

At any rate, I think you have made it clear that considering your idea and letting you know my thoughts wasn't a response you were interested in, in which case I'll try to remember not to do again.


#17

No, I liked your posts. The only thing I disagreed with is not that I thought that lobopods hadn't been accurately counted, but that echinoderms hadn't adequately been considered with the same rigor, that is all. It was a difference in approach, not intellect.

I was just looking to get past the authority and do some analysis on the merits, y'know? Of course there can be flaws in the echinoderm approach, I wanted to find out what they were. Either I gain something useful or hallucigenia gets more interesting, right?


#18

Actually. . . I missed something had a smart friend point it out to me.

I'd forgotten how the positioning of the echinoderms itself was kind of interesting.

Between that, Balanglossus, Hallucigenia, and all the rest I'm wondering if the real answer is that back in the Cambrian they were 'all kind of the same thing', especially given that they could easily have had a much smaller amount of DNA with more in common, the morphological differences could reflect something we have less of now . . . overlapping expression of multiple common plan elements.

It's certainly a more complex view, and one I hadn't thought about much. And most definitely not one I can take credit for, but I have to agree that it makes some sense that whatever genetic diversity we had was lost when we got our first mitochondrial chimera, since presumably a narrower subset of organisms would have that competitive advantage, so assuming that was a singular event that radiated outward, the early Cambrian fossils very possibly didn't share a fraction of the diversity we have. They may have had less building blocks in their cellular machinery, resulting in creatures already apparently down one morphological branch having a large shared repository of genes to express.

It does kind of complicate things if so, doesn't it?


#19

To do analysis on the merits, you have to look at why the "authorities" came to the conclusions they did and start showing how they may have been wrong. Science isn't an authority game, it's an evidence game; you need to start by looking at the finest details available for both this beastie and the others of its time period. Which means going to the experts at least long enough to get that data.

I've been trying to find the Steven Jay Gould quote on Hallucigenia where he apologized for, like everyone else, having misinterpreted it by holding it upside down. It amounted to "when that's corrected, this is a very standard body plan for this group, and I'm embarrassed not to have seen that immediately." I admit that tends to make me skeptical about trying to declare another reinterpretation on the basis of spines (which have independently evolved many times) and what you're interpreting as tube feet (which needs more investigation and which even if so might be a parallel evolution).

Certainly I don't see the radial symmetry which the echinoderm body plan generally shows; that's one obvious point you'd need an answer to. It's possible that's an artifact of the the beast having been pressed into a single plane during fossilization, but ...

All we can do here, unless there's an expert involved, is raise questions that you'll have to resolve. To resolve them you need to start digging. If you want it to be taken seriously, it's up to you to start by taking it seriously. Most scientists are delighted when someone shows interest in their work. They aren't hard to find; hit a college with a paleontology department (preferably one which has a history of publishing on the Burgess shale critters so they're more likely to have have direct access to specimens), or a natural history museum with a paleontology research department (I'd suggest the American Museum of Natural History), and ask them "Hey, has anyone considered... and if not, why not?" If you approach it that way, rather than asserting that you Have The Solution, odds are that you'll get expert assistance in understanding what it would take to defend or refute the idea, and if you've really got something worth investigating you should be able to find someone to help you take it forward.

Scientists are usually delighted when they can say "oh, that's interesting, we didn't consider that and it's plausible." But first you need to get involved in making it plausible.

If you're serious, you've got a direction to go. I'm sorry I don't have a specific individual to point you to, but you really shouldn't have trouble finding one or two; start by firing off some letters to department heads. Meanwhile, hitting libraries which carry the field's journals to see what's been said in the past shouldn't be hard and, if you're interested in the field, might actually be a lot of fun. Hitting the high-level popularizations like Scientific American might be an easier entry, though you'll probably have to go beyond that.

Have fun.


#20

Assuredly not. At one point, the deuterostomes should have all been similar worm-like creatures, and this is the general form you see in some more basal lines like graptolites and amphioxus. But by the Cambrian, the echinoderms already their own distinct lineage, with mostly flattened or vaguely crinoid-like fossils (I mentioned Gogia, and this pdf shows some others).

Sea cucumbers are an exception to this form, but while there is uncertainty over their placement, it's in how they relate to other eleutherozoans - sea urchins, starfish, and brittle stars. Molecular trees agree with morphology that they group with them separate from crinoids. So considering them as a model for the first echinoderms, in contrast to the earlier fossils and more basal groups, would seriously limit plausibility of a model on its own.

There are likely some Cambrian groups that branch between the modern deuterostome phyla. Some that have been invoked are the shelly carpoids and the Vetulicolia, which are vaguely larvacean-like but very ambiguous. These could count as remnants of a "same-thing" period and even show some overlapping expression, though the evidence would be poor and invoking that is another weakness, because it's an easy excuse for any bad phylogeny. At any rate, though, by then the echinoderms themselves have moved on.