Yicaris dianensis

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Early Cambrian shrimp! I just had to share this pretty little fellow, a newly described eucrustacean from the lower Cambrian, about 525 million years ago. It's small — the larva here is about 1.8mm long, and the adults are thought to have been 3mm long — but it was probably numerous, and I like to imagine clouds of these small arthropods swarming in ancient seas.

i-c756e0e5bdb78bf9c1a44de3ecced403-yicaris.gif
The head limbs are drawn in median view and the trunk limbs in lateral view.

There are a couple of notable things about this animal. One is that they're preserved in full 3-dimensional detail in an Orsten-type lagerstätte, which means they've got a dense collection in one spot with beautiful preservation of all the fine structure, right down to the fine setae (hairs) covering it. They also have multiple larval stages, so they have a developmental series revealing the post-embryonic development, and they can see how tiny cuticular structures develop. Look at these pieces:

i-9099df7e096c45b6b2b8acb79ae5c804-yicaris.jpg
(click for larger image)

a, Small larva, only head portion preserved (developmental stage 1); oblique lateral view (YKLP 10841). b, Reasonably complete, distorted specimen (developmental stage 2); lateral view (YKLP 10844). c, Distorted larva with five trunk segments (developmental stage 2); oblique anterolateral view (YKLP 10842). d, Distorted larva, only head portion preserved (developmental stage 2); oblique ventral view (YKLP 10843). e, Reasonably complete distorted specimen (developmental stage 3); oblique ventral view (YKLP 10845). f, g, Fragment of trunk (holotype; developmental stage 6); lateral view (f) and detail of epipodites on basipods (g) (YKLP 10840). h, Fragment of right side of trunk, comprising four-plus thoracomeres (developmental stage uncertain); ventral view (YKLP 10847). ik, Single post-maxillulary limb, proximal-most part with several endites broken off (developmental stage 6); anterolateral (i) and anterior (j) views, and two endites of basipod (k) (YKLP 10859). All scale bars represent 100 µm, except g (50 µm) and k (20 µm). a1, first antenna; a2c, coxa of second antenna; a2en, endopod of second antenna; a2ex, exopod of second antenna; as, anterior enditic setae; ba, basipod; cs, cephalic shield; en, endopod; ep, epipodite(s); ex, exopod; ey, eye(s); fr, furcal rami; fsb, folded soft body; la, labrum; lcl, laterocaudal lobe(s); mdc, mandibular coxa; mden, endopod of mandible; mdex, exopod of mandible; ms, median enditic seta or spine; mx1, first maxilla; mx1en, endopod of first maxilla; mx1ex, exopod of first maxilla; mx2, second maxilla; mx2en, endopod of second maxilla; ps, posterior enditic setae; t1en, endopod of first trunk limb; t3pe, proximal endite of third trunk limb; t7en, endopod of seventh trunk limb.

i-48ee1cb9fd89b47337c69e5374147a22-epipode.jpg

Two more things make it interesting. One is its age; this creature is very old, from the Atdabanian, which puts it back near the beginning of the Cambrian…yet it's also a eucrustacean. That means the divergence time of the arthropods has to be pushed back into the pre-Cambrian (which really isn't much of a surprise). Another is that it possesses curious little flaps of tissue on the limbs which don't look very impressive, but are actually epipodites, a branch of the limb. Epipods are cool structures that got coopted into respiratory functions and form epipod gills, and most impressively, are thought to have been thoroughly modified to form the wings of insects. Yicaris demonstrates the primitive origins of some very important arthropod characters.


Zhang X-g, Siveter DJ, Waloszek D, Maas A (2007) An epipodite-bearing crown-group crustacean from the Lower Cambrian. Nature 449:595-598.

More like this

Okay, a beautiful eucrustacean from the Atdabanian implies that crustaceans were running around during the Precambrian. This argument has been made for many clades of animals that first show up in the Cambrian fossil record.

So why is the Precambrian record for all of these groups missing, or at the best paltry? I'm not saying the first assertion doesn't make sense. It does. But it begs the next question.

"So why is the Precambrian record for all of these groups missing, or at the best paltry?"

The rabbits ate them.

Where'd they find them?

couple of reasons, Allen -

Precambrian rocks in good shape are harder to find. Thus fossils from them are harder to find. and good fossils harder still. Simply because there's been more time for the geological processes to grind up existing Precambrian rocks.

Also, if the most common sedimentary conditions in the Precambrian didn't lend themselves to making laggenstaten deposits as often as they did in the Cambrian, you get even *fewer* precambrian fossils.

(how much coastline was there in the Pre-Cam? lots of individual landmasses, with lots of coastline, or one big one?)

Phil, sure but do you have any good tips on how to hatch the 500 million year old eggs?

By Fernando Magyar (not verified) on 10 Oct 2007 #permalink

You really don't sleep, do you.

Please tell me the secret. I just slept through writing a paper that's due.

Paul Myers has died. He was a native of Washington state.

Of course this is just a person with a similar name to PZ--sorry creationists.

From gills to wings - tight.

OK, let's get this out of the way right now:
But if insects are descended from shrimp, why are there still shrimp?

PYGMIES and DWARFS! PYGMIES and DWARFS!

By Reginald Selkirk (not verified) on 10 Oct 2007 #permalink

"Paul Myers has died. He was a native of Washington state.
Of course this is just a person with a similar name to PZ--sorry creationists.
"

Weird. They found him a mortuary just for people named Paul.

OK, isn't anyone going to pony up a recipe for lower Cambrian cocktail sauce?

By Bill Dauphin (not verified) on 10 Oct 2007 #permalink

OK, isn't anyone going to pony up a recipe for lower Cambrian cocktail sauce?

They can't, because it's irreducibly complex!

Allen #2 says, "So why is the Precambrian record for all of these groups missing, or at the best paltry? I'm not saying the first assertion doesn't make sense. It does. But it begs the next question."

Well, that might just indicate the emergence of hard body (chitinous) parts around or just before that boundary, nay? Before that, you have mostly soft-bodied critters (of this same lineage) that hardly ever fossilize decently. After that you find these hard structures on critters that are relatively much easier to preserve.

By Arnosium Upinarum (not verified) on 10 Oct 2007 #permalink

Weird. They found him a mortuary just for people named Paul.

This makes it exceedingly easy to recruit Paul-bearers.

(how much coastline was there in the Pre-Cam? lots of individual landmasses, with lots of coastline, or one big one?)

Well, not a lot of coastline in comparison to some later times because so much land was submerged. But for what was subaereal, yeah...good amount of coast.

check out the following:

http://www.scotese.com/precambr.htm

Well since this is from the early Cambrian, then we can safely assume that the shrimp is its own kind. Cow kind... horse kind... dog kind... shrimp kind!

Walt Brown's take is interesting. But sadly, what is most interesting about it is how clearly it illustrates his ignorance of geology.

Yicaris dianensis Etouffee

First, peel and de-vein 20,000 Yicaris dianensis...

I'm in awe. Gawd was thinking 650 million years ahead to "Endless Shrimp Friday" at the Sizzler. The lord truly works in mysterious ways.

Yow! Nice epipods on that eucrustacean!

To be a eucrustacean means that the speciation events separating the lineage of today's crustaceans from the lineages that went on to become hexapods and chelicerates (and trilobites) were earlier--thus the chitinous exoskeleton with jointed appendages predates the Cambrian.

By Sven DiMilo (not verified) on 10 Oct 2007 #permalink

The Orsten is an absolutely exceptional kind of rock. There is one known from the whole Cambrian, and zero from the Precambrian, so far. Neither are any other exceptional kinds of deposits, like what is seen in the Burgess Shale and in Chengjiang, currently known from the Precambrian.

Aren't epipodites normal for arthropods including anomalocaridids?

The Atdabanian is near the end of the Early Cambrian, some 523 to 519 million years ago; the Cambrian began 542 million years ago. However, Parvancorina and friends are probably trilobite larvae, which means there really were arthropods in the narrowest sense quite some time before the Cambrian.

By David Marjanović (not verified) on 10 Oct 2007 #permalink

Oops... there are, of course, two Orsten-type rocks known from the Cambrian, because the Orsten itself is in Sweden, and Yicaris is from China...

By David Marjanović (not verified) on 10 Oct 2007 #permalink

Nice "bug"; PZ says it is from about 525 million years ago.

"The Atdabanian is near the end of the Early Cambrian, some 523 to 519 million years ago; the Cambrian began 542 million years ago."

Thank you David Marjanović. Now, the next two questions are,

(a) What determines the boundary/age between the pre-Cambrian and the Cambrian?

(b) How old is the Burgess Shale?

Re: #3

[guffaw!] That's some (J)BS!

-- CV

By CortxVortx (not verified) on 10 Oct 2007 #permalink

What's this I hear about calling the Etruscans "shrimp?" Why, the Etruscans made important contributions to Western civilizations! Sure, the poor Etruscans might have been of smaller stature than most people are these days, but no doubt they didn't have the nutritional advantages...

What's that you say?

Oh.

Never mind.

By Emily Litella (not verified) on 10 Oct 2007 #permalink

a) The boundary has been defined. It is a spike in the carbon isotope ratio, "2.4 m above base of Member 2 of Chapel Island Fm., Fortune Head, Burin Peninsula, southeast Newfoundland, Canada". There happens to be a nice site in Oman that has allowed radiometric dating of the boundary.
b) Oops! Forget "Early Cambrian". The Cambrian period is now divided into four epochs; the Atdabanian is probably in the 2nd one (still unnamed) -- I'll try to look that up tomorrow in the lab. The Burgess Shale is 510 million years old or something, IIRC, so probably it's in the 3rd epoch (also unnamed).

BTW, "Precambrian" is the correct spelling (following the Hyphen War sometime in the early 20th century, AFAIK), but that term isn't official anymore anyway...

By David Marjanović (not verified) on 10 Oct 2007 #permalink

Dear Changcho:

a) Stratigraphers determine the boundary between the Ediacaran Period of the Neoproterozoic Era and the Cambrian Period of the Cenozoic Era. :-) But the criteria they use is the same as for other boundaries: the define a "type section" with some attribute that can be correlated to other localities. The type section for the base of the Cambrian is in southeastern Newfoundland, and the attribute is the first appearance of the trace fossil (burrow) Phycodes pedum. You can read about the details here.

b) The Burgess Shale community is from the Middle Cambrian (sometime between 513 and 502 Ma, but I'm not a Cambrian worker and so don't know closer than that). Consequently, it is still some 30 million years or so younger than the beginning of the Cambrian (541 million years ago).

Hope this helps!

hey, thanks for that link, David!

that's a very handy resource.

That's not the first time I post that link! :-)

The 3rd epoch is supposed to have began 513 Ma ago and ended 502 Ma ago, so that's the same as the former Middle Cambrian, and the (very long) Early Cambrian has been divided in two. That means the Burgess Shale is in the 3rd epoch. (The page says "series" because it uses the nomenclature for rocks, not the one for time.)

and the Cambrian Period of the Cenozoic Era. :-)

...of the... Paleozoic Era. <duck & cover>

By David Marjanović, OM (not verified) on 10 Oct 2007 #permalink

I had to wait until I talked to a few people and was sent a copy of this paper before responding, we get Nature 2 weeks late here.

There are two questions, 1) is it a crustacean? and 2) does it have epipodites?

Is it a crustacean? Well yes, if you accept the authors classification which also makes insects and myriapods crustaceans. Hmm . . .

You say toh-may-toh, I say toh-mah-toh,
You say Crust-a-cea, I say group Man-dib-u-lata!

However, It does appear to be most closely related to the branchiopods + cephalocarids, and is certainly the most crustacean-like form we have found in the Cambrian.

Does it have epipodites? This identification has generated some discussion, and I am trying to get some info on exactly what that discussion is. So it may have, but let's not count our epipodites before they evolve into insect wings

Neat find though.

David Marjanović wrote:

However, Parvancorina and friends are probably trilobite larvae

Whoa. I don't think that's right. Some of the suckers got to over 5.08 cm long. If they are larvae, I'd hate to meet a fully grown adult! Besides where are the adults? if we get larvae preserved in coarse sandstone, why do we not find adults at all, anywhere, ever?

Oh yeah, and don't listen to Holtz, he's a cladogram-munching, dirtyfilthystinkingrottenvertebratist :-)

By Chris Nedin (not verified) on 10 Oct 2007 #permalink

The Atdabanian (which is Siberian, not official/international) does appear to be in stage 2 of the Cambrian.

Oops! Parvancorina and friends are supposed to be adult, yet still the sister-group of the trilobites. Follow the links from comments 235 and 236 in this monster-thread.

By David Marjanović (not verified) on 11 Oct 2007 #permalink

Very interesting, thanks! The stratigraphy.org link answers many of my questions as well.

Cheers.

I finally had a chance to read the paper and the supplementary information. No phylogenetic analysis was done, only a few characters the authors find convincing or important are mentioned. While several phylogenetic analyses are cited, only one uses molecular data, and the morphological ones all seem to use few taxa and probably few characters. I haven't seen a mention of Euthycarcinoida, for example (extinct; proposed elsewhere to be the sister-group of Crustacea + Hexapoda -- with Myriapoda being far away). It is also not quite clear what happens to the names they use if the phylogeny changes, because they don't use phylogenetic definitions.

Considering stratigraphy.org, visit it every once in a while. It keeps changing. :-)

By David Marjanović (not verified) on 11 Oct 2007 #permalink

Yep, and as someone pointed out to me, notice their Eucrustacea node. Insects are only excluded from being inside Eucrustacea because they lack a nauplius (a non-feeding pelagic larva). A non-feeding pelagic larva is not really likely to be retained by an animal that hatches out of an egg on the underside of a leaf in the desert after 400 million years of terrestrial ancestry!

By Chris Nedin (not verified) on 11 Oct 2007 #permalink

There have been raised so many interesting questions around our new fossil crustacean that it is difficult to comment upon them in just one mail. I think we wrote 520, so don't know why 525 crept in. Epipodites: this is a bigger thing, and many authors have mismatched a lot around these. I put some stuff already onto our CORE website, so please have a look there under evolutionary implications - epipodites. And no, anomalocarids had no such things. They are in our view exclusive for eucrustaceans. Orsten: the original limestone nodules, as in Sweden, have shown to be only one source. Other rock yielding Orsten 3D animals may be plate-like etc. The record ranges now from North America to Europe, Siberia, China and Australia, and in time from the Lower Cambrian to the Lower Ordovician. See our website. Orsten-type 3D phosphatised fossils are also embryos which have been found in Precambrian rock - Doushantuo formation, China. Younger rocks having yielded such animals are, e.g., from the Triassic (ostracodes and even protozoan ectoparasites on them) and even the Lower Cretaceous, where little ostracodes and a aprasitic copepod have been discovered on fish carcasses in the Santana Formation. For more details or questions, just write to me. Cheers, DIETER - sorry for typos and bad English, I am German

By Dieter Waloszek (not verified) on 17 Oct 2007 #permalink

There have been raised so many interesting questions around our new fossil crustacean that it is difficult to comment upon them in just one mail. I think we wrote 520, so don't know why 525 crept in. Epipodites: this is a bigger thing, and many authors have mismatched a lot around these. I put some stuff already onto our CORE website, so please have a look there under evolutionary implications - epipodites. And no, anomalocarids had no such things. They are in our view exclusive for eucrustaceans. Cheers, DIETER - sorry for typos and bad English, I am German

By Dieter Waloszek (not verified) on 17 Oct 2007 #permalink

In addition to his comments above, Prof. Waloßek just wrote me an e-mail saying I have misinterpreted the Yicaris paper in several important respects, and especially assumed stuff wasn't done just because it isn't mentioned in the paper (Nature has very harsh space restrictions). So don't take my word for anything.

Importantly, I seem to have confused epi- and exopodites...

Recommended further reading.

By David Marjanović (not verified) on 28 Oct 2007 #permalink

Prof. Waloßek also pointed out that, while interesting, the euthycarcinoids are currently difficult to compare to anything because their head anatomy is very poorly known and apparently not very similar to anything else. So it's not surprising they weren't considered in the paper. I suppose we'll just have to wait for new discoveries.

By David Marjanović, OM (not verified) on 28 Oct 2007 #permalink

The Orsten is an absolutely exceptional kind of rock. There is one known from the whole Cambrian, and zero from the Precambrian, so far. Neither are any other exceptional kinds of deposits, like what is seen in the Burgess Shale and in Chengjiang, currently known from the Precambrian.

Aren't epipodites normal for arthropods including anomalocaridids?

The Atdabanian is near the end of the Early Cambrian, some 523 to 519 million years ago; the Cambrian began 542 million years ago. However, Parvancorina and friends are probably trilobite larvae, which means there really were arthropods in the narrowest sense quite some time before the Cambrian.

By David Marjanović (not verified) on 10 Oct 2007 #permalink

Oops... there are, of course, two Orsten-type rocks known from the Cambrian, because the Orsten itself is in Sweden, and Yicaris is from China...

By David Marjanović (not verified) on 10 Oct 2007 #permalink

a) The boundary has been defined. It is a spike in the carbon isotope ratio, "2.4 m above base of Member 2 of Chapel Island Fm., Fortune Head, Burin Peninsula, southeast Newfoundland, Canada". There happens to be a nice site in Oman that has allowed radiometric dating of the boundary.
b) Oops! Forget "Early Cambrian". The Cambrian period is now divided into four epochs; the Atdabanian is probably in the 2nd one (still unnamed) -- I'll try to look that up tomorrow in the lab. The Burgess Shale is 510 million years old or something, IIRC, so probably it's in the 3rd epoch (also unnamed).

BTW, "Precambrian" is the correct spelling (following the Hyphen War sometime in the early 20th century, AFAIK), but that term isn't official anymore anyway...

By David Marjanović (not verified) on 10 Oct 2007 #permalink

That's not the first time I post that link! :-)

The 3rd epoch is supposed to have began 513 Ma ago and ended 502 Ma ago, so that's the same as the former Middle Cambrian, and the (very long) Early Cambrian has been divided in two. That means the Burgess Shale is in the 3rd epoch. (The page says "series" because it uses the nomenclature for rocks, not the one for time.)

and the Cambrian Period of the Cenozoic Era. :-)

...of the... Paleozoic Era. <duck & cover>

By David Marjanović, OM (not verified) on 10 Oct 2007 #permalink

The Atdabanian (which is Siberian, not official/international) does appear to be in stage 2 of the Cambrian.

Oops! Parvancorina and friends are supposed to be adult, yet still the sister-group of the trilobites. Follow the links from comments 235 and 236 in this monster-thread.

By David Marjanović (not verified) on 11 Oct 2007 #permalink

I finally had a chance to read the paper and the supplementary information. No phylogenetic analysis was done, only a few characters the authors find convincing or important are mentioned. While several phylogenetic analyses are cited, only one uses molecular data, and the morphological ones all seem to use few taxa and probably few characters. I haven't seen a mention of Euthycarcinoida, for example (extinct; proposed elsewhere to be the sister-group of Crustacea + Hexapoda -- with Myriapoda being far away). It is also not quite clear what happens to the names they use if the phylogeny changes, because they don't use phylogenetic definitions.

Considering stratigraphy.org, visit it every once in a while. It keeps changing. :-)

By David Marjanović (not verified) on 11 Oct 2007 #permalink

In addition to his comments above, Prof. Waloßek just wrote me an e-mail saying I have misinterpreted the Yicaris paper in several important respects, and especially assumed stuff wasn't done just because it isn't mentioned in the paper (Nature has very harsh space restrictions). So don't take my word for anything.

Importantly, I seem to have confused epi- and exopodites...

Recommended further reading.

By David Marjanović (not verified) on 28 Oct 2007 #permalink

Prof. Waloßek also pointed out that, while interesting, the euthycarcinoids are currently difficult to compare to anything because their head anatomy is very poorly known and apparently not very similar to anything else. So it's not surprising they weren't considered in the paper. I suppose we'll just have to wait for new discoveries.

By David Marjanović, OM (not verified) on 28 Oct 2007 #permalink