A new Anomalocaris mystery

by Matthew Cobb

[Originally posted at z-letter.com]

Anomalocaris – literally “unusual shrimp” – was first identified in 1892 by Joseph Frederick Whiteaves from mid-Cambrian deposits in British Columbia. It looked pretty much like this fossil, and was thought to look something like the drawing below.

One of the many things that was odd about this “shrimp” is that it never seemed to have a body or a head. All they ever found was the “tail”. There are plenty of these fossils about, and you can pick them up on eBay for a few hundred dollars (not recommended unless you are certain of provenance, that appropriate permission has been obtained, etc).

As is now well known, in 1985 Harry Whittington in Cambridge and Derek Briggs solved the mystery of the missing head of Anomalocaris, and at the same time also clarified the nature of Laggania, which was thought to be a non-descript sponge, and Peytoia, which was seen as a pineapple ring-like jellyfish thing:

They all turned out to be part of the same animal – a vicious predator which is now thought to be related to the arthropods. It still bears the nameAnomalocaris, but what was thought to be the body of the “strange shrimp” is in fact a predatorial claw, while the “legs” are thorny projections. Peytoia is the mouth of Anomalocaris, while Laggania turned out to be its body:

This was part of the Whittington/Briggs/Conway Morris redescription of the Burgess Shale animals which led Stephen Jay Gould to write Wonderful Life, and which is still the source of much debate today. At up to 60 centimetres long,Anomalocaris, and related members of the “great appendage” group are thought to have been the top predators in the Cambrian seas, spearing passing prey with their raptorial claws.

Here’s a nice model of Anomalocaris, from the Manchester Museum:

Here’s a close-up (annoyingly, I couldn’t get to see its mouth) – you can see a Burgess Shale fossil of Waptia below it:

Indeed, these predators are now known to have extended their domination of the seas into the Devonian, as shown by this recently discovered fossil ofSchinderhannes bartelsi from 407 MY ago (Kühl et al. 2009):

Many reconstructions of great appendage predators – and in particular ofAnomalocaris – show them munching away on trilobites. This video from Phleschbubble is particularly striking (Anomalocaris turns up at around 50 seconds. NB the file is pretty large so may take some time to download)

And this great drawing by Sam Gon III shows:

“two Anomalocaris canadensis converging on an Olenoides trilobite. This doesn’t necessarily imply that they engaged in cooperative hunting. The second Anomalocaris could have merely been attracted to the commotion caused by the activities of the other. It would be interesting to consider what kinds of agonistic behaviors occurred between individuals, and whether they engaged in any specialized territorial or courtship behaviors.”

This video (sorry about the music!) not only shows one eating what looks like a trilobite, it also has a pair engaging in either mating or intra-sexual conflict. This is cool but, of course, entirely gratuitous! NB the “streamers” seen on these reconstructions are typical of both Anomalocaris saron and a related anomalocaridid, Amplectobelua symbrachiata:


So, if you believe the videos (and you shouldn’t), the main diet of anomalocaridids would appear to be trilobites. But for the last couple of years Professor “Whitey” Hagadorn of Amherst College has been arguing that the evidence just isn’t there. In 2009 he presented a paper to “Walcott 2009”, a conference to mark the centenary of the discovery of the Burgess Shale deposits, and then three weeks ago he presented more data to the Geological Society of America’s annual meeting.

In an interview with Wired magazine, Hagadorn points out that there’s no direct evidence (e.g. trilobite traces in anomalocaridid guts, or clear anomalocaridid coprolites containing trilobite bits for example), and, as he explains in his 2009 abstract, while the teeth in the mouthparts look pretty sharp (see the picture above):

“Anomalocaridid mouth plates and their tips are never broken, nor are tips worn.  If plates were hard, and were used to manipulate, puncture, crush, or masticate biomineralized prey, they would be expected to show evidence of abrasion or breakage.  Absence of this evidence is striking given the frequency (0.01-1%) of healed malformations in extant marine arthropods, most of which are due to prey manipulation or feeding.  Moreover, anomalocaridid plates and their biting tips are commonly wrinkled, exhibit preburial shearing and tearing, and mantle or are deformed by biomineralized fossils such as brachiopods, trilobites, and Scenella.  Plates are preserved as organic carbon and exhibit fracture patterns typical of desiccating arthropod cuticle.  Thus anomalocaridid plates, including their tips, were unmineralized and pliable in life.”

Furthermore, in his latest presentation, Hagadorn has made a 3-D reconstruction of the mouth of Anomalocaris and found that not only was the mouth soft, it also couldn’t completely close. So – says Whitey – Anomalocaris and its fellows could do no more than suck nastily on stuff.

I’m neither a paleontologist nor do I do biomechanics, so will find it hard to judge when the data are eventually published (it may be in review, though there’s no trace of it on his website). On the basis of Hagadorn’s talks, opinion for the moment seems to be divided as to whether he is right. That may change when his work is published.

However, let’s assume he is right, and anomalocaridids didn’t eat trilobites. That simply begs the question – who did eat them? Because one thing is certain – those trilobites did get munched by something. There are apparent coprolites (= fossilised turds) that contain trilobite bits, as seen in this picture by Vannier & Chen (2005):

Furthermore, there are plenty of trilobite fossils that have chunks taken out of them, as seen here in this reference to the work of Babcock & Robinson (1989 – taken from my next Evolution of Invertebrates lecture):

The final answer will come, I suppose, when someone finds a clear association between a predator and a consumed trilobite. Until then, studies like that of Whitey Hagardorn are the best we can do.

h/t: Ray Moscow

References and links:

Babcock, L.E. and Robinson, R.A. 1989. Preferences of Palaeozoic predators.Nature, 337, 695-696.

Kühl, G., Briggs D E. G. & Rust J (2009) A great-appendage arthropod with a radial mouth from the Lower Devonian Hunsrück Slate, Germany. Science323:771-773

Vannier J. & Chen J. (2005) Early Cambrian food chain: New evidence from fossil aggregates in the Maotianshan Shale Biota, SW China. Palaios 20:3-26.

Whittington H. B. & Briggs D. E. G. (1985) The largest Cambrian animal,Anomalocaris, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London, Series B, 309, 569-609.

Anomalocaris homepage by Sam Gon III – this contains loads of anatomical and taxonomic information, as well as references, links and reconstructions – a goldmine! This is contained within an excellent website devoted to their apparent prey: trilobites.info

 

15 Comments

  1. Hempenstein
    Posted November 17, 2010 at 5:26 pm | Permalink

    Fascinating! Figure G in the Kühl plate is somewhat reminiscent of the golden catfish of Colombia of a few days ago.

  2. James Davies
    Posted November 17, 2010 at 7:05 pm | Permalink

    David Attenborough’s “First Life” program on BBC2 and Discovery channels has a very long segment on anomalocaris, including looks at the important fossils and reconstructed CGI models of what the critter looked like. Balled-up trilobites too.

  3. Diane G.
    Posted November 17, 2010 at 7:10 pm | Permalink

    However, let’s assume he is right, and anomalocaridids didn’t eat trilobites. That simply begs the question – who did eat them?

    Not to mention, “what did Anomalocaris suck nastily on?”

    (And leaving it to some other grammar-Nazi to point out that that should be “raises” the question, not “begs” it…)

    • randyextry
      Posted November 18, 2010 at 11:52 am | Permalink

      I was about to be the language nazi who points out the misuse of “begs the question,” but I’m happy to see you beat me to it.

      I think it’s a service, like telling a friend there’s food between his teeth or his fly is unzipped. And it’s educational.

  4. JoeBuddha
    Posted November 17, 2010 at 7:16 pm | Permalink

    Awesome! Whenever I get tired of variations on the same old tired body plans of modern animals, I reflect back on the bizarre Cambrian animals I first read about in Wonderful Life and all’s right with the world.

  5. Marella
    Posted November 17, 2010 at 8:25 pm | Permalink

    Maybe it used its side flaps to stir up the sediment and then fixed its mouth around exposed worm tubes and sucked out the worms, a bit like a manta ray which it somewhat resembles. Those eyestalks look like they might give a good view of the sea-floor too.

    • Dominic
      Posted November 18, 2010 at 1:24 pm | Permalink

      That sounds plausible – bottom feeder fish often have feelers – like barbel & as Hempenstein says above with catfish. [We should have a catfish-urday felid!] Also the downward pointing mouth – perhaps it sucked up mud for food particles.

  6. Posted November 18, 2010 at 12:35 am | Permalink

    If this is the sort of material that you use for your lectures – I would love to be in the class!

  7. Posted November 18, 2010 at 1:15 am | Permalink

    Excellent. I had been looking forward to your write-up.

  8. Dominic
    Posted November 18, 2010 at 5:27 am | Permalink

    Very interesting. Clearly I need to read z-letter regularly as well!

  9. Torbjörn Larsson, OM
    Posted November 18, 2010 at 6:44 am | Permalink

    So what did trilobites have to bite with?

    If some were predators (yup, says Wikipedia) and common (as I believe they were), why wouldn’t they be the likeliest suspect in cases of observed predation? If the mouth fits…

    • Dominic
      Posted November 18, 2010 at 1:09 pm | Permalink

      Predators also tend to be rarer being top of or higher up the food chain, so perhaps we have yet to find them?

      • Torbjörn Larsson, OM
        Posted November 18, 2010 at 4:36 pm | Permalink

        Good point. But if we don’t lack predators, we must eliminate the likeliest ones first.

  10. Jim Baerg
    Posted November 18, 2010 at 7:54 pm | Permalink

    BTW I take it that it is fairly common practice to name fossil creatures after local place names.

    As someone who hikes & X-C skies in the region near the Burgess Shale I recognize a lot of the names for the Burgess Shale animals. Eg: Laggans is an old name for what is now Lake Louise village & there is a Peyto Lake not far away.

    Jim Baerg 51° N 114° W

  11. Val F.
    Posted April 24, 2014 at 5:01 pm | Permalink

    I read Hagadorn’s article and I really can’t agree with his contention that the spiky appendages were used for stirring up sediment when then seem so perfectly designed for grabbing and holding. In nature, form follows function.

    If the mouth is too weak to crush trilobite shells, so be it. But isn’t it possible that the trilobites were flipped over and the soft underbelly exposed? They would then be held in this position by those same appendages and consumed at leisure.


4 Trackbacks/Pingbacks

  1. […] A mystery of Natural History has been solved! From Matthew Cobb: Anomalocaris – literally “unusual shrimp” – was first identified in […]

  2. […] exceptional, so it may not be Alu that makes us unique. Master Cobb is more interested in a new mystery. Well, two really. What did Anomalocaris suck on, and what ate the trilobites? Not […]

  3. […] the plates and tips have never shown any sign of wear and tear. In Hagadorn’s view, Anomalocaris targeted soft-bodied prey rather than being a fearsome […]

  4. […] the plates and tips have never shown any sign of wear and tear. In Hagadorn’s view, Anomalocaris targeted soft-bodied prey rather than being a fearsome […]

Follow

Get every new post delivered to your Inbox.

Join 30,197 other followers

%d bloggers like this: