Predation on Trilobites

Steve Forden

Nov 17, 2003
Hi Phil,

Here are the abstracts of the references I suggested to you over on the BBC board. None of them are exaclt what you call general reviews, but hopefully you can get something from them. Enjoy!

From Brandt:

A comparison of ecdysial patterns between trilobites and other macrobenthic marine arthropods (crabs, shrimp, lobsters, horseshoe crabs) reveals differences that may have evolutionary consequences. Limulus and many malacostracans apparently have a signature ecdysial style; conversely, a range of moult configurations characterized trilobite ecdysis, and this variation is evident even within individual species. A canalised ecdysial habit may be safer or metabolically more efficient and therefore, summed over the history of the class, evolutionarily advantageous. Some trilobite clades show evolutionary trends toward morphologies that would have facilitated ecdysis (e.g. reduction in the number of thoracic segments, reduction in the number and prominence of spines), but co-adaptation or multiple-use effects complicate the evolutionary signal of eedysial selection. Survivorship analysis supports a possible link between ecdysial habit and evolutionary success: genera with fewer thoracic segments (= easier ecdysis) are longer-lived. The increased predation pressure on trilobites through the Palaeozoic would have amplified the evolutionary impact of an inefficient moult habit. The cumulative effects of a less-than-optimal ecdysial habit, and a physiology that apparently required reconstituting a calcitic exoskeleton de novo with each moult, are compelling biotic factors to consider in examining functional interpretations, life histories, evolutionary trends, and ultimate disposition of the Trilobita.

From Nedin:

The giant Cambrian form Anomalocaris is considered to have been a raptoral predator of trilobites. However, doubt has been raised about its ability to successfully predate on strongly biomineralized forms (durophagy). A specimen of the trilobite Naraoia from the Early Cambrian Emu Bay Shale of South Australia represents the earliest direct body fossil evidence of predation on nonbiomineralized individuals. Analysis of arthropod cuticle rheology and examination of the injuries inflicted on this specimen suggest that Anomalocaris was the predator. It appears that some anomalocaridids actively utilized their large frontal appendages to rapidly flex trilobites during predation. Comparison with predation damage from mineralized trilobites and coprolites suggests that this method of flexing allowed durophagous predation.

The presence in the Early Cambrian of durophagous, nonbiomineralized predators may have important implications for the role of predation pressure in the acquisition of mineralized cuticles and the rise of enrollment in trilobites. Variation in the frontal appendages of anomalocaridids indicates that niche partitioning within the genus was well established by the late Early Cambrian.

From Pratt:

The lower Rabbitkettle Formation of northwestern Canada is a monofacial Upper Cambrian unit of variably calcareous, argillaceous siltstone and fine-grained sandstone with rare bioclastic grainstone, deposited on a gentle slope below fair-weather wave base with no discernible fluctuation in water depth. The trilobite fauna is a mixture of pandemic agnostoids and Lau rentian polymeroids. including protaspides and meraspides, and individuals are disarticulated, non-abraded and mostly oriented convex-upward. Bioclasts are interpreted as in situ elements affected only by weak bottom currents and storm-induced turbulence. A major proportion of the larger (greater than or equal to 5 mm across) polymeroid cranidia and pygidia in the lower parr (Marjuman) of the formation are broken; large thoracic segments are often broken at the axial furrow and some broken free cheeks occur, but essentially no broken agnostoids or hypostomes were observed. Trilobites are not broken in upper beds (Steptoean), above the base of the Glyptagnostus reticulatus Zone. Physical breakage cannot be dismissed entirely, but most damage is interpreted to be due to size-selective predation, possibly through lethal blows similar to those delivered by some extant stomatopod crustaceans. A possible culprit may be an animal akin to Yohoia, known from the Middle Cambrian Burgess Shale. The distribution of attacked trilobites serves as a prosy for the presence and disappearance of soft-bodied carnivores. In the Rabbitkettle Formation, it suggests that Burgess Shale-type animals may have persisted into the Late Cambrian but suffered extinction at the Marjuman-Steptoean 'biomere' event when most trilobite species vanished.
Thanks Steve.

Well, I almost understood the second extract, though I’m afraid most of the first and third extracts left me in a bit of a muddle. I think I need to find a ‘Dictionary of Arthropod Palaeontology’ to understand some of the terms used.

In one of the few parts I did understand, interesting to note that the arachnomorph Yohoia is considered to have been a possible trilobite predator, perhaps it was a form of mantis shrimp of its day. I wonder how exactly its forelimbs would have functioned? Perhaps the spines that Yohoia had on its front appendages were analogous to the ‘spearing’ form of mantis shrimp we have today.

If anyone is wondering what this topic is about, Steve and myself were discussing trilobite predation on a BBC web-site. I am trying to gather evidence of possible nautiloid predation on trilobites, after all, one simply cannot assume this happened.

I must do some reading.


Welcome to TONMO by the way!

:trilobit: :welcome:

Welcome to TONMO, where the past, present, and future is cephalopods!

I liked the abstracts. I can understand the evolutionary importance of ecdysis in arthropod evolution. I've never stopped to think about it, but it makes sense... slow moulting is a recipe for quick death.

So trilobites had different exoskeletal composition across the board, huh? Just like crustaceans.... Good to see that some things don't change with time. Do you know if the composition was dependent on pressure, diet, etc.?

Thanks for posting! Please post more! :smile:

Sushi and Sake,

I was just reading about Steve and his beached whales, and got to thinkin:
even if we could get in our Way-Back machine and go back 100my, or 350my, would we have to look for beached mosasaurs, or giant devonian fish, go through their stomach contents and find cephalopods, then go through the cephalopods stomach contents to see what cephalopods were eating? And would we stink afterwards? Or could someone just find a fossil that answered all the questions?

Still searching.

Architeuthoceras said:
...then go through the cephalopods stomach contents to see what cephalopods were eating?

I wonder if any studies have been done on Palaeozoic cephalopod faeces? It would be intriguing to find out if faecal matter has been discovered in context with conchs. It would also be interesting to find out the composition of Nautilus faeces and their form; perhaps ancient nautiloids excreted crustacean and trilobite exoskeleton fragments in a similar manner. (Are these in a form of a stream or pellet?)

I have no doubt that the due to their intrinsic buoyancy the majority of nautiloid shells were deposited at the whim of oceanic currents as opposed to deposition at the location of mortality, by which time the soft parts would have decayed. The faeces would certainly not be found in proximity to the body, if they could be identified at all. Perhaps though in lagerstatten or areas of sudden environmental event, such as, say, a mudslide killing and burying specimens, then faecal material would be preserved in the form of associated ejected material or stomach crop?

Here is a trilobite that displays predation. The culprit was almost certainly Anomalocaris as the trilobite predates predatory nautiloids and there was little else that preyed on them at that early time. Hope no-one minds an image of a trilobite that is not directly cephalopod related, but as this is an unusual specimen I thought it is worth an image.

I have not identified the trilobite species yet but it hails from the Cambrian Spence Shale in Utah. It is a primitive Ptycoparid trilobite, and if one looks closely one can see a bite mark in the distal end of its thorax and pygidium.

If anyone would like to see it, I have an even more unusual fossil, an actual Anomalocaris coprolite (excrement) containing ground up trilobite fragments from the same location. Please just shout and I'll scan an image.


:trilobit: :trilobit: :trilobit: :trilobit:
OK Kat, here you go.

The Anomalocaris coprolite specimen measures about three inches across and is, as you can see, a donut shape complete with a hole in the middle. The perimeter is composed of dozens of small fragments, I have labelled up a few of the more obvious ones, notably trilobite head-shields (cephalons). I have only labelled a few bits and pieces, otherwise the picture would be a mass of arrows. A few very ground up brachiopods are also visible. The trilobite fragments are mostly Ptychoparid, the ubiquiteous Elrathia is part of this group, though I think a tiny blind Agnostid is also visible. Precisely what species they are is something I will have to research, this specimen only arrived two days ago.

It dates from the middle-Cambrian Spence Shale in Utah and is, I think, a very unusual specimen indeed. This is the first one I have ever seen! How do we know Anomalocaris was responsible for producing this turd? Nothing else was big enough to produce a three inch donut shape at that time. Simple!
Phil said:
How do we know Anomalocaris was responsible for producing this turd? Nothing else was big enough to produce a three inch donut shape at that time. Simple!

How do we know that? :smile:

Thanks for posting this stuff, Phil. I've never seen or even heard of fossil poop that old before, and I'm very surprised that its condition is so good.

That is truly the shiznit.
um... said:
How do we know that? :smile:

Well um... I don't suppose anyone could ever be 100% certain given the incompleteness of the fossil record. However, as I'm sure you know that period of time has been recorded in three or four exceptional fossil sequences, e.g Burgess Shale, Chen Jiang, Sirius Passett, etc, and so far nothing has come to light that would indicate another animal of comparative size to Anomalocaris. Maybe some other animal will come to light in the future but as these fossils are some of the most intensely studied invertebrate faunas in the world I'm sure something would have been unearthed by now.

It would be interesting to find out if modern arthropods produce comparative ring shaped excreta. I wonder if the diameter of Anomalocaris' anus could be calculated? (I can't believe I'm writing this...)

If anyone is curious the chap who sold me the specimen has just told me the bitten trilobite posted above was Bythachelius typicum. It was described by Charles 'Doolittle' Walcott in 1908, the person who discovered the Burgess Shale.

(Thanks Jake, if you are reading this!)
Phil said:
Nothing else was big enough to produce a three inch donut shape at that time. Simple!

.... what kind of animal produces a donut-shaped turd? There must be a science involved, something like coprolitology; would not a turd come out like a sausage or liquefied splat?

I still haven't mastered blowing smoke rings ..... but I've just discovered a new challenge in my life.

(Ed, oooops, just saw your later post Phil; perhaps arthropods have a rather unique anus with some central tongue-shaped thing to make the hole .... but that just doesn't sound right; I never cease to be surprised though).
I’m just guessing here, but here’s a thought.

Perhaps we are not looking at a coprolite but regurgitated anomalocaridid vomit? It would certainly explain the shape as the anomalocaridids had ring shaped mouths of approximately corresponding dimensions. If the animal was sick close to the sea bed it might explain how the ring shape had remained pretty much intact as opposed to drifting down and fragmenting. It is hard to imagine the shape of an anus that could produce a ring shaped turd.

Perhaps the thing had one trilobite too many?

I'm just guessing, because I don't know anything about anomalocaridid butts, but I've seen stools produced by terrestrial critters (dogs) that were laid down in a spiral. Perhaps the anomalocaridid scat's ring-shape was produced as the result of a twisting motion started in the lower GI tract, or the animal actually moving in a circle whilst defecating?