In case you missed it, today marks the end of Cephalopod Awareness Day 2011. I cannot decide if it is comedy or tragedy that the cephalopod who garnered the most awareness this week is one that probably never existed. “Triassic Kraken” has already entered the hyper-meta phase: here is a reaction to the reaction to the reaction to the early “reporting” on the story.
But amidst the orgy of credulity, incredulity, joy, anguish, laughter and rage (and whatever this is supposed to be), it struck me that something was missing. I have seen loads of skeptical remarks from vert paleo types, and certainly we are well suited to critique the work, but it seems nobody thought to ask the opinions of those that have studied the middens left behind by living octopodes.
So I did.
I fired off a list of questions to two midden experts, Dr. Richard Ambrose and Dr. Jennifer Mather, both of whom have published multiple papers on the topic of octopus middens. Both were incredibly gracious in providing detailed and thoughtful replies within hours.
My interest here was not whether McMenamin’s scenario is realistic. Clearly it is, at best, wild and highly imaginative speculation.
But I was interested whether it might be feasible to identify octopus middens in the fossil record. How we might identify vertebrate victims of cephalopod predation? And, leaving aside the whole “self-portrait” thing, is it really feasible that a giant bathypelagic squid would be exhibiting behavior associated with shallow water octopods.
In short the answers seem to be: 1) “Probably” 2) “Hard to say” and 3) “No.”
Both Dr. Ambrose and Dr. Mather were kind enough to allow me to share their comments:
me: What are the prospects of successfully identifying octopus middens in the fossil record (i.e. are they permanent enough features that they would be likely to be buried by sediment, and would they be readily distinguishable from storm deposits)?
Richard Ambrose: I think middens could be discovered in the fossil record. Depending on the species, octopuses may den at the same location for a considerable time (“considerable” being relative, since octopuses are semelparous and most species live only a few years at most; even the giant Pacific octopus probably lives only 5 years or so) and they would continue to deposit midden items as long as they occupied the site. Moreover, good denning sites are often limited, so even once on octopus vacated the den site another would be likely to take up residence, further building up the midden. When we are looking for middens while diving, we focus only on the recent midden items because these are whiter and more conspicuous, but I would not be surprised to see an accumulation of midden items over many years.
Of course, many midden items are dispersed by currents. For example, we rarely find many crab exoskeletons because they are easily swept away by currents. Depending on the location, even heavier items like clam and snail shells can be dispersed. So for the middens to enter the fossil record, you would need some event, like dramatic sedimentation associated with a storm or perhaps an undersea slide, to preserve the items in place. But this is not inconceivable, especially after a storm. I do think they likely could be distinguished from storm deposits. Although storms might deposit a concentration of shells in one area because of local topography, most items would be widespread over the storm-affected area.
Jennifer Mather: Prospects would probably be good, some but not all fossil remains get buried in soft sediment. Distinguished from storm deposits would be possible. First they might have drill and chip marks on the shells–chips on clams, drills on clams, snails and sometimes crustacean claws. Drill holes of cephs are tiny, too and specifically placed (Marion Nixon did a lot on that). Not all shells are drilled or chipped, though. Second, they WOULD NOT be broken. Cephs have partial digestion externally, they scrape and digest out the soft parts leaving a disarticulated set of crab shell pieces or empty clean mollusc shells. Shell collectors prize octopus middens. So a midden would have a nice complete collection of crab parts, for instance, and if it was in soft sediment and got buried quite quickly, it might get well preserved. I remember watching the ‘fate’ of the eight blue shells of one octopuses chiton meal. They slipped down the pile and slowly got buried, when I exhumed the whole thing much later, the blue winged shells emerged one by one, very well preserved and with a drill hole in one valve.
me: Assuming vertebrate remains would not show the drill holes characteristic of shelled prey, what signs could we look for to indicate cephalopod predation?
RA: That’s true, only shells are likely to show indisputable evidence of octopus predation. (Octopuses also “drill” crabs, but those would be quite perishable.) For vertebrates, they would just eat the flesh. There might be some dis-articulation, but the fish eaten by the octopuses I’ve kept in the lab were not pulled apart, so I don’t know how common that would be. So it would be very hard to find marks or other characteristics that would indicate consumption by a cephalopod. There might be scrapes from the beak on bones, but I’ve never looked at/for these and I would think they would not be very distinctive.
me: How widely distributed is midden building behavior among octopus species? Has it evolved more than once? Is it known from deep sea or pelagic species?
RA: This is really the key issue, I think. Midden building is very common among octopuses, but it seems to me that it is most likely a simple consequence of their denning behavior and the fact that they often (but not always) bring food back to their den for consumption. Hence, they discard prey items outside of their dens. There is some manipulation of discarded food items and other items – like rocks – by octopuses in their dens, most often to close or partially close the opening to the den. But I’ve never noticed anything like a systematic arrangement of items as a means of communication (like some birds do, such as bower birds) or artistic expression – no self-portraits that I’ve ever noticed, despite the intelligence of the species I’ve studied! Note: this is not to say that something like communication through prey discard items isn’t possible. I could see how it could evolve (and maybe that would be something to look for!), I just don’t know of any examples of it occurring.
So, as far as I know midden formation is likely to occur anytime octopuses den in one place for any period of time. This is restricted to relatively shallow water octopuses. Even then, most octopuses living on soft bottom habitats would not produce dens under most circumstances. Deep sea octopuses and pelagic species do not, as far as I know, take shelter in dens or produce middens. This makes sense; there are no caves or holes in the deep sea, for the most part. Especially any species that would forage widely, like up in the water column, would have little reason to return to a particular place to eat.
I know of no examples of non-octopus cephalopods (squids or cuttlefish) producing middens. Cuttlefish closely associated with reefs might be a reasonable candidate for producing middens, but I have never heard of this. Any cuttlefish or squid living in the water column would be extremely unlikely to produce middens.
JM: Middens aren’t really built. Octopuses do build ‘walls’ of rocks in front of the home. But when they eat prey at home, they just push out or blow out with a jet of water, or leave shell remains in the home. It’s more like a garbage heap. We don’t know a lot about octopus species, we’re particularly short of field work. However, midden remains have been assessed in the Mediterranean, the Caribbean and Bermuda, off the coast of Brazil and up the Pacific coast of North America (these are published papers, there are probably other assessments). My guess is that it evolved fairly early in the ancestry of octopuses, it’s likely widespread because all you need is a sheltering home and the habit of tossing your trash out. It is limited by topography, remains aren’t found where there is a strong current, they obviously get whisked away. Middens are NOT found in pelagic species because there is no place to put them, squid do not make middens and cuttlefish probably do not either. Deep sea octopus species might, it depends on what they find to eat.
Top – Illustration from Victor Hugo’s Toilers of the Sea (1888 Crowell Edition).
Middle – Figure from Elizabeth Harper (2002) “Plio-Pleistocene Octopod Drilling Behavior in Scallops from Florida” Palaios 17:3 292-296 DOI: 10.1669/0883-1351(2002)017<0292:PPODBI>2.0.CO;2