Let's review a couple of key concepts that prove useful for this post. Decomposers- bacteria/fungi- do the actual breaking down of the key nutrients, organic and inorganic, from dead stuff. They chemically liberate the trace elements, proteins. lipids, starches, and carbs that in turn are more easily swallowed up by themselves or other organisms. Detritivores actually ingest internally discrete chunks of detritus. In doing so they are not only ingesting the dead material- but also consuming the decomposers already subsisting on it. And this is an important concept. By the time an earthworm gets to a leaf on the forest floor it has already been colonized by several stages of microbes who have themselves digested the lion's share of sugars, proteins and lipids. But the decayed leaf is not nutritionally void for the earthworm- it gets benefits from eating spore and bodies of the bacteria/fungi themselves which are full of lipids and proteins. Now it is true that many detritivores target the cellulose/lignin in plant stuff- but even here bacteria/protozoans are needed to digest it and are found in the consumers digestive system. But the relationship between decomposers and detritivores is not a one way street- detritivores "shred" material creating more surface area for microbial decomposers to take hold. Detritivores also spread microbes through faecal pellets. So both decomposers and detritivores work hand in hand for maximal nutrient cycling.
|Purple Snout Mite (c) USD|
It might sound strange and incongruous with what is seen in modern ecosystems but let me make an analogy with baleen whales. Baleen whales, including the largest animals ever evolved, are famous for subsisting on some of the more smaller critters of the ocean. Rorquals actually go after discrete chunks of schooling baitfish/krill. Their "lunge feeding" technique, which has been described as the 'single largest biomechanical action in nature' is best seen as a type of active predation. Something like a bowhead whale shows a more passive processing of large volumes of water. But I am drifting a bit here 'scuse me- the point here is that baleen whales take up ecological space that might otherwise be occupied by small fish, sea birds, squid etc etc.
So if you are following my torturous logic you probably see where I am going with this- were there ever any terrestrial mega-detritivores in earth history that hijacked ecological space traditionally occupied by less robust critters? Something like a giant walking compost bin? Interestingly there is a bit of evidence pointing to dinosaurs occasionally enjoying a bit of detritus.
In 2007 Karen Chin wrote a paper The Paleobiological Implications of Herbivorous Dinosaur Coprolites from Two Medicine Formation of Montana: Why Eat Wood? which addresses some unusual dino shit. The dino dung in question, (there are several), is unusual for being composed mainly of woody conifer fragments. That the conifer wood was already in a state of decay is evinced by the evidence of fungi degradation. And Chin makes the assertion that the dinosaur was seeking to exploit the nutritive benefits from the fungi and possibly other critters in the decaying wood- rather
|Nature of Robertson.blogspot|
It should not go without notice that the dino poop in question in the paper is most certainly from Maisaura peeblesorum. The Two Medicine formation is dominated by the famed "Good Mother Lizard" and both Maisaura eggshell and bones are found at this Late Cretaceous dino latrine. Now nesting colonies of large herbivorous dinos must have been special and weird places, we don't really have a proper modern analogue for what these areas were like. If extended parental care was practiced it can well be imagined that the local flora took a profound hit from possibly thousands of megaherbivores in a relatively small area. In this scenario the hadrosaurs were eating decaying wood because everything else in the vicinity had already been consumed.
But there is another possibility for what was going on here and this one really stretches the weirdness factor and involves some unabashed speculation on my part (but that has never stopped me before): Maisaura peeblesorum was a fungi farmer.
Consider that leaf-cutter ants are often the most important herbivores in many Central/South American ecosystems. But since the ants are not exactly eating the leaves they are cutting, but instead mincing them up for their fungal gardens, they are better described as mycophagists (fungi eaters)
So what I am I suggesting here- that Maisaura built huge underground fungi colonies? No of course not. What I am suggesting goes like this: We know that Maisaura showed strong site fidelity for nesting colonies and that these colonies may have been exceptionally large. Likely they returned during a specific time of year, most likely coincident with the rainy season and abundant plant growth. Based on crushed eggshells and the preservation of infants several months old in the nest it appears that the nestlings hung out around the nest for some time and were acquiring nutritious food either by foraging or some type of parental provisioning or a combination of the two. From faecal remains we can surmise that adults were consuming fungi-degraded wood and depositing faeeces adjacent to nesting areas. At this point is where the speculation comes in; Maisaura adults were targeting fungi infected wood, most likely of a specific species of fungi, in order to inoculate their own faeces with the spore of the fungi. They would then deposit said faeces in proximity to the nesting colony. The hatchling Maisaura which were somewhat precocial would then have a regular food supply delivered in proximity to the safety of their nest. The faeces would provide an ideal substrate for fruiting bodies (mushrooms) to form, protein rich insects/inverts would be attracted, and the faeces themselves would provide a larder of beneficial digestive microbes that the hatchlings would inoculate themselves with. This provisioning may well have lasted several
|Paneolus antillarum on Elephant dung|
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