To bring you up to speed it might prove useful to go review these old posts I put forth on the subject way back in the day.
Following the Poop Trail: Can Dinosaurs Be Blamed For Termites?
Some of the finer points may have changed but here I argued for unusual and novel food chains in Mesozoic ecosystems and possibly a conserved gut flora from sauropods to termites!!
Dinosaur Alternative Food Stuffs
Lichen munching dinosaurs? Sauropods browsing foliose lichens in high latitude polar beech forests? How did these cool, temperate high latitude forests operate?
Rot N' Roll in the Mesozoic Muck
It was in this last post Rot N' Roll in the Mesozoic Muck, from way back from May 21, 2013, that I first ventured forth an idea that I was very smitten with at the time and which has stayed with me since.
In short format: that the consumption of decayed wood by large ornithischians documented via coprololite remains from the Two Medicine Formation and often attributed to Maisaura peeblesorum (Chin, 2007) document a novel ecological relationship. Namely Maisaura was consuming rotten wood and fungi in order to deposit and provision hatchling Maisaura with a ready supply of beneficial gut flora via coprophagy (consumption of dung) but also grow tremendous fungal gardens that further nourished and provishioned young hatchlings with a readily digestible and nutritious bumper crop of sporocrops i.e. mushrooms. Like a giant version of a banana slug spores would pass through the dinosaurs' digestive system and find a nice dinosaur patty to set up shop in. Because fungi have a more complete and easily digestible protein profile than raw plants they serve as a nice energy and growth boost for the hatchling hadrosaurs. Basically the best analogy being to the large underground fungal gardens leaf cutter ants create. A very simple, diffuse, and elegant energy transfer from detrital food chains to parent hadrosaur to offspring. Because the environmental conditions could not be controlled as in the underground gardens of leaf cutter ants, some years would be better than others in terms of fungi production. Furthermore it is not an obligate food source, the dung and whatever foodstuffs come with it - insects, mollusks, crustaceans, fungi - merely augment the growing hatchlings needs. If there is no fungal bloom of sporocarps, the hatchlings feed on other stuff.
At the time I wrote it I didn't have much readership, nor was there any more compelling evidence at hand to argue such a hypothesis past the point of imaginative fantasy so I kinda let the idea sit fallow for a couple of years. Until I woke up the other day to check out my news feed to unexpectedly discover more evidence of rotten wood munching giant ornithischians has been unveiled via Karen Chin!! Only this time the coprololites hail from the Kaiparowits formation of Utah across multiple horizons and not only contained rotten conifer wood but sizable bits from crustaceans and mollusks!! Like mana from heaven these heavenly piles of shit keep dropping on my doorstep like flaming bags of shit!! But they are bags of poop I certainly don't want to stamp out!!
While the shellfish eating aspect of this study is getting the most attention, it really is the confirmation of rotten wood munching ornithischians (probably hadrosaurs) that has the most far reaching implications. This revelation confirms that dinosaurs tapping into detrital food chains was not some aberrant activity, or the result of some ecological catastrophe but really was just a pretty regular menu option.
If after reading Chin's latest study you come away thinking that mammalian mega-herbivores are the best analogy to dinosaurian megaherbivores I really can't do much for you. In fact you might just want to stop reading right now. Far from being the most "vanilla" of dinosaurs you might start to think of colony forming hadrosaurs as the most interesting of dinosaurs by the completion of this piece. Time to drop whatever preconceived notions you have of how dinosaurian herbivores operated ecologically compared to modern ones. Far from being the "cows of the Cretaceous" - really how can you be a cow without eating grass anyways (?!) - such a simplistic comparison belies the far more interesting ecology of these animals and how they slot into a non-grass world.
Indeed a main thrust of the Chin paper is that modern large mammalian herbivores don't compare favorably to the large ornithischians that harvested rotten wood, fungi, mollusks, and crustaceans - because quite literally large mega-herbivorous mammals don't really go after these resources to any appreciable extent. This is not to suggest that the paucity of large megaherbivorous mammals around today shows the full extent of dietary flexibility of the recently extinct gompotheres, ground sloths, notoungulates, and others. And sure everyone loves to point out the occasional deer eating field mice or eggs or whatever BUT no one is suggesting that natural wild populations of modern mammalian herbivores are stuffing their guts full of rotten wood and crabs, they simply don't go after detrital and invertebrate resources as a way of life… they are a lot more conservative dietarily compared at least to a subset of late Cretaceous ornithischians, most parsimoniously hadrosaurs according to Chin.
I think it is also important to make an important distinction that was not hammered in hard enough in the recent Chin paper. The Kaiparowits formation records a much wetter, lacustrine subtropical environment compared to the drier, more temperate Two Medicine. It therefore stands to reason that the exploitation of wood was not due to severe environmental stress as has been stipulated for the Two Medicine coprolites, that there was some sort of drought or environmental degradation that forced these animals into an unusual food resource. In short the repeated documentation of rotten wood foraging across at least two species, from multiple occurrences across multiple time periods forces us to conclude that this is not an aberrant or unusual adaptation - that we should not feel compelled to "explain it away" - but that it was a systematic and deliberate exploitation of a food source not usually associated with megaherbivores. But why?
I believe the key line of inquiry lies in elucidating the unique nature and ecology of dinosaurian reproductive biology, long incubation periods, nesting ecology, and the flow of nutrients in Cretaceous Laramidia.
Before I do that I want to stipulate two assumptions that will color my interpretations and which I shall disclose now. Keep in mind that these assumptions are not settled science, there is still disagreement. However for simplicities sake they are assumptions I will be working from. 1) Nesting colonies of hadrosaurs were in fact, real, and they were large. The parent(s) did stick around to at least guard the nest from predators until hatching. Given the long incubation time for Hypacrosaurus (6 months) such nest guarding activities were substantial investments in time and energy. 2) Hatchlings were precocial (Geist & Jones, 1996). They could and did upon hatching forage and move around on their own. They continued to use the nest for creche style groups, sleeping and protection for some time after hatching (nidicolous i.e. nest bound vs nidifugous i.e. nest leaving). Parental provisioning may have been negligible or non-existent, food stuffs gathered in the immediate vicinity of the nest by the hatchlings on foraging expeditions.
The Elephant(s) in the Room - Long Incubation Periods & Mega-herbivore Nesting Colony Environmental Dilemma
There is an elephant in the room that no one is talking about with regards to nesting colonies of hadrosaurs. In fact there are two elephants in the room that need to be coupled and dealt with. Elephant in the room #: Large herbivores don't stay tethered to one spot very long, they will quickly strip it of vegetation. Elephant in the room #2: Dinosaurs are showing strong signs of long incubation periods. Notice that elephant #2 collides with elephant #1 and exponentially increases the dilemma. This is not just some elephants in the room, this is a freaking blue whale in the room creating some titanic problems that are being ignored. There has been some scarce sentiment that hadrosaur nesting colonies posed some interesting environmental dilemmas, but as far as I know no one has attacked this question head on much less with respect to long incubation times.
If you have 6 months of incubation, that gives you a minimum of six months of nest guarding duties. Those six months will create an increasingly large radius of environmental devastation around the nesting colony. The hatchlings inherit a wasteland - not good!!
Although John R. Horner does not mention the dilemma of feeding stationary colonies of nesting hadrosaurs in his influential book Digging Dinosaurs he does at least acknowledge the destructive powers in the mega-herds of Maisaura he postulated (pg. 138) :
" I wonder a bit about how these kinds of herds affected the environment. Certainly the herds had to keep on the move. They must have stripped one area and then moved on to the next."
At least in the case of Maisaura, suggestions that not just one, but maybe several hundred or even thousand multi-ton herbivorous dinosaurs hunkered down for maybe half a year in a rather concentrated locale is mind boggling. The thought that several hundred tons of mega-herbivores could just hunker down in a small location for half a year and that the environment would just be Ok with that? Mega-herbivores don't do that, they keep on moving!! It should set your sense of ecological justice and reason on fire!! There would be an ever increasing radius of devastation surrounding such colonies, making it increasingly hard for nesting hadrosaurs to guard their nest and giving hatchling hadrosaurs a veritable wasteland to inherit.That pesky little problem people keep dancing around is the long incubation period of non-avian dinosaurs, especially pronounced in hadrosaurs. While the recent Chin paper is correct in pointing its nose in the direction of reproduction it does not go far enough in making the link between long incubation times, colonial nesting, and the unusual situation of many tons of mega-herbivores remaining in a relatively small area.
The recent work on dinosaur incubation times (Erickson et. al. 2017) is potentially every bit the game changer on the behavioral front as ornithoscelidia is on the phylogenetic front - I don't know why people have been sort of, "whatever" about it? Or just glossed right over it. Maybe they can't see the forest from the trees on this one, but, well, I'm not waiting for them… Hypacrosaurus was one of the dinosaurs in the Erickson study and analysis reveals it to have an incubation period of… wait for it… six months!! Which implies that other hadrosaurs - such as the ones that putatively laid those rotten wood coprolites in the Kaiparowits and Two Medicine formations respectively - had similarly long incubation periods. Not to mention that there is abundant evidence for large Hypacrosaurus nesting colonies (Horner & Currie, 1994). This chain of thought should get us thinking: how did such nesting colonies not become ecological wastelands, given the long incubation periods?
No wonder so many people are dismissive of the long incubation periods of dinosaurs, it creates a scenario too weird and unstable to justify ecologically. That is until we stop thinking so narrowly about what it means to be a dinosaurian "herbivore" and how long incubation periods are not the "negatives" so many people ascribe them to be but absolute positives.
From Dinosaurs' Long Egg Hatching Times Might Have Led to Their Demise paleontologist David Varricchio said:
"These long incubation times likely restricted dinosaurs… If they had parental care, for example, parents would be bound to a specific spot for months (up to six months) of a given year. This would limit migration. Perhaps it would also hinder dinosaurs' response to environmental change."
Long incubation periods and nest guarding - potentially via bonded mates - set the stage not for evolutionary failure but forced hadrosaurs into a unique kaiju hive mind of ecological terra-forming. It was the long incubation periods that let hadrosaurs exquisitely render and shape their own environment. They were not victims of long incubation times as often posited from the Erickson study (let's flip that on its head) but beneficiaries of them.
The key to imagining long incubation periods as absolute positives is the wood, the rotten wood. This allowed hadrosaurs to exploit a niche that no mammalian herbivore has done and really graft themselves into ecosystems that are today not notable for large abundant mega-herbivores but which dinosaurs, especially hadrosaurids, thrived in: large old growth coniferous forests.
Imagining Hadrosaurs as Analogous to Sea Birds - "Hunting Down" Patches of Rotten Wood
|public domain credit Duncan Wright USFWS. Seabird colony with Great Frigatebirds, Red-tailed Tropicbird, Red-footed Boobies, Sooty Terns and Black Noddies. Tern Island, French Frigate Shoals, Northwestern Hawaiian Islands|
Ever wander through the redwood cathedral forests of Northern California or the old growth coniferous forests of the Pacific Northwest? These temperate rain forests certainly inspire the mind, and if you are inclined towards Mesozoic paleontological musings, they certainly bend the mind towards thoughts of how dinosaurs slotted into these settings as forests very similar harken back to those days. An interesting dilemma occurs though in such mind questing: such forests today are not known for a particularly diverse or large mega-herbivorous bestiary. Sure you have your bears, deer, elk and what not - but even during the Pleistocene there is not much suggestion that things were much different with the large megafauna preferring open grasslands, savanna, and hardwood forests. Dinosaurs were doing something very different from mammals. Sauropods answer the question in part by being large enough to push over the great conifers or simply reach up and bite their foliage. Hadrosaurs cracked the code, that mammals have largely failed at, by consuming the entire tree itself after it died. They outsource digestion to fungal partners and then, in an exquisite transfer of nutrients they shuffle the organic wealth of the old growth forest to their nesting colonies - in more open conditions - which benefits hatchling recruitment. The also eventually die, quite possibly in a forest, where they return the nutrients they stole. They thus speed up the "slow" transfer of nutrients in modern old growth.
The reason detrital wood resources are important is that they let us think about hadrosaur nesting colonies like nesting colonies of seabirds. Seabirds provide a model for how large groups of active, high energy homeotherms can nest together for several months at one location. They have wings and the means to venture to sea to forage for high quality, dependable food stuffs. They can also follow other birds and marine life (dolphins) to predictably rich foraging grounds. Nesting hadrosaurs, I will venture, switched from a foraging strategy of mainly green, live growth towards detrital rotten wood resources not immediately prior to egg laying but subsequent to egg laying and during the nest guarding phase. This ensured several critical aspects that ameliorated conditions for the hatchlings; 1) vegetal resources were not demolished in the immediate vicinity of the nesting colony which ensured adequate forage and hiding for the hatchlings at a critical juncture; 2) parent hadrosaurs could follow known paths to localized patches of dead and rotten wood falls, the hadrosaur hive mind comes into play here that as soon as some hadrosaurs know where to find the rotten trees, they all just follow along (like seabirds); 3) because these dead trees might be several kilometers away from the nesting colony the net movement of rich partially degraded dung brings a net influx of nutrients into the immediate vicinity of the nesting colony; 4) this flips the notion of nesting grounds becoming "ecological wastelands" on its head, hadrosaurs were terraforming the area around nesting colonies to favor their own hatchlings; 5) hatchling dinosaurs could forage on dung itself via coprophagy, invertebrates attracted to dung, fungi within the dung, spores and seeds sprouting from the dung. In short, imagining detrital wood foraging in this manner solves every problem that long incubating, high metabolism, nesting "megaherbivorous" hadrosaurs presents. Nesting grounds don't become run down ecological wastelands but booming dinosaur baby metropolises the actions of the parents directly terra-forming the immediate vicinity of the nesting colony for the hatchlings benefit.
A Transfer of Nutrients: Dinosaur Terraforming
|Duane Nash w/fallen coastal redwood. Jedidiah Smith Park CA|
As we start to flip off the switch in our brains of giant Cretaceous cow to giant Cretaceous detrital hunting seabird-banana slug, the ecological scenario starts to switch. Large coniferous dead fall trees are predictable in old growth coniferous forests and they stick around for hundreds of years. A massive fallen old growth redwood Sequoia would provide adequate forage for possibly hundreds of Maisaura!! Indeed massive dead trees are the largest biological caloric windfalls of all, more than dead sauropods or whales. These are truly massive stockpiles of carbon, nitrogen, fungi, and invertebrates. Hadrosaurs would tap into the most productive and important trophic category in old growth forests - the detrital food chain - a niche largely unexploited by modern megaherbivorous mammals. Once located or "hunted down" - hadrosaurs may have had to march several kilometers to find them - hadrosaurs would make periodic trips from the nesting colony, perhaps even switching egg guarding duties between mates, to the dead falls. We start to imagine these hadrosaurs less like typical herbivores but more like giant macro plant scavengers that let fungi do the hard work of digestion while they reap the rewards. All the while a transfer of nutrients is occurring as dino dung patties are being deposited away from the old growth forests and adjacent to the nesting colony. This energy transfer creates a very different sort of ecosystem from the old growth coniferous forests of the Pacific Northwest of North America. Here decaying trees take centuries to break down and the nutrients stay in the forest. In hadrosaur mediated old growth forests the transfer of nutrients may have been much more rapid and multifaceted. Nutrients being cycled out of the forest to the nesting colonies and possibly back into the forest as hadrosaurs died in secluded forest haunts or dragged into deep redwood groves by tyrannosaurids.
When the hatchling hadrosaurs emerge, precocial and ready to fend for themselves, hopefully coincident with rains they are met with a riot of new, dino dung fertilized, growth. The carbon and nitrogen rich chewed up rotten wood dino patties built up over six months of nest guarding and potentially several hundred years worth of colony fidelity is literally dinosaur terra-forming. They have ameliorated conditions for their progeny on a grand scale. Far from being an ecological wasteland the areas around hadrosaur colonies may have been almost preternaturally abundant with life!!
A Diffuse Hive Mind Emerges: What is Good for the Colony is Good For the Individual
When we start to look at hadrosaur nesting colonies not as individuals in a collective but more as a meta-organism a "hive" if you will we can start to better make sense of how these giant amalgamations of bio-mass operated in a manner that did not ravage their environment but actually enhanced it. They were terraforming it. Remember that these were nesting operations that - at a minimum - may have required parental supervision of the nest for over half a year. When every rule of modern megaherbivorous mammals is broken by remaining stationary in a locale for such an extended time it is time to invent new rules. It is actually not hard to imagine a certain feed evolutionary back loop coming into play.
Rule #1: Clutch-mates are the social basis. Your clutch mates are family. You share a genetic heritage. Whatever you do to augment their chance of survival also enhances your genetic legacy via shared genes.
Rule #2: The nesting colony is sacrosanct. Just as clutch mates form the basis for social groupings in dinosaur life, it is indeed clutch mates that establish and form the nucleus for new breeding colonies. Over time these breeding colonies grow in size and scope but their is still a shared genetic legacy. This is part of the reason, I presume, Laramidia was so diverse in giant herbivorous dinosaurs. Colonial nest site fidelity and shared genetic heritage decreed a more insular evolutionary swap stakes.
Rule #3: Hatchlings are the future of the colony. Playing the numbers game against predators would push colonies towards the largest possible size. As colonies grew in size and scope they would reach an ecological imbalance. Food resources would become so impoverished and ravaged that the travel time to good patches of vegetation for adults would become untenably long. They could no longer make the treks to food and return to guard eggs in a timely and efficient manner. Likewise in such a scenario hatchlings would emerge to a world of utter devastation - all available vegetation was scoured to the ground in the vicinity of the colony ( I am going with the notion that hadrosaurs were fairly precocial, but may have still sheltered in the nest). In such scenarios we would see colony collapse. The increasingly long treks for vegetal resources by adults coupled with the increasing radius of environmental degradation would spell disaster for adults - increasingly exposed to predators, fatigue, disease, and stress - and hatchlings inheriting an impoverished ecosystem. Colonies would have to change their current ecological course OR FACE OBLITERATION. Unless such large colonies could find a way to skirt the issue of environmental devastation then small grouping or solitary egg laying would be more beneficial than colonies.
Corollary 1: Solution - for adults during nesting periods they eschew greenery and tap into detrital food chains. This solves the problem of environmental collapse within the vicinity of the colony. Such a diet, bolstered with fungi and animal protein, is evinced by the coprolite remains. Hadrosaurs now go on long distance foraging ventures to secure rotten wood, largely foregoing the greenery around the colony. It allows us to compare hadrosaur colonies to sea bird colonies which instead of "hunting down" discrete patches of rich oceanic life, hadrosaurs "hunted down" discrete patches of dependable detrital resources. Large dead coniferous trees are, then as now, the largest organisms that have ever lived. The haul of carbon, nitrogen, fungal, and animal resources is immense. In processing these giants hadrosaurs circumnavigated the "stationary megaherbivore dilemma", avoided competition with their offspring, and actually transferred nutrients via dung to the immediate vicinity of the colony. They thus terraformed their environment for the benefit of their offspring and enhanced their genetic legacy. It was a WIN-WIN situation for the hadrosaurs.
Corollary 2: The colony becomes a semi-permanent home. Once the detrital-dung-fertilizer feedback loop is set in motion, the bigger the colony gets the more successful the colony becomes. Quite simply the more animals are spreading dung around the vicinity of the colony, the better quality forage is produced for the young i.e. fresh growth, invertebrates, fungi, the more juvenile recruitment succeeds. The colony becomes a sort of metropolis where the richness provided actually allows hadrosaurs to remain there well past the hatchling stage - a phenomena evinced by the multiple growth stages present at Maisaura nesting colonies and mass death assemblages. In fact I will venture a speculative guess that many or most hadrosaur mass death assemblages do not represent migrating herds but more of a time averaged death assemblage pulled from hadrosaurine colonial metropolises.
Corollary 3: The glass ceiling, a potential limit to colony growth at which stage colonies may shrink or experience collapse. It is not necessarily the availability of green growth but the availability of dead growth. Once colonies have cleared all of the old, dead, rotten logs out of the area adjacent to their colony it may in fact be time to move the colony. The hive relocates. It secures a territory with untapped detrital resources and sets in motion the terraforming process anew.