How much poop did Argentinosaurus produce in a day?
May 25, 2018
I got an email a couple of days ago from Maija Karala, asking me a question I’d not come across before (among several other questions): how much poop did Argentinosaurus produce in a day?
I don’t recall this question having been addressed in the literature, though if anyone knows different please shout. Having thought about it a little, I sent the following really really vague and hand-wavy response.
Suppose Argentinosaurus massed 73 tonnes (Mazzetta et al. 2004). In cattle, food intake varies roughly with body mass to the power 0.7 (Taylor et al. 1986), so let’s assume that the same is true of sauropods.
Let’s also assume that sauropods are like scaled-up elephants, in that both would have subsisted on low-quality forage. Wikipedia says elephants “can consume as much as 150 kg (330 lb) of food and 40 L (11 US gal) of water in a day.” Let’s assume that the “as much as” suggests we’re talking about a big elephant here, maybe 6 tonnes. So Argentinosaurus is 73/6 = 12 times as heavy, which means its food intake would be 12 ^ 0.7 = 5.7 times as much. That’s 850 kg per day.
Hummel et al. (2008, table 1) show that for a range of foods, the indigestible “neutral detergent fibre” makes up something around half of the mass, so let’s assume that’s the bulk of what gets pooped out, and halve the input to get about 400 kg of poop per day.
References
- Hummel, Jürgen, Carole T. Gee, Karl-Heinz Südekum, P. Martin Sander, Gunther Nogge and Marcus Clauss. 2008. In vitro digestibility of fern and gymnosperm foliage: implications for sauropod feeding ecology and diet selection. Proceedings of the Royal Society B, 275:1015-1021. doi:10.1098/rspb.2007.1728
- Mazzetta, Gerardo V., Per Christiansen and Richard A. Farina. 2004. Giants and Bizarres: Body Size of Some Southern South American Cretaceous Dinosaurs. Historical Biology 2004:1-13.
- Taylor, C. S., A. J. Moore and R. B. Thiessen. 1986. Voluntary food intake in relation to body weight among British breeds of cattle. Animal Science 42(1):11-18.
You could drive several trucks through the holes in that reasoning, but it’s a start. Can anyone help to refine the reasoning, improve the references, and get a better estimate?
Sauropod Vertebra Picture of the Week 
May 25, 2018 at 2:48 pm
Two things come to mind.
First, air sacs. Is that going to throw off the food intake to body mass ratio? Should we be using scaled up forage estimates of geese instead of elephants (though I’d imagine once scaling is taken into account they might be more similar than one would think, given both are hind-gut fermenters and not very good at it)?
Second, are we assuming uric acid or urea is the primary means of excretion? Because if it’s uric acid like birds and some reptiles that may decrease the weight due to water reabsorption.
May 25, 2018 at 2:52 pm
Pneumaticity doesn’t come into play here (for once!), unless we use it up front to modify the mass estimate. Mazetta et al. didn’t do that, but since all mass estimates for Argentinosaurus are finger-in-the-wind anyway, I don’t think the 5%-10% difference that pneumaticity might make is going to be a big player.
On what animal’s forage to scale from: my guess — and I am only going on intuition here — is that the sauropod has more in common metabolically with a big-ass mammal than it does with a tiny, tiny bird. If we were doing this rigorously, of course, we’d make estimates based on extrapolations from lots of different animals — and we’d use better sources for their food intake than Wikipedia!
I’ve given no thought at all to urea. I don’t think it makes any difference here, but I’ll be happy to have someone show me why I’m wrong.
May 25, 2018 at 3:02 pm
Mike wrote:
I’ve given no thought at all to urea. I don’t think it makes any difference here, but I’ll be happy to have someone show me why I’m wrong.”
well now, it might make all the difference in the world if you happen to be a little mammal underfoot minding its own business when a passing sauropod released it’s load. On the one hand would be suddenly doused with warm, semi-solid uric acid and on the other just something warm and wet. (I am being flippant, of course).
May 25, 2018 at 5:21 pm
Uric acid means more water is getting reabsorbed by the body because the body needs less water to flush out its waste. Which means less water weight for feces, which based on a quick search comprises 75% of the weight of feces in humans.
The reason I brought up geese is that they might be a big more similar to sauropods because they don’t do signifiant oral processing (though I don’t know how much a gizzard in geese would change things). Elephants also have a very inefficient kg-for-kg digestive system but physically breaking apart plant matter can help burst cell walls and reduce the indigestible component.
I don’t have the reference on me, but I’d always heard that elephants only digest about 10% of their food due to not having much in the way of digestive specializations compared to, say, ruminants. Though it could be there are more accurate estimates since I saw that.
May 25, 2018 at 8:22 pm
I would be amazed if the value for elephants was really 10%.
May 25, 2018 at 9:05 pm
Double-checked it, several authors say elephants digest about 40% of what they eat, but they do not list any first-hand references.
May 25, 2018 at 9:11 pm
Did you not get all those references sent earlier today? Had that among them
May 25, 2018 at 9:12 pm
Ken, you may be surprised to hear that I have not yet had time to read nine papers! I really appreciate your sending them, but I have a lot of other stuff I need to be doing.
40% sounds a lot more credible to me than 10%, and is pretty well in line with the 50% that I hypothesized for sauropods.
May 25, 2018 at 9:14 pm
skim – read abstracts, fig captions and conclusions. Rest can be ignored (for now). That was how I got through all the readings I had to do in VP when I was a student (undergrad and grad).
May 25, 2018 at 9:15 pm
You know I have a day-job, right? :-)
May 25, 2018 at 9:17 pm
But it is after 10 at night for you. Don’t you read during lunch?
May 25, 2018 at 9:18 pm
pardon, it is after 22:00 for you
May 25, 2018 at 9:19 pm
I’m prepping Sunday’s sermon.
May 25, 2018 at 9:20 pm
Ah. That’s different. Be sure to squeeze in a hymn to Amphioxus
May 25, 2018 at 10:58 pm
I don’t think we have that one in our repertoire.
May 25, 2018 at 11:30 pm
“skim – read abstracts, fig captions and conclusions. Rest can be ignored (for now). That was how I got through all the readings I had to do in VP when I was a student (undergrad and grad).”
One of the more shocking things I remember hearing as a student getting into paleontology was a well-established scientist telling their graduate students “Just read the abstract, introduction, and the discussion. No one reads the methods, results, or descriptions anymore”.
May 25, 2018 at 11:39 pm
I discovered that on my own as a student trying to keep my head above water with all the reading of primary articles (I forgot to mention read discussion). The rest is fill (=justification) that you read at your leisure. If pressed for time, then just read to get the main points.
May 26, 2018 at 1:58 am
Mike, the NDF fraction of plant material isn’t indigestible to herbivorous animals with fermentation systems, which I presume sauropods had in spades. In ruminant animals (which I specialize in), the digestibility of NDF ranges from 30-70% (one easy source is https://fyi.uwex.edu/forage/understanding-ndf-digestibility-of-forages/https://fyi.uwex.edu/forage/understanding-ndf-digestibility-of-forages/). Hind-gut fermenting species don’t get quite as much out of it, but I wouldn’t presume that adult sauropods couldn’t best modern mammals. Since degree of fermentation is largely a function of GIT retention time (aka “passage rate”), they might have performed rather well. Also have to assume they were as selective about their diets as opportunity allowed, given the biomass they had to knock down daily. Modern large herbivores select for easily digestible plant species and parts insofar as they are available, with larger animals tending (with some variations) to accept more cellulose in their diets. (my understanding is that rhino species tend to vary a little in that regard) I have an MS thesis of a project investigating fecal output of grazing cattle in my file (Sprinkle, 1992) that gives their output at roughly 0.65% of body weight per day.
May 26, 2018 at 11:14 am
Thanks, Marc, that is really helpful!
Here’s another approach, then. Let’s model a sauropod as a scaled-up cow, and assume that poop mass is proportional to food intake, which goes with body mass ^ 0.7. A decent-sized cow weighs half a ton, or 500 kg, so 0.65 of body mass is 3.25 kg poop per day. Argentinosaurus is 73 / 0.5 = 146 times bigger, so its poop output should exceed that of the cow by 146 ^ 0.7, which is about 33. That gives a daily poop mass of 107 kg — not much more than a quarter of what I estimated by the first method.
Some of that discrepancy is accounted for by the decent digestibility of NDF in gut-fermenters, but that still leaves quite a gap. I wonder what the reason for that is?
May 26, 2018 at 11:31 am
I just went back to Weaver (1983), and found the equations he arrived at for simple metabolic rate (page 175). The “medium” equation for an endotherm is 67 x W ^ 0.756. For a 73,000 kg Argentinosaurus, that comes out as 67 x 73,000 ^ 0.756 = 3,700,000 kcal/day. Weaver’s table 4 gives wet-weight energy densities of five groups of food plants, averaging 1.637 kcal/g, which gives us 3,700,000 / 1.637 = 2,260,000 grams per day intake, or 2,260 kg, which is a rather breathtaking two and a quarter tons. That’s 2.7 times as much food as I got by scaling up the elephant.
And as Weaver points out (page 178), that is just to sustain metabolism. The cost of walking, foraging, digesting, etc. means that this needs to be multiplied by 1.3-4.
May 27, 2018 at 12:29 am
Yes, which is why modern ungulates in temperate climates commonly exhibit seasonal dietary plasticity – focusing on protein-rich foliage, and then energy-dense seeds and fruits during the periods when they are reproductively active, and idle along on less energy-dense fibrous materials, plus leaves of evergreen species during dormant seasons when their metabolic demands are lower (and burning through stored energy reserves to make up any shortages). I’m really curious about what the nutrient composition of the major plant genera that saurian herbivores would have used were like. There aren’t many extant species of herbivores that I’m familiar with that make significant use of gymnosperms and ferns, at least in North America (cervids use pine leaves over winter, to some extent – but angiosperms are generally the main course when available). I haven’t had much experience in tropical ecosystems. I assume there would be fruits and seeds on offer for more extended periods, though some species might exhibit some levels of seasonality with regards to wet/dry cycles.
May 27, 2018 at 7:32 am
See Hummel et al. (2008) on nutrient density of Mesozoic plants.
May 27, 2018 at 4:42 pm
While I was looking up Hummel’s article, I found that Carole Gee had posted one of her chapters (3, Dietary options for the sauropod dinosaurs) from “Biology of the Sauropod Dinosaurs: Understanding the Life of Giants” (2011) to ResearchGate. That was also a relevant, and interesting read.
May 28, 2018 at 4:52 am
Wet weights of fresh plant materials could definitely produce some impressive numbers, but, so far as nutritionists are concerned, its the dry weight that matters.
For ungulates, measured actual dry matter intake usually ranges from 1.5-3.5% of their live body weight. Using 2% as a typical estimate of an ungulate at maintenance, that gives me 1,460 kg of dry matter per day. Assuming the vegetation was 56% moisture (value for conifers from Weaver, 1983), that would be 2,607 kg fresh weight, daily.
Thanks for that reference to Hummel at al. (2008), Mike. This is getting much more interesting for me. The abundance of Araucaria in sauropod habitats and its potential energy value certainly is good reason to suppose it was a food source, but their low protein levels (~4% CP) begs for more explanation of how it would have worked in the diet. Modern ungulates that are chiefly fiber-feeders (what I’m most experienced with) generally need at least 6-7% crude protein in their diets in order to maintain themselves. Growing ungulates can require 12-15% protein. Cellulolytic bacteria have a NH3 requirement for manufacturing cellulases, much of which comes from dietary protein – so fiber-feeding animals really can’t afford to cut them short. Sugar gliders aside (I’m not sure why Hummel et al., thought mention of the very low protein requirement of sugar gliders was relevant to the sauropod discussion, as they don’t live on cellulose, but whatever) my guess would be that massive sauropods would have needed a minimum dietary protein intake not less than that of modern ungulates. Hummel et al. gave ginkos as examples of likely high-protein (~15% CP) sources available to sauropods, and Araucaria as high-energy but low protein (~4% CP) – but commonly available sources. Hitting the very lowest protein requirement of modern ungulates (6%) would require that 15% of the dietary dry matter (DDM) be ginko with 85% DDM from araucaria. Pushing the protein requirement to 14% would reverse those proportions. They mentioned that horsetail (Equisetum spp.) would be a likely food source for young sauropods, but at 11.6% CP (I have other references that show some modern Equisetum species down in the 6-7% CP range), that would have to be supplemented by still higher protein sources in order to support high growth rates. No question that mammals are less than an ideal physiological model for sauropods, but when I looked up the nutrient requirements of domesticated ratites – that seemed an even less plausible model, with breeding-age adults having a protein requirement of ~16%. That seemed a bit extreme for an herbivore. Holdover from that raptorial heritage, perhaps…
May 28, 2018 at 11:17 am
Thanks, Marc. I love how such a simple question as the one that started this can lead into such interesting areas. It’s astonishing to me that ungulates somehow manage for 6-7% of their diet to be protein. What are they eating? Nuts? Cheese? Invertebrates?
May 28, 2018 at 2:24 pm
According to a YouTube video that I sometimes use in an introduction to animal nutrition course, small birds are the ticket for deer (fun to shock the freshmen)…
Green leaf material is commonly >15% protein (all that RuBisCO enzyme used for photosynthesis), so during the growing season it isn’t that hard. Animals that have to deal with seasonally dormant vegetation (not sure that this was a common issue in the Mesozoic) have to exercise that dietary ‘plasticity’ and seek out green leaves from plants they don’t normally use to supplement the (then) protein-poor biomass from their usual forages. That’s the state of things in angiosperm-world, anyway.
May 29, 2018 at 8:24 pm
Just imagine the size of those dung beetles! ;)
May 30, 2018 at 2:21 am
And the number!
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