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Dinosaur dreams

Woody Lane, Ph.D., for Progressive Forage Published on 30 October 2019
Comparisons

We can never tell where ruminant nutrition will lead us. Start with a mundane topic like grass and, before we know it, we’re into microbes and methane and fiber and size.

Yes, size. That’s a particularly big topic this month. Let’s talk about dinosaurs, the biggest ones: the sauropods.

Were dinosaurs ruminants? We’ll get to that. First, let’s lay some groundwork.

Dinosaurs, of course, lived more than 100 million years ago. Mostly between 230 million and 65 million years ago, when a great extinction occurred, probably as the result of a collision with a large meteor. Let’s put aside the issue of meteor collisions and talk about nutrition.

I want to focus on a class of dinosaurs called the “sauropods.” These were the really big dinosaurs – the largest animals that ever lived. You know, the long-necked gigantisaurs (or whatever), many longer than 100 feet. (Ask any 12-year-old for details.) The sauropods were indeed enormous. The most massive was the Argentinosaurus, at probably 100 tons. That’s 200,000 pounds. In comparison, our largest land animal today is the African elephant, at a measly 10 tons.

Years ago, one of the finest nutritionists in the world, Peter Van Soest, the scientist who developed the NDF/ADF system of fiber analysis that forage labs everywhere use today, took an interest in species comparisons. Actually, that was quite logical because animals are fascinatingly variable in how they address the nutritional principles of gut anatomy, fermentation rates, fiber digestion and feed selection. Van Soest’s interest in comparative nutrition led to studies of diverse species such as wombats, dik-diks, giraffes and elephants. After these studies, it was perfectly logical to move from elephants to dinosaurs.

Which brings us to a Cornell Nutrition Conference of a few years ago. Amid two days of rather routine technical papers on protein nutrition, heifer development and such, Peter Van Soest gave a lecture that was not routine at all. His topic: the nutritional issues of sauropod dinosaurs and gigantism. As Van Soest covered point after point, the audience became very quiet. This month I want to share some of these points with you – aspects of nutrition generally not found in classic nutrition textbooks. Here’s a gentle warning: These points may not be the most practical tips for balancing your next ration (unless you raise some very large breeding stock), but sometimes it’s just nice to kick back and dream. This is what the best scientists do – and who knows where things may lead?

First, sauropods were herbivores – vegetarians that ate plants. What types of plants? Well, not grasses or legumes; those plants didn’t appear on Earth until 30 million years ago, long after dinosaurs had vanished. Scientists speculate these large dinosaurs ate leaves and ferns and shrubs. In any case, all these plants contained fiber.

But a fiber-based forage diet has definite implications. Since no vertebrate animal today has enzymes that can digest cellulose, it’s reasonable to assume dinosaurs didn’t have those enzymes either. Which means if they consumed plants that contained high levels of fiber, they had to digest that fiber the same way today’s herbivores do – by maintaining a population of fiber-fermenting microbes somewhere in their digestive tracts and then absorbing the nutrients synthesized by those microbes.

Today’s herbivore species have evolved many anatomical designs to solve this problem. Ruminants have a rumen, horses and elephants have a huge large intestine, rabbits and rats have a cecum. And dinosaurs had ... well ... something. They may not have had a rumen, and they probably didn’t chew cud, but their digestive tracts had to have someplace that contained fiber-fermenting microbes.

Which leads directly to another item, one with tantalizing implications: Fiber fermentation does not occur efficiently at low temperatures. In today’s world, many industries rely on fermentation products and, for fiber-loving microbes to thrive, those fermentation vats must be warmer than 60ºF.

But if dinosaurs were cold-blooded, how did they maintain their internal body temperatures above 60ºF? Sure, the Jurassic period was warmer than today, but the Earth still had nighttime temperatures that were cooler than daytime temperatures, and the Earth also had four seasons, as well as land masses far from the equator. A large herbivore that was cold-blooded would be at a nutritional and evolutionary disadvantage if its body temperature remained low or fluctuated greatly for any period of time.

But thanks to the laws of physics, being huge may have provided some distinct anatomical advantages for staying warm. A large animal has a low ratio of surface area to bodyweight, which means a large animal has a relatively harder time dissipating heat than a small animal. If their internal metabolism generated some heat, sauropods would have had a difficult time getting rid of it.

Similarly, if these dinosaurs had become warm during the day, their body size would have helped them retain heat for many hours into the night, similar to the warming strategy of today’s cold-blooded animals, like snakes and tortoises, who lie on rocks and asphalt roads during the day. Which means, because of the principles of simple physics, the sauropods could have been passively warm-blooded or, alternatively, they could have been actively warm-blooded through mechanisms we don’t yet understand.

Either way, these animals ate forage, and they had to eat a lot of it. Let’s consider our Argentinosaurus at 100 tons (equal to 200,000 pounds). How much did this animal eat, and what does that imply? Well, if we assume a low rate of dry matter intake (DMI), say at only 1% to 1.5% bodyweight, this animal consumed 2,000 to 3,000 pounds of dry matter each day. (Compare this to a high-producing Holstein cow that eats 60 pounds of dry matter per day.)

If Jurassic plant material contained 25% dry matter, which is typical for living green plants, then our dinosaur needed more than 8,000 pounds of green leaves each day. Or if someone made hay for this monster, they would have fed at least 44 square bales each day (50-pound bales). At the very least, this level of intake implies these animals had to keep moving throughout the day, just to find enough forage to eat. Which, in turn, implies strong legs and lots of bites.

Which brings up a technical issue: retention time. This is defined as the average time feed material remains in the digestive tract. Retention time in herbivores is inversely related to feed intake. The higher the feed intake, the shorter the retention time. But short retention times reduce fiber digestibility because the microbes need enough hours to ferment the cellulose. Sauropod dinosaurs had to consume huge amounts of feed, but they also had to retain this feed in their digestive tracts long enough for extensive fiber digestion. But long retention times are not good either.

No herbivore today has a retention time longer than four days. Why? Because after four days in a fermentation vat, some of the nutritional two-carbon and three-carbon VFAs (volatile fatty acids) produced by the bacteria are further reduced to the one-carbon compound methane that has no nutritional value and is lost as gas. Our sauropods, therefore, were caught in a nutritional bind: They needed a high feed intake to support their great body mass, but they also needed a carefully balanced retention time to allow for productive fermentation. One possible strategy they might have used to cope with this quandary is to carefully select their feed, similar to the feeding behavior of some herbivore species today. It’s too bad we didn’t have digestion crates back then ... digestion trials with sauropods would have kept a few graduate students quite busy.

Well, the lecture at that nutrition conference was classic Peter Van Soest: fascinating and definitely outside the box. But I must end here. I’ve decided to rent the movie Jurassic Park. I need to make some observations about forage intake.  end mark

ILLUSTRATION: Illlustration by Corey Lewis.

Woody Lane is a certified forage and grassland professional with AFGC and teaches forage/grazing and nutrition courses in Oregon, with an affiliate appointment with the Crop and Soil Science Department at Oregon State. His book, From The Feed Trough: Essays and Insights on Livestock Nutrition in a Complex World, is available through Woody Lane.

Woody Lane, Ph.D.
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