Dinosaur footsteps heavy as tractors

Once in a while, some research comes along that combines two things that I never considered together.

Such was the case with a recent paper in the Proceedings of the National Academy of Sciences, which linked farm machinery and dinosaurs.

The increasing human population requires more food production and more efficient use of arable (crop-producing) land. To increase efficiency, farm machinery has become larger, with combines having wider cutters and larger grain capacities. Over the last few decades, the weight of laden combines has increased almost 10fold, from around 9,000 pounds in 1958 to 79,000 pounds today.

That has resulted in a little-known but growing problem, the compaction of soil below the tillage zone. That subsoil area is where plant roots go, and its compaction has resulted in reduced crop yields.

Analyzing a wide range of data, the scientists suggest that currently about 20% of the arable land on our planet has lost productivity due to subsoil compaction, and that percentage is growing as mechanization spreads and farm machinery gets bigger.

As that machinery has gotten bigger, so has the size of its tires, to spread the load. Studies of mammals in general, and of African ungulates (hooved animals) in particular, have shown that animals have done the same thing, increasing the contact area of their feet with increasing weight.

The authors then did the same analyses for sauropods, the longnecked, long-tailed quadrupedal herbivorous dinosaurs popularly known as “brontosaurs.”

The largest may have weighed 80 tons — 160,000 pounds. With one foot in motion and the others on the ground while walking, each foot would have been pressing into the ground with over 40,000 pounds, more than even modern farm machinery.

That would certainly have led to subsoil compaction. Did that lead to reduced plant productivity?

Not judging from the fossil record. Sauropods were one of the most successful groups of dinosaurs, with a couple hundred species known. Their fossil remains have been found on every continent, in rocks from the earliest Jurassic to the end of the Cretaceous, a span of over 140 million years.

Feeding those large bodies, the teeth got a lot of wear and were replaced rapidly. In the iconic American sauropod Diplodocus, each tooth was replaced every 35 days, and in Nigersaurus of Africa, every 14 days.

Sauropods didn’t chew their food (despite the Brachiosaurus in the first “Jurassic Park” movie, shown chewing like a cow) but just grabbed and gulped, with the processing going on in their huge guts.

Those guts were fermentation vats, where food was broken down with the help of bacteria. The idea that they used stones, called gastroliths, to grind their food is a myth.

All that food resulted in huge amounts of manure, which would have acted like fertilizer. Would that have offset the lowered productivity caused by their immense weight compacting the subsoil? Who knows?

Dale Gnidovec is curator of the Orton Geological Museum at Ohio State University.

gnidovec.1@osu.edu