In a lush, bygone landscape, hungry triceratops are thrown on low-lying ferns and cone-shaped cicada plants to power its 10-ton frame. The animal swallows huge volleys of roughage, seeds and everything else before heading off in search of new food.
Days later, and miles away, Triceratops emptied his gut, sowing the seeds of the plants he had eaten, along with manure, in more distant soil than could be reached without him.
The scattering of plant seeds in animal bodies, known as zoochoria, is so common in modern ecosystems that plants often adapt their fruits and flowers to attract specific carriers. Fossils of poop and gut contents indicate that plant seeds also reached dinosaur bellies, although it is not clear whether these relationships were as widespread and sophisticated as they are today.
“I know from modern ecosystems that large animals are important seed spreaders,” said Dr. Perry. “I thought I had all the pieces: What is the most massive animal ever and how far can it have moved the seeds?”
In a study published Wednesday in Biology Letters, Dr. Perry set out a framework for calculating the extent to which dinosaurs – weighing about 20 pounds to 90 tons – could carry the seeds of prehistoric plants. He found that dinosaurs like Triceratops or Stegosaurus had the right combination of size and speed to deposit seeds between three and 20 miles from the parent plants. This is comparable to the African bush elephant, which transports seeds an average of a mile and a half on average, but can move them up to 40 miles.
Dr. Perry’s simulations depend on two main factors: the speed of the dinosaur and the time it retains the seeds before eliminating them. These values are difficult to determine due to the limitations of fossil records. However, body weight is related to walking speed and seed retention time in modern animals, which can be used as a rough analogue for past ecosystems.
“What we really want to be able to do is take a GPS tracker and put it on a dinosaur and follow it around, but we can’t do it,” Dr. Perry said. For that reason, the study’s assumptions are “reasonably conservative,” he added.
Large animals usually travel farther and keep the seeds longer than smaller animals. But extremely massive dinosaurs, such as the 90-ton Argentinosaurus, may have been slower than the average herbivore. This means that pastures like Triceratops were perhaps the most effective seed spreaders due to their more modest body size, but still incredible appetites.
“The distribution of the seeds of extinct animals is of great importance, and Dr. Perry reasonably assessed those of the dinosaurs,” said Tetsuro Yoshikawa, a plant ecologist at Japan’s National Institute for Environmental Research, who has published research on the subject.
“Because existing terrestrial animals, such as elephants and bears, can in some cases transport seeds several kilometers away, large dinosaurs may have similar potential.”
Dr. Perry’s study is “a great example of how, with smart lateral thinking, a scientist can come up with ways to penetrate a question that – nominally – can only be answered with a time machine,” said John Hall, a plant ecologist at University of Queensland and an expert on cicada plants.
Of course, it would be great if scientists could dip their elbows deep into the real dinosaur, and la Ellie Satler into Jurassic Park. Alas, the finer details of these complex ecosystems are likely to remain shrouded in mystery and speculation.
“When we look at the natural world today, the diversity and closeness of the close symbiotic relationships between plants and animals that pollinate flowers and scatter seeds is simply staggering,” said Dr. Hall.
There is no reason not to think that the spectrum of such relationships must have been equally complex and diverse in prehistoric times, he added, even if “these relationships must remain annoyingly lost to us.”