ScienceDaily (Nov. 27, 2012) — Every kid
knows that giant carnivores like Tyrannosaurus rexdominated the Cretaceous
period, but they weren't the only big guys in town. Giant plant-eating
theropods -- close relatives of both T. rex and today's birds -- also lived and
thrived alongside their meat-eating cousins. Now researchers have started looking
at why dinosaurs that abandoned meat in favor of vegetarian diets got so big,
and their results may call conventional wisdom about plant-eaters and body size
into question.
Scientists have theorized that bigger was better
when it came to plant eaters, because larger digestive tracts would allow
dinosaurs to maximize the nutrition they could extract from high-fiber,
low-calorie food. Therefore, natural selection may have favored increasing body
sizes in groups of animals that went meatless.
Three groups of giant feathered theropods from
the Cretaceous period seemed to follow that rule of thumb -- the biggest
specimens were also the plant-eaters. Lindsay Zanno, research assistant
professor of biology at North Carolina State University and director of the
Paleontology & Geology Research Lab at the North Carolina Museum of Natural
Sciences, and Peter Makovicky, associate curator of paleontology at the Field
Museum in Chicago, decided to see if diet was the determining factor when it
came to size. Makovicky notes that "Having three closely related lineages
of dinosaurs adapting to herbivory over the same geological time span and
showing evidence of increasing size provided a near perfect test case."
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