Hadrosaur diet
[6] However, because they lack the complex flexible lower jaw joint of today's mammals, it has been difficult for scientists to determine exactly how the hadrosaurs broke down their food and ate.
[8] A 2008–2009 study by University of Leicester researchers analyzed hundreds of microscopic scratches on the teeth of a fossilized Edmontosaurus jaw and determined hadrosaurs had a unique way of eating unlike any creature living today.
[11][13] His vague inference of amphibious habits would later be expanded upon by Edward Drinker Cope, who contributed the mistaken conclusion that hadrosaur teeth and jaws were weak and suitable only for eating soft water plants.
[2] Cope described the next piece of the puzzle in 1874: a more complete jaw fragment in 1874 he named Cionodon arctatus,[14] which revealed for the first time the complex hadrosaur tooth battery.
[2][20] The early study of hadrosaurid dietary adaptations and feeding behavior was summarized in a 1942 monograph by Richard Swann Lull and Nelda Wright.
Unlike previous authors, they moved away from soft water plants as the major part of the diet, but retained the interpretation of an amphibious lifestyle.
However, they found the purpose of the dental batteries uncertain: hadrosaur jaws were unlike those of any modern reptiles, and there did not appear to be an evolutionary pressure on hadrosaurids like grasses were for horses.
Instead, they proposed equisetaleans (horsetails) as the major food source, as these plants existed in the same times and places as hadrosaurids, are known to be rich in starch, and contain abrasive silica which would necessitate teeth that could be replaced.
[22] The general preexisting consensus on hadrosaurid paleobiology was challenged in 1964 by John Ostrom, who found little evidence to support either a diet of aquatic plants or an amphibious lifestyle.
Like Lull and Wright, he drew attention to the robust dental batteries, and found that hard, resistant foods were the most likely diet (such as woody, silica–rich, or fibrous materials).
A terrestrial diet was also supported by the 1922 gut content study, which found conifer needles and twigs, seeds, and fruits inside the specimen.
Ostrom found that hadrosaurid skeletal anatomy indicated that the animals were well–adapted to move on land, and were well–supported by ossified tendons along the vertebral spines, which would have hindered swimming.
[23] The theory remained largely unproven until the study by Purnell, Williams and Barrett, which Science magazine called, "The strongest independent evidence yet for this unique jaw motion".
[24] However, in 2008, a group of American and Canadian researchers, led by vertebrate paleobiologist Natalia Rybczynski, replicated Weishampel's proposed chewing motion using a computerized three-dimensional animation model.
[25] In 2008, a team led by University of Colorado at Boulder graduate student Justin S. Tweet found a homogeneous accumulation of millimeter-scale leaf fragments in the gut region of a well-preserved partially grown Brachylophosaurus.
[30] Williams, Barrett, and Purnell conducted their study using the jaws of an Edmontosaurus, a hadrosaurid that lived between 68 and 66 million years ago in what is now the United States and Canada.
As a result, the study determined that the hadrosaur diet was probably made of leaves and lacked the bulkier items such as twigs or stems, which might have required a different chewing method and created different wear patterns.
[8] Grasses had evolved by the Late Cretaceous period, but were not particularly common, so the study concluded it probably did not play a major component in the hadrosaur's diet.
The study was published under the title, "Quantitative analysis of dental microwear in hadrosaurid dinosaurs, and the implications for hypotheses of jaw mechanics and feeding".
Because hadrosaurs were the dominant terrestrial herbivores of that time, they played a major role in structure the ecosystem of the Late Cretaceous period.
"[8] Lawrence Witmer, a paleontologist with Ohio University College of Osteopathic Medicine in Athens, called the study, "One of the best microwear papers I've seen", although he said he was not yet convinced the hadrosaurid upper jaw could flex.
[33] Williams et al..'s hypothesis of hadrosaurids as grazers who ate vegetation close to the ground, rather than browsing higher-growing leaves and twigs, would also contradict the portrayal of hadrosaurs in Jurassic Park, the 1990 science fiction novel by Michael Crichton.
