Rapid tooth replacement by sauropods, the largest dinosaurs in the fossil record, likely contributed to their evolutionary success, according to a research paper by Stony Brook University paleontologist Michael D'Emic, PhD, and colleagues. Published in PLOS ONE, the study also hypothesizes that differences in tooth replacement rates among the giant herbivores likely meant their diets varied, an important factor that allowed multiple species to share the same ecosystems for several million years.
Paleontologists have long wondered how sauropods digested massive amounts of foliage that would have been necessary for their immense sizes. In "Evolution of high tooth replacement rates in sauropod dinosaurs," the team of paleontologists reveal that their new research into the microscopic structure of sauropod teeth shows the dinosaurs formed and replaced teeth faster than any other type of dinosaurs -- more like sharks and crocodiles -- and this process kept teeth fresh given the immense amount of wear they underwent from clipping off enormous volumes of food required for them.
"The microscopic structure of teeth and bones records aspects of an animal's physiology, giving us a window into the biology of long-extinct animals," said Dr. D'Emic, Research Instructor in the Department of Anatomical Sciences at Stony Brook University School of Medicine. "We determined that for the gigantic sauropods, each tooth took just a few months to form. Effectively, sauropods took a 'quantity over quality' approach."
Dr. D'Emic explained that unlike mammals and some other dinosaurs, sauropods did not chew their food. They snipped food into smaller pieces before swallowing.
"At least twice during their evolution, sauropods evolved small, peg-like teeth that formed and replaced quickly," said Dr. D'Emic. "This characteristic may have led to the evolutionary success of sauropods."
The team developed a novel method to estimate sauropod tooth formation and replacement rate without destructively sampling the teeth by making microscopic sections. Using these estimates, the researchers could track the evolution of tooth formation and replacement rates through time in species whose fossil remains are too rare to section.
With computed tomography (CT) scanning and microscopic anatomical methods, they measured tooth formation time, replacement rate, crown volume and enamel thickness in sectioned teeth of Camarasaurus and Diplodocus, two dinosaurs from the Late Jurassic Formation of North America. The technology and method enabled the researchers to count the number of growth lines in each tooth. Growth lines are a fraction of the thickness of a human hair. A tally of the lines gives the formation of each tooth in days.
To find out how fast these teeth were replaced, D'Emic and colleagues subtracted the ages of successive teeth from one another. The results indicated that replacement in these animals was extremely fast.
"A nearly 100-foot-long sauropod would have had a fresh tooth in each position about every one to two months, sometimes less" said Dr. D'Emic.
The tooth replacement rate, size and shape data collected by the team indicates that despite their somewhat stereotyped body plan and large body size, sauropods exhibited varied approaches to feeding. The paper indicates that this variation "represents a potential factor that allowed multiple giant species such as Camarasurus and Diplodocus to partition the same ecosystem."
Dr. D'Emic added that the research also contributes to a new view of sauropods, which were once thought to be more primitive than other dinosaur groups such as horned and duckbilled dinosaurs.
The paper co-authors include John Whitlock of Mount Aloysius College, Kathlyn Smith of Georgia Southern University, and Jeffrey Wilson and Daniel Fisher of the University of Michigan.
The dinosaur specimens used for the research were loaned to the paleontologists from the Yale Peabody Museum, Utah Museum of Natural History, Staatliches Museum für Naturkunde and the Iziko South African Museum.
Sauropod Dinosaur Facts:
1. Sauropod dinosaurs were the largest animals that ever walked the land.
2. Familiar examples of sauropods are Diplodocus, Brachiosaurus, and Apatosaurus. Apatosaurus was formerly called "Brontosaurus." These are genera (plural of genus) and should be italicized.
3. Sauropods had tiny heads for their bodies -- even a 100-foot-long animal would have a head only slightly larger than that of a horse.
4. Along with their tiny heads, sauropods had tiny teeth, ranging from the diameter of a pencil to a wide marker and only a few inches long.
5. Sauropods did not chew their food, but clipped it and swallowed it, where it was broken down in their digestive system.
6. In living animals, daily incremental lines are laid down in teeth. These lines are thinner than a human hair. The total number of lines indicates how long it took for the tooth to form.
7. Most animals have only one or two replacement teeth in a given socket (or tooth position), but sauropods had up to nine.
8. Sauropod teeth formed quickly -- in just a few months.
9. Sauropods replaced their teeth more quickly than most animals, including other dinosaurs. A new tooth was replaced in each tooth position every month or so.
10. Sauropods twice evolved small teeth that formed and replaced quickly.
- Michael D. D’Emic, John A. Whitlock, Kathlyn M. Smith, Daniel C. Fisher, Jeffrey A. Wilson. Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs. PLoS ONE, 2013; 8 (7): e69235 DOI: 10.1371/journal.pone.0069235
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