Featured Research

from universities, journals, and other organizations

For some feathered dinosaurs, bigger not always better

Date:
November 28, 2012
Source:
North Carolina State University
Summary:
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.

This scale illustration shows size of feathered theropod herbivores compared to humans.
Credit: Lindsay Zanno, NC State and NC Museum of Natural Sciences

Every kid knows that giant carnivores like Tyrannosaurus rex dominated 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."

Zanno and Makovicky estimated body mass for 47 extinct species of feathered dinosaur, representing three major groups that abandoned a strictly meat-eating diet -- ornithomimosaurs ("bird-mimics"), oviraptorosaurs ("egg-thieves"), and the bizarre therizinosaurs ("scythe-lizards"). Most species in these lineages also possessed a toothless beak, three-toed feet, and shorter tails than your average dinosaur, making them look a lot like modern birds.

All three groups evolved gigantic proportions: the largest oviraptorosaur weighed over 7,000 pounds, and the biggest ornithomimosaurs and therizinosaurs topped out at over 13,000 pounds. "The largest feathered dinosaurs were more than 100 times more massive than your average person," says Zanno. "The reality is that for most of us, it is downright difficult to imagine a feathered animal of gigantic proportions."

The researchers also found that average body mass did increase in these groups over time (on average, the earliest members were smallest and the last species to evolve were among the largest). But this simple correlation didn't indicate whether large size was an evolutionary advantage.

To test whether these groups were being driven to get bigger by natural selection, Zanno and Makovicky fitted different evolutionary models to the data, looking to see which model best described the patterns of body mass from ancestor species to descendant species. They found that these theropod groups were experimenting with different body masses as they evolved, with some getting bigger, while others were getting smaller. In short, there was no clear-cut drive to get big -- size seemed to provide no overwhelming advantage during the evolution of these animals.

The researchers' results appear in Proceedings of the Royal Society B.

"Results of our study don't rule out diet as affecting body mass, but do seem to indicate that fluctuating environmental conditions over time were trumping the benefit of becoming a giant," Zanno says. "The long and short of it is that for plant-eating theropods, bigger wasn't always better."

"Where resources permitted, these animals could get as big as elephants, but that clearly was not the case in all environments and time periods," says Makovicky. "Factors such as resource abundance and competition with other herbivores likely played a more significant role." He added that uneven sampling in the fossil record, such as preferential preservation of smaller species in earlier time periods and larger species in later ones, could also impact the results.


Story Source:

The above story is based on materials provided by North Carolina State University. Note: Materials may be edited for content and length.


Journal Reference:

  1. L. E. Zanno, P. J. Makovicky. No evidence for directional evolution of body mass in herbivorous theropod dinosaurs. Proceedings of the Royal Society B: Biological Sciences, 2012; 280 (1751): 20122526 DOI: 10.1098/rspb.2012.2526

Cite This Page:

North Carolina State University. "For some feathered dinosaurs, bigger not always better." ScienceDaily. ScienceDaily, 28 November 2012. <www.sciencedaily.com/releases/2012/11/121128093254.htm>.
North Carolina State University. (2012, November 28). For some feathered dinosaurs, bigger not always better. ScienceDaily. Retrieved July 25, 2014 from www.sciencedaily.com/releases/2012/11/121128093254.htm
North Carolina State University. "For some feathered dinosaurs, bigger not always better." ScienceDaily. www.sciencedaily.com/releases/2012/11/121128093254.htm (accessed July 25, 2014).

Share This




More Fossils & Ruins News

Friday, July 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Mobile App Gives Tour of Battle of Atlanta Sites

Mobile App Gives Tour of Battle of Atlanta Sites

AP (July 25, 2014) Emory University's Center for Digital Scholarship has launched a self-guided mobile tour app to coincide with the 150th anniversary of the Civil War's Battle of Atlanta. (July 25) Video provided by AP
Powered by NewsLook.com
Tyrannosaur Pack-Hunting Theory Aided By New Footprints

Tyrannosaur Pack-Hunting Theory Aided By New Footprints

Newsy (July 24, 2014) A new study claims a set of prehistoric T-Rex footprints supports the theory that the giant predators hunted in packs instead of alone. Video provided by Newsy
Powered by NewsLook.com
Mint Gives JFK Coin a Face-Lift

Mint Gives JFK Coin a Face-Lift

AP (July 24, 2014) The U.S. Mint has re-designed the John F. Kennedy half dollar coin to better match the former president's likeness. (July 24) Video provided by AP
Powered by NewsLook.com
Raw: MD Church Built in 1773 Ravaged by Fire

Raw: MD Church Built in 1773 Ravaged by Fire

AP (July 22, 2014) Authorities say a 241-year-old church on the National Register of Historic Places has been ravaged by fire in Maryland. (July 22) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

    Health News

      Environment News

        Technology News



          Save/Print:
          Share:

          Free Subscriptions


          Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

          Get Social & Mobile


          Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

          Have Feedback?


          Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
          Mobile: iPhone Android Web
          Follow: Facebook Twitter Google+
          Subscribe: RSS Feeds Email Newsletters
          Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins