Were dinosaurs destined to be big? Testing Cope's rule

GSA Annual Meeting Presentation: Testing Cope's rule and the existence of an upper bound for body size in non-avian dinosaurs

2012-11-02

(Press-News.org) Boulder, CO, USA – In the evolutionary long run, small critters tend to evolve into bigger beasts -- at least according to the idea attributed to paleontologist Edward Cope, now known as Cope's Rule. Using the latest advanced statistical modeling methods, a new test of this rule as it applies dinosaurs shows that Cope was right -- sometimes.

"For a long time, dinosaurs were thought to be the example of Cope's Rule," says Gene Hunt, curator in the Department of Paleobiology at the National Museum of Natural History (NMNH) in Washington, D.C. Other groups, particularly mammals, also provide plenty of classic examples of the rule, Hunt says.

To see if Cope's rule really applies to dinosaurs, Hunt and colleagues Richard FitzJohn of the University of British Columbia and Matthew Carrano of the NMNH used dinosaur thigh bones (aka femurs) as proxies for animal size. They then used that femur data in their statistical model to look for two things: directional trends in size over time and whether there were any detectable upper limits for body size.

"What we did then was explore how constant a rule is this Cope's Rule trend within dinosaurs," said Hunt. They looked across the "family tree" of dinosaurs and found that some groups, or clades, of dinosaurs do indeed trend larger over time, following Cope's Rule. Ceratopsids and hadrosaurs, for instance, show more increases in size than decreases over time, according to Hunt. Although birds evolved from theropod dinosaurs, the team excluded them from the study because of the evolutionary pressure birds faced to lighten up and get smaller so they could fly better.

As for the upper limits to size, the results were sometimes yes, sometimes no. The four-legged sauropods (i.e., long-necked, small-headed herbivores) and ornithopod (i.e., iguanodons, ceratopsids) clades showed no indication of upper limits to how large they could evolve. And indeed, these groups contain the largest land animals that ever lived.

Theropods, which include the famous Tyrannosaurus rex, on the other hand, did show what appears to be an upper limit on body size. This may not be particularly surprising, says Hunt, because theropods were bipedal, and there are physical limits to how massive you can get while still being able to move around on two legs.

Hunt, FitzJohn, and Carrano will be presenting the results of their study on the afternoon of Sunday, Nov. 4, at the annual meeting of The Geological Society of America in Charlotte, North Carolina, USA.

As for why Cope's Rule works at all, that is not very well understood, says Hunt. "It does happen sometimes, but not always," he added. The traditional idea that somehow "bigger is better" because a bigger animal is less likely to be preyed upon is naïve, Hunt says. After all, even the biggest animals start out small enough to be preyed upon and spend a long, vulnerable, time getting gigantic.

### WHAT: Testing Cope's Rule and the Existence of an Upper Bound for Body Size in Non-Avian Dinosaurs WHEN: 4:15-4:30 p.m., Sunday 4 November WHERE: Charlotte Convention Center, Room 217D ABSTRACT: https://gsa.confex.com/gsa/2012AM/webprogram/Paper211594.html

CONTACT: Gene Hunt
National Museum of Natural History, Smithsonian Institution
+1-202-633-1331
http://paleobiology.si.edu/staff/individuals/hunt.cfm

Find out what else is new and newsworthy by browsing the complete technical program schedule at https://gsa.confex.com/gsa/2012AM/finalprogram/.

To identify presentations in specific areas of interest, search topical sessions by discipline categories or sponsors using the drop-down menus at www.geosociety.org/meetings/2012/sessions/topical.asp, or use your browser's "find" feature to search for keywords or convener names.

Representatives of the media and public information officers from universities, government agencies, and research institutions, may participate in technical sessions, field trips, and other special events at the Annual Meeting. Eligible media personnel will receive complimentary registration and are invited to use GSA's newsroom facilities while at the meeting. Journalists and PIOs must pay for any short courses or field trips in which they wish to participate.

For information on media eligibility, go to www.geosociety.org/meetings/2012/media.htm. Media personnel may register onsite in the GSA Newsroom (room 204) at the Charlotte Convention Center. Wireless Internet access and a quiet space for interviews will be provided in the newsroom, along with beverages and light snacks throughout the day.

Newsroom Hours of Operation Saturday, 3 Nov., 3 p.m. to 5 p.m. Sunday, 4 Nov., through Tuesday, 6 Nov., 7:30 a.m. to 6 p.m. Wednesday, 7 Nov., 7:30 a.m. to 5:30 p.m. Newsroom telephone number (incoming calls): +1-704-339-6207 (starting Saturday afternoon).

Contact Christa Stratton, GSA Director of Communications & Marketing, for additional information and assistance.

www.geosociety.org/meetings/2012/

The Geological Society of America, founded in 1888, is a scientific society with more than 25,000 members from academia, government, and industry in more than 100 countries. Through its meetings, publications, and programs, GSA enhances the professional growth of its members and promotes the geosciences in the service of humankind. Headquartered in Boulder, Colorado, USA, GSA encourages cooperative research among earth, life, planetary, and social scientists, fosters public dialogue on geoscience issues, and supports all levels of earth science education.

www.geosociety.org

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