Featured Research

from universities, journals, and other organizations

Were dinosaurs undergoing long-term decline before mass extinction?

Date:
May 1, 2012
Source:
American Museum of Natural History
Summary:
Despite years of intensive research about the extinction of non-avian dinosaurs about 65.5 million years ago, a fundamental question remains: Were dinosaurs already undergoing a long-term decline before an asteroid hit at the end of the Cretaceous? A new study suggests that in general, large-bodied, "bulk-feeding" herbivores were declining during the last 12 million years of the Cretaceous. But carnivorous dinosaurs and mid-sized herbivores were not.

Like other meat-eaters analyzed in the new research, Troodon formosus, a coelurosaur, maintained a stable level of biodiversity leading up to the mass extinction at the end of the Cretaceous.
Credit: AMNH/J. Brougham

Despite years of intensive research about the extinction of non-avian dinosaurs about 65.5 million years ago, a fundamental question remains: were dinosaurs already undergoing a long-term decline before an asteroid hit at the end of the Cretaceous? A study led by scientists at the American Museum of Natural History gives a multifaceted answer.

Related Articles


The findings, published online May 1 in Nature Communications, suggest that in general, large-bodied, "bulk-feeding" herbivores were declining during the last 12 million years of the Cretaceous. But carnivorous dinosaurs and mid-sized herbivores were not. In some cases, geographic location might have been a factor in the animals' biological success.

"Few issues in the history of paleontology have fueled as much research and popular fascination as the extinction of non-avian dinosaurs," said lead author Steve Brusatte, a Columbia University graduate student affiliated with the Museum's Division of Paleontology. "Did sudden volcanic eruptions or an asteroid impact strike down dinosaurs during their prime? We found that it was probably much more complex than that, and maybe not the sudden catastrophe that is often portrayed."

The research team, which includes Brusatte; Mark Norell, chair of the Museum's Division of Paleontology; and scientists Richard Butler of Ludwig Maximilian University of Munich and Albert Prieto-M‡rquez from the Bavarian State Collection for Palaeontology, both in Germany, is the first to look at dinosaur extinction based on "morphological disparity"-the variability of body structure within particular groups of dinosaurs. Previous research was based almost exclusively on estimates of changes in the number of dinosaur species over time. However, it can be very difficult to do this accurately.

"By looking just at trends in taxonomic diversity, you get conflicting answers about the state of dinosaurs prior to extinction," Brusatte said. "This is because the results can be biased by uneven sampling of the fossil record. In places where more rock and fossils were formed, like in America's Great Plains, you'll find more species. We wanted to go beyond a simple species count for this study."

By looking at the change in biodiversity within a given dinosaur group over time, researchers can create a rough snapshot of the animals' overall well-being. This is because groups that show an increase in variability might have been evolving into more species, giving them an ecological edge. On the other hand, decreasing variability might be a warning sign of extinction in the long term.

The researchers calculated morphological disparity for seven major dinosaur groups using databases that include wide-ranging characteristics about the intricate skeletal structure of nearly 150 different species.

"People often think of dinosaurs as being monolithic-we say 'The dinosaurs did this, and the dinosaurs did that,'" Butler said. "But dinosaurs were hugely diverse. There were hundreds of species living in the Late Cretaceous, and these differed enormously in diet, shape, and size. Different groups were probably evolving in different ways and the results of our study show that very clearly."

The researchers found that hadrosaurs and ceratopsids, two groups of large-bodied, bulk-feeding herbivores-animals that did not feed selectively-may have experienced a decline in biodiversity in the 12 million years before the dinosaurs ultimately went extinct. In contrast, small herbivores (ankylosaurs and pachycephalosaurs), carnivorous dinosaurs (tyrannosaurs and coelurosaurs), and enormous herbivores without advanced chewing abilities (sauropods) remained relatively stable or even slightly increased in biodiversity.

As a complication, hadrosaurs showed different levels of disparity in different locations. While declining in North America, the disparity of this dinosaur group seems to have been increasing in Asia during the latest Cretaceous.

"These disparity calculations paint a more nuanced picture of the final 12 million years of dinosaur history," Brusatte said. "Contrary to how things are often perceived, the Late Cretaceous wasn't a static 'lost world' that was violently interrupted by an asteroid impact. Some dinosaurs were undergoing dramatic changes during this time, and the large herbivores seem to have been mired in a long-term decline, at least in North America."

In North America, extreme fluctuations of the inland Western Interior Sea and mountain building might have affected the evolution of dinosaurs in distinct ways from species on other continents. Therefore, the authors say, the North American record might not be representative of a global pattern, if one exists. They also note that there is no way to tell whether a declining dinosaur group would have survived if the asteroid had not struck Earth.

"Even if the disparity of some dinosaur clades or regional faunas were in decline, this does not automatically mean that dinosaurs were doomed to extinction," Norell said. "Dinosaur diversity fluctuated throughout the Mesozoic, and small increases or decreases between two or three time intervals may not be noteworthy within the context of the entire 150-million-year history of the group."

Funding for this study was provided by the National Science Foundation through the Division of Earth Sciences, the Division of Biological Infrastructure, a Graduate Research Fellowship, and a Doctoral Dissertation Improvement Grant; the German Research Foundation's Emmy Noether Programme; the Alexander von Humboldt Foundation; the Charlotte and Walter Kohler Charitable Trust; the American Museum of Natural History; and Columbia University.


Story Source:

The above story is based on materials provided by American Museum of Natural History. Note: Materials may be edited for content and length.


Journal Reference:

  1. Stephen L. Brusatte, Richard J. Butler, Albert Prieto-Mαrquez, Mark A. Norell. Dinosaur morphological diversity and the end-Cretaceous extinction. Nature Communications, 2012; 3: 804 DOI: 10.1038/ncomms1815

Cite This Page:

American Museum of Natural History. "Were dinosaurs undergoing long-term decline before mass extinction?." ScienceDaily. ScienceDaily, 1 May 2012. <www.sciencedaily.com/releases/2012/05/120501134159.htm>.
American Museum of Natural History. (2012, May 1). Were dinosaurs undergoing long-term decline before mass extinction?. ScienceDaily. Retrieved October 31, 2014 from www.sciencedaily.com/releases/2012/05/120501134159.htm
American Museum of Natural History. "Were dinosaurs undergoing long-term decline before mass extinction?." ScienceDaily. www.sciencedaily.com/releases/2012/05/120501134159.htm (accessed October 31, 2014).

Share This



More Fossils & Ruins News

Friday, October 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Killer History on Display at Museum of Death

Killer History on Display at Museum of Death

AP (Oct. 30, 2014) — Visitors take a trip down murderer memory lane at the Museum of Death located in the heart of Hollywood. (Oct. 30) Video provided by AP
Powered by NewsLook.com
Major Clue Found In Amelia Earhart Mystery

Major Clue Found In Amelia Earhart Mystery

Newsy (Oct. 29, 2014) — Researchers believe they have identified a fragment from Amelia Earhart's plane. Video provided by Newsy
Powered by NewsLook.com
Dracula's Dungeon May Have Been Found in Turkey

Dracula's Dungeon May Have Been Found in Turkey

AP (Oct. 29, 2014) — Historians think they may have discovered a dungeon in Turkey where the Romanian prince who inspired Count Dracula was once held captive. (Oct. 29) Video provided by AP
Powered by NewsLook.com
Study Doesn't Prove Megalodons Are Extinct, Never Needed To

Study Doesn't Prove Megalodons Are Extinct, Never Needed To

Newsy (Oct. 27, 2014) — How and why a study about when the giant prehistoric shark Megalodon went extinct got picked up as "proof" that it is. Video provided by Newsy
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:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

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