Featured Research

from universities, journals, and other organizations

'Head-first' diversity shown to drive vertebrate evolution

Date:
December 31, 2011
Source:
University of Chicago Medical Center
Summary:
A new analysis of two adaptive radiations in the fossil record found that these diversifications proceeded "head first." Head features diversified before body shapes and types. This suggests that feeding-related evolutionary pressures are the initial drivers of diversification.

Fossil fish. A new study of fish fossil records near extinction events contradicts previous models.
Credit: © psamtik / Fotolia

The history of evolution is periodically marked by explosions in biodiversity, as groups of species try out a wide range of shapes and sizes. With a new analysis of two such adaptive radiations in the fossil record, researchers have discovered that these diversifications proceeded head-first.

By analyzing the physical features of fossil fish that diversified around the time of two separate extinction events, scientists from the University of Chicago and the University of Oxford found that head features diversified before body shapes and types. The discovery disputes previous models of adaptive radiations and suggests that feeding-related evolutionary pressures are the initial drivers of diversification.

"It seems like resources, feeding and diet are the most important factors at the initial stage," said lead author Lauren Sallan, graduate student in the Department of Organismal Biology and Anatomy at the University of Chicago. "Strange heads show up first -- crushing jaws, animals with big teeth, with long jaws -- but they're all pretty much attached to the same body."

Adaptive radiations underlie the evolution of dominant and diverse groups. After a major disruption, such as an extinction event, surviving species diversify into a myriad variety of forms. Modern examples of this diversity are the fish family of cichlids, with more than 1,000 documented species, or "Darwin's finches" of the Galapagos Islands, which exhibit many different beak types.

Evolutionary biologists have used these living species to propose at least two models of how adaptive radiations work. One model proposes a single "burst" of divergence followed by a long period of relative stability. Another, sometimes known as the "general vertebrate model," introduced the idea of staged divergences, with habitat-driven changes in body type preceding diversification of head types.

However, these models had not yet been tested with the rich data sets available in the fossil record.

"There hadn't been any tests of these things using fossils," said Sallan, a graduate student in the laboratory of University of Chicago Professor Michael Coates. "You have all these analyses of diversification, yet not one of them goes back to the fossil record and says what's happening at this time period, and the next time period, and the one after that."

Sallan and co-author Matt Friedman, PhD, lecturer in paleobiology at the University of Oxford and a former member of Coates' laboratory, looked at two different adaptive radiations in the fossil record. The first was the explosion of ray-finned fishes after the Hangenberg extinction, an event 360 million years ago that decimated ocean life on Earth. The second group was the acanthomorphs, a group of fish that exhibited a burst in diversity around the time of the end-Cretaceous extinction that ended the age of dinosaurs.

In both datasets, the researchers used a method called geometric morphometrics to quantify differences in features such as body depth, fin position and jaw shape between species. Crucially, Sallan and Friedman separated head features from body features in their analysis, to better detect the timing of when each compartment showed a burst of diversity in the record.

The results of the two analyses were in agreement: Diversification in cranial features preceded diversification in body types. Unusual head features such as jaws lined with sharp teeth or blunt teeth for crushing appeared before diverse body shapes on a spectrum from slender and eel-like to broad and disc-shaped.

"We have these two entirely separate radiations, and in both of them the pattern is heads first. So feeding might be more important to diversification than habitat use," Sallan said. "It's against both the adaptive radiation model and the proposed stage model."

The pattern detected with the new analyses suggests that the appearance of new sources of food drives a burst of diversity before species begin to change to adapt to new habitats.

"Ecological limits are taken away," Sallan said. "There's more opportunity out there, more available resources, and they're taking advantage of that. Later, they're taking advantage of specializing to new habitats. So it's not something within the animals themselves; it's more opportunity that matters."

While the new study offers two distinct examples of head-first diversification separated by hundreds of millions of years, the universality of the model remains to be conclusively proven.

"Evolution is really complex, and it's not really clear that there should be only one model," Sallan said. "It might be that this model might apply to fishes in certain time periods, or might apply to vertebrates, but a lot more investigation is needed to see whether that is actually true."

The paper, "Heads or Tails: Staged Diversification in Vertebrate Evolutionary Radiations," was published online Dec. 21 by the journal Proceedings of the Royal Society B.

Funding for the study was provided by the National Science Foundation, the Paleontological Association, the Paleontological Society, the American Society of Ichthyologists and Herpetologists, the Evolving Earth Foundation, the Natural Environment Research Council, the Fell Fund of the University of Oxford, the Environmental Protection Agency, and the Lerner-Grey Fund of the American Museum of Natural History.


Story Source:

The above story is based on materials provided by University of Chicago Medical Center. Note: Materials may be edited for content and length.


Journal Reference:

  1. L. C. Sallan, M. Friedman. Heads or tails: staged diversification in vertebrate evolutionary radiations. Proceedings of the Royal Society B: Biological Sciences, 2011; DOI: 10.1098/rspb.2011.2454

Cite This Page:

University of Chicago Medical Center. "'Head-first' diversity shown to drive vertebrate evolution." ScienceDaily. ScienceDaily, 31 December 2011. <www.sciencedaily.com/releases/2011/12/111221092001.htm>.
University of Chicago Medical Center. (2011, December 31). 'Head-first' diversity shown to drive vertebrate evolution. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2011/12/111221092001.htm
University of Chicago Medical Center. "'Head-first' diversity shown to drive vertebrate evolution." ScienceDaily. www.sciencedaily.com/releases/2011/12/111221092001.htm (accessed July 28, 2014).

Share This




More Fossils & Ruins News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Newsy (July 28, 2014) The asteroid that killed the dinosaurs struck at the worst time for them. A new study says that if it hit earlier or later, they might've survived. Video provided by Newsy
Powered by NewsLook.com
Did ISIS Destroy Jonah's Tomb?

Did ISIS Destroy Jonah's Tomb?

Newsy (July 25, 2014) Unverified footage posted to YouTube purportedly shows ISIS militants destroying a shrine widely believed to be the tomb of the prophet Jonah. Video provided by Newsy
Powered by NewsLook.com
Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
Richard III's Car Park Burial Site Opens to Public

Richard III's Car Park Burial Site Opens to Public

AFP (July 25, 2014) Visitors will be able to look down from a glass walkway on the grave of King Richard III when a new centre opens in the English cathedral city of Leicester, where the infamous hunchback was found under a car park in 2012. Duration: 00:35 Video provided by AFP
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