Featured Research

from universities, journals, and other organizations

Animal Interaction Behind Cambrian Explosion? 'Missing' Ancestors Of Today's Animals May Not Be Missing After All

Date:
May 8, 2008
Source:
Harvard University
Summary:
An event as simple as the world's first bite may have sparked an ancient "explosion" of life 500 million years ago that led to the rise of the broad groups of animals that are still alive today. A Harvard professor suggests that it was an increase in interactions between species, such as predation, that drove an escalating evolutionary process that led to the development of teeth and claws and the wide variety of characteristics that we see among Earth's animals today.

Charles Marshall recently presented his theory that it was an increase in interactions between species that drove an escalating evolutionary process that led to the wide variety of characteristics that we see among Earth's animals today.
Credit: Staff photo Matt Craig/Harvard News Office

An event as simple as the world’s first bite may have sparked an ancient “explosion” of life 500 million years ago that led to the rise of the broad groups of animals that are still alive today.

Related Articles


The cause of what is known as the “Cambrian Explosion” — which occurred during the Cambrian Period 542 million to 490 million years ago — has puzzled scientists for years. Theories about the event’s cause include an increase in the amount of atmospheric oxygen, a recovery from a global glaciation, and key genetic changes in precursor animals that allowed the development of bilateral symmetry, hard shells and bones, and rapid locomotion.

Harvard Professor of Biology and of Geology Charles Marshall presented his alternate theory Tuesday (April 29), suggesting that it was an increase in interactions between species, such as predation, that drove an escalating evolutionary process that led to the development of teeth and claws and the wide variety of characteristics that we see among Earth’s animals today.

The Cambrian Explosion was unique, Marshall said, because, though there have been mass extinctions — such as that of the dinosaurs — and recoveries since, there has never been another event as sweeping as that which occurred in the Cambrian seas 500 million years ago. It was during that time when all the modern phyla of animals first arose. Phyla are major classifications of life that include broad groups of creatures. The phylum Chordata, for example, includes all vertebrates, such as mammals, reptiles, amphibians, and birds.

Marshall, who spoke in the Geological Lecture Hall Tuesday evening as part of the Harvard Museum of Natural History’s annual lecture series, started off his talk by disputing whether the event commonly termed an “explosion” was rapid enough to earn that moniker. The rise of modern animal groups happened over millions of years. Only looking back over 500 million years of history could the expansion of life that occurred be termed an “explosion,” Marshall said.

Prior to the Cambrian Explosion, life on land was unknown and life in the sea was made up of soft-bodied multicellular creatures that strained food from the seawater around them or fed on mats of bacteria on the ocean floor. Though these animals virtually disappeared at the beginning of the Cambrian, the ancestors of the new modern phyla that replaced them haven’t been found.

Marshall reviewed other theories explaining the explosion and said that though each of them has merit — an increase in atmospheric oxygen, for example, would be needed to fuel more active lifestyles — each also falls short in some way.

As Marshall pondered alternatives, he began to think that it was possible that the creatures in the pre-Cambrian seas during the Ediacaran Period didn’t entirely disappear. Though they were very different from what followed, they may have been genetically complex enough to hold the genetic seeds of the explosion.

Marshall cited recent findings from genetic studies that indicate even creatures as diverse as flies and fish share many of the same genes. They differ, he said, more in how the genes are used — whether they’re switched on or off — than in the genes’ presence or absence.

“It’s not new genes that create new morphological innovation, but rather the way they’re wired together,” Marshall said. “[Different-looking creatures] are not apples and oranges.”

If the precursors to the creatures that arose during the Cambrian Period were swimming in the Ediacaran seas, something had to spark the dramatic change.

Marshall said that computer modeling of the forms that plants would take under different environmental conditions provided a clue. The models showed that widely divergent plants can result from a simple ancestor whose descendants are subjected to different environmental conditions. The model started with a simple primitive plant form and applied six basic genetic rules. It then added four selective pressures to drive evolutionary change — reproductive success, mechanical stability, light interception, and minimized surface area. The model produced 20 widely different body types. When researchers checked the fossil record, they found all types represented.

Applying that lesson to animals, Marshall began to search for an environmental force that might have driven such dramatic change in the fleshy animals that populated the oceans before the Cambrian began. Marshall realized that those creatures had no organs of interaction — no eyes, no antennae, no jaws or claws — and began to think that the new force on the scene was the ability of animals to interact with each other.

“Ediacarans were not interacting with each other as animals do today,” Marshall said. “I think what drove the Cambrian Explosion was ecological interactions.”

The other factors that have been cited as playing a role in the Cambrian Explosion very well may have had a hand, Marshall said, but they made the conditions ripe for the change driven by interactions among animals. Just what the trigger was that sparked those changing interactions, Marshall didn’t know, but, in a world populated by what he described as fleshy “beefsteaks” lying on the ocean floor, it may have been something as simple as the evolution of jaws with toothlike projections that allowed the world’s first painful bite.

“I believe … the explosion was driven by the onset of adult-adult interactions,” Marshall said. “Maybe the evolution of jaws or a large enough gut, or the evolution of something like chitin so they could bite rather than just giving a nasty suck.”


Story Source:

The above story is based on materials provided by Harvard University. The original article was written by Alvin Powell, Harvard News Office. Note: Materials may be edited for content and length.


Cite This Page:

Harvard University. "Animal Interaction Behind Cambrian Explosion? 'Missing' Ancestors Of Today's Animals May Not Be Missing After All." ScienceDaily. ScienceDaily, 8 May 2008. <www.sciencedaily.com/releases/2008/05/080506195605.htm>.
Harvard University. (2008, May 8). Animal Interaction Behind Cambrian Explosion? 'Missing' Ancestors Of Today's Animals May Not Be Missing After All. ScienceDaily. Retrieved December 20, 2014 from www.sciencedaily.com/releases/2008/05/080506195605.htm
Harvard University. "Animal Interaction Behind Cambrian Explosion? 'Missing' Ancestors Of Today's Animals May Not Be Missing After All." ScienceDaily. www.sciencedaily.com/releases/2008/05/080506195605.htm (accessed December 20, 2014).

Share This


More From ScienceDaily



More Fossils & Ruins News

Saturday, December 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Researchers Bring Player Pianos Back to Life

Researchers Bring Player Pianos Back to Life

AP (Dec. 17, 2014) Stanford University wants to unlock the secrets of the player piano. Researchers are restoring and studying self-playing pianos and the music rolls that recorded major composers performing their own work. (Dec. 17) Video provided by AP
Powered by NewsLook.com
Domestication Might've Been Bad For Horses

Domestication Might've Been Bad For Horses

Newsy (Dec. 16, 2014) A group of scientists looked at the genetics behind the domestication of the horse and showed how human manipulation changed horses' DNA. Video provided by Newsy
Powered by NewsLook.com
Mozart, Beethoven, Shubert and Bizet Manuscripts to Go on Sale

Mozart, Beethoven, Shubert and Bizet Manuscripts to Go on Sale

AFP (Dec. 16, 2014) A collection of rare manuscripts by composers Mozart, Beethoven, Shubert and Bizet are due to go on sale at auction on December 17. Duration: 00:57 Video provided by AFP
Powered by NewsLook.com
Old Ship Records to Shed Light on Arctic Ice Loss

Old Ship Records to Shed Light on Arctic Ice Loss

Reuters - Innovations Video Online (Dec. 15, 2014) Researchers are looking to the past to gain a clearer picture of what the future holds for ice in the Arctic. A project to analyse and digitize ship logs dating back to the 1850's aims to lengthen the timeline of recorded ice data. Ben Gruber reports. Video provided by Reuters
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