Featured Research

from universities, journals, and other organizations

From Fish To Landlubber: Fossils Suggest Earlier Land-water Transition Of Tetrapod

Date:
April 19, 2009
Source:
Duke University
Summary:
New evidence gleaned from CT scans of fossils locked inside rocks may flip the order in which two kinds of four-limbed animals with backbones were known to have moved from fish to landlubber.

CT-scanned reconstruction of the left humerus (upper arm bone) and shoulder girdle of a juvenile Ichthyostega.
Credit: Viviane Callier, Jennifer Clack and Per Ahlberg

New evidence gleaned from CT scans of fossils locked inside rocks may flip the order in which two kinds of four-limbed animals with backbones were known to have moved from fish to landlubber.

Both extinct species, known as Ichthyostega and Acanthostega, lived an estimated 360-370 million years ago in what is now Greenland. Acanthostega was thought to have been the most primitive tetrapod, that is, the first vertebrate animal to possess limbs with digits rather than fish fins.

But the latest evidence from a Duke graduate student's research indicates that Ichthyostega may have been closer to the first tetrapod. In fact, Acanthostega may have had a terrestrial ancestor and then returned full time to the water, said Viviane Callier, who is the first author of a report on the findings to be published in today's issue of the journal Science.

"If there is one take-home message, it is that the evolutionary relationship between these early tetrapods is not well resolved," Callier said.

Co-author Jennifer Clack of the University Museum of Zoology in Cambridge, England -- where she supervised Callier's work for a master's degree -- found the fossils embedded in rocks collected from East Greenland.

Rather than trying to remove them -- an action that would have destroyed much of the evidence -- the researchers studied the fossils inside the stone with computed tomography (CT) scanning. Callier "reconstructed" the animals using imaging software (Amira and Mimics) to analyze the CT scans, focusing on the shapes of the two species' upper arm bones, or humeri.

The CT slices revealed that Clack had found the first juvenile forms of Ichthyostega. Previously known fossils of Ichthyostega had come from adults.

Anatomies can morph as animals move towards adulthood, Callier said. And such shifts can help scientists deduce when in development the animal acquired the terrestrial habit. The fossils suggest that Ichthyostega juveniles were aquatically adapted, and that the terrestrial habit was acquired relatively late in development. The fossils bore evidence that the muscle arrangement in adults was better suited to weight-bearing, terrestrial locomotion than the juvenile morphology. It is possible that Ichthyostega came out of the water only as a fully mature adult.

In contrast, in Acanthostega "there is less change from the juvenile to the adult. Although Acanthostega appears to be aquatically adapted throughout the recorded developmental span, its humerus exhibits subtle traits that make it more similar to the later, fully terrestrial tetrapods," Callier said

Because the shapes of its adult limbs seemed the most fin-like, scientists had previously concluded that Acanthostega was "more primitive," Callier said. "But now, if we look at the details of the humeri, Ichthyostega's are actually more similar to earlier fishes."

Ironically, the shape of Acanthostegas limb's, in both adult and the newly-discovered juvenile forms, is more "paddle-like" than Ichthyostega's, Callier said. "They would have been really good swimmers. So, although Acanthostega had limbs with digits, we don't think it was really terrestrial. We think even the adults were aquatic."

"If Ichthyostega is actually more primitive than Acanthostega, then maybe animals evolved towards a terrestrial existence a lot earlier than originally believed," she said. "Maybe Acanthostega was actually derived from a terrestrial ancestor, and then, went back to an aquatic lifestyle."

Per Ahlberg, a Swedish paleontologist who was previously Clack's graduate student, also joined Clack in a comparative analysis of other more fish-like species living at about the same time as Ichthyostega and Acanthostega.

Those include Tiktaalik, another animal that has made the news because of scientists' deductions that it was in transition from water to land.

"It seems like there were different species evolving the same or similar traits independently -- evidence of parallel evolution," Callier said. "The terrestrial environment posed new challenges like feeding and moving on land and breathing air, to which the first tetrapods had to evolve solutions. Sometimes different lineages stumbled upon similar solutions."

Ahlberg, now professor at the University of Uppsala in Sweden, is corresponding author of the new Science report. The research was funded by the Winston Churchill Foundation and the Swedish Research Council.


Story Source:

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


Journal Reference:

  1. Viviane Callier, Jennifer A. Clack, and Per E. Ahlberg. Contrasting Developmental Trajectories in the Earliest Known Tetrapod Forelimbs. Science, 2009; 324 (5925): 364-367 DOI: 10.1126/science.1167542

Cite This Page:

Duke University. "From Fish To Landlubber: Fossils Suggest Earlier Land-water Transition Of Tetrapod." ScienceDaily. ScienceDaily, 19 April 2009. <www.sciencedaily.com/releases/2009/04/090417144848.htm>.
Duke University. (2009, April 19). From Fish To Landlubber: Fossils Suggest Earlier Land-water Transition Of Tetrapod. ScienceDaily. Retrieved July 22, 2014 from www.sciencedaily.com/releases/2009/04/090417144848.htm
Duke University. "From Fish To Landlubber: Fossils Suggest Earlier Land-water Transition Of Tetrapod." ScienceDaily. www.sciencedaily.com/releases/2009/04/090417144848.htm (accessed July 22, 2014).

Share This




More Fossils & Ruins News

Tuesday, July 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Neil Armstrong's Post-Apollo 11 Life

Neil Armstrong's Post-Apollo 11 Life

Newsy (July 19, 2014) — Neil Armstrong gained international fame after becoming the first man to walk on the moon in 1969. But what was his life like after the historic trip? Video provided by Newsy
Powered by NewsLook.com
A Centuries' Old British Tradition Is Far from a Swan Song

A Centuries' Old British Tradition Is Far from a Swan Song

AFP (July 19, 2014) — As if it weren't enough that the Queen is the Sovereign of the UK and 15 other Commonwealth realms, she is also the owner of all Britain's unmarked swans. Duration: 02:18 Video provided by AFP
Powered by NewsLook.com
Tooth Plaque Provides Insight Into Diets Of Ancient People

Tooth Plaque Provides Insight Into Diets Of Ancient People

Newsy (July 19, 2014) — Research on plaque from ancient teeth shows that our prehistoric ancestor's had a detailed understanding of plants long before developing agriculture. Video provided by Newsy
Powered by NewsLook.com
45 Years Later, Buzz Aldrin on Walking on Moon

45 Years Later, Buzz Aldrin on Walking on Moon

AP (July 18, 2014) — Forty-five years ago Sunday, Apollo 11's Neil Armstrong and Buzz Aldrin became the first humans to set foot on the moon. Speaking at the Intrepid Sea, Air & Space Museum, Aldrin described what he was thinking right before the historic walk. (July 18) 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