Featured Research

from universities, journals, and other organizations

The origin of the turtle shell: Mystery solved

Date:
July 9, 2013
Source:
RIKEN
Summary:
Biologists have finally solved the riddle of the origin of the turtle shell. By observing the development of different animal species and confirming their results with fossil analysis and genomic data, researchers show that the shell on the turtle's back derives only from its ancestors' ribcage and not from a combination of internal and external bone structures as is often thought.

Juvenile soft-shelled turtle swimming up to breathe the air. In most reptiles, birds and mammals, the rib cage movement aids breathing, but in the evolution towards turtles, the rib cage was transformed into the immovable shell covering the animal's back.
Credit: Image courtesy of RIKEN

A team of researchers from Japan has finally solved the riddle of the origin of the turtle shell.

By observing the development of different animal species and confirming their results with fossil analysis and genomic data, researchers from the RIKEN Center for Developmental Biology show that the shell on the turtle's back derives only from its ancestors' ribcage and not from a combination of internal and external bone structures as is often thought. Their study is published today in the journal Nature Communications.

The skeleton of vertebrates has evolved throughout history from two different structures, called the endo- and exoskeleton. In the human skeleton, the backbone and bones of the limbs evolved from the endoskeleton, whereas most of the skull elements derive from the exoskeleton. Fish scales and the alligator's bony skin nodules are other examples of exoskeletons.

The origin of the shell on the turtle's back, or carapace, was unclear until now because it comprises parts of obvious endoskeletal origin and others that look more like the exoskeleton of alligators and fish. The outer part of the turtle carapace was thought to have derived from exoskeletal bones, while the internal part has been shown to originate from ribs and vertebrae and to be connected to the internal skeleton of the animal. However, no direct evidence has been obtained to show that the bony structures developing outside the ribcage in turtles derived from the exoskeleton.

To investigate whether the turtle carapace evolved with any contribution from its ancestors' exoskeleton, Dr. Tatsuya Hirasawa and his team carefully observed developing embryos of Chinese soft-shell turtles, chickens and alligators.

In their analysis, they compared the development of the turtle carapace, the chick's ribs and the alligator's bony skin nodules.

The researchers found that the major part of the turtle's carapace is made from hypertrophied ribs and vertebrae and therefore derives solely from endoskeletal tissue.

This finding was confirmed by the observation of fossils of the ancient turtle Odontochelys and the ancient reptile Sinosaurosphargis, that both exhibit shells of endoskeletal origin. Odontochelys has a rigid shell instead of a flexible ribcage. And Sinosaurosphargis possesses an endoskeletal shell similar to the turtle's under, and separate from, a layer of exoskeletal bones.

Taken together these results show that the turtle carapace has evolved independently from the exoskeleton. This scenario is also consistent with the recent phylogenetic analyses based on genomic data that have placed turtles in the same group as birds, crocodiles and marine reptiles like Sinosaurophargis, contradicting recent studies based solely on fossil record.

"Recently, genomic analyses had given us evidence that turtles evolved from reptiles closely related to alligators and dinosaurs, not from primitive reptiles as once thought. Our findings match the evolutionary history revealed by the genomic analyses, and we are about to unravel the mystery of when and how the turtle shell evolved," explains Dr. Tatsuya Hirasawa who led the research.

"Our aim is to one day understand it as well as we understand the evolution of birds from dinosaurs," he concludes.


Story Source:

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


Journal Reference:

  1. Tatsuya Hirasawa, Hiroshi Nagashima, Shigeru Kuratani. The endoskeletal origin of the turtle carapace. Nature Communications, 2013; 4 DOI: 10.1038/ncomms3107

Cite This Page:

RIKEN. "The origin of the turtle shell: Mystery solved." ScienceDaily. ScienceDaily, 9 July 2013. <www.sciencedaily.com/releases/2013/07/130709094430.htm>.
RIKEN. (2013, July 9). The origin of the turtle shell: Mystery solved. ScienceDaily. Retrieved October 19, 2014 from www.sciencedaily.com/releases/2013/07/130709094430.htm
RIKEN. "The origin of the turtle shell: Mystery solved." ScienceDaily. www.sciencedaily.com/releases/2013/07/130709094430.htm (accessed October 19, 2014).

Share This



More Plants & Animals News

Sunday, October 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Rare Lion Cubs Make Debut at Belgrade Zoo

Raw: Rare Lion Cubs Make Debut at Belgrade Zoo

AP (Oct. 17, 2014) — Two white lion cubs were born in Belgrade zoo three weeks ago. White lions are a rare mutation of a species found in South Africa and some cultures consider them divine. (Oct. 17) Video provided by AP
Powered by NewsLook.com
The Best Foods To Boost Your Mood

The Best Foods To Boost Your Mood

Buzz60 (Oct. 17, 2014) — Feeling down? Reach for the refrigerator, not the medicine cabinet! TC Newman (@PurpleTCNewman) shares some of the best foods to boost your mood. Video provided by Buzz60
Powered by NewsLook.com
Sweet Times for Hard Cider Makers

Sweet Times for Hard Cider Makers

AP (Oct. 16, 2014) — With hard cider making a hardcore comeback across the country, craft makers are trying to keep up with demand and apple growers are tapping a juicy new revenue stream. (Oct. 16) Video provided by AP
Powered by NewsLook.com
Meet Garfi the Angry Cat

Meet Garfi the Angry Cat

Buzz60 (Oct. 16, 2014) — Garfi is one frowny, feisty feline - downright angry! Ko Im (@koimtv) introduces us to the latest animal celebrity taking over the Internet. You can follow more of Garfi's adventures on Twitter (@MeetGarfi) and Facebook (Garfi). Video provided by Buzz60
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