Featured Research

from universities, journals, and other organizations

When vertebrae cross dress: How sloths got their long neck

Date:
October 19, 2010
Source:
University of Cambridge
Summary:
By examining the development of bones in the vertebral column, limbs and ribcage, scientists have discovered how sloths evolved their unique neck skeleton.

Lateral view of 3D reconstruction of computerized tomography (CT) scan of skeleton in the three-toed sloth Bradypus tridactylus (Paris Museum, MNHN 1881-111). This specimen represents a fetus and is approximately 100mm in length. The blue centra extending into the base of the neck are rib-cage vertebrae that have been coopted to form neck vertebrae. During the course of evolution, the shoulder, ribcage, and pelvis have shifted down the vertebral column to make the neck longer. Vertebral neural arches are in red, vertebral centra are in blue, scapula and clavicle are in green, and ischium, ilium, and pubis are in orange
Credit: L. Hautier and R. Asher

By examining the development of bones in the vertebral column, limbs, and ribcage, scientists at the University of Cambridge have discovered how sloths evolved their unique neck skeleton.

From mice to giraffes, mammals are remarkable in that all but a handful of their 5000 species have exactly seven vertebrae in the neck. Among the few that deviate from this number are three-toed sloths, which may have up to ten ribless vertebrae in the neck.

Traditionally, vertebrae above the shoulders that lack ribs are known as cervical or neck vertebrae. Animals such as birds and lizards show great variety in the number of vertebrae in their neck. For example, a swan may have twice as many as a songbird.

Mammals, on the other hand, are much more conservative. A giraffe has the same number of neck vertebrae as a human, mouse, elephant, or armadillo; all have exactly seven. Sloths are an exception, with up to 10 vertebrae in their neck.

In order to discover if patterns of bone formation in these strange animals give any clues to their divergent vertebral anatomy, scientists based at the University of Cambridge have investigated the development of the skeleton in mammals, focusing on the vertebral column in sloths.

The scientists found that in all mammals except for sloths, bone formation always took place earlier in the body of first few vertebrae of the ribcage than in the neck. The only exception was among three-toed sloths, which show early bone-formation in the bodies of their distal, ribless neck vertebrae, before those of the ribcage.

However, by observing the position of bone-formation within the vertebral column, the investigators made a startling discovery: all mammals, including sloths, show early development of the body of the eighth vertebra down from the head, whether or not it is part of the neck.

In other words, the bottom neck vertebrae of sloths show a similar sequence of development as the top ribcage vertebrae of other mammals, both of which start at eight vertebrae down from the head. This shows that the bottom "neck" vertebrae of sloths are developmentally the same as ribcage vertebrae of other mammals, but lack ribs.

Dr Robert Asher, of the Department of Zoology at the University of Cambridge, said: "The remarkable conservatism of the mammalian neck is apparent even in those few species that superficially seem to be exceptions, like sloths. Even though they've got eight to ten ribless vertebrae above the shoulders, unlike the seven of giraffes, humans, and nearly every other species of mammal, those extra few are actually ribcage vertebrae masquerading as neck vertebrae."

These new results -- published in the Proceedings of the National Academy of Sciences -- support the interpretation that the limb girdles and at least part of the ribcage derive from different embryonic tissues than the vertebrae, and that during the course of evolution, they have moved in concert with each other relative to the vertebral column. In three-toed sloths, the position of the shoulders, pelvis, and ribcage are linked with one another, and compared to their common ancestor shared with other mammals, have shifted down the vertebral column to make the neck longer.


Story Source:

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


Journal Reference:

  1. Lionel Hautier, Vera Weisbecker, Marcelo R. Sαnchez-Villagra, Anjali Goswami, Robert J. Asher. Skeletal development in sloths and the evolution of mammalian vertebral patterning. Proceedings of the National Academy of Sciences, 2010; DOI: 10.1073/pnas.1010335107

Cite This Page:

University of Cambridge. "When vertebrae cross dress: How sloths got their long neck." ScienceDaily. ScienceDaily, 19 October 2010. <www.sciencedaily.com/releases/2010/10/101018163102.htm>.
University of Cambridge. (2010, October 19). When vertebrae cross dress: How sloths got their long neck. ScienceDaily. Retrieved October 2, 2014 from www.sciencedaily.com/releases/2010/10/101018163102.htm
University of Cambridge. "When vertebrae cross dress: How sloths got their long neck." ScienceDaily. www.sciencedaily.com/releases/2010/10/101018163102.htm (accessed October 2, 2014).

Share This



More Plants & Animals News

Thursday, October 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Attacking Superbugs

Attacking Superbugs

Ivanhoe (Oct. 1, 2014) — Two weapons hospitals can use to attack superbugs. Scientists in Ireland created a new gel resistant to superbugs, and a robot that can disinfect a room in minutes. Video provided by Ivanhoe
Powered by NewsLook.com
Cultural Learning In Wild Chimps Observed For The First Time

Cultural Learning In Wild Chimps Observed For The First Time

Newsy (Oct. 1, 2014) — Cultural transmission — the passing of knowledge from one animal to another — has been caught on camera with chimps teaching other chimps. Video provided by Newsy
Powered by NewsLook.com
Earth Has Lost Half Its Vertebrate Wildlife Since 1970: WWF

Earth Has Lost Half Its Vertebrate Wildlife Since 1970: WWF

Newsy (Sep. 30, 2014) — A new study published by the World Wide Fund for Nature found that more than half of the world's wildlife population has declined since 1970. Video provided by Newsy
Powered by NewsLook.com
Annual Dog Surfing Competition Draws California Crowds

Annual Dog Surfing Competition Draws California Crowds

AFP (Sep. 30, 2014) — The best canine surfers gathered for Huntington Beach's annual dog surfing competition, "Surf City, Surf Dog." Duration: 01:15 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:

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