Tongue Makes the Difference in How Fish and Mammals Chew
ScienceDaily (July 3, 2011) — New research from Brown University shows that fish and mammals chew differently. Fish use tongue muscles to thrust food backward, while mammals use tongue muscles to position food for grinding. The evolutionary divergence is believed to have occurred with amphibians, though further research is needed to identify which species and when. Results are published in Integrative and Comparative Biology.
Chewing styles for different purposes. Fish use tongue muscles to thrust food backward, while mammals use tongue muscles to position food for grinding. (Credit: Image courtesy of Brown University)
Evolution has made its marks -- large and small -- in innumerable patterns of life. New research from Brown University shows chewing has evolved too.
Researchers looked at muscles that control the movement of the jaw and tongue in fish and in mammals. They learned that fish use tongue muscles primarily to funnel the food farther into the mouth for processing, as if the morsel were an object in an assembly line. Mammals use tongue muscles to position the food, so that jaw muscles can best use teeth to chew the food.
Chewing styles for different purposes
Fish use tongue muscles to thrust food backward, while mammals use tongue muscles to position food for grinding.The difference in chewing shows that animals have changed the way they chew and digest their food and that evolution must have played a role.
"It's pretty clear that all of these animals chew, but the involvement of the tongue in chewing differs," said Nicolai Konow, a postdoctoral researcher at Brown and the lead author on the study, published in the journal of Integrative and Comparative Biology. "And that brings up the question of what the muscles associated with the tongue and the jaw are doing."
...
...
Read more here: Science Daily
+++++
Evolution of Muscle Activity Patterns Driving Motions of the Jaw and Hyoid during Chewing in Gnathostomes
Nicolai Konow1,*, Anthony Herrel†, Callum F. Ross‡, Susan H. Williams§, Rebecca Z. German¶, Christopher P. J. Sanford‖ and Chris Gintof‖
Author Affiliations
*Department of Ecology and Evolutionary Biology, Brown University, Box G-B204, Providence, RI 02912, USA; †Département d’Ecologie et de Gestion de la Biodiversité, UMR 7179 C.N.R.S/M.N.H.N., 57 rue Cuvier, Case postale 55, 75231, Paris Cedex 5, France; ‡Department of Organismal Biology and Anatomy, University of Chicago, 1027 E. 57th Street, Chicago, IL 60637, USA; §Department of Biomedical Sciences, Ohio University College of Osteopathic Medicine, 228 Irvine Hall, Athens, OH 45701, USA;¶Department of Physical Medicine and Rehabilitation, Johns Hopkins University School of Medicine, 98 N. Broadway, Suite 409, Baltimore, MD 21231, USA; ‖Department of Biology, 114 Hofstra University, Hempstead, NY 11549, USA
1E-mail: nkonow@brown.edu
Abstract
Although chewing has been suggested to be a basal gnathostome trait retained in most major vertebrate lineages, it has not been studied broadly and comparatively across vertebrates. To redress this imbalance, we recorded EMG from muscles powering anteroposterior movement of the hyoid, and dorsoventral movement of the mandibular jaw during chewing. We compared muscle activity patterns (MAP) during chewing in jawed vertebrate taxa belonging to unrelated groups of basal bony fishes and artiodactyl mammals. Our aim was to outline the evolution of coordination in MAP. Comparisons of activity in muscles of the jaw and hyoid that power chewing in closely related artiodactyls using cross-correlation analyses identified reorganizations of jaw and hyoid MAP between herbivores and omnivores. EMG data from basal bony fishes revealed a tighter coordination of jaw and hyoid MAP during chewing than seen in artiodactyls. Across this broad phylogenetic range, there have been major structural reorganizations, including a reduction of the bony hyoid suspension, which is robust in fishes, to the acquisition in a mammalian ancestor of a muscle sling suspending the hyoid. These changes appear to be reflected in a shift in chewing MAP that occurred in an unidentified anamniote stem-lineage. This shift matches observations that, when compared with fishes, the pattern of hyoid motion in tetrapods is reversed and also time-shifted relative to the pattern of jaw movement.
© The Author 2011. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved.
+++++
+++++
