Scientists at the University of Basel in Switzerland say they have identified a gene regulatory switch that has led to cattle losing three toes.
In a release on their study published in the journal Nature this week, the scientists say the fossil record shows that the first primitive even-toed ungulates (hoofed animals) had legs with five toes just like modern mice and humans. During their evolution, the basic limb skeletal structure was significantly modified such that today’s hippopotami have four toes, while the second and fifth toe face backwards in pigs. Cattle have two rudimentary dew claws and two symmetrical and elongated middle digits that form the cloven hoof, which provides good traction for walking and running on different terrains.
The scientists compared the activity of genes in mouse and cattle embryos which control the development of fingers and toes during embryonic development.
“The identified genetic alterations affecting this regulatory switch offer unprecedented molecular insights into how the limbs of even-toed ungulates diverged from those of other mammals roughly 55 million years ago,” professor Rolf Zeller from the Department of Biomedicine at the University of Basel said in the release.
“We assume that it is the result of progressive evolution, as this switch degenerated in cattle and other even-toed ungulates, while it remained fully functional in some vertebrates such as mice and humans.”