New research reveals that horses in utero briefly have five tiny toes. When born, a horse has a single digit flanked by remnants of two other digits; it was long thought that they had evolved from three-toed animals to a single-digit animal. The evolution of the equine limb is considered one of the most iconic evolutionary transitional stories shown through fossil records.
Dr. Kavanagh, a biologist at the University of Massachusetts, was looking at preserved embryos and realized that in early gestation that they have five clusters of cells in the area where the foot will develop. She was surprised by her discovery and enlisted the help of Drs. Scott Bailey and Karen Sears to re-examine available information on the initial stages of digit condensation in four-limbed animals.
A research paper suggested that horses had five ancestral digits and that the frog was the remnant of each of these digits. This hypothesis was based on equine fossils, but evidence was lacking. To see if this hypothesis was correct, the research team created a study that assessed early digit development by studying the limbs of horses that were 29 to 35 days old. They found five digits in these embryos, but this lasted only a few days. About a month after the embryo forms, the central digit is already fairly large and the two digits that become the remnants are reduced.
Read the full study here.
Read more at HorseTalk.
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