When you ask yourself the question ‘how many toes does a horse have?’ what answer comes to mind? Well, for most they would say merely ‘one,’ but its a bit more complicated than that.

According to a study published in the journal Royal Society Open Science, the assumption that the hoof is made of one toe (the middle toe to be exact) is quite false. The study author Nikos Solounias claims there is evidence that the missing toes are still present, but have merged together and now form the hooves we see in modern times. You see horses had to adapt just like everything else did as time went by.

The study states as follows:

‘We show that the evolutionary change to monodactyly is not as dramatic as previously thought and that the horse forelimb is more similar to that of its pentadactyl, tetradactyl and tridactyl ancestors. Although the modern horse maintains only one complete digit, the identities of all five digits are preserved in both the skeletal and soft anatomy as embedded elements into the dominant digit, and the digit positions are consistent with horses in earlier stages of evolution. We propose an hourglass pattern of reduction where the proximal- and distal-most parts of the digits are retained, the middle regions of the digits are completely reduced. We question the degree of digit reduction in both extinct and extant horses and rethink the status quo of monodactyly in Equus. Our study suggests elements of pentadactyly among the most famous single-toed species.’

‘The hoof of a full-term Equus specimen was cut in three coronal sections perpendicular to the axis of the distal phalanx, creating three sections. These sections include the proximal end of the distal phalanx including the hoof cartilages, middle end of the distal phalanx including the frog, and the distal end of the distal phalanx. An additional adult Equus hoof was sectioned in two coronal cuts, creating two sections. These sections include the proximal end of the distal phalanx and middle end of the distal phalanx near the merging of the frog. These three full-term sections and two adult sections were used to examine the gross morphology of the frog and keratinous hoof.’

Their results in the long run, were that it does seem apparent there are more phantom fingers (5 total) hidden that we were not able to see. I am sure this is something that many people will argue over, but it is still quite interesting to think that horses do truly have more than one finger technically.

Their conclusion reads as follows:

‘The morphology of the distal forelimb in the horse suggests an altered paradigm of monodactyly, in which remnants of the additional four digits are present both proximally and distally. The dominant digit remains as III. The splint metacarpals, previously interpreted as reduced digits II and IV, also contain remnants of digits I and V compressed as ridges onto the ventral surface. Our proposed locations of the proximal metacarpals are confirmed by their carpal articulations, which are consistent with those of the pentadactyl Phenacodus. The tridactyl equid Mesohippus shares the ventral ridges on the side digit bones, many of which appear to have a distinct fusion line, and exhibits a lesser degree of digit reduction than previously thought. The frog is a double structure unique to the modern horse, which is newly theorized to represent partially differentiated distal digits II and IV. The wings and hoof cartilages of the distal phalanx represent distal digits I and V. The frog and hoof wings each exhibit regions on the hoof with distinct keratinous lamellar fibres and germinating properties, further supporting our proposal that they represent additional digits. We reinterpret the famous Hipparion Laetoli footprints as exhibiting side expansions of the hoof wings (proposed digits I and V), rather than impressions from the complete side digits II and IV, and suggest the presence of a median claw in extinct equids, explaining the midline cleft on their distal phalanges. The nerves and arteries are more numerous than expected for a true mondactyl taxon, and better reflect the pentadactyl forefoot anatomy. Our study shows anatomical evidence for the presence of digits I and V proximally, in addition to the previously interpreted digits II, III and IV in the horse manus. In addition, we find remnants of digits I, II, IV and V distally surrounding dominant digit III. Our study suggests evidence of pentadactyly hidden within the single complete digit of Equus.’

What do you think about this? I for one am a bit blown away. I guess now when the question comes up you will have the best possible answer.

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