Ancient Horse Fossils
(Equus cf. E. complicatus)
(Click on the hoof, heel or toes to learn more about them.)
(Click on a thumbnail to learn more about it.)
Different species of fossil horses can only be conclusively identified by their teeth. Unfortunately, there are no teeth among the horse fossils in the Thomas Jefferson Fossil Collection. However, other horse fossils from Big Bone Lick can be positively identified as Equus complicatus. These foot bones compare favorably (cf.) with that species.
Metatarsal (ANSP 11457)
Horses' feet have undergone extensive modification which have enabled these animals to become powerful runners. The most conspicuous change is the reduction of the number of digits. All members of the genus Equus, which includes all modern species as well as the Ancient Horse, have retained only a single functional digit. This digit corresponds to the third toe in humans.
The metatarsal is one the most highly modified bones in the "foot". It's been so lengthened that it seems more part of the leg than the foot; human metatarsals are located in the arch. Unlike true leg bones, however, it's not directly powered by muscles. Instead, the metatarsal employs spring-like forces from massive ligaments.
The joint at the top (1) of the metatarsal articulates with (joins to) the ankle. That at the bottom (2) articulates with the first phalanx in the toe.
A nickel is shown for scale.
Hoof (ANSP 11457)
The hoof of the Ancient Horse (and all modern horses) is the last toe bone in the foot. It corresponds to the last bone on our third (middle) toe or finger.
This view shows the top and side of the hoof. The smooth surface on the right (1) is the where the hoof articulates with (joins to) the a toe bone. In life, an enlarged nail grows along the rough exterior (2) of the hoof. A portion of the hoof bone is missing (3).
A nickel is shown for scale.
Calcaneum (ANSP 11454)
The calcaneum is also known as the heel bone. In horses (including the Ancient Horse), the calcaneum appears to be located well up the leg, but it's still in the same relative position (near the ankle and lower tibia (shin bone) as the heel is in our own legs. Greatly enlarged bones in the horse's "foot", especially the metatarsal, distances the calcaneum from the ground.
The Achilles Tendon extends up from the heel end (1) of this bone to powerful muscles attached to the back of the tibia (shin bone); these muscles correspond to our calf muscles. The scooped joint surfaces (2) are where the calcaneum articulates with (joins to) the ankle.
A nickel is shown to indicate scale.
Toe (ANSP 11457)
Toe (ANSP 11455)
The photograph to the left shows two toe bones (phalanges) from the Ancient Horse. Both are proximal phalanges, which means that both are the toe bones closest (proximal) to the body. These bones articulate with (join to) the metatarsals (or metacarpals) on one end (the top in this photo) and with another toe bone on the other.
The top toe bone (ANSP 11457) appears healthy but the bottom specimen (ANSP 11455) is diseased. The rough and enlarged upper end suggest some kind of joint disorder, possibly arthritis.
A nickel is shown for scale.