Our collection of dinosaur footprint fossils mainly consists of theropod and ornithopod footprints. These are three-toed footprints made by dinosaurs that walk on their toes. This is not uncommon, dogs and cats walk on their toes. This is called digitgrade. Digitgrade animals generally move quicker than those that put their feet flat on the ground (plantigrade).
Humans are plantigrade, meaning we walk with our ankle bones near the ground.
Although both theropod and ornithopod dinosaurs commonly leave three-toed footprints, they actually have four toes. There is a hallux toe, called a dew claw on dogs, that normally does not touch the ground. The hallux claw is on the inside of the foot and is numbered as toe #1. Note that numbering of toes is traditionally done using Roman Numerals.
The next toe is numbered as "II" (#2) and what is commonly seen as the center toe is "III" (#3). The toe on the outside of the foot is number "IV" (#4).
Looking at a fossil dinosaur footprint (theropod above) we can see how this numbering works. This footprint has been stained to make it easier to see.
The #I toe (hallux) did not leave an impression. We'll see what a hallux toe impression looks like when we get to ornithopod tracks. Since there is no #I toe impression, we start numbering the toes with #II.
