While there are many species of modern day kangaroos, one thing they all share is the tendency to hop. Hopping is one of  the trademarks of the kangaroo, and one of the species defining factors. However, the Sydney Morning Herald reports that this was not always the case.

A recent study shows that ancestors of the kangaroo did not hop, but rather they walked on two legs much like humans. It is a rather strange sight to imagine, but according to researchers this was seen within a sub-set species of sthenurine kangaroos. This information comes from studying the bone structure of the sthenurine kangaroo and comparing it to that of the modern day species. The now extinct species had a rigid spine and lacked a springy, flexible tail that would have supported hopping. In addition, they also had larger hips than their modern day cousin, and also had knee joints. All of this points to the sthenurine being able to support their body weight on one leg at a time, which is required for walking.

The main reason that the sthenurine kangaroo didn’t hop was because it didn’t make any sense. Not only was their bone structure not built for the hopping motion, but they also were much heavier (almost three times the weight) than modern day kangaroos. Carrying that much weight would of made jumping very difficult if not impossible. Modern kangaroos hop as a form of speed, and their ancestors could not of hopped in the same way do to their size and bone structure.

While the study concluded that sthenurines exclusively walked, researchers also concluded that they may have initially hopped. However, as the species evolved and grew in size they eventually slowly hopped less until they gave up it up entirely. This makes sense from an evolution standpoint, and suggest why they were built the way they were.