A short video showcasing some of the unique body rigging features of the wolfspiders in 'The Croods: A New Age.'
Body Rig by Evan Boucher
Face Rig by Cheng-Chia Kiera Yang
The wolfspiders had to be able to support transitioning from a wolf-like running gait to a spider-like gait seamlessly. This required giving animators maximum flexibility to position and shape the legs as needed to sell the look.
The key to this system was having the model separated out so the legs were different meshes from the rest of the body. The main skeleton containing the spine and head would then drive the body, which would then deform an intermediate mesh. There was then a second skeleton consisting of the eight legs, whose parents were attached to this deforming mesh. Controls were added to allow animators to slide the attachment location of the legs anywhere they wanted to on the body of the wolfspider. This helped the grouping of the legs.
Since the joint layout in a spider leg is very different from a wolf leg, we had to sell the idea without the anatomy being accurate to either animal. The leg was more of a simplified biped leg animated to sell the idea that it functioned like a dog leg. In order to transition into spider-mode, the elbows on the front arms needed to bend the opposite direction to mimic the knee bend of the back legs. A control was added to all of the elbows and knees to allow the animators to choose which direction the IK leg bent. This control combined with scaling the length of the legs was used to imply a more spidery leg setup, without having to add more leg segments.
Finally, a lot of careful work had to be done in the Character FX to hide leg connections with the long fur.