What tissue forms the basic structural framework of the skeleton in many animals, including humans?

Cartilage serves as the essential structural framework of the skeleton in many animals, including humans, particularly during developmental stages. It is a flexible tissue that provides support while allowing for greater mobility in joints compared to bone. In embryos, the skeleton is initially composed largely of cartilage before it is gradually replaced by bone through a process called endochondral ossification. This cartilage also plays crucial roles in cushioning joints and providing a smooth surface for movements.

While bone is a major component of the adult skeleton and provides a rigid structure, cartilage is the foundational tissue that forms the initial skeletal structure in the formative stages. Other connective tissues, such as fibrous tissue, do not serve as primary skeleton frameworks but support structures in different aspects of the body. Thus, cartilage is the correct answer as it takes precedence in forming the initial structural framework of the skeleton before bone predominates in adulthood.