Quadrupedalism is an ancient, fundamental trait inherited from the earliest land vertebrates (tetrapods).

The four-limbed body plan emerged approximately 375 million years ago with the evolution of tetrapods from lobe-finned fish. This transition marked a pivotal moment in vertebrate history, as these early creatures developed limbs suitable for navigating terrestrial environments. The genetic toolkit for limb development, including critical regulatory genes like HOX genes, was established during this period and has been conserved across most terrestrial vertebrates, including mammals like dogs. Therefore, dogs possess four legs not as a unique canine invention, but as a legacy of their deep evolutionary lineage shared with amphibians, reptiles, birds, and other mammals. This ancestral blueprint provided a stable foundation for movement on land, offering a distinct advantage over the aquatic locomotion of their fish ancestors. The development of paired limbs, each with a specific skeletal structure adapted for weight-bearing and propulsion, allowed these pioneers to explore new ecological niches, eventually leading to the incredible diversity of land animals we see today.