While there are other limbless vertebrates like caecilians and some lizards, snakes are found in far greater numbers and diversity across the globe.

Here's why:

* Wide Distribution: Snakes live on every continent except Antarctica, inhabiting diverse environments from tropical rainforests to deserts.

* Species Diversity: There are over 3,600 species of snakes, compared to around 200 species of caecilians and a few dozen limbless lizard species.

* Population Abundance: Many snake species thrive in large populations, contributing to their overall prevalence.

Therefore, based on these factors, snakes are considered the most common limbless vertebrate.