Urocordylidae are characterized by their very long, paddle-like tails. In life they were newt-like and aquatic.Urocordylids are distinguished by their elongated tails. Each tail vertebra has an upper crest of bone called a neural arch and a lower crest called a haemal arch, and each of these arches is square-shaped and laterally compressed (flattened side-to-side). These arches give the tails of urocordylids a paddle-like shape. The urocordylids Sauropleura and Crossotelos have holes in their tail vertebrae that are thought to have served as passageways for spinal nerves, an unusual feature given that spinal nerves pass between successive vertebrae in most vertebrates. Salamanders also have spinal nerves passing through their vertebrae, although the holes are in different positions and do not indicate a close evolutionary relationship with urocordylids.