Tunicates of the subphylum Urochordata (1) represent the most basal branch of known chordates, presumably having arisen ≈543 million years ago in the “Cambrian explosion,” or even earlier (2). However, no reliable fossil tunicates have ever been reported.

What did tunicates evolve?

More than 140 years ago the Russian embryologist, Alexander Kowalevsky, first recognized that tunicates (also known as urochordates) have vertebrate-like characteristics and postulated that both vertebrates and cephalochordate may have evolved from a tunicate-like ancestor during or prior to the Cambrian explosion.

Where did tunicates come from?

Most tunicates live attached to a hard surface on the ocean floor and are commonly known as sea squirts (or cunjevois) and sea pork. They are found at all depths of the ocean. Other tunicates – such as salps, doliolids and pyrosomes – live in the pelagic zone as adults and are free-swimming or drifters..