Wikipedia
Promissum is an extinct genus of conodonts, primitive chordates, that lived from the Ordovician to the Devonian period (about 500 million years ago). Some call it the Niagara Foundation fish.
A conodont, Promissum had a primitive mouth under its eyes with mineralized teeth, which are both typical for conodonts. It had a primitive backbone and probably looked like a small eel or large worm, lacking any kind of fins except for perhaps a small one on the tail. It was relatively large for a conodont, reaching about 40 cm (16 inch) in length.
Well-preserved specimens were discovered in the Soom shale of South Africa in 1994.
Promissum was probably capable of maintaining a cruising speed, but not of bursts of speed.
The type species is Promissum pulchrum.