Temporal range: Upper Ordovician 
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.
Promissum was probably capable of maintaining a cruising speed, but not of bursts of speed.
- Gabbott, S.E.; Aldridge, R.J.; Theron, J.N. (1998). "Chitinozoan chains and cocoons from the Upper Ordovician Soom Shale lagerstatte, South Africa; implications for affinity". Journal of the Geological Society 155 (3): 447–452. doi:10.1144/gsjgs.155.3.0447. Bibcode: 1998JGSoc.155..447G.
- Palmer, D., ed (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 23. ISBN 1-84028-152-9.
- Gabbott, S.E.; R. J. Aldridge; J. N. Theron (1995). "A giant conodont with preserved muscle tissue from the Upper Ordovician of South Africa". Nature 374 (6525): 800–803. doi:10.1038/374800a0. Bibcode: 1995Natur.374..800G.
Original source: https://en.wikipedia.org/wiki/Promissum. Read more