Larval radiodont (Anomalocarid)
Early Ordovician (Arenigian)
Upper Fezouata Formation
Zagora, Draa Valley
Morocco

4mm complete larval anomalocarid on 80mm slab

This is one of the most unusual specimens we have ever had. The larval stages of several species of radiodonts are known, but only from the Cambrian (see the references below), but this is the first we have ever seen from the Ordovician. Several species of anomalocarids are known from the Fezouata Formation such as Aegirocassis and Pseudangustidontus, but no larval specimens have ever been reported before.

As expected, this specimen is very tiny (4mm – it’s a larva after all), but since it is complete you can easily see the stalked eyes, the dorsal “flaps” which agree in shape and number with known larval radiodonts as well as the classic overall shape. We have photographed the specimen both dry and wet (in isopropyl alcohol – the darker images) so you can see details clearly.

See: An extensive paper on radiodont growth and molting: Moysiuk, J. and Caron, J.-B. (2024) ‘A quantitative assessment of ontogeny and molting in a Cambrian radiodont and the evolution of arthropod development’, Paleobiology, 50(1), pp. 54–69. doi:10.1017/pab.2023.18. 

See also: Wikipedia – Radiodonta