Rare and Unusual Illaenus atavus Russian Trilobite

Name: Illaenus atavus Russian trilobites

Age: Lower Ordovician

Size (25.4 mm = 1 inch): 98 mm long by 42 mm wide on a 90 by 85 mm matrix

Location: Kunda Horizon deposits of the Wolchow River region near Saint Petersburg, Russia

Description: This is an example of an unusual trilobite of the genus Illaenus known as Illaenus atavus. The species derives its name from its age; coming from the Lower Ordovician Kunda Horizon, it is one of the oldest members of the genus. It has a very distinctive pygidium which can be mistaken for no other member of the genus. This is one of the 50-odd members of the genus, and all are known for the high profile of the cephalon which is thought to have aided the trilobite in plowing through the substrate in search of a meal. Typically, the large cephalon is pulled under, probably as a result of the contraction of muscles as the trilobite died. This one, however, is quite prone, making for a dramatic and uncommon presentation of this unusual taxon. Additionally, the effacement (erosion) of the details to the cephalon thought to be a consequence of its plowing habit, is not seen -- the terracing of the cephalon is quite evident.

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