Rare and Unusual Illaenus atavus Russian Trilobite

일반명(Common name) : Rare and Unusual Russian Ordovician Trilobite

학명(Scientific Name) : Illaenus atavus

지질시대(Geological Time) : 고생대오르도비스기(Middle Ordovician 500 Million years old)

발견지(Location) : Asery Horizon, Wolchow River Region, St Petersburg, Russia

Size of trilobite : 60mm long(70 x 45mm Matrix

Division Name

Phylum : Arthropoda

Class : Trilobita

Order : Corynexochida

Suborder : Illaenina

Superfamily : Illaenoidea

Family : Illaenidae

Genus : Illaenus

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. This is only the second example of the taxon I have ever had to offer, and is in a remarkable state of preservation.