Asaphus lepidurus Basal Russian Lower Ordovician Trilobite

Asaphus lepidurus

Trilobite Order Asaphida, Superfamily Asaphoidea, Family Asaphidae

Geologic Time: Lower Ordovician; Wolchovian Horizon

Size: 64 mm

Fossil Site: St. Petersburg region, Wolchow River, Russia

Asaphus lepidurusDescription: A well-inflated example of an ancient member of the Asaphidae, this is Asaphus lepidurus. The region in which these trilobites lived was subject to dramatic changes in salinity and turbidity, and the trilobites were able to make rapid (geologically speaking) evolutionary adjustments. These adjustments were thought to be able to allow them to see both predator and prey more easily. This taxon was a basal trilobite, younger only than the founding Asaphus broggeri, that ultimately led to the dramatic radiation of the Asaphids in the region. Notice the distinctive terrace lines on the axial lobe, a distinguishing feature of the taxon. This large example also has a 37 mm by 25 mm on the same matrix plate, making for a nice association piece.

Coming from an inland sea during the lower to middle Ordovician, the Russian trilobites from near Saint Petersburg, Russia participated in the Great Ordovician Radiation, which saw marine animal diversity increase three-fold more than the Cambrian Explosion. The Russian asaphid trilobites are a particularly interesting example of descent with modification.

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