Description:
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. |