Trilobites
Order Phacopida Suborder Phacopina, Superfamily Phacopoidea,
Family Phacopidae
Geologic Age: Middle Devonian
Trilobite is 24 mm long
Jorf, Morocco
Remarks: Eocryphops presents somewhat of an evolutionary mystery. Note
the very small number of Schizochroal
Eye facets. Some three-to four fold more is more typical in Suborder
Phacopina. Such a reduction eyes
was not uncommon in phacopida, especially in the
Devonian period, and is also seen in genus Plagiolaria (Holloway,
2005) - also see (Crônier and
Fortey, 2006). This trilobite cames from Jorf in Morocco where a reduced
eye Gerastos
proetid and a blind
Gerastos also occur.
Apparently the environment at Jorf in the Devonian lacked positive
selection for eye sight in some trilobites. Mysteriously, trilobites
with reduced eyes are found in association with species with typical
eyes. While the environment is believed to
have been in deep water, it was still one
in the photic zone, where good eye sight would seem to have been a
survival benefit and selected for. Was there a particular niche in
the environment
where good sight was not selected for, or even selected against, leading
to secondary
eye loss? Was the Eocryphops trilobite we see here actually blind,
and its reduced eyes just vistigal organs?
Also see: Moroccan Trilobites Evolutionary Secondary Blindness Among Trilobites Trilobite Eyes
