''Acuticryphops'' is a genus of trilobite that lived during the late

Frasnian The Frasnian is one of two faunal stages in the Late Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Givetian Stage and followed by the Famennian Stage. Major reef-building was under way during t ...

, particularly between the Lower and Upper Kellwasser horizons. It is known from mid-European

Avalonia Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent underlie south-west Great Britain, southern Ireland, and the eastern coast of North America. It is the source of many of the older rocks of We ...

(Harz Mountains and Rhenish Slate Mountains) and

Armorica Armorica or Aremorica ( Gaulish: ; br, Arvorig, ) is the name given in ancient times to the part of Gaul between the Seine and the Loire that includes the Brittany Peninsula, extending inland to an indeterminate point and down the Atlantic Co ...

(Thuringia: Schleiz) and the North

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...

margin (Coumiac, France and central Morocco). cited in

Taxonomy

''Acuticryphops'' was probably ancestral to the species of the genus ''

Trimerocephalus ''Trimerocephalus'' is a genus of eyeless trilobites from the order Phacopida, family Phacopidae. It lived during the final stage of the Devonian, the Famennian, and became extinct at the end of this stage, together with all other trilobites with ...

'', and mainly differs from its supposed eyeless descendants by retaining small eyes.

Evolution

''Acuticryphops acuticeps'' is an example of rapid evolution. Subsequent populations exhibit a declining average and an increasing variation in the number of lenses per eye from about 10 to between 7 and 1. This rapid trend does not occur in other characters of the exoskeleton. This suggests the absence rather than the presence of selective pressure on the number of lenses per eye. This is presumably associated with the eustatic deepening that occurred.

Description

In dorsal view, ''Acuticryphops acuticeps'' has a rounded triangular headshield (or

cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont Company. Baldino ...

). The central raised area of the cephalon (or

glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior to ...

) is roughly pentangular, and it substantially overhangs the frontal cephalic border. The cheeks are roughly triangular, with the eyes (or palpebral lobes) occupying the frontal quarter of its length. The eye has between 1 and 11 or more individual lenses. The pygidium is more than 3 times wider than long and is almost rectangular because the posterior thorax segments angle backwards when approaching the side of the exoskeleton.

References

Phacopidae Devonian trilobites of Europe Fossils of France Fossils of Germany Fossils of Morocco Devonian trilobites of Africa {{phacopida-stub