Pricyclopyge

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Pricyclopyge
Temporal range: Ordovician
Pricyclopyge.jpg
P. binodosa
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class:† Trilobita
Order:† Asaphida
Family:† Cyclopygidae
Genus:† Pricyclopyge
Richter & Richter, 1954
Type species
Aeglina prisca
Species
  • P. prisca(Barrande, 1872)
  • P. binodosa(Salter, 1859)
    • P. b. binodosa
    • P. b. eurycephala Fortey & Owens, 1987
    • P. b. synophthalma (Koucek, 1916)

Pricyclopyge is a genus of trilobites assigned to the family Cyclopygidae that occurs throughout the Ordovician. Pricyclopyge had an extratropical distribution, and there is evidence that it lived in darker parts of the water column (around 175m deep). Pricyclopyge has huge eyes, an inverted pear-shaped glabella, six thorax segments, with on the 3rd two small discs. [1] [2] Pricyclopyge is known from what are today China, the Czech Republic, France, and the United Kingdom. [3]

Contents

Description

Pygidium of P. longicephala Pricyclopyge longicephala pygidium CRF.jpg
Pygidium of P. longicephala

Like other cyclopygids, Pricyclopyge lacks genal spines. Pricyclopyge has six thorax segments of which the third from the front carries two very characteristic round discs that are presumed to have been bioluminescent organs, and if true, this suggests that Pricyclopyge swam upside down. It has a wide and stout axis, that tapers gradually backwards until it ends in a semicircle close to the border of the pygidium. The short side lobes (or pleurae) of the thorax segments gradually become wider further back so that the thorax is widest at its back, with the tips of the pleurae of the 6th segment sometimes enlarged, bent backwards and so bordering the pygidium. [1] The pygidium is more than twice as wide as long, the axis showing 3 or 4 clearly defined rings, while segmentation of the pleural area is barely visible. The pygidial border furrow is clear.

Eyes

Eye of P. binodosa, lenses missing, showing the arrangement of the ommatidia Pricyclopyge binodosa eye.jpg
Eye of P. binodosa, lenses missing, showing the arrangement of the ommatidia

Like all cyclopygids, Pricyclopyge has huge eyes, that largely encircle the inverted pear-shaped glabella. These eyes have a wide angle of view, both horizontal and vertical, reminiscent of the eyes of dragonflies. The individual lenses in the eyes are hexagonally arranged, with their centers approximately 0.25 mm apart. [4] Merger of both eyes, creating a visor, has appeared in several cyclopigid genera, but only in Pricyclopyge binodosa several stages in this development can be seen as a consecutive series of subspecies collected from successive zones in the late Arenig to the Llanvirn. [4] This development improves the sensitivity of the eye for objects that move relative to the eye, which might have been particularly useful under low-light conditions and when rapidly moving. The extant hyperiid amphipod Cystisoma also has such fused eyes. [5] Although the distance between the eyes varies within any one population of the earlier subspecies, the eyes only touch and merge in P. binodosa synophthalma. Monocular trilobites are always younger than closely related species with normal paired eyes, and is an example of a trend that occurred several times in parallel. [2] [4]

Ecology

It is presumed that Pricyclopyge swam upside down in dimly lit oceanic waters outside the tropic belt. It occurs together with other cyclopygids, blind or nearly blind deepwater benthic trilobites, and free-floating oceanic graptolites. [5] It probably hunted the zooplankton and may have migrated in the evening towards the surface and in the morning to greater depths, following prey and possibly avoiding some of its potential predators.

Related Research Articles

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<i>Olenoides</i> Genus of trilobites

Olenoides was a trilobite from the Cambrian period. Its fossils are found well-preserved in the Burgess Shale in Canada. It grew up to 10 cm long.

<i>Meteoraspis</i>

Meteoraspis is an extinct genus of ptychopariid trilobites of the family Tricrepicephalidae. The various species lived from 501 to 497 million years ago during the Dresbachian faunal stage of the late Cambrian Period. Fossils of Meteoraspis are characteristic of Late Cambrian strata in North America, though they are found in Late Cambrian strata elsewhere in the world, such as M. nevensis from Victoria Land, Antarctica.

<i>Lonchodomas</i> Extinct genus of trilobites

Lonchodomas is a genus of trilobites, that lived during the Ordovician. It was eyeless, like all raphiophorids, and had a long straight sword-like frontal spine, that gradually transforms into the relatively long glabella. Both the glabellar spine and the backward directed genal spines are subquadrate in section. Lonchodomas has five thorax segments and the pleural area of the pygidium has two narrow furrows. Lonchodomas occurred in what are today Argentina, Canada (Newfoundland), Estonia, Latvia, Norway, Sweden, the Russian Federation and the United States.

<span class="mw-page-title-main">Alokistocaridae</span>

Alokistocaridae is a family of ptychopariid trilobites that lived from the Botomian epoch of the Early Cambrian until the Late Cambrian. Alokistocarids were particle feeders and left small furrows which are occasionally preserved. Their remains are found worldwide. Elrathia kingii, one of the most collected trilobites in the world, is a typical alokistocarid.

<i>Biceratops</i>

Biceratops is an extinct genus of olenelloid redlichiid trilobites, of average size, with the largest specimen 8 centimetres or 3.1 inches long, not including the huge pleural spines of the 3rd segment of the thorax. It lived during the Toyonian stage, in what is today the South-Western United States. Biceratops can easily be distinguished from other members of Biceratopsidae by the absence of genal spines, in combination with effaced features of the raised axial area of the head shield, that is bordering the two horn-like projections that carry the eyes. Biceratops nevadensis is the only known species in this genus.

<i>Conocoryphe</i>

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<i>Odontochile</i> Genus of trilobites

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<i>Ogygiocarella</i> Extinct genus of trilobites

Ogygiocarella Brongniart, 1822, is a genus of asaphid trilobites. It occurred during the Middle Ordovician.

<i>Cyclopyge</i> (trilobite) Extinct genus of trilobites

Cyclopyge is a genus of small to average size trilobites that lived during the Ordovician. Like all members of the family Cyclopigidae, it has very large convex eyes, that cover most of the free cheeks, and in some species touch each other. The eyes almost touch the large glabella. The occipital ring has merged with the rest of the glabella. The glabella does not extend into a frontal thorn. The cephalon lacks genal spines. The 6 thorax segments have short pleurae. The pygidium is rather large, and often rather effaced. These are features that also occur in other Cyclopygidae, and are indications of a pelagic lifestyle.

<i>Symphysops</i> Extinct genus of trilobites

Symphysops is a genus of trilobites of average size, belonging to the Cyclopygidae family. It had a cosmopolitan distribution and lived from the Middle to the Upper Ordovician. It has been found in Canada, China, the Czech Republic (Bohemia), Iran, Ireland, Kazakhstan, Poland, Morocco, Spain, Scotland and Wales. The name Symphysops refers to the fused eyes, common to the species of this genus. Some (sub)species of the cyclopygid genera Cyclopyge and Pricyclopyge share this character, but Symphysops uniquely combines the merged eye with a frontal thorn on the head and the "lower eyelid".

<span class="mw-page-title-main">Cyclopygidae</span> Extinct family of trilobites

Cyclopygidae is a family of asaphid trilobites from the Ordovician. Cyclopygids had an extratropical distribution, and there is evidence that they lived in darker parts of the water column. Cyclopygids are characterized by enlarged eyes, with a wide angle of view, both horizontal and vertical, reminiscent of the eyes of dragonflies. These typically touch the glabella directly on the side. Cyclopygids all lack genal spines, but Symphysops carries a forward directed frontal spine on the glabella. It is presumed that at least the members of the genus Pricyclopyge swam upside down and had bioluminescent organs on the third thorax segment. Cyclopygids had between 7 and 5 thorax segments, a wide and stout axis, and short side lobes.

<i>Pliomera</i>

Pliomera is a genus of trilobites that lived during the Middle Ordovician on the paleocontinent Baltica, now Norway, Sweden, Estonia and the Russian Federation, and in Argentina. It can be recognized for its pentagonal glabella widest between the frontal corners, with an inverted V-shaped occipital ring. In front of the occipital furrow that crosses the entire glabella, two pairs of dead-ending furrows create three side lobes left and right. The front of the glabella also has three dead-ending furrows, a very short one on the midline and left and right a longer one, directed inward and slightly backward. The eyes are small and are not connected to the glabella by an eye ridge. The thorax and pygidium are very regularly divided into up to 23 rather narrow segments, without a furrow within each of the pleurae. The pleurae are clearly wider than the axis. The pygidium ends in downward pointing toothlike spines.

<i>Cedaria</i>

Cedaria is an extinct genus of trilobites from the late Cambrian.

<i>Kendallina</i> Genus of trilobites

Kendallina is a genus of parabolinoidid trilobite with an inverted egg-shaped outline, a wide headshield, small eyes, small deflected spines, 12 thorax segments and a small, short tailshield. It lived during the Late Cambrian in what are today Canada and the United States.

<i>Orygmaspis</i> Genus of trilobites

Orygmaspis is a genus of asaphid trilobite with an inverted egg-shaped outline, a wide headshield, small eyes, long genal spines, 12 spined thorax segments and a small, short tailshield, with four pairs of spines. It lived during the Upper Cambrian in what are today Canada and the United States.

<i>Placoparia</i> Genus of trilobites

Placoparia is a genus of trilobites of average size that lived during the late Lower to the early Upper Ordovician on the paleocontinents Gondwana, Avalonia and Laurentia, now the Czech Republic, France, Germany, Morocco, Portugal, Spain and Wales. Its headshield is semi-circular to rectangular with rounded frontal corners. It lacks eyes, but eye ridges are present. The fact that the facial sutures are opisthoparian is an exception in the otherwise proparian Cheirurina. The thorax has 11 or 12 segments, with the axis slightly wider than the ribs to its sides. The tips of the pleurae are free, which resembles an old-fashion central heating radiator. The axis in the small tailshield consists of four rings and a minute endpiece. The four pleurae end in spatulate spines that fit to corresponding indentations in the cephalon.

<i>Tricrepicephalus</i>

Tricrepicephalus is an extinct genus of ptychopariid trilobites of the family Tricrepicephalidae with species of average size. Its species lived from 501 to 497 million years ago during the Dresbachian faunal stage of the late Cambrian Period. Fossils of Tricrepicephalus are widespread in Late Cambrian deposits in North America, but is also known from one location in South America. Tricrepicephalus has an inverted egg-shaped exoskeleton, with three characteristic pits in the fold that parallels the margin of the headshield just in front of the central raised area. The articulating middle part of the body has 12 segments and the tailshield carries two long, tubular, curved pygidial spines that are reminiscent of earwig's pincers that rise backwards from the plain of the body at approximately 30°.

<span class="mw-page-title-main">Telephinidae</span> Extinct family of trilobites

Telephinidae is a family of pelagic trilobites with large wide-angle eyes, occupying most of the free cheeks, downward directed facial spines and 9-10 thorax segments. The family is known during the entire Ordovician and occurred in deep water around the globe.

<i>Viaphacops</i>

Viaphacops is a genus of trilobites in the order Phacopida, family Phacopidae, that lived during the Middle Devonian, and is known from North and South America, Asia.

References

  1. 1 2 R.C. Moore, ed. (1959). Treatise on Invertebrate Paleontology. Part O – Arthropoda 1 – Arthropoda general features, Proarthropoda, Euarthropoda general features, Trilobitomorpha. Geological Society of America and University of Kansas Press.
  2. 1 2 Whittington, H. B. et al. (1997) Treatise on Invertebrate Paleontology. Part O, Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida.
  3. ↑ Paleobiology Database
  4. 1 2 3 Schoenemann, B.; Clarkson, E.N.K. (2011). "The Eyes of Bohemian Trilobites" (PDF). Geol. Výzk. Mor. Slez.: 45–50. Archived from the original (PDF) on 2016-03-04. Retrieved 2013-08-13.
  5. 1 2 McCormick, T.; Fortey, R.A. (1998). "Independent testing of a paleobiological hypothesis: the optical design of two Ordovician pelagic trilobites reveals their relative paleobathymetry". Paleobiology. 24 (2): 235–253. doi:10.1666/0094-8373(1998)024[0235:ITOAPH]2.3.CO;2. JSTOR   2401241. S2CID   132509541.
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