''Eldredgeops rana'' (formerly ''Phacops rana'') is a species of

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

from the middle

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...

period. Their

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s are found chiefly in the northeastern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

, and southwestern

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...

. Because of its abundance and popularity with collectors, ''Eldredgeops rana'' was designated the

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

state fossil Most American states have made a state fossil designation, in many cases during the 1980s. It is common to designate one species in which fossilization has occurred, rather than a single specimen, or a category of fossils not limited to a single ...

by the state's General Assembly on December 5, 1988.

Description

''Eldredgeops rana'' can be recognized by its large eyes (which remind some observers of a

frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...

's eyes—the specific name ''rana'' is a reference to a common frog), its fairly large size (up to 6 inches long), and its habit of rolling up into a ball like a pill bug (" volvation"). In order to protect themselves from

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...

s, ''Eldredgeops rana'' would roll into a ball with its hard

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton ( endoskeleton) in for example, a human. In usage, some of the ...

on the outside as protection. Many other trilobites possessed the same ability, but ''Eldredgeops rana'' nearly perfected it. The slightest amount of

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

would trigger their senses, and ''Eldredgeops rana'' would be hidden in a tiny shelter made of its own body. Although this safety feature often helped them to evade predators, occasionally it backfired and the trilobite would be buried under heavy sediment. Their

s can still be found in balled-up positions 400 million years later.

Fossilisation

''Eldredgeops rana'' is found in the northeastern U.S, southwestern Ontario, and in Morocco; North America was attached to the

African plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plate ...

during the Devonian.

Phacopid eyes

The most striking feature of the morphology of ''Eldredgeops rana'' and its relatives is their eyes. These differed from the eyes of most trilobites in having comparatively few lenses spaced between deep

sclera The sclera, also known as the white of the eye or, in older literature, as the tunica albuginea oculi, is the opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some crucial elastic fiber. In humans, and so ...

. The lenses themselves were very rounded instead of largely flat. The eyes were mounted on turret-like structures which could swivel, providing the animal with an almost 360-degree field of view. This type of eye is known as the schizochroal eye. Eldredgeops eye

References

* Some of the information in this article was taken from the websit
A Guide to the Orders of Trilobites
by Sam Gon III. * Picture courtesy of * Color reconstruction of ''Eldredgeops (Phacops) rana'' a
www.emilydamstra.com
* {{Taxonbar, from=Q7179955 Phacopidae Devonian trilobites of North America Devonian trilobites of Africa Jeffersonville Limestone Symbols of Pennsylvania Fossil taxa described in 1832 Fossils of Morocco