Telephinidae is a family of

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

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.

Distribution

The Telephinidae probably evolved from a species assigned to the Hystricuridae. Telephinids first occur during the late Tremadocian, with ''Carolinites'' and ''Opipeuterella'' being globally very common at low latitudes at the end of the Floian. ''Carolinites'' survived into the

Darriwilian The Darriwilian is the upper stage of the Middle Ordovician. It is preceded by the Dapingian and succeeded by the Upper Ordovician Sandbian Stage. The lower boundary of the Darriwilian is defined as the first appearance of the graptolite specie ...

, at which time a second major radiation occurred, that includes ''Telephina'' and ''Telephops'', and these genera only became extinct at the end of the Ordovician.

Description

The central raised area of the headshield (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 t ...

) is strongly convex. The most backward segment (called occipital ring) is wide and is defined by a deep furrow. No further segments can be determined in front of the occipital ring, but sometimes 2-4 pairs of muscle impressions are visible, of which the one just in front of the occipital ring may be deepened at its inner end (in some ''Telephina'' species) to form a lengthwise furrow. The fixed cheeks have broad palpebral lobes (between the eye and the glabella) that take up most of the length of headshield. The frontal border of the headshield is arched, with a circular cross section, or modified to form a pair of short spines. The free cheeks curve strongly downwards and have prominent borders, particularly to the side and the back, and these bear long tube- or blade-like genal spines. The articulating middle part of the body (or

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the c ...

) consists of 9 or 10 segments. The axis is extremely convex and the side-lobes (or pleurae) are narrow. The tailshield (or

pygidium The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compo ...

) is convex and its axis is prominent and has 2-4 rings. The most backward piece may bear a long spine. The seam of the exoskeleton (or doublure) is narrow.

Differences with the Cyclopygidae

Cyclopigids lack genal spines and palpebral lobes. Their thorax has 5 to 7 segments. The occipital ring is present only in the Ellipsotaphrinae subfamily.

Ecology

Like the contemporary but unrelated

Cyclopygidae Cyclopygidae is a family of asaphid trilobites from the Ordovician. Cyclopygids had aextratropicaldistribution, and there is evidence that they lived in darker parts of the water column (around 175m deep). Cyclopygids are characterized by enl ...

, Telephinidae occur with blind or nearly blind

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning " ...

trilobites, a typical adaptation to a lightless environment, and oceanic free-floating graptolites. Telephinidae however also occur with sighted benthic trilobites and other organisms. Comparison of the angles and densities of the facets shows that the eyes of the Telephinidae were less adapted to low-light levels and therefore cyclopygids are considered to have been confined to deeper water, swimming at the lower limit of the photic zone (or mesopelagic). This implies Telephinidae lived higher up in the water column, possibly hunting

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...

. Because of the weight, Telephinidae probably swam back-down.

References

{{Taxonbar, from=Q18558819 Proetida Early Ordovician first appearances Late Ordovician extinctions Trilobite families