Collection: Didactic collection (systematic)

Systematic - Paleontology

Reign: Animalia
Phylum / Division: Arthropoda
Class: Trilobita
Order: Ptychopariida
Family: Ellipsocephalidae
Scientific name: Ellipsocephalus hoffi (Schlotheim, 1823)

Geological age

Geochronology (Chronostratigraphy)

Eon (Eontema): Phanerozoic
Era (Eratema): Paleozoic
Period (System): Cambrian
Other chronological subdivisions : Middle Cambrian

Description: Trilobites belong to an extinct group of marine Artropoda, limited to the Palaeozoic Era. The name comes from their elongated, oval, body shape, divided in three longitudinal lobes on the dorsal side (one elevated central lobe and two lateral pleural lobes). They had a mineralized exoskeleton, most commonly only on the dorsal side, made of calcite. The body can be divided in cephalon (head), consisting of a single plate made of fused segments; thorax (main body) consisting of several articulated segments; and pygidium (tail) consisting of a single plate made of fused segments like the cephalon. Several appendages are connected to the ventral side of the exoskeleton, not mineralized: two elongated antennae are attached to the cephalon, and every segment of the torax has a pair of branched legs, very fragile and seldom fossilized. The trilobites are the first known pluricellular organisms. They were mostly benthic animals living in shallow waters, and were a very important component of the Palaeozoic fauna. They appeared in the lower Cambrian and showed the maximum development in the Ordovician. After this period there was a slow decrease of the number of genera, until they went totally extinguished at the end of the upper Permian. The trilobites changed little their basic body shape during the 350 million years of their existence, although showed many variations. Over 1500 genera and several thousands of trilobite species are known, many of which are important stratigraphic fossils, especially for the Cambrian and Ordovician epochs. Apart from the fossils of their body and the exuviae (the exoskeleton left back after the animal periodically changed it while growing), the trilobites left traces of their activity like resting and walking traces. Fossil trilobites can be found in Sardinia, the Carnian Alps and Sicily.

Università degli Studi di Padova, Museo di Geologia e Paleontologia

Item code: 11920

Bibliography

• Allasinaz A., 1991 - Paleontologia generale e sistematica degli Invertebrati, ECIG, Genova; Allasinaz A., 1999 - Invertebrati fossili, UTET, Torino.