trilobite


trilobite
trilobitic /truy'leuh bit"ik/, adj.
/truy"leuh buyt'/, n.
any marine arthropod of the extinct class Trilobita, from the Paleozoic Era, having a flattened, oval body varying in length from 1 in. (2.5 cm) or less to 2 ft. (61 cm).
[1825-35; < NL Trilobites, equiv. to Gk trílob(os) three-lobed (see TRI-, LOBE) + -ites -ITE1]

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Any of a group of ovate arthropods (subphylum Trilobita) that came to dominate the seas с 540 million years ago and became extinct с 245 million years ago.

Trilobites had a chitinous exoskeleton and three body lobes: a raised middle lobe with a lower lobe on each side. The head, thorax, and tail were segmented; each segment bore two appendages. The forwardmost appendages were sense and feeding organs. Most species had two compound eyes, though some were eyeless. Some were predators, others were scavengers, and still others probably ate plankton. Paradoxides harlani, found near Boston, grew to 18 in. (45 cm) long and may have weighed 10 lbs (4.5 kg). Other species were small.

Trilobite

Leslie Jackman
Natural History Photographic Agency

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▪ fossil subphylum
 any member of a group of extinct fossil arthropods easily recognized by their distinctive three-lobed, three-segmented form. Trilobites, exclusively marine animals, first appeared at the beginning of the Cambrian Period, about 542 million years ago, when they dominated the seas. Although they became less abundant in succeeding geologic periods, a few forms persisted into the Permian Period, which ended about 251 million years ago.

      Because trilobites appear fully developed in the Cambrian Period, it appears likely that the ancestral trilobites originated during the Ediacaran Period (630 million to 542 million years ago) of Precambrian times. An organism that may be ancestral to the trilobites, as well as to other arthropods, may be represented by Spriggina, which is known from Precambrian shallow-water marine deposits in Australia. Trilobites are frequently used for stratigraphic correlations.

      Trilobites had three body lobes, two of which lay on each side of a longitudinal axial lobe. The trilobite body was segmented and divided into three regions from head to tail: the cephalon, or head region, separated from the thorax, which was followed in turn by the pygidium, or tail region. Trilobites, like other arthropods, had an external skeleton, called exoskeleton, composed of chitinous material. For the animal to grow, the exoskeleton had to be shed, and shed trilobite exoskeletons, or portions of them, are fossils that are relatively common.

      Each trilobite body segment bore a pair of jointed appendages. The forwardmost appendages were modified into sense and feeding organs. Most trilobites had a pair of compound eyes; some of them, however, were eyeless.

      Some trilobites were active predators, whereas others were scavengers, and still others probably ate plankton. Some trilobites grew to large size; Paradoxides harlani, which has been found near Boston in rocks of the Middle Cambrian Epoch (521 million to 501 million years ago), grew to be more than 45 cm (18 inches) in length and may have weighed as much as 4.5 kg (10 pounds). Others were small.

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Universalium. 2010.

Look at other dictionaries:

  • trilobite — ● trilobite nom masculin (latin scientifique trilobites, du latin classique lobus, lobe) Classe de grands proarthropodes marins munis d antennes, fossiles dans les terrains primaires. ⇒TRILOBITE, subst. masc. ZOOL. ,,Arthropode marin fossile à… …   Encyclopédie Universelle

  • Trilobite — Tri lo*bite (tr[imac] l[ o]*b[imac]t), n. [Cf. F. trilobite. See {Trilobate}.] (Paleon.) Any one of numerous species of extinct arthropods belonging to the order Trilobita. Trilobites were very common in the Silurian and Devonian periods, but… …   The Collaborative International Dictionary of English

  • trilobite — extinct marine arthropod, 1832, from Mod.L. Trilobites (Walch, 1771), from Gk. tri three + lobos lobe, so called because its body is divided into three lobes …   Etymology dictionary

  • trilobite — [trī′lə bīt΄] n. [< ModL Trilobites, Trilobita: see TRI , LOBE, ITE1] any of a large class (Trilobita) of extinct marine arthropods having the body divided by two furrows into three parts, found as fossils in Paleozoic rocks trilobitic… …   English World dictionary

  • Trilobite — ] Highly complex compound eyes are another obvious feature of the cephalon (see below). Figure 3 shows gross morphology of the cephalon. The cheeks (genae) are the pleural lobes on each side of the axial feature, the glabella. When trilobites… …   Wikipedia

  • Trilobite — Trilobita Trilobites …   Wikipédia en Français

  • trilobite — noun Etymology: ultimately from Greek trilobos three lobed, from tri + lobos lobe Date: 1832 any of numerous extinct Paleozoic marine arthropods (group Trilobita) having the segments of the body divided by furrows on the dorsal surface into three …   New Collegiate Dictionary

  • TRILOBITE — n. m. T. d’Histoire naturelle Crustacé de l’époque primaire …   Dictionnaire de l'Academie Francaise, 8eme edition (1935)

  • trilobite — noun /ˈtraɪləˌbaɪt/ An extinct arthropod of the class Trilobita, whose body had three large lobes …   Wiktionary

  • trilobite — tri·lo·bì·te s.f. TS paleont. invertebrato fossile marino della classe delle Trilobiti, diffuso nel Paleozoico | pl. con iniz. maiusc., classe del phylum degli Artropodi {{line}} {{/line}} DATA: 1840. ETIMO: dal lat. scient. Trilobītae, der. del… …   Dizionario italiano


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