The World's Largest Trilobites
This page last revised 17 August 2005 by S.M. Gon III

Among the evolutionary trends of trilobites, gigantism yielded some spectacularly large species, expressed maximally in the orders Asaphida, Redlichiida, and Lichida. Below, depicted in scale alongside a familiar object, are some of the largest recorded specimens: Isotelus rex, the largest known species of trilobite, at nearly three quarters of a meter in length (720 mm), was found in Canada recently in a nearly complete state, and can be seen at the Manitoba Museum in Winnipeg.

The second and third largest species Uralichas hispanicus (from Spain) and Terataspis grandis (from New York), in contrast, have not been found at full size as complete specimens, but large disarticulated parts result in reconstructions of the sizes indicated below. However, many large specimens of Paradoxides (Acadoparadoxides) briareus (from Morocco) at or near 450 mm have been found, and the large asaphoid Isotelus brachycephalus has likewise been found as a complete specimen over 300 mm in length. The total length of Isotelus rex is not augmented by long spines, as in Uralichas and Terataspis.

Comparison Chart of the Largest Trilobites

largest trilobites


Isotelus rex
Isotelus brachycephalus

Isotelus rex is a moderately effaced asaphid trilobite lacking terminal spines or prolongations, and the holotype specimen was found in a carbonate unit showing little evidence of distortion or compaction. All dorsal sclerites of the holotype are closely articulated, suggesting this is not an exuvium. At about 720 mm long, 400 mm in maximum width (across the cephalon), and 70 mm in height (at the posterior midpoint of the cephalon), it is the largest complete trilobite specimen ever found. Large representatives of Isotelus occur elsewhere in the Late Ordovician succession of North America and some of the earliest described species were considered to be among the biggest trilobites then known. Indeed, several specific epithets, including those of I. gigas Dekay, 1824 and I. maximus Locke, 1838, were coined in reference to their comparatively large size. Hansen (1989) reported complete specimens of I. brachycephalus Foerste, 1919 from Ohio with lengths up to 410 mm. Prior to the discovery of the 720 mm Isotelus rex, the largest confirmed complete trilobite specimen was a fully articulated isoteline measuring 430 mm in length (Whittington in Kaesler, 1997). It is from the same locality as Isotelus rex and is considered a smaller individual of that species. 


Cambropallas telesto
Acadoparadoxides nobilis
Examples of large non-asaphide trilobites include redlichiide Cambropallas (Holmidae, 230 mm) and Acadoparadoxides (Paradoxididae, 390 mm), out of the Cambrian of Morocco (Geyer, 1993). Many large specimens emerge each year out of Morocco, but they are often at least partially restored. However, some very large complete specimens have been prepared.


Uralichas sp.
Terataspis grandis (model)
Persistent reports of large lichid trilobites are based on fragmentary remains or large disarticulated sclerites preserved in shaly, compacted facies (e.g., Reimann, 1942; Rabano, 1989; Whittington in Kaesler, 1997). The widely cited maximum length of 660 mm for the Ordovician Uralichas hispanicus from the Iberian Peninsula is based on extrapolations of separate cephalic, thoracic, and pygidial elements (Rabano, 1989). The long, narrow posterior median spine accounts for at least 20 percent of the total sagittal length. Sclerites of Uralichas often show considerable tectonic deformation (Rabano, 1989), rendering dimensions suspect; approximations at best. The size of the spinose lichid Terataspis (Devonian; eastern North America, estimated restored length up to 600 mm) is also determined from separate disarticulated sclerites; frequently compacted and distorted (Reimann, 1942).

References for this page

Geyer, G. 1993. The giant Cambrian trilobites of Morocco. Beringeria 8:71–107.

Hansen, M. C. 1989. Large Isotelus found: Ohio Geology Newsletter (Spring 1989):6.

Kaesler, R. L. (ED.). 1997. Treatise on Invertebrate Paleontology, Pt. O, Arthropoda 1, Trilobita, Revised, Volume 1. Geological Society of America and University of Kansas Press, Lawrence, 530 p.

Rabano, I. 1989. El genero Uralichas Delgado, 1892 (Trilobite, Lichida) en al Ordovicico de la Peninsula Iberica. Boletin Geologico y Minero, 100(1):21–47.

Reimann, I. G. 1942. A new restoration of Terataspis. Bulletin of the Buffalo Society of Natural Sciences, 17:39–51.

Rudkin, D.M., G.A. Young, R.J. Elias, & E.P. Dobrzanski. 2003. The world’s biggest trilobite—Isotelus rex new species from the Upper Ordovician of Northern Manitoba, Canada. J. Paleontol. 77(1):99–112.

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