Asaphida

Isotelus rex

Order Asaphida / Superfamily Asaphoidea / Family Asaphidae

Katian (Late Ordovician)Canada

Isotelus rex — photo 1 — Photo 1 · P. Holotype MMMN I-2950 (Canada; left: Rudkin et al., 2003; right figure from fossilshk.com) Restoration (modified from Photograph of the type specimen at the collection site Rudkin et al., 2003) (from palaeocast.com)

Isotelus rex — photo 2 — Photo 2 · P. Holotype MMMN I-2950 (Canada; left: Rudkin et al., 2003; right figure from fossilshk.com) Restoration (modified from Photograph of the type specimen at the collection site Rudkin et al., 2003) (from palaeocast.com)

Isotelus rex — photo 3 — Photo 3 · P. Holotype MMMN I-2950 (Canada; left: Rudkin et al., 2003; right figure from fossilshk.com) Restoration (modified from Photograph of the type specimen at the collection site Rudkin et al., 2003) (from palaeocast.com)

Isotelus rex — photo 4 — Photo 4 · P. Holotype MMMN I-2950 (Canada; left: Rudkin et al., 2003; right figure from fossilshk.com) Restoration (modified from Photograph of the type specimen at the collection site Rudkin et al., 2003) (from palaeocast.com)

Classification

Order Asaphida / Superfamily Asaphoidea / Family Asaphidae

Genus

Isotelus Dekay, 1824

Genus author

Dekay J. E.

Genus etymology

iso-, Greek, equal; tel-, Greek, far, end

Species

I. rex Rudkin, Young, Elias & Dobrzanski, 2003

Species author

Rudkin D. M., Young G. A., Elias R. J., Dobrzanski E.

Species etymology

rex, Latin, king, describing its enormous size

Age

Katian (Late Ordovician)

Distribution

Canada

Diagnosis

Dorsal shield long-ovate, cephalon and pygidium nearly subequal. Cephalon rounded-triangular, gently convex; cranidium wide; glabella indistinct; eyes small; librigenae without genal spines. Thorax of 8 segments, each as long as wide; pleural spines absent. Pygidium subtriangular; axis indistinct.

Remarks

The holotype of Isotelus rex is the largest complete dorsal exoskeleton specimen in the world, 68.3 cm long, 40 cm wide and 7 cm high; with a natural 4 cm deficiency of the pygidium, the restored body length is 72 cm