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Temporal range: Late Silurian–Early Devonian
The Eurypterida of New York plate 75.jpg
Illustration of Acutiramus cummingsi
Scientific classification e
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Merostomata
Order: Eurypterida
Superfamily: Pterygotioidea
Family: Pterygotidae
Genus: Acutiramus
Ruedemann, 1935

See text

Acutiramus is an extinct genus[1] of eurypterid which lived in the Late Silurian (Ludlow) to Early Devonian.

Acutiramus is one of the largest eurypterids with pincers 5 cm and length about 2 m. The genus closely related to Pterygotus, of which several species were originally placed in, and to the giant Jaekelopterus.


Restoration of A. cummingsi

Pterygotids, which lived from the Ordovician to Devonian periods, were characterized by small to large exoskeletons with semilunar scales. The telson, (tail) was expanded, or flatter than it was tall. Pterygotids also had chelicerae (claws in front of the mouth) that were large and long, with strong, well developed teeth on the claws. Their walking legs were small and slender, without spines.[2]

Acutiramus is distinguishable from other pterygotids by the distal margin of the chelae, where the final tooth is at an acute angle to the rest of the claw (hence the name Acutiramus, or “acute arm”). The large tooth in the center of the claw is distally inclined, which is to say it points forwards. The prosoma (head) is subquadrate, with compound eyes located at the edge of the front corners. The telson has a low row of knobs running down its center.[2]


  • Acutiramus Ruedemann, 1935
    • Acutiramus bohemicus (Barrande, 1872) — Silurian, Czech Republic
      • syn.= Pterygotus comes Barrande, 1872 — Silurian, Czech Republic
      • syn.= Pterygotus mediocris Barrande, 1872 — Silurian, Czech Republic
      • syn.= Pterygotus blahai Semper, 1898 — Silurian, Czech Republic
      • syn.= Pterygotus fissus Seemann, 1906 — Silurian, Czech Republic
    • Acutiramus cummingsi (Grote & Pitt, 1875) — Silurian USA & Canada
      • syn.= Pterygotus acuticaudatus Pohlman, 1882 — Silurian, USA
      • syn.= Pterygotus buffaloensis Pohlman, 1881 — Silurian, USA
      • syn.= Pterygotus quadraticaudatus Pohlman, 1882 — Silurian, USA
    • Acutiramus floweri Kjellesvig-Waering & Caster, 1955 — Silurian, USA
    • Acutiramus macrophthalmus (Hall, 1859) — Silurian USA & Canada
      • syn.= Pterygotus osborni Hall, 1859 — Silurian, USA
      • syn.= Pterygotus cobbi var. juvenis Clarke & Ruedemann, 1912 — Silurian, USA
    • Acutiramus perneri Chlupáč, 1994 — Devonian, Czech Republic
    • Acutiramus perryensis Leutze, 1958 — Silurian, USA
    • Acutiramus suwanneensis Kjellesvig-Waering, 1955 — Silurian?, USA


See also[edit]


  1. ^ Tollerton, V. P. Jr 1997 "The Type Species of the Eurypterid Genus Acutiramus Ruedemann, 1935" Journal of Paleontology 71(5):950-951
  2. ^ a b Størmer, L. 1955. Merostomata. Treatise on Invertebrate Paleontology, Part P Arthropoda 2, Chelicerata, P: 30–31.

External links[edit]