Open Paleo

Mercuriceratops

Ryan et al., 2014 mur-kyuh-ree-seh-ruh-tops

From Latin 'Mercurius' (the Roman messenger god, whose winged helmet is evoked by the rod-and-flange shape of the squamosal) and Greek 'keras' (horn) and 'ops' (face); meaning 'Mercury's horned face'.

83.6–72.2 million years ago Campanian, Late Cretaceous
Late Cretaceous stages

Mercuriceratops is an extinct genus of chasmosaurine ceratopsid from the late Campanian of northern Laramidia, with the holotype recovered from the upper Judith River Formation of Fergus County, Montana, and a paratype squamosal from the lower Dinosaur Park Formation of Dinosaur Provincial Park, Alberta. The single species, Mercuriceratops gemini, is diagnosed by a uniquely rod-shaped posterior ramus of the squamosal — constricted into a mediolaterally compressed bar instead of the tapering triangle typical of chasmosaurines — with a hatchet-shaped lateral margin bearing four tab-shaped episquamosals. The "twin" species name refers to the two right squamosals from two formations on either side of the Canada-Montana border.

Diagnosis

  1. Squamosal posterior ramus constricted into a rod-shaped (mediolaterally compressed, subrectangular cross-section) bar rather than a tapering obtuse or broadly rounded triangle in dorsal view.
  2. Lateral margin of the squamosal hatchet-shaped in dorsal view, with the posterolateral bar offset from the anterolateral flange by a deep embayment (notch).
  3. Anterolateral flange bears four large, tab-shaped, well-fused episquamosals on its lateral margin.
  4. Elongate episquamosals extending along the lateral margin of the posteriorly projecting rod-shaped squamosal bar.
  5. Deeply incised longitudinal grooves on the medioventral surface of the posterior squamosal shaft forming a robust, tightly interdigitating sutural contact for the parietal.

Species

Mercuriceratops gemini Ryan et al., 2014

Type species

From Latin 'gemini' (twins), referring to the paired right squamosals from Montana and Alberta and to the mythological twins Castor and Pollux who became the Gemini constellation.

Holotype
ROM 64222 , Royal Ontario Museum
Material
Almost complete right squamosal (maximum preserved length 793 mm), preserving the anterior postorbital contact, medial supraorbital fenestra margin, parietal contact surface, and most of the lateral margin.
Horizon
Coal Ridge Member, Judith River Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
Montana, United States

References

  1. Ryan, M. J.; Evans, D. C.; Currie, P. J.; Loewen, M. A. (2014). A new chasmosaurine from northern Laramidia expands frill disparity in ceratopsid dinosaurs. Naturwissenschaften 101(6): 505-512. Springer Science and Business Media LLC. doi:10.1007/s00114-014-1183-1

    Erects Mercuriceratops gemini on a Montana holotype (ROM 64222) and Alberta paratype (UALVP 54559); both are right squamosals of the same hatchet-shaped, rod-tipped morphology.

    ryan2014a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the body length estimate, and the appearance features.

    jones2026a
  3. Arbour, V. M.; Evans, D. C. (2017). A new ankylosaurine dinosaur from the Judith River Formation of Montana, USA, based on an exceptional skeleton with soft tissue preservation. Royal Society Open Science 4(5). The Royal Society. doi:10.1098/rsos.161086

    Names this taxon among the Coal Ridge Member occurrences.

    arbour2017a