Lokiceratops

Lokiceratops Temporal range: Late Cretaceous (Campanian), ~
Reconstructed skeleton with known material in orange
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Ceratopsia
Family:	†Ceratopsidae
Subfamily:	†Centrosaurinae
Clade:	†Albertaceratopsini
Genus:	†Lokiceratops Loewen et al., 2024
Species:	†L. rangiformis
Binomial name
†Lokiceratops rangiformis Loewen et al., 2024

Lokiceratops (meaning "Loki horned face") is an extinct genus of centrosaurine ceratopsian dinosaurs from the Late Cretaceous (Campanian) Judith River Formation of Montana, United States. The genus contains a single species, L. rangiformis, known from most of the skull and a partial skeleton. Four other ceratopsians are known from the same stratigraphic interval as Lokiceratops—more than in any other locality—suggesting that this clade was very diverse during the Late Cretaceous of northern Laramidia.

Discovery and naming

The Lokiceratops holotype specimen, EMK 0012, was discovered in 2019 in the Loki Quarry, representing outcrops of the Judith River Formation (McClelland Ferry Member) in Kennedy Coulee. This locality is near the town of Rudyard and Milk River in Hill County, northern Montana, United States. The specimen was discovered disarticulated but in association, consisting of many bones of the skull and fragmentary postcrania, comprising a cervical vertebra, the right scapula and coracoid, a partial pelvic girdle, a caudal vertebra, and a chevron.

In 2024, Loewen et al. described Lokiceratops rangiformis as a new genus and species of centrosaurine ceratopsian based on these fossil remains. The generic name, Lokiceratops, combines a reference to Loki, the shapeshifting Norse god, with the Greek word "ceratops", meaning "horned face". The specific name, rangiformis, references the mammal genus Rangifer (caribou/reindeer) whose antlers are said to be bilaterally asymmetrical as in the frill ornamentations of Lokiceratops.

Description

Reconstructed skull of Lokiceratops

The fossil material of Lokiceratops is about 20% larger than putative adult individuals of the coeval ceratopsian Medusaceratops. The skull has a basal length of about 0.95 metres (3.1 ft). The holotype individual was likely around 6.7 metres (22 ft) long, with a weight of about 5 tonnes (11,000 lb). As such, it represents one of the largest known centrosaurines.

Unlike its closest relatives, Lokiceratops appears to lack a nasal horn. The second epiparietal is hypertrophied (excessively enlarged) and bladelike, curving laterally along the same plane as the frill. These horns are larger than any other known centrosaurine frill ossification.

Classification

Pneumatic regions of the Lokiceratops skull, including the round external narial fossa (enf) characteristic of centrosaurines

Frill of Lokiceratops

To determine the relationships of Lokiceratops, Loewen et al. (2024) tested it using a phylogenetic analysis. Based on several characters—including the presence of more than six epiparietals on each side of the frill, the large, flat, bladelike epiparietals, the round premaxillary external narial fossa, and the fan-like squamosal—it could be identified as a member of the ceratopsian subfamily Centrosaurinae. More precisely, they recovered it as the sister taxon to the clade formed by Albertaceratops and the contemporary Medusaceratops. Loewen et al. named the clade to which the three species belong the Albertaceratopsini. All three of these genera share a rounded (rather than narrow) frontoparietal fontanelle, as well as a first epiparietal situated in the same lateral plane as the frill. Their results are displayed in the cladogram below, along with comparative illustrations of the reconstructed frills of well-known genera:

Centrosaurinae	Diabloceratops Machairoceratops Yehuecauhceratops Menefeeceratops Xenoceratops ? CPC 279 (Cerro del Pueblo Fm. centrosaurine) Nasutoceratopsini Crittendenceratops Nasutoceratops Avaceratops specimens Albertaceratopsini Lokiceratops Albertaceratops Medusaceratops Wendiceratops Sinoceratops Eucentrosaura Coronosaurus Spinops Centrosaurus Styracosaurus spp. Stellasaurus Pachyrhinosaurini

Following the peer-reviewed description of Lokiceratops, some paleontologists expressed criticism regarding its validity and distinction from its closest albertaceratopsin relatives, Alberaceratops and Medusaceratops. Paleontologist Denver Fowler explained that some ceratopsians, such as the well-studied Triceratops, are known to change noticeably in morphology throughout the course of their lives. He further noted that some of the anatomical characteristics of Lokiceratops may actually be indicative of a fully mature Medusaceratops, rather than a distinct taxon; as in mature Triceratops, the brow horns are hollow, compared to younger individuals' solid horns. This would imply some degree of intraspecific variability (differences between individuals of the same species) within centrosaurines.

Environment

The Loki Quarry is characterized by carbonaceous fine-grained sandstones, siltstones, and mudstones, with depositional features indicating a poorly-drained fluvial system. Gar scales & mollusks occur in the quarry, as well as carbonized plant fragments and wood, and beads of amber.