''Judiceratops'' ( ; meaning " Judith River horned face") is an extinct horned

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

. It lived around 78

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...

, during the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

Period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

in what is now

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

, United States. Like other horned dinosaurs, ''Judiceratops'' was a large,

quadrupedal Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor ...

herbivore. It is the oldest known

chasmosaurine Chasmosaurinae is a subfamily of ceratopsid dinosaurs. They were one of the most successful groups of herbivores of their time. Chasmosaurines appeared in the early Campanian, and became extinct, along with all other non- avian dinosaurs, durin ...

Description

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

YPM VPPU 022404 consists of an incomplete skull including the horns, parts of the frills, and fragments from the back of the frill. Other fragmentary specimens are known from the same area, which preserve distinctive features of the frill. ''Judiceratops'' shows a distinctive combination of characters, not seen in other ceratopsids. Its frill (

parietal bone The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is nam ...

) has a broad midline bar, a rounded caudal margin, and reduced

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinc ...

s (bony projections) on the rear edge of the frill, the epiparietals. The

s on the lateral margins of the frill are large near the front, but small towards the back. The

postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ...

(located above the eyes) horns are moderately elongate, inclined forward and outwards, and have an unusual teardrop-shaped cross section.

Classification

''Judiceratops'' is a basal

. It is more primitive than most genera within the subfamily with the exception of '' Mercuriceratops''. The below cladogram follows Longrich (2015), who named a new species of ''Pentaceratops'', and included nearly all species of chasmosaurine. Despite the fragmentary nature of the fossils, they can be identified as a distinct species. Frills of horned dinosaurs are highly distinctive, with different species having distinct arrangements of the epoccipital hornlets. From species to species, hornlets differed in their number, arrangement, size, and shape, and the bones of the frill, the squamosal and parietal, differ as well. This probably reflects rapid evolution of the frill in response to

sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex ( ...

, similar to how sexual selection creates a large variety of display feathers in living dinosaurs such as birds of paradise.

Paleoecology

Provenance and occurrence

The remains of the

specimen of ''Judiceratops'' YPM VPPU 022404 were recovered from the

Judith River Formation The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the Late Cretaceous, between 79 and 75.3 million years ago, corresponding to the "Judithian" land vertebrate age. It ...

in Hill County,

. The specimen was collected in brown/green mudstone and gray/yellow sandstone which dates to the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...

stage of

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

period, approximately 78 million years ago. This specimen is housed at the Yale Peabody Museum.

Fauna and habitat

''Judiceratops'' shared its paleoenvironment with bony fishes, amphibians, the Choristoderan ''

Champsosaurus ''Champsosaurus'' is an extinct genus of crocodile-like choristodere reptile, known from the Late Cretaceous and early Paleogene periods of North America and Europe (Campanian-Paleocene). The name ''Champsosaurus'' is thought to come from , () ...

'', the

hadrosaur Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which incl ...

Brachylophosaurus ''Brachylophosaurus'' ( or ; meaning "short-crested lizard", Greek ''brachys'' = short + ''lophos'' = crest + ''sauros'' = lizard, referring to its small crest) was a mid-sized member of the hadrosaurid family of dinosaurs. It is known from sev ...

canadensis'', the pachycephalosaur '' Colepiocephale lambei'', the

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

s '' Dromaeosaurus'', ''

Gorgosaurus ''Gorgosaurus'' ( ; ) is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.6 and 75.1 million years ago. Fossil remains have been found in the Ca ...

'' and ''

Troodon ''Troodon'' ( ; ''Troödon'' in older sources) is a wastebasket taxon and a dubious genus of relatively small, bird-like dinosaurs known definitively from the Campanian age of the Late Cretaceous period (about 77 mya). It includes at leas ...

'', and with fellow

ceratopsians Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic ...

'' Albertaceratops'', ''

Medusaceratops ''Medusaceratops'' is an extinct genus of centrosaurine ceratopsian dinosaur known from the Late Cretaceous Judith River Formation (middle Campanian stage) of Montana, northern United States. It contains a single species, ''Medusaceratops lokii'' ...

'' and ''

Avaceratops ''Avaceratops'' is a genus of small herbivorous ceratopsian dinosaurs which lived during the late Campanian during the Late Cretaceous Period in what are now the Northwest United States. Most fossils come from the Judith River Formation. Discov ...

''.

Evolution

''Judiceratops'' is the oldest known member of the Chasmosaurinae, but already shows many of the distinctive features of the group. Along with the presence of specialized centrosaurines such as '' Albertaceratops'' at the same time, it suggests rapid evolution of the horned dinosaurs between the Turonian (when the oldest horned dinosaur in North America,

Zuniceratops ''Zuniceratops'' ('Zuni-horned face') was a ceratopsian dinosaur from the mid Turonian of the Late Cretaceous Period of what is now New Mexico, United States. It lived about 10 million years earlier than the more familiar horned Ceratopsi ...

, appears) and the middle Campanian, when Chasmosaurinae and Centrosaurinae show up in the fossil record. This period spans about 15 million years- a relatively short period in terms of dinosaur evolution. Although ''Judiceratops'' is currently the oldest known chasmosaurine, it is clearly not ancestral to later horned dinosaurs such as ''Chasmosaurus'' and ''Pentaceratops''. Instead the specialized features of the frill- the large winglike hornlets on the margins of the frill, and the reduced ones on the back- show that it represents a side branch in chasmosaurine evolution. No fossils from this lineage are known from later rocks, consistent with a pattern of high turnover- species rapidly evolved, and became extinct- as seen in other horned dinosaurs in the latest Cretaceous.

References

{{Taxonbar, from=Q11878380 Chasmosaurines Fossil taxa described in 2013 Late Cretaceous dinosaurs of North America Paleontology in Montana Campanian genus first appearances Campanian genus extinctions Ornithischian genera