''Judiceratops'' ( ; meaning "

Judith River The Judith River is a tributary of the Missouri River, approximately 124 mi (200 km) long, running through central Montana in the United States. It rises in the Little Belt Mountains and flows northeast past Utica and Hobson. It is ...

horned face") is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

horned A horn is a permanent pointed projection on the head of various animals that consists of a covering of keratin and other proteins surrounding a core of live bone. Horns are distinct from antlers, which are not permanent. In mammals, true horns ...

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 th ...

Period 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 Columbi ...

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

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

. 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, during t ...

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 several ...

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

ceratopsid Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', ''Centrosaurus'', and ''Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species are k ...

s. Its frill (

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

) 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 (extinct amp ...

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 (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 ''Mercuriceratops'' is an extinct genus of herbivorous chasmosaurine ceratopsid dinosaur known from the Late Cretaceous (Campanian stage) of Alberta, Canada and Montana, United States. It contains a single species, ''Mercuriceratops gemini''. D ...

''. 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 mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...

, 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 in Hill County,

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

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

Fauna and habitat

''Judiceratops'' shared its

paleoenvironment Paleoecology (also spelled palaeoecology) is the study of interactions between organisms and/or interactions between organisms and their environments across geologic timescales. As a discipline, paleoecology interacts with, depends on and informs ...

with bony fishes,

amphibians Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbore ...

, the

Choristodera Choristodera (from the Greek χωριστός ''chōristos'' + δέρη ''dérē'', 'separated neck') is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the late Miocene (168 to 1 ...

n ''

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 , () sa ...

'', 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 includ ...

'' Brachylophosaurus canadensis'', the pachycephalosaur ''

Colepiocephale lambei ''Colepiocephale'' (meaning "knucklehead") is a genus of pachycephalosaurid dinosaur from Late Cretaceous (middle Campanian stage) deposits of Alberta, Canada. It was collected from the Foremost Formation (middle Campanian, 80–77.5 ma). The t ...

'', the theropods ''

Dromaeosaurus ''Dromaeosaurus'' (, "running lizard") is a genus of dromaeosaurid theropod dinosaur which lived during the Late Cretaceous period (middle late Campanian and Maastrichtian), sometime between 80 and 69 million years ago, in Alberta, Canada and the ...

'', '' Gorgosaurus'' and '' Troodon'', and with fellow ceratopsians ''

Albertaceratops ''Albertaceratops'' (meaning "Alberta horned face") was a genus of centrosaurine horned dinosaur from the middle Campanian-age Upper Cretaceous Oldman Formation of Alberta, Canada. Description ''Albertaceratops'' is unusual in combining long ...

'', '' Medusaceratops'' and '' Avaceratops''.

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 ''

'' 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 Ceratopsidae ...

, 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