''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 an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce 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 Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

. It lived around 78

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

, during the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

in what is now

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

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

quadrupedal Quadrupedalism is a form of Animal locomotion, locomotion in which animals have four legs that are used to weight-bearing, bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four l ...

herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

. 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 ...

Discovery

The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

YPM VPPU 022404 consists of an incomplete skull including the horns, parts of the frills, and fragments from the back 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 ...

s. 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 ve ...

(located above the eyes) horns are moderately elongate, inclined forward and outwards, and have an unusual teardrop-shaped cross section.Other fragmentary specimens are known from the same area, which preserve distinctive features of the frill. A referred specimen, YPM VPPU 023262, overlaps the holotype in two areas, including the distal blade of the squamosal, and the postorbital horns. It resembles the holotype in several features, including the shape of the marginal hornlets and the concave lateral margin of the distal blade. Critically, it shares the same unusual horn shape seen in the holotype, supporting referral of the two fossils to the same species, and it helps to provide additional information on the anatomy of ''Judiceratops''. It shows that the animal had large scallops on the frill's proximal margins, and a very broad, platelike bar in the center of the frill.

Description

Its frill (

parietal bone The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...

) 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 amph ...

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.

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 mechanism of evolution in which members of one 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 the opposite sex ...

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

Evolution

''Judiceratops'' is the oldest known member of the Chasmosaurinae, but already shows many of the distinctive features of the group including the long, concave squamosals and pointed epioccipitals. 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') is a genus of ceratopsian dinosaurs that lived during the Turonian stage of the Late Cretaceous in what is now New Mexico, United States. Only a single species is known, ''Zuniceratops christopheri''. Histor ...

'', 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, suggesting rapid evolution. Although ''Judiceratops'' is currently the oldest known chasmosaurine, it does not seem to be 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. Its precise relationships to other members of the group are unclear, but given its relatively early appearance and the lack of features clearly linking it to later members of the Chasmosaurinae, it seems to represent a deep divergence within Chasmosaurinae.

Paleoecology

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 Montana Group. It dates to the Late Cretaceous, between 79 and 75.3 million years ago, corresponding to the "Judithian" land vertebrate age. It was ...

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. Campa ...

stage of

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

period, approximately 78 million years ago. This specimen is housed at the Yale Peabody Museum. ''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 ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

, 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 Miocene (168 to 20 or p ...

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 , () ...

'', the

hadrosaur Hadrosaurids (), also hadrosaurs 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 fami ...

Brachylophosaurus ''Brachylophosaurus'' ( or ) is a genus of hadrosaurid dinosaur that lived during the Late Cretaceous period of western North America. It was first named in 1953 by Charles Mortram Sternberg for a skull and skeleton he discovered in 1936 in th ...

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

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

s ''

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

'', ''

Gorgosaurus ''Gorgosaurus'' ( ; ) is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.5 and 75 million years ago. Fossil remains have been found in the Ca ...

'' and ''

Troodon ''Troodon'' ( ; ''Troödon'' in older sources) is a controversial genus of relatively small, bird-like theropod dinosaurs definitively known from the Campanian age of the Late Cretaceous period (about 77 million years ago). It includes at l ...

'', 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, Asia and Europe, during the Cretaceous Period, although ancestral forms lived earlier, in the Late Jura ...

'' Albertaceratops'', '' Medusaceratops'' and ''

Avaceratops ''Avaceratops'' is a genus of small herbivorous ceratopsian dinosaurs which lived during the late Campanian in what are now the Northwest United States. Most fossils come from the Judith River Formation. Discovery and naming The first remains ...

''.

References