Medusaceratops

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Medusaceratops
Temporal range: Middle Campanian, 77.5  Ma
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Medusaceratops lokii.jpg
Skeleton at Wyoming Dinosaur Museum formerly referred to Albertaceratops
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Suborder: Ceratopsia
Family: Ceratopsidae
Subfamily: Centrosaurinae
Genus: Medusaceratops
Ryan, Russell & Hartman, 2010
Species:
M. lokii
Binomial name
Medusaceratops lokii
Ryan, Russell & Hartman, 2010

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. [1]

Contents

Discovery

Side view of skeleton Medusaceratops side.jpg
Side view of skeleton

The known material of Medusaceratops came from a bonebed in the badlands on the west side of Kennedy Coulee adjacent to the Milk River, in the Milk River Natural Area, near Havre, Hill County of Montana. The material was first reported by Sweeney and Boyden (1993), who considered it to represent the southernmost occurrence of Styracosaurus albertensis , based on misidentified frill spikes. Trexler and Sweeney (1995) reinterpreted the spikes as eye-socket horncores and noted their similarity to those of the nomen dubium Ceratops montanus from a nearby area, however, could not refer the bonebed material to any valid existing taxon. The bonebed, known as the Mansfield Bonebed honoring its landowner, is located on private land and historically has been excavated by several commercial companies. The type material of Medusaceratops and other specimens were excavated more recently and have been purchased by the Wyoming Dinosaur Center from Canada Fossils, Ltd., of Calgary, Alberta. Additional material from the same excavation was purchased and accessioned by the Royal Tyrrell Museum of Palaeontology. Canada Fossils, Ltd., also assembled two composite skeletons using the Mansfield Bonebed material which are in the collections of the Wyoming Dinosaur Center and the Fukui Prefectural Dinosaur Museum, however neither of the casts has an exact reconstruction of Medusaceratops as it was later described. [1]

The name Medusaceratops was coined by Canadian paleontologist Michael J. Ryan of the Cleveland Museum of Natural History in 2003 in a dissertation. Its fossils were subsequently confused with those of Albertaceratops , another centrosaurine ceratopsian from Alberta which had been described by Ryan in 2007. Later, Ryan realized that the Mansfield Bonebed fossils did not belong to Albertaceratops. Medusaceratops was formally described and name by Michael J. Ryan, Anthony P. Russell and Scott Hartman in 2010 and the type species is Medusaceratops lokii. The generic name refers to Medusa, a monster from Greek mythology whose "hair" consists of snakes and its gaze could turn men to stone, alluding to a unique trait of this genus - the large, thick snake-like spikes that extend to the sides of the frill, in combination with Latinized Greek ceratops, meaning "horned-face", which is a common suffix for ceratopsian genera names. The specific name lokii honors Loki, a troublemaking god in the Norse mythology, in reference to the years confusion that surrounded the taxonomic designations of the Mansfield Bonebed material before it was given its own name. [1]

The Mansfield Bonebed material was collected from the upper part of the Judith River Formation, in a region where it is lithologically equivalent to the Oldman Formation of Canada. The bonebed is located at approximately the same level as the holotype of Albertaceratops , dating to 77.5 million years ago, to the middle Campanian stage of the Late Cretaceous. Thus, Medusaceratops was considered to represent the oldest known chasmosaurine, [1] until the naming of Judiceratops by Longrich (2013), also from the Judith River Formation, but from an area equivalent to the lower Oldman Formation or upper Foremost Formation. [2]

However, Ryan had already indicated that part of the Mansfield material represented not a chasmosaurine, but a centrosaurine. Chiba et al. in 2017 described new material of Medusaceratops from the Mansfield Bonebed, found in 2011 and 2012 by David Trexler, indicating the presence of traits that were characteristic of Centrosaurinae in the skeleton of M. lokii. They concluded that all the material could be referred to a single species. The phylogenetic analysis conducted by the authors indicated that Medusaceratops was not a member of Chasmosaurinae after all, but rather an early centrosaurine ceratopsid that was more closely related to Centrosaurini and Pachyrhinosaurini than Nasutoceratopsini. [3]

Description

Restoration Medusaceratops NT.jpg
Restoration

Two partial parietals (frills) that are housed at the Wyoming Dinosaur Center were chosen as the type material of Medusaceratops, including the holotype WDC DJR 001 and the paratype WDC DJR 002. Although all the chasmosaurine material from the Mansfield Bonebed was thought to be referable to Medusaceratops, which totals at several hundred individual elements, upon its original description only these two partial frills have been scientifically described while the rest of the material was being reexamined. Many of the other elements are not diagnosable to a genus level and can only be confidently referable to Ceratopsidae. [1] [3]

Upon its original description Medusaceratops was thought to represent a chasmosaurine. It was suggested that based on its type material alone, Medusaceratops is unique among Chasmosaurinae in having only three epiparietals (frill spikes) on each side of the frill. The first frill spike pair is large and the second is smaller, and both are uniquely widened at base, pachyostotic, curve down the sides of the frill, and are depressed down the front of the frill. The third frill spike pair is small and triangular, unmodified in comparison to early chasmosaurines, but similarly depressed, and borders the squamosal bone. The highly broadened and curved first frill spike pair of Medusaceratops closely resembles the third pair of the frill ornamentation of Albertaceratops , however Medusaceratops was thought to differ (like all chasmosaurines) in lacking tab-shaped, frequently overlapping fourth to seventh pairs of the frill ornamentation of centrosaurines. [1]

This was challenged in 2018, by the description of additional Mansfield Bonebed material assignable to Medusaceratops. It became apparent that the 1-3 frill spikes mentioned above are in fact spikes 2–4. The first epiparietal is small and variably procurving and thus was misinterpreted before. At least one more epiparietal pair was also identified (after the fourth), resulting in a total of at least 5 pairs, consistent with centrosaurines like Albertaceratops and Wendiceratops , but not with chasmosaurines. The midline ramus of Medusaceratops, a bone separating the two sides of the frill, was also among the newly described material. It is broad, resulting in rounder and smaller frill fenestrae (holes) like in other centrosaurines. Thus, the new study reassigned Medusaceratops to Centrosaurinae, among which it is most similar to Albertaceratops and Wendiceratops. [3]

In 2010, a length of roughly 6 meters (~20 feet) was estimated for Medusaceratops lokii. [4]

Classification

Reconstruction of parietals of various centrosaurines, including Wendiceratops (A) showing 5 epiparietal pairs and broad midline ramus. Medusaceratops itself is marked by letter (F). Wendiceratops parietal.PNG
Reconstruction of parietals of various centrosaurines, including Wendiceratops (A) showing 5 epiparietal pairs and broad midline ramus. Medusaceratops itself is marked by letter (F).

Among valid ceratopsids from the Judith River Formation, Medusaceratops can be directly distinguished from centrosaurine Avaceratops , [3] and chasmosaurines Judiceratops and Spiclypeus [5] based on its unique frill ornamentation. It differs from chasmosaurine Mercuriceratops based on its less unique squamosal bone, [6] as evident from newly described squamosal bones of Medusaceratops. [3] All material previously assigned to the centrosaurine Albertaceratops from the formation is now assigned to Medusaceratops or considered too fragmentary. [1] [3]

The cladogram presented below follows a phylogenetic analysis by Chiba et al. (2017) who redescribed Medusaceratops as a centrosaurine: [3]

Centrosaurinae

Diabloceratops eatoni

Machairoceratops cronusi

Nasutoceratopsini

Avaceratops lammersi (ANSP 15800)

MOR 692

CMN 8804

Nasutoceratops titusi

Malta new taxon

Xenoceratops foremostensis

Sinoceratops zhuchengensis

Wendiceratops pinhornensis

Albertaceratops nesmoi

Medusaceratops lokii

Eucentrosaura

Centrosaurini

Pachyrhinosaurini

See also

Related Research Articles

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Styracosaurus is a genus of herbivorous ceratopsian dinosaur from the Cretaceous Period, about 75.5 to 74.5 million years ago. It had four to six long parietal spikes extending from its neck frill, a smaller jugal horn on each of its cheeks, and a single horn protruding from its nose, which may have been up to 60 centimeters long and 15 centimeters wide. The function or functions of the horns and frills have been debated for many years.

<i>Einiosaurus</i> Ceratopsian dinosaur genus from Upper Cretaceous period

Einiosaurus is a genus of herbivorous centrosaurine ceratopsian dinosaur from the Upper Cretaceous of northwestern Montana. The name means 'bison lizard', in a combination of Blackfeet Indian eini and Latinized Ancient Greek sauros; the specific name (procurvicornis) means 'with a forward-curving horn' in Latin. Einiosaurus is medium-sized with an estimated body length at 4.5 metres (15 ft).

<i>Ceratops</i> Extinct genus of dinosaurs

Ceratops is a dubious genus of herbivorous ceratopsian dinosaur which lived during the Late Cretaceous. Its fossils have been found in the Judith River Formation in Montana. Although poorly known, Ceratops is important in the history of dinosaurs, since it is the type genus for which both the Ceratopsia and the Ceratopsidae have been named.

<i>Albertaceratops</i> Extinct genus of dinosaurs

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<span class="mw-page-title-main">Centrosaurinae</span> Extinct subfamily of dinosaurs

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<i>Sinoceratops</i> Extinct genus of dinosaurs

Sinoceratops is an extinct genus of ceratopsian dinosaur that lived approximately 73 million years ago during the latter part of the Cretaceous Period in what is now Shandong province in China. It was named in 2010 by Xu Xing et al. for three skulls from Zhucheng, China. The name of its type species Sinoceratops zhuchengensis means "Chinese horned face from Zhucheng", after the location of its discovery.

<i>Kosmoceratops</i> Dinosaur genus from the Late Cretaceous period

Kosmoceratops is a genus of ceratopsid dinosaur that lived in North America about 76–75.9 million years ago during the Late Cretaceous period. Specimens were discovered in Utah in the Kaiparowits Formation of the Grand Staircase–Escalante National Monument in 2006 and 2007, including an adult skull and postcranial skeleton and partial subadults. In 2010, the adult was made the holotype of the new genus and species Kosmoceratops richardsoni; the generic name means "ornate horned face", and the specific name honors Scott Richardson, who found the specimens. The find was part of a spate of ceratopsian discoveries in the early 21st century, and Kosmoceratops was considered significant due to its elaborate skull ornamentation.

<span class="mw-page-title-main">Pachyrhinosaurini</span> Extinct tribe of dinosaurs

Pachyrhinosaurini is a tribe of centrosaurine dinosaurs. The clade existed during the Late Cretaceous, about 83.6 to 68.5 million years ago, evolving during the early Campanian, and becoming extinct in the Maastrichtian. The tribe contains five genera: Styracosaurus, Stellasaurus, Einiosaurus, Achelousaurus, and Pachyrhinosaurus. Pachyrhinosaurus and Achelousaurus form the clade of pachyrhinosaurins called the Pachyrostra ("thick-snouts"), characterized primarily by their nasal bosses.

<i>Nasutoceratops</i> Extinct genus of dinosaurs

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<i>Xenoceratops</i> Extinct genus of dinosaurs

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<i>Coronosaurus</i> Extinct genus of dinosaurs

Coronosaurus is a genus of centrosaurine ceratopsian dinosaurs which lived in the Late Cretaceous, in the middle Campanian stage. Its remains, two bone beds, were discovered by Phillip J. Currie in the Oldman Formation of Alberta, Canada, and its type and only species, Coronosaurus brinkmani, was first described in 2005, as a new species within the genus Centrosaurus. Later studies questioned the presence of a direct relationship, and in 2012 it was named as a separate genus. Coronosaurus means "crowned lizard", coming from "corona", Latin for crown, and "sauros", Greek for lizard; this name refers to the unique, crown-like shape of the horns on the top of its frill.

<i>Judiceratops</i> Extinct genus of dinosaurs

Judiceratops is an extinct horned dinosaur. It lived around 78 million years ago, during the Late Cretaceous Period in what is now Montana, United States. Like other horned dinosaurs, Judiceratops was a large, quadrupedal herbivore. It is the oldest known chasmosaurine.

Bravoceratops is a genus of large chasmosaurine ceratopsid dinosaur that lived approximately 70 million years ago, and is known from the Late Cretaceous Javelina Formation in what is now Texas, United States.

<i>Mercuriceratops</i> Extinct genus of dinosaurs

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

<i>Regaliceratops</i> Extinct genus of dinosaurs

Regaliceratops is a monospecific genus of chasmosaurine ceratopsid dinosaur from Alberta, Canada that lived during the Late Cretaceous in what is now the St. Mary River Formation. The type and only species, Regaliceratops peterhewsi, is known only from an adult individual with a nearly complete skull lacking the lower jaw, which was nicknamed "Hellboy". Regaliceratops was named in 2015 by Caleb M. Brown and Donald M. Henderson. Regaliceratops has an estimated length of 5 metres (16 ft) and body mass of 2 metric tons. The skull of Regaliceratops displays features more similar to centrosaurines, which suggests convergent evolution in display morphology in ceratopsids.

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<i>Spiclypeus</i> Extinct genus of dinosaurs

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<i>Yehuecauhceratops</i> Extinct genus of dinosaurs

Yehuecauhceratops is a genus of horned centrosaurine ceratopsid dinosaur from the Late Cretaceous of Coahuila, Mexico. It contains a single species, Y. mudei, described from two partial specimens by Rivera-Sylva et al. in 2016 and formally named by Rivera-Sylva et al. in 2017. It was a small centrosaurine with a body length of 3 metres (9.8 ft), making it smaller than Agujaceratops and Coahuilaceratops, the other two ceratopsids in its environment; the three may have been ecologically segregated. A ridge bearing a single roughened projection near the bottom of the squamosal bone, which probably supported a small horn, allows Yehuecauhceratops to be distinguished from other centrosaurines. Its affinities to nasutoceratopsin centrosaurines, such as Avaceratops and Nasutoceratops, are supported by various morphological similarities to the former.

<i>Furcatoceratops</i> Extinct genus of dinosaurs

Furcatoceratops is a genus of centrosaurine ceratopsid dinosaur from the Late Cretaceous Judith River Formation of Montana. The type species is Furcatoceratops elucidans.

References

  1. 1 2 3 4 5 6 7 Ryan, Michael J.; Russell, Anthony P., and Hartman, Scott. (2010). "A New Chasmosaurine Ceratopsid from the Judith River Formation, Montana", In: Michael J. Ryan, Brenda J. Chinnery-Allgeier, and David A. Eberth (eds), New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium, Indiana University Press, 656 pp. ISBN   0-253-35358-0.
  2. Longrich, N. R. (2013). "Judiceratops tigris, a New Horned Dinosaur from the Middle Campanian Judith River Formation of Montana". Bulletin of the Peabody Museum of Natural History. 54: 51–65. doi:10.3374/014.054.0103. S2CID   129801786.
  3. 1 2 3 4 5 6 7 Kentaro Chiba; Michael J. Ryan; Federico Fanti; Mark A. Loewen; David C. Evans (2018). "New material and systematic re-evaluation of Medusaceratops lokii (Dinosauria, Ceratopsidae) from the Judith River Formation (Campanian, Montana)". Journal of Paleontology. 92 (2): 272–288. doi:10.1017/jpa.2017.62. S2CID   134031275.
  4. Cleveland Museum of Natural History (30 May 2010). "New horned dinosaur: Two-ton plant-eater lived 78 million years ago in Montana". ScienceDaily. ScienceDaily. Retrieved 24 January 2022.
  5. Jordan C. Mallon; Christopher J. Ott; Peter L. Larson; Edward M. Iuliano; David C. Evans (2016). "Spiclypeus shipporum gen. et sp. nov., a Boldly Audacious New Chasmosaurine Ceratopsid (Dinosauria: Ornithischia) from the Judith River Formation (Upper Cretaceous: Campanian) of Montana, USA". PLOS ONE. 11 (5): e0154218. Bibcode:2016PLoSO..1154218M. doi: 10.1371/journal.pone.0154218 . PMC   4871577 . PMID   27191389.
  6. 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. Bibcode:2014NW....101..505R. doi:10.1007/s00114-014-1183-1. PMID   24859020. S2CID   13957187.