Xenoceratops
 | This article may be too technical for most readers to understand. (November 2012) |
| Xenoceratops Temporal range: Late Cretaceous,
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Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Family: | †Ceratopsidae |
| Subfamily: | †Centrosaurinae |
| Genus: | †Xenoceratops Ryan, Evans & Shepherd, 2012 |
| Type species | |
| †Xenoceratops foremostensis Ryan, Evans & Shepherd, 2012
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Xenoceratops is an extinct genus of centrosaurine ceratopsid dinosaur known from the Late Cretaceous (middle Campanian stage) of Alberta, Canada. It contains one known species, Xenoceratops foremostensis. Its remains were discovered in Foremost Formation.[1]
Discovery
In 1958, Wann Langston, Jr., excavated skull fragments from the moderately developed[clarification needed] Foremost Formation badlands of Chin Coulee, located approximately 7 km northeast of Foremost, Alberta. All the material was collected from a low-diversity bone bed in Chin Coulee Site No. 2. Langston described it as "soft gray-brown slightly carbonaceous shale that is 17 feet above the massive yellow-weathering Ostrea bed". The bone bed dates to the middle Campanian stage of the Late Cretaceous period, about 78 million years ago. The precise locality is archived at the Canadian Museum of Nature in Ottawa, Ontario.[1][2]
Langston stored the fragments in cabinets at the that Museum. Around 2003, David C. Evans and Michael J. Ryan became curious about the specimens, and more thorough investigation was conducted in 2009.[3] Evans, Ryan and Kieran M. Shepherd referred all these specimens to a new species and genus of ceratopsian. At the time of discovery, X. foremostensis is the oldest known Canadian ceratopsid, approximately 0.5 Ma older than Albertaceratops from the lower Oldman Formation of Canada and Medusaceratops from the Judith River Formation of Montana, and approximately 1.0 Ma younger than Diabloceratops from the Wahweap Formation of Utah. Additionally, it is the first ceratopsian described from the Foremost Formation. With the exception of the pachycephalosaur Colepiocephale lambei, all other dinosaur taxa from the Foremost Formation have been erected based on teeth collected primarily from microvertebrate fossil localities. The relative lack of diagnosable skeletal material is related to the limited amount of exposures in the near-shore terrestrial sequence that constitutes the top of the formation.[1]
The material originally catalogued as CMN 53282 was found to be a composite of at least three adult-sized individuals. CMN 53282, a partial parietal, is retained for the holotype, with CMN 54950 and CMN 54951 designated as paratype parietals representing two other individuals. The remainder of the specimens which were referred to Xenoceratops is assigned sequential specimen numbers CMN 54952 to CMN 54964. These specimens likely pertain to the holotype or paratypes owing to their close association, although none of it can be confidently referred to the type specimens. The referred material includes the four parietals CMN 54952, CMN 54953, CMN 54958 and CMN 54964; the three squamosals CMN 54954, CMN 54956 and CMN 54957; the nasal CMN 54955; three epiparietals CMN 54961, CMN 54962 and CMN 54963; a parietal P4 process CMN 54959; and parietal with P3 suture CMN 54960. CMN 54965 is assigned to all remaining unidentified fragments originally part of the CMN 53282 designation.[1]
Description
Xenoceratops is a centrosaurine ceratopsid that had two epiparietals (P2–P3) on the posterior parietal ramus. The wide-based, short, pachystotic (thick), and procurved processes (P2) adjacent medially to a U-shaped posterior margin. In overall, the P2 processes morphology resembles the P4 processes of Albertaceratops, but the P2 of Xenoceratops has a pronounced dorsal inflection. In some specimens of Xenoceratops, the P2 process has an almost hook-like shape when viewed in lateral profile. The P3 process is a depressed, wide-based, elongate, straight spike that is posterolaterally oriented. The large right P3 process is similar to all centrosaurines except some specimens of Centrosaurus, although it differs from all other centrosaurines except Albertaceratops and the chasmosaurine Medusaceratops in being wide-based and pachystotic, and differs from those two ceratopsids in that the process is straight. Its ventral margins of parietal at the contact with the epiparietals are greatly inflated. The thickened U-shaped midline posterior margin of the parietal is similar to that seen in centrosaurines that support large P3 spikes, like Albertaceratops and Diabloceratops.[1]
Additional epiparietals (a minimum of two, probably five, as in other centrosaurines based on inference from the available fragments) fuse into ovoid depressions on it lateral ramus. Xenoceratops is apomorphic in having ovoid depressions with arched ventral margins occurring at these positions where epiparietals contact and fuse on other centrosaurines. The epiparietal that partially straddles the contact between the parietal and squamosal appears to have the typical centrosaurine contact of overlapping an outgrowth of the parietal. As in all centrosaurines, it has a narrow groove that runs across the medial surface at the angle of the "stepped up" on the squamosal. As reconstructed, when viewed dorsally, the parietal has fenestrae of typical centrosaurine size adjacent to a wide midline ramus. Xenoceratops shares with Albertaceratops and most chasmosaurines the lack of "bumps" on the midline parietal ramus, and unlike other centrosaurines, it lacks the development of imbricated epiparietals on the lateral ramus. Xenoceratops also lacks P1 processes, as do the other basal centrosaurines, Albertaceratops and Diabloceratops, as well as the derived pachyrhinosaurinis.[1]
Xenoceratops nasal is known from a fragmentary right nasal preserving the base of the ornamentation and a portion of the lateral wall. The specimen is very similar to isolated, unfused Medusaceratops nasals recovered from the Mansfield bone bed in the Judith River Formation. These unfused nasals are mediolaterally flattened with low, elongate ornamentation that is also seen on the basal centrosaurines Albertaceratops and Diabloceratops, and suggest that Xenoceratops had a similar nasal ornamentation. Basal length of the ornamentation cannot be estimated due to the incompleteness of the specimen, and the surficial texture is poorly preserved. Although no identifiable portions of the postorbitals were preserved with the specimens, an additional, unprepared fragmentary skull (TMP 2010.76.24) was collected from the Foremost Formation in the same region in 2010 that does preserve portions of two large-diameter, elongate postorbital horncores. The skull can be referred to Xenoceratops based on the presence of apomorphic, shallow epiparietal contacts on parietal fragments of the specimen. Thus, it can be inferred that Xenoceratops had elongate, robust postorbital horncores similar to the similarly aged basal centrosaurines Albertaceratops and Diabloceratops.[1]
Phylogeny
Ryan, Evans & Shepherd (2012) used the data matrix of Farke et al. (2011) to assess the phylogenetic position of Xenoceratops using two different coding systems. Their revised analysis had significantly better resolution than that presented by Farke et al. (2011) probably due in part to the additional scoring of missing characters for some taxa based on direct observation of their specimens. This analysis found Xenoceratops to be the basalmost known centrosaurine. The cladogram below shows Xenoceratops phylogenetic position among other centrosaurines following Ryan, Evans & Shepherd (2012).[1]
| Ceratopidae |
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Etymology
Xenoceratops was first described and named by Michael J. Ryan, David C. Evans and Kieran M. Shepherd in 2012 and the type species is Xenoceratops foremostensis. The generic name is derived from the Ancient Greek xenos, meaning "foreign" or "alien", and ceratops, meaning "horned face".[2] The combination is in reference to the lack of ceratopsian specimens known from the Foremost Formation. The specific name foremostensis is named after the town of Foremost, Alberta.[1]
References
- ^ a b c d e f g h i Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1139/e2012-056, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
|doi=10.1139/e2012-056instead. - ^ a b Gayle, Damien (9 November 2012). "The ferocious vegetarian: Two ton, 20ft long 'alien horned-face' dinosaur discovered in Canada". Daily Mail. Retrieved 10 November 2012.
- ^ Tutton, Michael (November 8, 2012). "Fossilized horn that sat in museum for decades leads to new Alberta dinosaur discovery". The Canadian Press. Retrieved November 9, 2012.
