Anchiceratops ( ) is an extinct genus of chasmosaurine ceratopsid dinosaur that lived approximately 73 to 68 million years ago during the latter part of the Cretaceous Period in what is now Alberta, Canada. Anchiceratops was a medium-sized, heavily built, ground-dwelling, quadrupedal herbivore that could grow up to an estimated long. Its skull featured two long brow horns and a short horn on the nose. The skull frill was elongated and rectangular, its edges adorned by coarse triangular projections. About a dozen skulls of the genus have been found.
History of discovery
The first remains of Anchiceratops were discovered along the Red Deer River in the Canadian province of Alberta in 1912 by an expedition led by Barnum Brown. The holotype, specimen AMNH 5251, is the back half of a skull, including the long frill, and two other partial skulls, specimens AMNH 5259 (the paratype) and AMNH 5273, were found at the same time, which are now stored in the American Museum of Natural History in New York City. A complete skull designated NMC 8535, was discovered by Charles M. Sternberg at Morrin in 1924, and was described as A. longirostris five years later, in 1929. but this species is widely considered a junior synonym of A. ornatus today. In total, at least ten incomplete skulls have been recovered. The skulls are different with respect to their proportions (e.g. size of the supraorbital horn cores, the dimensions of the frill) which had led researchers to conclude that the disparity is ontogenetic.
The genus name Anchiceratops, means "near horned face", and is derived from the Greek words "anchi" (αγχι-) meaning "near", "keras" (κερας) meaning "horn", and "ops" (ωψ) meaning "face". Anchiceratops was described and named by American paleontologist Barnum Brown, in 1914, as he believed that this dinosaur represented a transitional form closely related to both Monoclonius and Triceratops and intermediate between them, but closest in the development of the skull frill to the latter, hence the generic name meaning "near Ceratops". The type and only valid species known today is Anchiceratops ornatus, whose name refers to the ornate margin of its frill.
Another specimen, NMC 8547 (or CMN 8547) collected by Sternberg in 1925, lacks most of the skull but is otherwise the most complete skeleton known from any ceratopsid, preserving a complete spinal column down to the last tail vertebra. Sternberg's material is now housed in the Canadian Museum of Nature in Ottawa. NMC 8547 is displayed as a half-mount with the better preserved right side showing, and completed with a cast skull replica of NMC 8535. Other material has been found since, including one or two possible bonebed deposits in Alberta, but very little Anchiceratops material has been described.Dodson, P. 1996. The Horned Dinosaurs. Princeton: Princeton University Press. 346 pp
Most Anchiceratops fossils have been discovered in the Horseshoe Canyon Formation of Alberta, which belongs to the later part of the Campanian stage of the Late Cretaceous Period (Anchiceratops remains are known from the lower part of the formation, and range in age between 72.5 and 71 million years ago). Frill fragments found in the early Maastrichtian Almond Formation of Wyoming in the United States resemble Anchiceratops. However, brown horn fragments (specimens NMC 9590 and 10645) and frill pieces (specimens NMC 9813, 9814 and 9829) have been found from two localities in the older OldmanWeishampel, D.B., Barrett, P.M., Coria, R.A., Le Loueff, J., Xu X., Zhao X., Sahni, A., Gomani, E.M.P., & Noto, C.N. 2004. Dinosaur distribution. In: Weishampel, D.B., Dodson, P., & Osmólska, H. (Eds.). The Dinosauria (2nd Edition). Berkeley: University of California Press. Pp. 517-606. and Dinosaur Park Formations (late Campanian, 76.5-75 million years ago) with the characteristic pattern of points seen in Anchiceratops frills. These may represent early records of A. ornatus or possibly a second, related species. Anchiceratops remains were also recovered in terrestrial sediments from the St. Mary River Formation at the Scabby Butte locality in southwestern Alberta, however, the fossils cannot be referred to a specific species.
In 2012, Mallon concluded that many more Anchiceratops fossils had been collected than previously had been realized. These included the specimens TMP 1983.001.0001, a nearly complete skull of a juvenile; UW 2419, a nearly complete skull; ROM 802, a skull lacking the snout; FMNH P15003, the upper side of a skull lacking the snout; CMN 11838, a left skull frill; CMN 12–1915, frill fragments; and UALVP 1618, the rear edge of a frill. This larger number of fossils can be examined by statistical analysis to solve certain long-standing controversies about the genus.
Description
Like other ceratopsids, A. ornatus was a quadrupedal herbivore with three horns on its face, a parrot-like beak, and a long frill extending from the back of its head. The two horns above the eyes were longer than the single horn on its snout, as in other chasmosaurines.
Anchiceratops was a medium-sized ceratopsid. If specimen NMC 8547 is not taken into account, no very exact estimations of the body length of Anchiceratops can be given. Some popular science books state that it approached 20 feet (6 m) in length."Anchiceratops." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 124. . In 2010 Gregory S. Paul, on the assumption that specimen NMC 8547 represented Anchiceratops, estimated its length at 4.3 metres, its weight at 1.2 tonnes.Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 268
Anchiceratops frills are very distinctive. Rectangular in shape, the frill is edged by large epoccipitals, which are osteoderms in the form of triangular bony projections. These are exceptionally wide and coarse. Some of these epoccipitals are on the side of the frill, formed by the squamosal; these episquamosals vary between five and nine in number. The last episquamosal is very large, approaching the size of the three osteoderms per side on the rear edge of the frill, the epiparietals. Another characteristic feature is the pair of bony knobs located on either side of the midline, towards the end of the frill. These are pointing sideways and are very variable in form and size between individuals. The parietal bone, forming the rear edge and the middle of the frill, has smaller parietal fenestrae, window-like openings, than those seen in other chasmosaurines like Pentaceratops and Torosaurus. The frill has deep arterial grooves on both the upper and the underside.
Specimen NMC 8547, on which traditionally descriptions of the postcrania of Anchiceratops have been based, has many traits that are unique in the Chasmosaurinae. The vertebral column contains seventy-four vertebrae: ten of the neck, thirteen dorsals, twelve sacrals and thirty-nine caudals. Typically chasmosaurines have twelve dorsals, ten sacrals and up to forty-six tail vertebrae. Mallon presumed that the synsacrum, the fused vertebrae supporting the pelvis, had shifted to the rear. The neck of NMC 8547 is exceptionally long, with four syncervicals, fused anterior cervical vertebrae. Also the pelvis is very long. The tail is short. The forelimbs are very robust, with a large deltopectoral crest on the humerus, indicating a heavy musculature.
Classification
Brown in 1914 assigned Anchiceratops to the Ceratopsia. In 1915, William Diller Matthew refined this to the Ceratopsidae.W.D. Matthew, 1915 Dinosaurs, with Special Reference to the American Museum Collections. American Museum of Natural History, New York 162 pp In the same year Lawrence Lambe assigned this genus to a new taxon that he erected, "eoceratopsinae", which included "Eoceratops" (now Chasmosaurus), "Diceratops" (now Nedoceratops) and Triceratops. "Eoceratopsinae" however soon fell into disuse as a taxon. Ironically, in the same study Lambe erected Chasmosaurinae, the taxon that Anchiceratops is assigned to currently.L. M. Lambe. 1915. On Eoceratops canadensis, gen. nov., with remarks on other genera of Cretaceous horned dinosaurs. Canada Geological Survey Museum Bulletin 12, Geological Series 24:1-49 Over the decades Lull (1933),R. S. Lull. 1933. A revision of the Ceratopsia or horned dinosaurs. Memoirs of the Peabody Museum of Natural History 3(3):1-175 Romer (1956),A. S. Romer. 1956. Osteology of the Reptiles, University of Chicago Press 1-772 Russell and Chamney (1967),D. A. Russell and T. P. Chamney. 1967. Notes on the biostratigraphy of dinosaurian and microfossil faunas in the Edmonton Formation (Cretaceous), Alberta. National Museum of Canada Natural History Papers 35:1-22 Molnar (1980)R. E. Molnar. 1980. Australian late Mesozoic continental tetrapods: some implications. Mémoires de la Société Géologique de France, Nouvelle Série 139:131-143 agreed with the assignment to Ceratopsidae.
In 1990, Peter Dodson and Phil Currie placed it in the Chasmosaurinae.P. Dodson and P.J. Currie. 1990. "Neoceratopsia", pp 593-618 in: D.B. Weishampel, H. Osmolska, and P. Dodson (eds.), The Dinosauria. First Edition, University of California Press, Berkeley, The phylogenetic analysis conducted by Ryan et al. (2010) confirmed this assignment.M. J. Ryan, A. P. Russell, and S. Hartman. 2010. A new chasmosaurine ceratopsid from the Judith River Formation, Montana. In M. J. Ryan, B. J. Chinnery-Allgeier, D. A. Eberth (eds.), New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium. Indiana University Press, Bloomington 181-188 Modern cladistic analyses usually recover Anchiceratops in a more advanced position within the Chasmosaurinae, closer to Arrhinoceratops than to Chasmosaurus. Mallon's study of 2012 concluded however, that Anchiceratops was more closely related to Chasmosaurus than to Triceratops, suggesting that this genus was less derived than previously thought.
C.M. Sternberg had originally designated a smaller skull as the type specimen for a new species Anchiceratops longirostris, because of its size and its horns which are significantly more slender and point forward instead of upward. Later however, paleontologists had concluded that the size and form of this skull falls within the expected range of variation seen in A. ornatus and that it was probably a member of that species.
In 2010 Mallon removed specimen NMC 8547 from the fossil material of Anchiceratops because of the few frill elements associated with it and because it could not be determined with certainty whether the material belonged to this taxon. The related Arrhinoceratops is known from the same formation, and has a comparable frill surface structure. According to Mallon, in 1925 C.M. Sternberg had referred the material to Anchiceratops because he had been unaware that Arrhinoceratops had been described in March of that year. If correct, this would mean that no unequivocal postcrania (all skeletal elements posterior to the skull) of Anchiceratops are known.J.C. Mallon and R. Holmes (2010) "Description of a complete and fully articulated chasmosaurine postcranium previously assigned to Anchiceratops (Dinosauria: Ceratopsia)", In: M. J. Ryan, B. J. Chinnery-Allgeier, and D. A. Eberth (eds.), New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium. Indiana University Press, Bloomington, Indiana. pp 189–202
Paleobiology