Anchiceratops

Anchiceratops (pronounced /ˌæŋkiˈsɛrətɒps/ ANG-ki-SER-a-tops; meaning "near horned face", derived from the Greek "anchi -/αγχι-" "near", "cerat-/κερατ-" "horn", "-ops/ωψ" "face") is a genus of chasmosaurine ceratopsid dinosaur from the Late Cretaceous Period of western North America. Like other ceratopsids, it 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 approached 20 feet (6 m) in length.

Discoveries and species

American paleontologist Barnum Brown named Anchiceratops in 1914, as he believed Anchiceratops was a transitional form closely related to both Monoclonius and Triceratops and intermediate between them. There is one valid species known today (A. ornatus), whose name refers to the ornate margin of its frill. A second species was named A. longirostris by Charles M. Sternberg in 1929, but this species is widely considered a junior synonym of A. ornatus today.

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.[1] The holotype is the back half of a skull, including the long frill,[1] and several other partial skulls were found at the same time, which are now stored in the American Museum of Natural History in New York City. A complete skull was discovered by C.M. Sternberg in 1924, and described as A. longirostris[1] five years later. Another specimen, collected by Sternberg in 1925, lacks 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. Other material has been found since, including one or two bonebed deposits in Alberta, but very little Anchiceratops material has been described (Dodson, 1996).
Anchiceratops frills are very distinctive. Rectangular in shape, the frill is edged by large epoccipitals (triangular bony projections), and has smaller fenestrae (window-like openings) than those seen in other chasmosaurines like Pentaceratops and Torosaurus.[1] Another characteristic feature is the pair of bony knobs located on either side of the midline, towards the end of the frill.

Most Anchiceratops fossils have been discovered in the Horseshoe Canyon Formation of Alberta, which belongs to the early part of the Maastrichtian stage of the Late Cretaceous Period (74-70 million years ago). Frill fragments found in the early Maastrichtian Almond Formation of Wyoming in the United States resemble Anchiceratops (Farke, 2004). However, pieces of a frill have been found from two localities in the older Dinosaur Park Formation (late Campanian, 78-74 million years ago) with the characteristic pattern of points seen in Anchiceratops frills. This may represent an early record of A. ornatus or possibly a second, related species (Langston, 1959).

Anchiceratops skull cast, National Dinosaur Museum, Canberra (*)

Paleobiology

Anchiceratops is rare compared to other ceratopsians in the area, and usually found near marine sediments, in both the Horseshoe Canyon and Dinosaur Park Formations. This indicates that Anchiceratops may have lived in estuaries where other ceratopsids did not live. Flowering plants were increasingly common but still rare compared to the conifers, cycads and ferns which probably made up the majority of ceratopsian diets.

Sexual dimorphism

C.M. Sternberg originally designated a smaller skull as the new species Anchiceratops longirostris, because of its size, and also its proportionally longer snout and much shorter horns that point forwards instead of upwards. However, modern paleontologists find that the size and form of this skull falls within the range of variation seen in A. ornatus and so it is probably a member of that species.

It has been proposed that Anchiceratops is a sexually dimorphic species, where the skull of A. longirostris actually represents a female. Other Anchiceratops skulls are larger and show shorter, more robust snouts, as well as much longer horns that point more vertically. This form is thought to represent the male. Sexual dimorphism is also seen in most other chasmosaurine genera, very strongly in some (Triceratops, Torosaurus, Pentaceratops), and more weakly in others (Chasmosaurus). The basal ceratopsian Protoceratops also exhibits strong sexual dimorphism (Lehman, 1990).

References

1. ^ a b c d e "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. ISBN 0-7853-0443-6.

* Brown, B. 1914. Anchiceratops, a new genus of horned dinosaurs from the Edmonton Cretaceous of Alberta. With a discussion of the origin of the ceratopsian crest and the brain casts of Anchiceratops and Trachodon. Bulletin of the American Museum of Natural History. 33: 539-548.
* Dodson, P. 1996. The Horned Dinosaurs. Princeton: Princeton University Press. 346pp.
* Farke, A.A. 2004. Ceratopsid dinosaurs from the Upper Cretaceous Almond Formation of southwestern Wyoming. Rocky Mountain Geology. 39: 1-5.
* Langston, W.J. 1959. Anchiceratops from the Oldman Formation of Alberta. National Museum of Canada Natural History Papers. 3: 1-11.
* Lehman, T.M. 1990. The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics. In: Carpenter, K. & Currie, P.J. (Eds.). Dinosaur Systematics: Approaches and Perspectives. Cambridge: Cambridge University Press. Pp. 211-219.
* Sternberg, C.M. 1929. A new species of horned dinosaur from the Upper Cretaceous of Alberta. National Museum of Canada Bulletin. 54: 34-37.

Dinosaurs