| Arrhinoceratops | |
|---|---|
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| Arrhinoceratops brachyops at theRoyal Ontario Museum | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ceratopsia |
| Family: | †Ceratopsidae |
| Subfamily: | †Chasmosaurinae |
| Genus: | †Arrhinoceratops Parks,1925 |
| Species: | †A. brachyops |
| Binomial name | |
| †Arrhinoceratops brachyops Parks, 1925 | |
Arrhinoceratops (meaning "no nose-horn face", derived from theAncient Greek"a-/α-" "no",rhis/ῥίς "nose""keras/κέρας" "horn","-ops/ὤψ" "face") is agenus of herbivorousceratopsiandinosaur. The name was coined as its original describer concluded it was special because the nose-horn was not a separate bone, however further analysis revealed this was based on a misunderstanding.[1] It lived during the latestCampanian/earliestMaastrichtian stage of the LateCretaceous, predating its famous relativeTriceratops by a few million years, although it was contemporary withAnchiceratops.[1] Its remains have been found inCanada.[1]
Described byWilliam Arthur Parks in 1925,Arrhinoceratops is known from a partially crushed, slightly distortedskull which lacked thelower jaws. The remains were collected from the Neill's Ranch site, along theRed Deer River inAlberta by a 1923 expedition from theUniversity of Toronto.[2]
Parks named thetype speciesArrhinoceratops brachyops. The generic name is derived from Greek α~, "without", ῥίς,rhis, "nose", κέρας,keras, "horn", and ὤψ,ops, "face" as Parks had established that no separate nose-horn was present. Thespecific name means "short-faced" from Greek βραχύς,brachys, "short".[2]
Theholotype isROM 796 (earlier ROM 5135), which was found in a layer of theHorseshoe Canyon Formation dating from the latest Campanian or perhaps earliestMaastrichtian. It consists of the original skull.
Other material fromUtah, found in the 1930s, was posthumously namedArrhinoceratops? utahensis byCharles Whitney Gilmore in 1946. It is based on holotype USNM 15583. The question mark indicates that Gilmore himself had doubts about the identification.[3] In 1976,Douglas A. Lawson transferred the species toTorosaurus, as aTorosaurus utahensis.[4][5]
Apart from the holotype skull little fossil material ofArrhinoceratops brachyops has been found. In 1981Helen Tyson in a revision of the genus, provisionally referred specimen ROM 1439,[6] but in 2007Andrew Farke moved this toTorosaurus.[7]
Since this dinosaur is known only from its skull, scientists have few data about its overall anatomy. The skull, as restored, features a broad, square, neck frill with two oval shaped openings.[1] The frill is deeply veined on both the top and the underside by arterial grooves. The sides of the frill are adorned by about nineosteoderms. The rear edge of the frill is lightly scalloped. The leftsquamosal in the frill side of the holotype shows a pathological opening, perhaps the result of a wound. Its brow horns were moderately long, but its nose horn was shorter and blunter than most ceratopsids. The snout is short and high.[1] Its body is assumed to be typical of the Ceratopsidae. Based on the skull some popular-science books estimate the body length to be 6 m (20 ft) long when fully grown.[1] In 2010,Gregory S. Paul estimated its length at 4.5 metres (15 ft), its weight at 1.3 tonnes (2,900 lb).[8]
AlreadyRichard Swann Lull had in 1933 been politely critical of Parks' original description,[9] and Tyson discovered that Parks, anentomologist, had made many mistakes. The most notable of these was that the very trait the genus was named after, the lack of a separate ossification oros epinasale for the nose-horn, is in fact normal for the ceratopsids, in which group this horn is an outgrowth of thenasal bone, not a distinct element. Other incorrect observations by Parks included the conclusion that theos rostrale, the bone core of the upper beak, directly touched the nasals instead of being separated from them by thepremaxillae; a presumed anterior process of thejugal touching the premaxilla; and thinking that the interparietal bar of the frill presented a separate skeletal element, anos interparietale.[6]
Arrhinoceratops was by Parks placed within theCeratopsia (this name is Ancient Greek for "horned faces"), a group of herbivorous dinosaurs withparrot-like beaks which thrived inNorth America andAsia during the Cretaceous Period, which ended roughly 66 million years ago. In 1930Lori Russell refined this to theCeratopsidae.[10] Tyson concluded it was closely related toTorosaurus, probably even its direct ancestor.[1][6]
Modern research indicates thatArrhinoceratops is a member of theChasmosaurinae.[11]Cladistic analyses recover it close toAnchiceratops.
The followingcladogram shows thephylogeny ofArrhinoceratops according to a study byScott Sampson e.a. in 2010.[12]
Arrhinoceratops lived in a wet coast-land with warm summers but cool winters. It was likely preyed upon byAlbertosaurus.[8]
Arrhinoceratops, like all ceratopsians, was aherbivore. During the Cretaceous, flowering plants were "geographically limited on the landscape", and so it is likely that this dinosaur fed on the predominant plants of the era: ferns, cycads and conifers. It would have used its sharp ceratopsian beak to bite off the leaves or needles. Itshabitat was densely forested.[8]
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