ARTICLE

Implications of finding a ceratopsian horncore in the Danekbonebed1

Philip J. Currie and Eva B. Koppelhus

Abstract: In connection with the excavation of the Danek Bonebed in 2011, a half-metre long, well preserved right ceratopsianorbital horncore was recovered. The horncore belongs to the taphonomic group of larger, heavier elements from the bonebed.So far, no other ceratopsian elements have been identified from the bonebed. Ceratopsids from the Horseshoe Canyon Forma-tion of southern Alberta include Anchiceratops, Arrhinoceratops, Eotriceratops, and Pachyrhinosaurus. The size, proportions, andgently anterolaterally procurving morphology of the horncore indicates that it is from a chasmosaurine ceratopsid. There isweak morphological information to suggest that it may represent Anchiceratops ornatus, which is the most common chasmosau-rine at this stratigraphic level. The base of the specimen has been hollowed out by a sinus system, which in conjunction with itslarge size indicates it is probably from a mature animal. The rarity of ceratopsian remains in this and other hadrosaur bonebedssuggests horned dinosaurs were excluded from anywhere that was occupied by herds of large numbers of Edmontosaurus.

Résumé : Un cornillon orbital droit de cératopsien bien préservé d’un demi-mètre de long a été récupéré en lien avec l’excavation dulit a ossements de Danek en 2011. Le cornillon appartient au groupe taphonomique des éléments relativement plus imposants etlourds issus du lit a ossements. À ce jour, aucun autre élément provenant de cératopsien n’a été identifié de ce lit a ossements. Lescératopsidés de la Formation de Horseshoe Canyon du sud de l’Alberta comprennent Anchiceratops, Arrhinoceratops, Eotriceratops etPachyrhinosaurus. La taille, les proportions et la morphologie légèrement procourbée antérolatéralement du cornillon indiquent qu’ilprovient d’un cératopsien chasmosauriné. Des renseignements morphologiques suggèrent vaguement qu’il pourrait s’agird’Anchiceratops ornatus, qui est le chasmosauriné le plus répandu a ce niveau stratigraphique. La base du spécimen a été vidée par unréseau sinusal, ce qui, combiné a sa grande taille, indique qu’il provient probablement d’un individu mature. La rareté des restes decératopsiens dans ce lit, ainsi que dans d’autres lits a ossements d’hadrosaures semblables donne a penser que les dinosaures a cornesétaient exclus des endroits occupés par de grands troupeaux d’Edmontosaurus. [Traduit par le Rédaction]

IntroductionThe Danek Bonebed (Royal Tyrrell Museum of Palaeontology local-

ity number TMP L2379) is dominated by the bones of Edmontosaurusregalis, of which there were at least 12 individuals (Bramble et al.2014). Tyrannosaurids are also relatively common, mostly becauseof teeth that were shed when the hadrosaur carcasses were beingscavenged. Other dinosaurs (ceratopsids, dromaeosaurids, orni-thomimids, troodontids) are poorly represented in the bonebedby a few isolated elements, which suggests that their remains mayhave been fortuitously washed into the deposit from farther awaythan the hadrosaurid and tyrannosaurid remains. Nevertheless,their remains are no more worn than those of Edmontosaurus, andconsequently were probably not transported any great distances;presumably the ceratopsian inhabited the same geographic re-gion as Edmontosaurus regalis.

In 2011, a half-metre long, well preserved right ceratopsian orbitalhorncore (UALVP 53301) was recovered from the central region of thebonebed. To date, it is the only ceratopsian element recovered fromthis site. Ceratopsids from the Horseshoe Canyon Formation of south-ern Alberta include Anchiceratops, Arrhinoceratops, Eotriceratops, andPachyrhinosaurus. A different species of Edmontosaurus (Edmontosaurusannectens) has been recovered from the overlying Scollard Formation,which also produces the remains of Triceratops in southern Alberta. Thesize, proportions, and gentle anterolateral curvature of the horncore

indicates that it is from a chasmosaurine ceratopsid; Pachyrhinosaurusis a centrosaurine and thus can be excluded from further con-sideration. Although Edmontosaurus regalis has never been re-covered from the same quarry as either Anchiceratops ornatus orArrhinoceratops brachyops, all three genera are recovered from overlap-ping stratigraphic levels (Fig. 1). Eotriceratops is only known from onespecimen that came from a higher stratigraphic level than anyknown specimen of Edmontosaurus regalis.

Institutional abbreviationsAMNH, American Museum of Natural History, New York, USA;

CMN, Canadian Museum of Nature, Ottawa, Ontario, Canada; ROM,Royal Ontario Museum, Toronto, Ontario, Canada; TMP, Royal Tyr-rell Museum of Palaeontology, Drumheller, Alberta, Canada; UALVP,University of Alberta Laboratory for Vertebrate Paleontology, Ed-monton, Alberta, Canada.

DescriptionUALVP 53301 (Fig. 2) was recovered from the central region of

Quarry 2 in the Danek Bonebed and was assigned the coordinates“N.6, 38.2”. Like the associated hadrosaur bones, the horncoredoes not show any sign of predepositional weathering. The factthat the thin-walled base of the horncore was preserved intactsuggests that it was probably not exposed for long before it was

Received 21 March 2014. Accepted 26 May 2014.

Paper handled by Associate Editor Andrew Farke.

P.J. Currie and E.B. Koppelhus. Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.Corresponding author: Philip J. Currie (e-mail: philip.currie@ualberta.ca).1This article is part of a Special Issue entitled “The Danek Edmontosaurus Bonebed: new insights on the systematics, biogeography, and palaeoecology of LateCretaceous dinosaur communities”.

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Can. J. Earth Sci. 51: 1034–1038 (2014) dx.doi.org/10.1139/cjes-2014-0065 Published at www.nrcresearchpress.com/cjes on 15 December 2014.

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buried and was probably not transported any significant distance.Because of the nature of the entombing sediments, however, it iscrushed lateromedially and has been fractured every few centime-tres. Anterior, dorsal, and posterior margins of the orbit are pre-served, and the orbit was 82 mm long anteroposteriorly. Althoughthe ventral margins of the orbit are not preserved, the preservedposterior margin of the orbit is 90 mm high and shows that theorbit was taller than it was anteroposteriorly long. The tip of thehorncore is 490 mm from the dorsal orbital margin, and the an-terior edge of the horncore measures 540 mm along the curve.The base of the horn has a maximum anteroposterior diameter of190 mm, but its maximum width is less than 75 mm. The basalcircumference is 445 mm. The taphonomic histories of bones inthis quarry (Baert et al. 2014) suggests that the length of the horn-core and the anteroposterior basal diameter are close to what theywould have been when the animal was alive, but that laterome-dial width of the horn is less than half of what it should be. Inanterior view, the horncore appears flattened (Fig. 1C), whereas inthe living animal it was probably circular in section as in Anchiceratops(Sternberg 1929) and Arrhinoceratops (Parks 1925). The size of thehorncore, when compared with other long-horned chasmosau-rines, suggests that the basal skull length (rostrum to occipitalcondyle) of the specimen would have been about 80 cm.

The specimen includes most of the postorbital bone (Brown andSchlaikjer 1940; Dodson et al. 2004), plus large parts of the rightfrontal and palpebral. These identifications are inferred because thesutures between the three bones have been obliterated by fusion.The fusion suggests that this was a relatively mature individualwhen it died, although these sutures tend to be obliterated beforematurity in chasmosaurines. The supracranial cavity extendedlaterodorsally into a cornual sinus (Forster 1996) that hollowedout the base of the horncore. This sinus penetrates to about 15%the length of the horncore and forms a vaulted dome near the

Fig. 2. Right orbital horncore (UALVP 53301) from the DanekBonebed in (A) lateral, (B) medial, (C) anterior, and (D) ventral views.White dots in A mark the edge of the orbit. Scale bar = 10 cm.acs, anterior cornual sinus; pcs, posterior cornual sinus; orb, orbit.

Table 1. Measurements of basal circumference versus length of thepostorbital horncore of chasmosaurines used to generate Fig. 3.

Genus Species Specimen No. x y

Agujaceratops mariscalensis UTEP P.37.7.082† 279 306Anchiceratops ornatus CMN 08535 350 310Anchiceratops ornatus UALVP 53301 445 490Anchiceratops ornatus TMP 1984.12.16* 443 600Anchiceratops ornatus TMP 1983.1.1‡ 447 600Anchiceratops ornatus ROM 802 425 620Anchiceratops ornatus UW 2419 484 672Chasmosaurinae indet. SMNH P2613.1* 117 64Chasmosaurinae indet. SMNH P2299.1* 170 88Chasmosaurinae indet. AMNH 5006* 171 117Pentaceratops sternbergii NMMNH P.21098* 294 378Torosaurus utahensis USNM 16169* 612 710

Note: All measurements were logarithmically transformed and produced theequation log y = 1.6292(log x) – 1.5702, with an R2 value of 0.954. The allometriccoefficient (1.6292) shows that there is strong positive allometry of horn lengthwhen compared with its basal circumference. x, basal circumference of horncore; y,length of horncore (measured from dorsal margin of the orbit to the tip of thehorncore).

*Data from Farke (2006).†Data from Mallon and Holmes (2010).‡Data from Lehman (1982).

Fig. 1. Stratigraphic relationships of Horseshoe Canyon andScollard Formation specimens of Edmontosaurus and chasmosaurineceratopsians from southern Alberta. Derived from Eberth andBraman (2012) and Eberth et al. (2013).

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centre of the horncore as in TMP 1984.12.16 (Farke 2006) and isetched by shallow neurovascular impressions. The degree of pen-etration into the base of the horn is more extensive than it is inTMP 1984.12.16 (Farke 2006), but it is less extensive than largerspecimens of Torosaurus and Triceratops (Hatcher et al. 1907; Farke2006). The degree of resorption of bone in the base of the horncoreis probably another sign of maturity (Tokaryk 1997; Lehman 1998;Farke 2006; Scannella and Horner 2010). As in Eotriceratops (Wuet al. 2007) and Triceratops (Lull 1933; Forster 1996; Farke 2006), thecornual sinus is divided into anterior and posterior sinuses by awell-developed anterolateral-posteromedial septum that is morethan 35 mm high. The anterior cornual sinus is 200 mm long; thewidth of 80 mm has almost certainly been reduced in size by latero-medial crushing. The posterior cornual sinus is posterior to the orbit,105 mm long anteroposteriorly, 50 mm wide, and penetrates only ashort distance into the posterior third of the base of the horncore.The roof of the orbit (formed by postorbital and frontal) has beendeformed so that it is oriented more laterally than ventrally. Thedeformation and crushing reduced the distance between the dorsalorbital margin and the lateral edge of the frontal fontanelle (the exitof the supracranial cavity) to 100 mm. The interfrontal suture is notpreserved.

The horncore curves anterodorsally, has a concave anteriormargin in lateral view (Figs. 2A, 2B), and has a convex posterioredge. The lateral surface of the horncore is shallowly concavesuggesting it also would have curved dorsolaterally from the or-bit. However, in anterior view, the curvature has been reduced bycrushing; the basal region curves somewhat laterally, whereas thedistal half curves medially (Fig. 2C).

The outer surface of the horncore is covered with shallow, lon-gitudinal grooves for blood vessels. Most are approximately 1 mmin width. The outer surface of the base of the horncore is rugose,whereas both the roof of the orbit and the floor of the supracra-nial cavity are relatively smooth.

Two sets of comparative measurements were used to producebivariate regressions. A comparison of the basal circumferenceversus the length of the postorbital horncore (Table 1; Fig. 3)shows that chasmosaurine horns grew with strong positive allom-etry. When regressions are done comparing anteroposterior basallength (Table 2) with horncore length in chasmosaurines, UALVP

Table 2. Measurements of anteroposterior length of the base versus lengthof the supraorbital of chasmosaurine horncores used to generate Fig. 4.

Genus Species Specimen No. x y

Anchiceratops ornatus UALVP 53301 190 490Agujaceratops mariscalensis UTEP P.37.7.083* 55 140Agujaceratops mariscalensis UTEP P.37.7.090* 67 145Agujaceratops mariscalensis UTEP P.37.7.043* 70 153Agujaceratops mariscalensis UTEP P.37.7.079* 88 175Agujaceratops mariscalensis UTEP P.37.7.044* 78 190Agujaceratops mariscalensis UTEP P.37.7.091* 82 205Agujaceratops mariscalensis UTEP P.37.7.042* 105 273Agujaceratops mariscalensis UTEP P.37.7.082* 94 306Agujaceratops mariscalensis UTEP P.37.7.086* 126 350Chasmosaurus russelli UALVP 052613 22 19Chasmosaurus belli TMP 1981.16.499† 39 50Chasmosaurus belli TMP 1979.14.813† 47 69Chasmosaurus belli AMNH 5402† 60 70Chasmosaurus belli ROM 0839 (5436) 85 108Chasmosaurus belli TMP 1967.17.005† 66 115Chasmosaurus belli TMP 1981.23.024† 61 127Chasmosaurus russelli TMP 1981.19.175 94 130Chasmosaurus belli CMN 02280 86 134Chasmosaurus belli UALVP 000040 78 186Chasmosaurus belli TMP 1979.14.814† 116 240Chasmosaurus belli TMP 1979.11.147 123 260Mojoceratops perifania CMN 01254† 105 216Mojoceratops perifania AMNH 5401 111 370Pentaceratops sternbergii OMNH 10165‡ 260 900Triceratops prorsus YPM 1822 195 550Triceratops sp. UCMP 154452 26 39Triceratops sp. USNM 001201 310 740Triceratops sp. SMNH P.2623.1§ 51 65Triceratops sp. SMNH P.2299.1§ 61 95

Note: All measurements were logarithmically transformed and trendlineswere produced for Agujaceratops, Chasmosaurus, and Triceratops. Points not tiedinto the allometric equations and trendlines include Anchiceratops, Mojoceratops,and Pentaceratops. Allometric coefficients show there is strong positive allometryof horn length in chasmosaurines when a postorbital horncore is comparedwith its anteroposterior basal length in any allometric series. x, anteroposteriorlength of base of horncore; y, length of horncore (measured from dorsal marginof the orbit to the tip of the horncore).

*Data from Lehman (1982).†Data from Godfrey and Holmes (1995).‡Data from Lehman (1993).§Data from Tokaryk (1997).

Fig. 3. Regression of basal circumferences versus length of the postorbital horncores of chasmosaurines (data from Table 1). All measurementswere logarithmically transformed. The allometric coefficient (1.6292) shows that there is strong positive allometry of horn length when comparedwith its basal circumference. Arrow points to UALVP 53301.

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53301 shows proportions comparable for its size to Chasmosaurus,Pentaceratops, and Triceratops (Fig. 4).

DiscussionCeratopsids from the Horseshoe Canyon Formation of southern

Alberta include Anchiceratops, Arrhinoceratops, Eotriceratops, andPachyrhinosaurus. UALVP 53301 is clearly not Pachyrhinosaurus,which is a centrosaurine that lacks orbital horns (Sternberg 1950;Currie et al. 2008). Eotriceratops (Wu et al. 2007) is a much largeranimal from a higher level (the Carbon Member) of the HorseshoeCanyon Formation (Eberth and Braman 2012). Only a single spec-imen is known from this member (and it has not been found inlower members of the Horseshoe Canyon Formation), but it rep-resents the only identifiable ceratopsian remains from the CarbonMember. The fact that it is a more derived ceratopsian that isclosely related to Triceratops suggests that it is unlikely to be re-covered from lower stratigraphic levels where other chasmosaurineswere common. This leaves two possible candidates (Anchiceratops,Arrhinoceratops) for identifying the ceratopsian from the DanekBonebed, assuming that it does not represent a new taxon.

Arrhinoceratops brachyops was described on the basis of a speci-men from the Horseshoe Canyon Formation along the Red DeerRiver, ROM 796 (Parks 1925; Tyson 1981). The postorbital horn-cores of ROM 796 are round in cross-section and stout. The lengthalong the strongly convex upper margin is 555 mm, whereas it is460 mm along the concave ventral margin. The length of thehorncore from roof of the orbit to the tip is approximately520 mm, whereas the circumference of the base is 425 mm (Parks1925). The ratio of horn length to basal circumference is 1.22,whereas that of UALVP 53301 is 1.10. The orbital horncore is cov-ered with shallow vascular impressions such as those found in allceratopsids. However, in addition there is a shallow longitudinalsulcus on the anterior surface (Parks 1925) that extends halfwaydown the horncore from the tip. The orbit is about 25% taller thanits anteroposterior length, as it is in UALVP 53301 and at least onespecimen (AMNH 5251) of Anchiceratops. The orbit is below theanterior third of the base of the postorbital horncore. The curvatureof the orbital horncore (Tyson 1981) is visibly stronger than that ofUALVP 53301 and most known specimens of Anchiceratops. How-

ever, this is a character that is probably variable between individ-uals, just as it is in other ceratopsians (Dodson et al. 2004). Thevagarities of post-depositional variation compound this problem.

Anchiceratops is the most common chasmosaurine known fromthe Horseshoe Canyon Formation (Mallon et al. 2011), and it hasbeen recovered from at least the Horsethief, Morrin, and TolmanMembers (Eberth and Braman 2012). Arrhinoceratops is knownfrom two good specimens from the upper level of the HorsethiefMember (Mallon et al. 2014), but other possible specimens mayextend the range down into the Drumheller Member (Eberth andBraman 2012). The Danek Bonebed is probably in the HorsethiefMember (D.A. Eberth, personal communication, 2013), so strati-graphic distribution does not help in determining whether it islikely Anchiceratops or Arrhinoceratops.

Mallon et al. (2011) make a strong case for all specimens ofAnchiceratops belonging to a single species (Anchiceratops ornatus).UALVP 53301 falls within the range measurements for knownspecimens of this species, which has relatively gracile, procurvedhorns (Sternberg 1929; Mallon et al. 2011). The horncore of theparatype of Anchiceratops ornatus (AMNH 5259) is 600 mm from thedorsal margin of the orbit to the tip, and the base is 150 mm inanteroposterior diameter (Brown 1914). The anterior third of thepostorbital horncore is positioned above the orbit.

Mallon et al. (2011) described a shallow depression (35 mm across)inside the right orbit of the holotype of Anchiceratops ornatus (AMNH5251), which may communicate anterolaterally with the orbit (Brown1914). Although the inner (dorsomedial) wall of this depression is notpreserved in UALVP 53301, the curvature of the edge of the depres-sion or opening on the ceiling of the orbit shows this feature waspresent.

ConclusionsAssuming that UALVP 53301 does not represent a new taxon, it

can be identified as either Anchiceratops ornatus or Arrhinoceratopsbrachyops. Both taxa have been recovered from equivalent parts ofthe Horseshoe Canyon Formation 200–300 km south of the DanekBonebed. There are presently no diagnostic features known in thepostorbital horncore that can be used to separate these taxa,which also have horncores of the same approximate size. How-

Fig. 4. Anteroposterior length of the base versus length of the supraorbital of chasmosaurine horncores (data from Table 2). Allmeasurements were logarithmically transformed and trendlines were produced for Agujaceratops (squares), Chasmosaurus (diamonds), andTriceratops (X). Points that are not tied into the allometric equations and trendlines include Anchiceratops (circle, arrow points to UALVP 53301)and Pentaceratops (triangle). Allometric coefficients show there is strong positive allometry of horn length in chasmosaurines when apostorbital horncore is compared with its anteroposterior basal length in any allometric series.

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ever, the horncore of Arrhinoceratops is not like that of UALVP53301 in that it is more strongly curved, has a distinct sulcus on itsanterior edge, and has a circular cross-section at the base. Further-more, Anchiceratops is relatively more common (at least it is up-stream from Drumheller on the Red Deer River), and it has adepression or opening in the roof of the orbit that appears to bepresent in UALVP 53301. For these reasons, the specimen from theDanek Bonebed is tentatively identified as Anchiceratops ornatus.

UALVP 53301 is the only ceratopsian fossil known from theDanek Bonebed, which may suggest that these animals were notcommon in the region. However, it is perhaps more likely thatceratopsians were excluded by the number of Edmontosaurus in thearea at around the time of death and burial. Langston (1975) re-ported possible Anchiceratops postorbital horncore fragmentsfrom coeval beds at Scabby Butte in southern Alberta. They wereassociated with Edmontosaurus in a bonebed composed mostly ofPachyrhinosaurus remains.

AcknowledgementsThe research on UALVP 53301 would not have been possible

without the help of all the students and volunteers who excavatedand prepared the Danek Bonebed material. We would also like tothank Robert Holmes (University of Alberta) and Michael Ryan(Cleveland Museum of Natural History) for discussions and advice.Reviews by Jordan Mallon (Canadian Museum of Nature) and ananonymous reviewer greatly improved this paper. Clive Coy didan expert job preparing UALVP 53301, which was found by thesecond author.

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1038 Can. J. Earth Sci. Vol. 51, 2014

Published by NRC Research Press

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