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Lucas, S. G. and Sullivan, R.M., eds., 2006, Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35.

ANASAZISAURUS, A HADROSAURIAN DINOSAUR FROMTHE UPPER CRETACEOUS OF NEW MEXICO

SPENCER G. LUCAS1, JUSTIN A. SPIELMANN1, ROBERT M. SULLIVAN2, ADRIAN P. HUNT1 AND TERRY GATES3

1New Mexico Museum of Natural History and Science, 1801 Mountain Road N. W., Albuquerque, NM 87104; 2State Museum of Pennsylvania, 300 North St.,Harrisburg, PA 17108; 3Utah Museum of Natural History, 1390 E. President’s Circle, Salt Lake City, Utah 84112

Abstract—We redescribe and illustrate the completely prepared holotype skull of Anasazisaurus horneri, a hadrosauriandinosaur from the Upper Cretaceous (Kirtlandian, Campanian) Kirtland Formation, San Juan Basin, New Mexico.The validity of Anasazisaurus horneri rests on its distinctive, posteriorly-projecting nasal crest, which distinguishes itfrom other hadrosaurines. Skull material that overlaps with Kritosaurus reveals similarities, but a paucity of equiva-lent material prevents definitive comparisons.

INTRODUCTION

In 1993, Hunt and Lucas named a new hadrosaurian dinosaur,Anasazisaurus horneri, from the Upper Cretaceous Kirtland Formation inthe San Juan Basin, New Mexico. In the decade that has ensued, the taxo-nomic status of A. horneri has been uncertain, some workers consideringit to be a junior synonym of Kritosaurus navajovius (Brown, 1910),whereas others have regarded it as a valid, distinct genus. Part of this un-certainty has stemmed in part from the fact that no complete descriptionand adequate illustrations of A. horneri have been published (Fig. 1), andthat the specimen had not been fully prepared until recently. Furthermore,a lack of knowledge of the structure of the nasals in the type specimen ofKritosaurus navajovius also added to the uncertainty. Here, we provide amore thorough description and illustrations of the holotype of A. horneriafter complete preparation of the fossil. Comparison to the type specimenof K. navajovius affords little diagnostic information, therefore we con-tinue to provisionally consider A. horneri a distinct taxon. Institutionalabbreviations: AMNH–American Museum of Natural History, New York,New York; BYU–Brigham Young University, Provo, Utah.

PREVIOUS STUDIES

In 1977, one of us (SGL) discovered an incomplete hadrosaur skullin the Kirtland Formation on the northwestern flank of Betonnie TsosieWash in the San Juan Basin, New Mexico (locality 4 of Rigby, 1981, text-fig. 5.2; SE1/4 sec. 8, T22N, R9W, San Juan County). This locality is inthe Farmington Member of the Kirtland Formation, and is of Kirtlandian(Campanian) age, a little older than 73 Ma (Lucas and Sullivan, 2000;Sullivan and Lucas, 2003, 2006). In 1979, the skull was collected by afield party from Brigham Young University and catalogued as BYU 12950.

Jack Horner subsequently borrowed the specimen and illustrated itfor the first time (Horner, 1992, pl. 45) (Fig. 1). Although he did not de-scribe the skull in detail, Horner (1992, p. 14) drew attention to salientfeatures that he felt justified identifying it as Kritosaurus navajovius.

Nevertheless, Hunt and Lucas (1993) argued that the holotype ofKritosaurus navajovius is not diagnostic, so the taxon is a nomen dubium.Therefore, they created the new taxon Anasazisaurus horneri for BYU12950, diagnosing it as “a hadrosaurid that can be distinguished from allothers by possessing a short, posteriorly folded nasal crest that is above thelevel of the frontals but does not extend posterior to the anterior end of thefrontal” (Hunt and Lucas, 1993, p. 80). Hunt and Lucas (1993) did notdescribe BYU 12950, and their only illustration of the specimen was asimple line drawing (Fig. 2).

Williamson (2000, fig. 7) provided the first photographic illustra-tions of the holotype of Anasazisaurus horneri. He considered Kritosaurusnavajovius to be a valid taxon, and judged A. horneri to be a junior subjec-tive synonym.

Horner et al. (2004, p. 439) treated Anasazisaurus horneri as avalid, distinct taxon and regarded Kritosaurus navajovius as a nomen du-

bium, but at the same time accepted Naashoibitosaurus (Hunt and Lucas,1993) as representative of K. navajovius. The only comment they maderelevant to the A. horneri–K. navajovius debate is that “little can be saidabout the relationships of Kritosaurus navajovius and Anasazisaurushorneri… They are diagnostic at the species level, but are currently tooincompletely known to allow placement within the context ofeuhadrosaurian phylogeny.”

FIGURE 1. Holotype skull of Anasazisaurus horneri, BYU 12950, in A, left lateraland B, dorsal views, and part of the dentary tooth battery in C, medial view. Modifiedfrom Horner (1992)

294SYSTEMATIC PALEONTOLOGY

Family HADROSAURIDAESubfamily Hadrosaurinae

Genus Anasazisaurus Hunt and Lucas, 19931992 Kritosaurus (in part): Horner, p. 141993 Anasazisaurus: Hunt and Lucas, p. 802000 Kritosaurus (in part): Williamson, p. 2002004 Anasazisaurus: Horner, Weishampel, and Forster, p. 439

Type species–Anasazisaurus horneri Hunt and Lucas, 1993.Included species–Known only from the type species.Distribution–Upper Cretaceous (Kirtlandian, Campanian) of the

San Juan Basin, New Mexico.Revised Diagnosis–A hadrosaurine most similar to Kritosaurus

navajovius but distinguished from it by possessing a short, rugose dorsalcrest of the nasals that extends posteriorly to a position above the middleorbit.

Anasazisaurus horneri1992 Kritosaurus navajovius: Horner, p. 14, pl. 451993 Anasazisaurus horneri: Hunt and Lucas, p. 80, fig. 72000 Kritosaurus navajovius: Williamson, p. 200, fig. 72004 Anasazisaurus horneri: Horner, Weishampel, Forster, p. 439

Holotype–BYU 12950, incomplete skull plus part of the right lowerjaw, including part of the coronoid process, right dental tooth battery andpredentary (Horner, 1992, pl. 45; Hunt and Lucas, 1993, fig. 7; Williamson,2000, fig. 7) (Figs. 1-4).

Horizon and locality of holotype–Farmington Member of KirtlandFormation, northwest flank of Betonnie Tsosie Wash, SE1/4, sec. 8, T22N,R9W, San Juan County, New Mexico.

Revised diagnosis–Same as for the genus.

DESCRIPTION

BYU 12950 is an incomplete skull and parts of the lower jaw of alarge hadrosaurine. Viewed dorsally the anterior portion of the skull is verynarrow. The skull reaches its maximum width above the posterior marginof the orbit. The lower jaw consists of the predentary, a fragment of theright coronoid process and part of the dentary tooth battery, which hasbeen displaced dorsally immediately ventral to the right orbit and lateraltemporal fenestra (Figs. 3-4). Williamson (2000, fig. 7) illustrated the coro-noid fragment and predentary; the morphology of these fragments is iden-tical to that of other hadrosaurines. The preserved portion of the dentaltooth battery consists of 22 tooth rows with a total length of 268 mm andalso is like that of other hadrosaurines.

The maximum length of the preserved skull (from the broken ante-rior tip of the premaxilla to the posterior end of the squamosal) is ~900mm. The maximum anteroposterior diameter of the orbit is 175 mm. Theestimated maximum width of the skull above the posterior margin of theorbit is ~360 mm. The depth of the skull from the top of the narial crest tothe ventral edge of the maxilla is ~440 mm.

The skull is missing the anterior end of the premaxilla so that theanterior portion of the external nares is not preserved. The dorsal premax-illa process forms the midline of the anterior region of the skull and isflanked laterally by the nasals. They project nearly half the length of thenasals. The lateral premaxilla process is quite wide, more so than mostother species of hadrosaur, with the possible exception of Kritosaurus. Thelateral process forms most of the ventral margin of the external nares, whichare oval and narrow because of the large size of the lateral process. Thetermination of the lateral premaxilla process is obscured, but it overlaps thelacrimal as in other hadrosaurines. The lacrimal is a long triangular bone

that borders the prefrontal, the anterior margin of the orbit, the anteriorprocess of the jugal, and, ventrally, the maxilla. A large rugosity on theventrolateral region of the orbit may be formed by the lacrimal or the pre-frontal, but is also obscured by matrix.

Most of the external surface of the maxilla is exfoliated, but it is arobust trapezoidal bone. A prominent rounded lateral ridge rises from thebase of the premaxillary shelf, dominating the anterior half of the maxilla.This ridge is positioned at the most lateral region of the maxilla and elimi-nates the typical horizontal depression,or “step”, seen in hadrosaurine max-illae that held the premaxilla lateral process. The ridge terminates posteri-orly at the dorsal process, which is a robust feature mostly hidden fromview. The ectopterygoid shelf drops dramatically posterior to the dorsalprocess. It is not level as in other taxa but instead slopes ventrally for mostof its length before planing off a few centimeters above the tooth row. Theectopterygoid ridge is not strong as in the cf. Kritosaurus specimen de-scribed by Kirkland et al. (this volume). The jugal articulation on the max-illa has been eroded slightly; therefore, its exact position is difficult to de-termine. Still, it appears that the jugal resided low on the skull.

The jugal has been broken and displaced posteroventrally, but resto-ration to its original position indicates it has a relatively thin postorbitalprocess ascending at 90º to contact the postorbital and form the posteriormargin of the orbit. The anterior jugal is robust and dorso-ventrally ex-panded with large prominent protuberances both dorsally and ventrally.There is a distinct, blunt jugal process that projects ventrally from its poste-rior ramus.

The orbit is subtriangular in outline and extremely large. The pre-frontal is a rugose arc of bone that forms the anterodorsal margin of theorbit. It articulates with the lacrimal ventrally and the nasals anteriorly, butthis latter contact, unfortunately, cannot be seen. The relationship betweenthe prefrontal, postorbital, and frontal is also contentious. We estimate thatthe prefrontal articulates with the postorbital posteriorly, eliminating thefrontals from the orbital rim. If this is the condition seen in Anasazisaurus,then it shares this character with Kritosaurus (Naashoibitosaurus of Horner

FIGURE 2. Holotype skull of Anasazisaurus horneri, BYU 12950, in left lateral(above) and dorsal (below) views. From Hunt and Lucas (1993). Abbreviations: F= frontal , J = jugal, L = lacrimal, M = maxilla, N = nasal, P = parietal, PO =postorbital, PF = prefrontal, PM = premaxilla, SQ = squamosal.

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FIGURE 3. The fully prepared holotype skull of Anasazisaurus horneri, BYU 12950 in A, right lateral and B, dorsal views, C-D, close-ups of the narial crest in C, rightlateral and D, dorsal views.

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FIGURE 4. Line drawings of the holotype skull of Anasazisaurus horneri, BYU 12590 in A, right lateral and B, dorsal views. Black areas are holes in the originalspecimen, crosshatched areas indicate matrix, and stippled areas indicate opening in the skull. Abbreviations: en = external nares, f = frontal , j = jugal, l = lacrimal, ltf =lateral temporal fenestra, m = maxilla, n = nasal, o = orbit, p = parietal, po = postorbital, pf = prefrontal, pm = premaxilla, sq = squamosal, stf = supratemporal fenestra,tb = tooth battery.

297et al., 2004) and Prosaurolophus. The postorbital forms the posterodorsalmargin of the orbit and the dorsal margin of the lateral temporal fenestra.The squamosal process of the postorbital is broad and thick. It spans thelong dorsal margin of the lateral temporal fenestra to contact the squamo-sal.

The squamosal and parietal are poorly preserved. The squamosalhas a similar morphology to that of Gryposaurus. The precotyloid processis robust and curved anteroventrally. The postcotyloid process is deep andextends lateroventrally. The quadrate cotylus is concealed by matrix. Theparietal articulates with the frontal anteriorly. The interfrontal process isobscured but does not appear to be a large feature. Anterolaterally, the pari-etal contacts the medial portion of the postorbital. Contact with thelaterosphenoid is observed ventrally. The supratemporal fenestrae are longand ovoid. The infratemporal fenestrae, though not fully preserved, wouldhave been quite large.

The nasals expand posteriorly from the tip of the narrow anteriorprocess to form a broad, axe shaped bone, superficially similar toGryposaurus. The ventral margin articulates with the premaxilla lateralprocess and the lacrimal. Posteriorly, the prefrontal contacts the nasal. Im-portantly, the nasals contact the frontals along the posterior midline in anapparently concave rounded suture that retracts a small process into thenasals along the midline. The exact details of this suture are difficult todiscern, and better preserved material is required to obtain a more detaileddescription. Along the midline, the nasals rise dorsally approximately 2/3along their length to form a rugose ridge that extends nearly to their poste-rior margin. The terminus of this ridge is marked by a lateral flare andsubsequent extension of a crestal lip or vestibule over the remaining por-tion of the nasal. The ridge terminates at the frontal-nasal contact, aboutthe mid-point of the orbit. This nasal ornamentation is distinct fromGryposaurus in that it lies higher on the nasals, and it consists of a laterallyexpanded but relatively low lip structure, as opposed to the mediolaterallycompressed midline bump of Gryposaurus (Horner, 1992). Prosaurolophus(Horner, 1992) and Lophorothon (Langston, 1960) both have solid raisedpyramidal nasal ornamentation near the level of the orbit, though the crestof Lophorothon is positioned anterior to the orbits, while Prosaurolophusand Anasazisaurus share an equivalent position dorsal to the orbits. Unfor-tunately, Kritosaurus lacks the nasals so an adequate comparison cannotbe made.

DISCUSSION

The taxonomic validity of Anasazisaurus horneri has been heavilyreliant upon the perceived taxonomic status of Kritosaurus navajovius.Further, the legitimacy of K. navajovius has also long been debated be-cause the holotype (AMNH 5799) apparently lacked the key cranial ele-ments (especially the nasals) used to differentiate many hadrosaurine taxa.

Indeed, the entire nasal region of the holotype of K. navajovius was re-stored in plaster and painted (Williamson, 2000, fig. 6).

Williamson (2000) published photographs and a description of thesupposed nasals of Kritosaurus (see also Hernandez et al., 2003). How-ever, Kirkland et al. (this volume) contradict this and present the samebone fragments illustrated in Williamson (2000) as the lateral portion ofthe right premaxilla. Kirkland et al. (this volume) also present a fragmentthat they interpret as a portion of the posterior nasals, but until the frag-ment is reconstructed more thoroughly or a more complete Kritosaurusskull is found, the validity of this nasal fragment remains to be demon-strated. Therefore, no substantial comparison can be made betweenAnasazisaurus and Kritosaurus based on nasal ornamentation.

There is a great deal of morphological similarity between the typespecimen of Kritosaurus and Anasazisaurus, such as the apparent exclu-sion of the frontals from the orbital rim and the distinctive maxilla, butessential overlapping material like the nasals and the braincase are not avail-able. In addition, the type specimen of K. navajovius, found in the De-na-zin Member of the Kirtland Formation in the San Juan Basin, isstratigraphically higher than the Anasazisaurus holotype locality in theFarmington Member.

A large portion of the skull roof exists for both taxa. However, poorpreservation of the Anasazisaurus type and limited access to the Kritosaurustype, creates difficulties in establishing a link between the two hadrosaurs.Other material referred to Kritosaurus (or Naashoibitosaurus by Horneret al., 2004), that was also found in the De-Na-Zin Member of the Kirtland,demonstrate a rugose ridge similar to that seen in Anasazisaurus, but lacksthe extended lip as in the latter taxa. Horner (1992) stated that these differ-ences may be ontogenetic and, with further growth, the specimens lackingthe crestal vestibule would develop such a structure, but without moremature specimens, this developmental hypothesis cannot be tested. How-ever, similarities such as the nasal ornamentation and the distinctive max-illa shared between Anasazisaurus and Naashoibitosaurus (Kritosaurus)hint at a close relationship between the two taxa, which may eventuallyresult in generic synonymization, leaving two species of Kritosaurus. Yet,given the stratigraphic disparity and the limited amount of morphologicalinformation available from both type specimens, Kritosaurus andAnasazisaurus are considered distinct taxa until more adequate materialfrom both species is recovered.

ACKNOWLEDGMENTS

Wade Miller, Ken Stadtman, Rod Scheetz, and Brooks Britt madestudy and preparation of the holotype specimen of Anasazisaurus horneripossible. George Edgerly and Larry Rinehart undertook the preparation.We thank Jim Kirkland and Dave Evans for many useful conversations,and John Foster and Jim Kirkland for their comments on the manuscript.

REFERENCES

Brown, B., 1910, The Cretaceous Ojo Alamo beds of New Mexico with descriptionof the new dinosaur genus Kritosaurus: Bulletin of the American Museum ofNatural History, v. 28, p. 267-274.

Hernandez, R., Kirkland, J. I., Paul, G. S., Serrano, C. B. and Garcia, J. P., 2003, Alarge hadrosaurine from the Sabinas basin, Coahuila, Mexico: Journal of Verte-brate Paleontology, v. 23, supplement to no. 3, p. 61A.

Horner, J. R., 1992, Cranial morphology of Prosaurolophus (Ornithischia:Hadrosauridae). With descriptions of two new hadrosaurid species and an evalu-ation of hadrosaurid phylogenetic relationships: Museum of the Rockies Occa-sional Paper 3, 119 p.

Horner, J. R., Weishampel, D. B. and Forster, C. A., 2004, Hadrosauridae; inWeishampel, D. B., Dodson, P and Osmólska, H., eds., The Dinosauria secondedition: Berkeley, University of California Press, p. 438-463.

Hunt, A.P., and Lucas, S.G., 1993, Cretaceous vertebrates of New Mexico: NewMexico Museum Natural History and Science Bulletin 2, p. 77-91.

Lucas, S.G., and Sullivan, R.M., 2000, Stratigraphy and vertebrate biostratigraphyacross the Cretaceous-Tertiary boundary, Betonnie Tsosie Wash, San Juan Ba-sin, New Mexico: New Mexico Museum of Natural History and Science, Bulle-

tin 17, p. 95-103.Rigby, J. K., Jr., 1981, A skeleton of Gillisonchus gillianus (Mammalia;

Condylarthra) from the early Paleocene (Puercan) Ojo Alamo Sandstone, SanJuan Basin, New Mexico, with comments on the local stratigraphy of BetonnieTsosie Wash; in Lucas, S. G., Rigby, J. K., Jr., and Kues, B. S., eds., Advances inSan Juan Basin paleontology: Albuquerque, University of New Mexico Press,p. 89-126.

Sullivan, R.M. and Lucas, S.G., 2003, The Kirtlandian, a new land-vertebrate “age”for the Late Cretaceous of Western North America: New Mexico GeologicalSociety, 54th Field Conference, Guidebook, p. 369-377.

Sullivan, R.M. and Lucas, S.G., 2006, The Kirtlandian land-vertebrate “age”—faunal composition, temporal position and biostratigraphic correlation in thenonmarine Upper Cretaceous of western North America: New Mexico Museumof Natural History and Science Bulletin, this volume.

Williamson, T.E., 2000, Review of Hadrosauridae (Dinosauria, Ornithischia) fromthe San Juan Basin, New Mexico: New Mexico Museum of Natural History andScience, Bulletin 17, p. 191-213.

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