THE JORDAN THEROPOD (, , U.S.A.)

REFERRED TO THE

by

Ralph e. MOLNAR* & Kenneth carpenter**

Abstract Résumé

The Jordan theropod is shown to belong to Aublyso- Aublysodon mirandus, un théropode dinosaurien reconnu don mirandus, a theropod previously known only auparavant seulement par des dents isolées. Bien que le crane from isolated teeth. Although the skull is incomplete, it retains soit incomplet, il a conservé de nombreux caractères primitifs numerous primitive characters that set it apart from all other qui le distinguent de tous les autres théropodes reconnus a la known Late theropods. These features include a fin du Crétacé. Ses traits comprennent un museau allongé et long, low muzzle, relatively large teeth, frontals longer than bas, des dents relativement grandes, les frontaux plus longs wide, smooth nasals, V-shaped anterior margin of antorbital que larges, les nasaux lisses, le bord antérieur de la fosse pré- fossa, premaxillary- maxillary suture acutely inclined, and low orbitaire en forme de V, la suture du prémaxillaire vivement angle of symphysis. Aublysodon is characterized by premaxilla­ inclinée au bord ventral et le faible angle ventral de la sym- ry teeth D-shaped in cross section and with posteriorly directed physe. Aublysodon est caractérisé par des dents prémaxillaires carinae, a V-shaped frontoparietal suture, and a peculiar first dont la section est en forme de D et avec des carènes dirigées dentary tooth. It probably possessed small premaxillaries. Au­ postérieurement, une suture fronto-pariétaie en forme de V et blysodon is an aberrant theropod which at this time is best re­ la première des dents du dentaire caractéristique. Il possédait tained in its own family, the Aublysodontidae. probablement de petits prémaxillaires. Aublysodon est consi- déré comme un théropode aberrant qu’il est préférable de maintenir dans sa propre familie, les Aublysodontidae.

KEY-WORDS : DINOSAURIA (), UPPER CRETACEOUS, MONTANA, MAASTRICHTIAN, AUBLYSODONTIDAE. MOTS-CLÉS : DINOSAURIA (THEROPODA), CRÉTACÉ SUPÉRIEUR, MONTANA, MAASTRICHTIEN, AUBLYSODONTIDAE.

* Queensland Museum, Queensland Cultural Centre, South Brisbane, Qld 4101, Australia. ** Museum of the Rockies, Montana State University, Bozeman, Montana 59717, U.SA.

Geobios, n° 22, fasc. 4 p. 445-454, 4 fig., 2 tabl. Lyon, aoüt 1989 - 446 -

I - INTRODUCTION

During the summer of 1966 Harley Garbani, (Museum of its teeth. In addition, it lends credence to the recognition of Natural History, Los Angeles County ; LACM) collected a partial distinctive dinosaurian taxa based on teeth (see also Currie et small theropod skull and jaws from the Hell Creek Formation, alii in press). Montana. This specimen was later described (Molnar 1978) but was not assigned to any taxon below familial level. The skull was designated "the Jordan theropod" in reference to its Collection designations: discovery near Jordan, Montana. AMNH, American Museum of Natural History, New York Ci­ The skull was recovered from a dark grey clay of the Hell ty; Creek Formation on the L.D. Engdahl Ranch, LACM Loc. 7245 ANSP, Academy of Natural Sciences, Philadelphia; (Sec. 34, T.21N, R.36E) (Molnar 1979). It was described as KU, University of Kansas, Lawrence ; representing an individual, possibly juvenile, of an otherwise LACM, Los Angeles County Museum of Natural History, Los unknown genus of large dromaeosaurid (Molnar 1978). Al­ Angeles; though the premaxillae were not preserved, a single premaxil­ NMC, National Museum of Natural History, Ottawa ; lary tooth was found adhering to the left maxilla. It is this ROM, Royal Ontario Museum, Toronto ; tooth, together with Carpenter’s (1982) revision of Leidy’s ge­ TMP, Tyrrell Museum of Palaeontology, Drumheller; nus Aublysodon, which allows the referral of the Jordan thero­ UCM, University of Colorado Museum, Boulder ; pod to Aublysodon, cf. A. mirandus. UCMP, University of California Museum of Paleontology, Berkeley; Such an identification is significant in being one of the few YPM, Peabody Museum of Natural History, New Haven ; instances of the recognition of more complete material pertai­ YPM-PU, Peabody Museum of Natural History-Princeton ning to a dinosaurian taxon known for over a century only from University Collection, New Haven.

II - TAXONOMIC HISTORY

Aublysodon mirandus has a confusing taxonomic history ther or not they were serrate at the posterolateral margins. because it was originally based on teeth now known to include Cope (1869) later defended his restriction of "Dinodon" to the two taxa. These teeth were among the dozen or so collected by teeth of D-shaped cross section, but accepted Aublysodon (as F.V. Hayden in 1854, while exploring the along the Ju­ A. borridus) in the mistaken belief that Dinodon was preoccu­ dith River of north central Montana. The specimens were brie­ pied (Hay 1899). Cope did not accept the name Aublysodon fly described by Leidy in 1856 and figured in I860. The ser­ mirandus (Cope 1876a, 1876b). He (Cope 1869) also ventu­ rate, blade-like teeth and teeth which were D-shaped in cross red the opinion that the blade-like teeth were without a name, section were designated Deinodon borridus. Leidy expressed although he did not propose one. This was left to Hay (1899) doubt that all of the teeth assigned to D. borridus belonged to who proposed the name kenabekides for these a single species, a doubt reaterated in I860 when he described teeth. all of the Judith River teeth in greater detail. Marsh (1892) described two new species of Aublysodon, A. Cope (1866) agreed with Leidy that more than a single spe­ amplus and A. cristatus (which, because of their unusual cies was present among the Deinodon borridus material and form, he felt were probably mammalian). In this paper he restricted the name (as Dinodon) to those teeth that were D- drew attention to the disparity in form of Leidy’s (1856) three shaped in cross section. The blade-like teeth he placed in his figured teeth of D-shaped cross section. Careful reading of his genus (=Dryptosaurus of Marsh). Leidy (1868) disa­ words suggests that he recognized the third unusual premaxil­ greed with Cope and reinstated the name Deinodon for the lary tooth described by Leidy as distinct from the others. blade-like teeth that he felt were distinct from Laelaps. He agreed, however, that those teeth D-shaped in cross section As for the placement of the D-shaped teeth (i.e., Aublyso­ were distinct from the blade-like teeth and proposed the name don mirandus), Leidy speculated that they came from the rear Aublysodon mirandus for them. As initially conceived, this in­ of the maxilla or dentary. Cope (1876b), on the other hand, af­ cluded all teeth of D-shaped cross section regardless of whe­ ter a study of the skull of Laelaps incrassatus (= Dryptosau- - 447 -

rus incrassatus of Lambe 1904 = sarcophagus different taxon. Matthew and Brown (1922) had available to Osborn 1905), concluded that the teeth were from the front of them several of Albertosaurus and agreed with Osborn the jaw. Osborn (1905) decided that the serrate Aublysodon and Hay as to the synonymy of Aublysodon and Deino- teeth were the anterior teeth of Deinodon after a comparative don. They did not, however, distinguish between serrate and study of . He was less certain of the taxonomic sta­ unserrate teeth D-shaped in cross section, nor have most sub­ tus of the single unserrate tooth Leidy had included in Aublyso­ sequent paleontologists (e.g. Sahni 1968). don. Nevertheless, Osborn treathed Aublysodon as a junior sy­ nonym of Deinodon. Hay (1908) agreed, and went so far as to Recently one of us (Carpenter 1982) re-examined the Au- suggest that Deinodon and Albertosaurus sarcophagus might blysodon-Deinodon problem and designated as lectotype of be one and the same. Lambe (1917 came to the same conclu­ Aublysodon mirandus that tooth (ANSP 9535) D-shaped in sion as Osborn, that the serrate teeth of Aublysodon were in cross section and lacking serrations. This action is supported fact the anterior teeth of Deinodon. He was, however, more by the numerous additional isolated teeth referable to the A. certain that the small unserrate Aublysodon tooth was from a mirandus and by our re-examination of the Jordan theropod.

Ill - SYSTEMATIC PALEONTOLOGY

Family Aublysodontidae 80.8.192, 80.16.485, 80.16.1202, 81.16.197, 81.19.79, Aublysodon mirandus Leidy, 1868 82.20.457, 85.6.134, 86.77.122, 86.77.123, 87.36.81, fig. 4A 87.46.24, 88.4.7, (, Dinosaur Provincial Park and adjacent area, Alberta) ; YPM-PU 22252, 23328, Deinodon horridus Leidy, 1856 (in part) 23385, 23389, 23390 (Judith River Formation, Hill County, Dinodon horridus (Leidy) Cope, 1866 (in part) Montana), YPM-PU 23391 (Judith River Formation, Choteau Aublysodon mirandus Leidy, 1868 County, Montana) ; YPM.PU 23387 (Two Medicine Formation, Aublysodon mirandus (LEIDY) Cope, 1869 Teton County, Montana); UCMP 124367, 124399, 124406, Aublysodon amplus Marsh, I892 124978, 124979, 124980, 124981, 124982, 124994 (Hell Aublysodon cristatus Marsh, 1892 Creek Formation, Garfield County and McCone County, Monta­ Ornitbomimus altus Lambe 1902 (in part) na) ; TMP 87.112.33, 87.114.7 (Heli Creek Formation, Monta­ na); UCM 37878, 43447 (, Niobrara County, LECTOTYPE : Wyoming) ; UCMP 73091, 73101, 85141, 124993, 124995, 124996, 125229, 125230, 125233, 125234, 125237 (Lance ANSP 9535, premaxillary tooth ; TMP 85.10.11 (cast of Formation, Niobrara County, Wyoming) ; YPM 296 (holotype of ANSP 9535). Aublysodon ampins'), 297 (holotype of Aublysodon cristatus) (Lance Formation, Niobrara, County, Wyoming) ; UCM 38060 (, Arapahoe County, Colorado) ; KU 12419 locality : (, San Juan County, New Mexico). Currie (1987) has suggested that the frontal, TMP 80,16.485, may al­ Judith River Formation "from the vicinity of the Judith Ri­ so pertain to Aublysodon. ver, one of the tributaries near the source of the Missouri Ri­ ver." (Leidy I860, p. 139).

Revised diagnosis : Referred material : A moderate size theropod apparently with a long, low skull. LACM 28471, partial skull, including a premaxillary tooth, Some (probably premaxillary) teeth D-shaped in cross section most of both maxillae, nasals, and frontals, the parietal and and lacking serrations along the posterolateral and posterome­ portions of the surangular and dentaries (holotype of Aublyso­ dial carinae ; posterolateral carina shifted progressively further don molnaris) (Heli Creek Formation, Garfield County, Monta­ posteriorly, giving the crown a twist, in progressively more late­ na). TMP 87.127.1, cast of frontals and parietal of LACM ral premaxillary teeth. Dentaries slender with a "step" in the 28471. Isolated teeth : NMC 116a, 1822 (Judith River Forma­ alveolar border just posterior to the third tooth ; anteroventral tion, Dinosaur Provincial Park, Alberta) ; TMP 66.31.93, border of dentaries with an acuthe angle relative to alveolar -448-

border. First dentary tooth with anterior carinae displaced me­ half-way down the anterior edge, and to the base of the crown dially, but not D-shaped in cross section. Except for the first on the posterior edge ; anterior serrations finer than posterior dentary tooth, the dentary teeth are laterally compressed ones. blades, as are those of the maxilla. Serrations extend about

IV - DISCUSSION

The discovery of the Jordan theropod, with its unique cra­ a slight slope at the edge of the prefrontal contact surface (the nial features, strengthens the arguments for the distinctiveness dorsal surface adjacent to the postorbital contact is worn). The of Aublysodon mirandus. Although the skull is not from the contact of the frontals at the midline is such that the dorsal Judith River Formation, it has a tooth similar to the type of.

The taxanomic assignment of LACM skull is based on the observed similarity of certain characters, here details of the premaxillary tooth form. While it is recognized that such simi­ larity may arise in unrelated lines in parallel, no such parallel is known in this case. We therefore refer the cranial material to the genus Aublysodon on the basis of an observed similarity, rather than refrain from referring it on the basis of a hypotheti­ cal parallelism.

The recent survey of the frontals of the Judith River thero- pods of Dinosaur Provincial Park (Alberta, Canada) by Currie (1987) exemplifies the taxonomic significance of this element. Thus it is useful to discuss the frontal of Aublysodon in the light of Currie's work. The posterolateral portions of both fron­ tals are missing and the posterior part of the dorsal surface is worn. The frontal is elongate, and probably triangular in out­ Fig. 1 - Frontals and parietal of Aublysodon cf. A .mirandus (LACM line (fig. 1) : the postorbital process is not preserved. The orbi­ 28471) in dorsal view. Diagonal lines indicate regions of damaged or mis­ tal rim is very short, or possibly absent (cf. Molnar 1978). sing bone surface. Scale bar represents 10 mm. While there is nothing further to add to the published descrip­ tion (Molnar 1978) of the prefrontal and postorbital contacts, Lcs frontaux et le parietal d'Aublysodon cf. A. mirandus (LACM the groove ventrally adjacent to that of the prefrontal is here ta­ 28471) en vue dorsale. Les parties des ossements endommagées ou ab- sentes sont hachurées. Echelle = 10 mm. ken to be the lachrymal contact. The lachrymal contact appa­ rently did not encroach onto the dorsal face of the frontal, and it does not split the frontal margin as it does in Dromaeosau- The isolated frontal, NMG 12355, is similar to that of Aubly­ nts albertensis (Currie 1987). The lateral prong of the nasal sodon in outline when viewed from above, in the shape of the extends further posterior over the frontal than the medial (fig. cristae cranii, and in the form and proportions of the contact 1). The posterior margins of the frontal separate at the midline for the nasal. However, it differs in two significant ways. It has to accomodate the anterior process of the fused parietals. The a sutural contact with the prefrontal (Currie 1987) rather than dorsal face is almost flat, with a slight rise at the midline, and -449

a triangular pit or socket and its dorsal surface is longitudinally carinae, they curve toward one another and merge with the low concave (Currie 1987) rather than flat. Thus this frontal does posterior ridge near the base of the crown. In profile, the low not pertain to Aublysodon. posterior ridge is visible from the tip down to three-quarters or one-half the height of the crown. Below this the carinae hide The sample of isolated teeth falls into two categories, with the ridge. many resembling the lectotype tooth, ANSP 9535. At the base of the crown these teeth are longer anteroposteriorly than wide. Many other teeth, however, vary from the lectotype tooth. The anterior face is broadly rounded, and the posterior face is These have lateral (?) carinae displaced posteriorly, sometimes slightly narrower and truncated, producing the characteristic giving the tooth a twisted spatulate appearance (e.g. UCM D-shaped cross section. Along the posterior face is a low, roun­ 43447, see Carpenter 1982). Comparison with tyrannosaurids ded ridge bounded laterally and medially by sharp carinae ; a and Dromaeosaurus albertensis (Colbert & Russell 1969, fig. faint sulcus may separate each carina from the ridge. The cari­ 12) suggests that these teeth occupy a more lateral position in nae emerge near the tip of the crown from the low rounded the premaxilla, with those having the twisted spatulate appea­ ridge on the posterior face. The carinae extend downwards and rance occurring near the premaxillary-maxillary suture. Measu­ are flush with the sides of the crown. Near the midpoint of the rements for all teeth are given in Table 1.

Besides Aublysodon mirandus, four other species have Specimen Number anterioposterior width been named : A. lateralis Cope, A. cristatus Marsh, A. amplus length Marsh and 4. molnaris Paul. Paul (1988) has also referred Shanshanosaitrus huoyanshanensis (Dong 3 977) to the genus KU 12919 11.5 min 11.5 mm Aublysodon. Cope’s (1876b) description of A. lateralis, with its serrate posterior and lateral margins, suggests that this UCM 43447 30 25 tooth is a lateral premaxillary tooth of Dromaeosaurus (see UCM 38OÓO 80 45 Colbert and Russell 1969. On the other hand, A. cristatus Marsh (1892), with its slight twist and spatulate crown, resem­ UCMP 64143 60 45 bles the posterolateral (?) premaxillary tooth of A. mirandus UCMP 7309I 65 4o described above (UCM 43447) ; it is, therefore, synonymized with 4. mirandus. A. amplus is also synonymized with A. mi­ UCMP 73l0l 50 25 randus as the holotype tooth cannot be distinguished from the UCMP 85141 35 25 isolated teeth referred to A. mirandus listed in Table 1. The

UCMP 124367 25 20 faint crenulations reported by Marsh (1892) are apparently chips in the enamel of the carinae, a condition seen in other 4. UCMP 124398 45 25 mirandus teeth, especially those from the Two Medicine For­ UCMP 124971 40 25 mation.

UCMP 124980 30 35 Aublysodon molnaris was proposed by Paul (1988) for the UCMP 129981 35 25 Jordan theropod of Molnar (1978). Paul differentiates the new species essentially on the larger size of its teeth and similarity UCMP 124982 25 20 to undescribed material from the Judith River Formation. Until UCMP 124993 30 20 the latter material is described Paul’s assignment cannot be evaluated, thus here the more conservative course of referring UCMP 124999 45 30 this specimen to Aublysodon cf. A. mirandus is taken. Simi­ UCMP 124995 75 45 larly Paul’s reference of Sbanshanosaurus bouyanshanensis to Aublysodon cannot be properly evaluated without examina­ UCMP 124996 55 10 tion of the specimen. USNM 8355 60 10 Aublysodon premaxillary teeth generally resemble those of the in form, if not in size. They differ, howe­ ver, in having a distinct rounded ridge extending down the Tabl. 1 - Length and width measurements for Aublysotlon mirandus length of an otherwise flat posterior face. Such a ridge is not teeth. found in tyrannosaurid premaxillary teeth, although in some Mesures des longueur et largeur des dents de Aublysotlon mi­ tyrannosaurid taxa this face may be gently convex overall (see randus. Lambe 1917, fig. 10E). - 450 -

Fig. 2 - Cheek teeth of Aubtysodon mirandus. Left sixth maxillary tooth, as preserved, in lateral (A) and posterior (B) aspects. Right fourth dentary tooth, rendered in unworn condition, in anterior (C) and labial (D) aspects. Scale bar represents 10 mm.

Les dents jugales de VAubtysodon mirandus. Sixième dent maxiliaire gauche telle qu’elle est conservée en vue laterale (A) et vue postérieure (B). Quatrième dent du dentaire droit, figurées sans usure en vue antérieure (C) et en vue labiale (D). Echelle : 10 mm.

The maxillary and dentary teeth of Aublysodon are less dis­ the lack of an apex on the denticles ; 3, the presence of the ba­ tinctive than the premaxillary teeth. Both maxillary and dentary sal angulation ; 4, the proportions of the denticles (those of teeth are recurved, trenchant teeth of lenticular cross section being even more squat) ; and 5, denticles of the same (fig. 2). Both anterior and posterior edges of the crown are ser­ size in both anterior and posterior serrations. The denticles of rate. Anterior and posterior serrations are of the same size (13 Aublysodon differ from those of in : 1, the per 5 mm) and form. The denticles are squatly cylindrical in denticles being arranged perpendicular, rather than inclined, form, bluntly rounded, and lack an apex (fig. 3 A, B). The den­ to the edge of the crown ; and 2, denticles of the same size in ticles however do not wear evenly, so that worn denticles do both anterior and posterior serrations. The denticles are most give the impression of an apex directed toward the tip of the similar to those of Dromaeosaurus from which they cannot be crown. The denticles sit perpendicular to the margin of the distinguished in lateral views. Those of Aublysodon are trans­ tooth. Each denticle of the serration is symmetrically lozenge­ versely broader and less rounded when viewed from along the shaped, broader (transversely) than high when viewed along the axis of the denticle (fig. 3C), A distinct angulation at their bases sets them off from the convex lateral and medial faces of the crown (fig. 2). This prominent angulation is seen along both sides of the anterior serrations, but along only one side of the posterior. The anterior serrations tend to be more heavily worn than the posterior.

P. Currie (personal communication) is studying dental morphology of the smaller Upper Cretaceous North American Fig. 3 - Serrations of left sixth maxillary tooth. A, posterior serrations viewed theropods, and through his courtesy we can compare the struc­ from the left; B, anterior serrations viewed from the right; C, posterior ture of the serrations of Aublysodon with that of Troodon, serrations viewed from behind. These serrations are rendered as unworn, Saurornitholestes and Dromaeosaurus. So far information is not as preserved. Scale bar represents 1.5 mm. available only on the form of the serrations of premaxillary teeth for two of the three forms, thus limiting the value of the hes crénelures de la sixième dent maxijlaire gauche. A, crénelures postérieures vues de la gauche ; B, crénelures antérieures vues de la comparison. The denticles of Aublysodon differ from those of droite ; C, les crénelures postérieures vues de l'arrière. Ces crénelures Troodon in : 1, the size of the serrations relative to the size of sont figurées sans usure, non telles qu’elles sont conservées. Echelle = the crown (the ratio being much smaller than in Troodon); 2, 1,5 mm. -451-

Fig. 4 - Comparison of The skulls of A, Aubtysodon ; B, Coelopbysis (AMNB 7224); C, Dromaeosaurus (modified from Coibert & Russell, 1969, Fig. 1); D, Velociraptor (mo­ dified from Barsbold, 1982, Fig. la) ; E, Sauromitboides (modified from Barsbold, 1974, Pl. 1), V, Dromiceiomimus (modified from Russell, 1972, Fig. 5, and ROM 840); G, Caegnatbus (modified from Sternberg, 1949, Fig. 1, and Barsbold, 1982, Fig. c); H, Albeltosaurus libratus (modified from Gilmore, 1946, Pl. 4, Fig. 3); I, torosus (modified from Russell, 1970, Fig. 6) ; J, "Albertosaurus" lancensis (modified from Gilmore, 1946, Pl. 1) ; H, (modified from Osborn, 1912, Fig. 1) ; L, lingual (top) and labial (bottom) views of the dentaries of "Cbirostenotes" (modified from Gilmore, 1924, Fig. 3). Scale bar represents 10 cm. Comparaison des cranes des divers théropodes : A, Aubtysodon ; B, Coelopbysis (AMNB 7224) ; C, Dromaeosaurus (modifiés d’après Colbert & Russell 1969, Fig. 1); D, Velociraptor (modifié d’après Barsbold 1982, Fig. la) ; E, Sauromitboides (modifié d’après Barsbold 1974, Pl. 1) ; F, Dromiceiomimus (modifié d’après Russell 1972, Fig. 5 et ROM 840) ; C, Caenagnatbus (modifié d’après Sternberg 1949, Fig. 1 et Barsbold 1982, Fig. c); H, Albertosaurus libratus (modifié d’après Gilmore 1946, PI. 4, Fig. 3); I, Daspletosaurus torosus (modifié d’après Russell 1970, Fig. 6) ;J, "Albertosaurud' lancensis (modifié d’après Gilmore 1946, Pl. 1); K, Tyran­ nosaurus (modifié d’après Osborn 1912, Fig. 1) ; L, les vues linguale (en haut) et labiale (en bas) des dentaires du "Cbirostenotes" (modifié d’après Gilmore 1924, Fig. 3). Echelle = 10 cm. -452 -

axis of the denticle. If as seems likely from the third genus the comparisons with Troodon and Sauromitbolestes from Dromaeosaurus, the form of premaxillary and maxillary dental knowing the form of only the premaxillary serrations is unlike­ serrations was basically the same, the limitation imposed on ly to be significant.

V - TAXONOMIC POSITION OF AUBLYSODON

With the inclusion of the Jordan theropod material, Aubly- Aublysodon shares with the following primitive soclon is known from premaxillary teeth, anterior portions of characters: muzzle long and low, teeth relatively large, frontals the dentaries (with teeth), maxillae (with teeth), nasals, fron- longer than wide, nasals smooth, anterior margin of antorbital tals, parietals, articular portion of right surangular, and a fossa V-shaped, angle of premaxillary contact with ventral mar­ pair of unidentified cranial elements not described earlier gin acute, ventral angle of symphysis low, interdental plates (Molnar 1978). The preserved portions of the snout indicate probaby fused. Some of these features also characterize Veloci- that the skull was long and slender and permit a hypothetical raptor and possibly Dromaeosaurus : long low muzzle, large skull restoration (fig. 4A). teeth, frontals longer than wide and surface of nasals smooth. It shares with Syntarsus rhodesiensis premaxillary teeth that To assess the taxonomic affinities of Aublysodon, this re­ lack serrations (Raath 1977) and a prefrontal articular surface constructed skull is compared to that of the primitive theropod on the frontal that is an elongate groove (Raath 1985). Dromi­ Coelophysis and to typical and Maastrichtian thero- ceiomimus also shares a number of these characters : long low pods from (fig. 4). Features used in this section muzzle, frontals longer than wide, and smooth nasals. Troodon are given in Table 2. These include the dromaeosaurids Veloci- also shares the long, low muzzle, and frontals which are longer raptor (= Sauromitbolestes Paul 1988) and Dromaeosau­ than wide, but apparently has rugose nasals in the adult (Bars- rus, the troodontid Troodon (= Saurornithoides = Stenony- bold 1974, pl. 1a). chosaurus'), the ornithomimid Dromiceiomimus (considered here as representing all North American ornithomimids), the In a number of features, however, Aublysodon is distinct oviraptorid Caenagnathus, and the tyrannosaurids Alberto- from these three theropod groups. The presence of teeth readi­ saurus libratus, "Albertosaurus" lancensis, Daspletosaurus ly excludes Aublysodon from the ornithomimids (and the ovi- and Tyrannosaurus. Comparison is also made with the enig­ raptorids). That these teeth are large would seem to ally it with matic "Chirostenotes" (referred to by Gilmore, 1924, and to be the dromaeosaurids, rather than with the troodontids in which described as a new genus by Currie et alii, in press). the teeth are small. The apparent small premaxillary, peculiar

character plesiomorphic/apomorphic

1. premaxillary teeth D-shaped in section a 2. premaxillary teeth not serrate p 3. premaxillary teeth with low ridge on posterior face a 4. cheek teeth relatively large (with respect to depth of muzzle and jaw) p 5. muzzle long and low p 6. frontals longer than wide p 7. two or three prongs of nasal overlap frontal a 8. dorsolaterally directed prefrontal contact on frontal p 9. socket for prefrontal on frontal p 10. elongate contact for prefrontal on frontal p 11. orbital rim on frontal very short p 12. frontal-prefrontal suture expanded p 13. pronounced buttress at frontal-postorbital contact p 14. parietal process separates frontal posteriorly p 15. sagittal crest extends onto frontals p 16. frontals essentially flat between orbits p 17. nasals smooth p 18. anterior margin of antorbital fossa v-shaped p 19. acute angle of premaxillary-maxillary contact with ventral margin of snout p 20. ventral margin of symphysis only slightly inclined to horizontal p

Characters 1 to 8, 10, and 17 to 20 discussed in text, characters 9 and 11 to 16 from Currie (1987).

Tabl. 2 - Characters used in determining the relationships of Aublysodon. Caractères utilises pour determiner la position systématique Ae Aublysodon. - 453 -

first dentary tooth and the "stepped" dentary excludes Aublyso­ solaterally directed, and there is no pronounced buttress at the don from the known dromaeosaurids. The "stepped" dentary anterior end of the postorbital contact. and primitive condition of large teeth with small serrations se­ parate Aublysodon from the apomorphic small teeth with large Finally, comparison of the dentaries of Aublysodon with the serrations which characterize Troodon. The relatively deeper equally fragmentary dentaries of "Chirostenotes" indicates that maxilla of Aublysodon also distinguishes it from Troodon. both were long and had fused interdental plates. However, Au­ blysodon has a "step" in the dorsal margin near the symphy- Aublysodon has characters in common with the tyranno­ seal region, which is absent in "Chirostenoes". The lateral sur­ saurids, the most derived theropods known. One character sha­ face of the Aublysodon dentary does not have the dental fora­ red by both is D-shaped premaxillary teeth. This character is mina connected by a shallow horizontal groove. The cheek reported in some other theropods (Matthews & Brow 1922, teeth of Aublysodon differ from those of "Chirostenotes” in Madsen 1976). This suggests that D-shaped premaxillary teeth their relatively much larger size and in being recurved (the may have been independently acquired (see Molnar 1978), at teeth of "Chirostenotes" are not recurved : R. Sloan, personal least once, in Omitholestes. It leaves this character doubtful as communication). a link between Aublysodon and the tyrannosaurids. In any case, if tyrannosaurids and Aublysodon are related to Allosau- From these comparisons, it would appear that Aublysodon rus, D-shaped premaxillary teeth would be plesiomorphic for is relatively primitive compared to other Sate Cretaceous thero­ both taxa. pods. It is clearly related to tyrannosaurids. In the nine fea­ tures given by Currie (1987) which may be observed on the Currie (1987) has presented a suite of twelve features that cranial material of Aublysodon (Table 2), together with twelve distinguish tyrannosaurid frontals. Of these, three features further features of the skull and teeth, Aublysodon either (postorbital overlap of frontal, extension of supratemporal fos­ agrees with tyrannosaurids, or is plesiomorphic, for all but sa onto dorsal surface of frontal and anterior boundary of su­ one. That one is the low ridge of the posterior face of the pre­ pratemporal fossa marked by a low sinuous ridge) cannot be maxillary teeth. In view, however, of the little of the skull of determined from the known frontals of Aublysodon. Of the re­ Aublysodon that is yet known, and not wishing to anticipate maining nine features, Aublysodon differs from tyrannosaurids the results of taxonomic studies of advanced carnosaurs cur­ in only two : the prefrontal socket is laterally rather than dor­ rently in progress by both authors, we here retain it in its own family, the Aublysodontidae.

Acknowledgements

We would like to thank the following individiuals for allo­ (The Academy of Natural Sciences) and D. Whistler (Museum wing us access to specimens in their care : D. Baird (Princeton of Natural History, Los Angeles County). For other assistance in University), W. Clemens and H. Hutchison (University of Cali­ this study we are grateful to K.E. Campbell, P.J. Currie, R.A. fornia, Berkeley), J. Horner (Museum of the Rockies), D.A. Long, S. A McLeod, D.A. Russell, P. Taquet and S.P. Welles. Russell and R. Day (National Museums of Canada), C. Smart Mme. D. Dubos provided the translation into French.

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Manuscrit déposé le 14.03-1988 Manuscrit définitif regu le 13.12.1988