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PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3580, 17 pp., 5 figures, 1 table September 6, 2007 First Jurassic Triconodont from South America GUILLERMOW.ROUGIER,1,2 ALBERTOGARRIDO,3 LEANDROGAETANO,4 PABLO F. PUERTA,5 CYNTHIA CORBITT,6 AND MICHAEL J. NOVACEK7 ABSTRACT AnewmammalfromtheMiddleJurassicCanãdonAsfaltoFormation,Patagonia,Argentina,is reported.Thespecimen,anisolatedlower?molariform,iserectedasthetypeofanewgenusand species of triconodont, Argentoconodon fariasorum. The molariform presents a peculiar combinationofprimitiveandderivedfeaturesthatmakesrecognitionofitsaffinitieschallenging. Argentoconodon shares similarities with poorly known triconodonts from the Jurassic of North America and Morocco and lacks the diagnostic traits of the triconodontid triconodonts. Argentoconodonresemblesingeneraltheparaphyletic‘‘amphilestid’’triconodonts.Thespecimenis tooincompletetowarrantbroaderinterpretations,butitsuggeststhatatleastthislineageofSouth Americanmammalswasdistinctlyautapomorphic,perhapswithanorigininformswithabroader geographicaldistribution. INTRODUCTION Matilde Formation (Callovian-Oxfordian) of Santa Cruz province, Argentina. In the type ThepresenceofJurassicmammalsinSouth locality, several trackways are known for this America has long been known, or at least ichnogenus that represent several locomotory presumed, based on the description by modes ranging from galloping to asymmetri- Casamiquela (1964) of Ameghinichnus patago- cal gait (Casamiquela, 1964; Rainforth and nicus, an ichnofossil from the Jurassic La Lockley, 1996; Leonardi, 1994). Ameghini- 1Department of Anatomical Sciences and Neurobiology, University of Louisville, Louisville 40292, KY (grougier@ louisville.edu). 2ResearchAssociate,DivisionofPaleontology,AmericanMuseumofNaturalHistory. 3MuseoMunicipalCarmenFunes,PlazaHuincul,8318Neuqueń,Argentina([email protected]). 4Museo Argentino de Ciencias Naturales Bernardino Rivadavia, 1405 Buenos Aires, Argentina (leandrocg1@gmail. com). 5MuseoPaleontolo´gicoEgidioFeruglio,9100Trelew,Argentina([email protected]). 6DepartmentofBiology,UniversityofLouisville,Louisville40292([email protected]). 7DivisionofPaleontology,AmericanMuseumofNaturalHistory,NewYork10024([email protected]). CopyrightEAmericanMuseumofNaturalHistory2007 ISSN0003-0082 2 AMERICAN MUSEUMNOVITATES NO. 3580 chnus ichnofossils were attributed to ‘‘pan- (Bonaparte, 1986a, 1992) but the identifica- totheres’’ by Casamiquela (1964) and to tion is problematic (see below). We report multituberculates by Kielan-Jaworowska and herein on a new triconodont from the Juras- Gambaryan (1994). Olsen (1980) described sic Canãdon Asfalto Formation, Chubut, a series of ichnofossils from the Lower Argentina, that shows all of the definitive Jurassic Newark supergroup as belonging to features of triconodonts. This new tricono- unidentified cynodonts; he later recognized dont highlights how precarious is our knowl- these tracks as representing several species of edgeoftheearlyMesozoicmammalianfaunas Ameghinichnus (Olsen et al., 2002), and he inSouthAmericaandaffordsnewpossibilities referred to them as possible tritheledontids. for comparing the faunal development of the Ichnofossils from North America are much South American mammalian communities larger than those from Patagonia and bring during the Mesozoic. into question the original identification of There is significant overlap and ambiguity those ichnites as mammalian. The status of among the terms collectively used to describe Ameghinichnus is therefore uncertain at pres- early mammaliamorphs. We use the term ent. Footprints of advanced cynodonts or triconodont to refer to any mammaliamorph early mammals with hair impressions, howev- with three major crown cusps mesiodistally er, have been recorded in the Triassic aligned; this term, as defined here, does not Stomberg group (Ellenberger, 1972, 1974, correspondtoamonophyleticunit(Rougieret 1975). al., 1996, 2001; Hu et al., 1997, 1998; Ji et al., Despite encouraging ichnological finds in 1999; Luo et al., 2001, 2002, 2003: Kielan- Patagonia, Jurassic osteological remains of Jaworowska et al., 2004) and is used simply South American mammals have eluded pa- for ease of reference. The term triconodontid leontologists until recently (Rauhut et al., is used strictly for the members of the mono- 2002; Forasiepi et al., 2004a, 2004b; Rougier phyletic clade Triconodontidae (Kermack, and Apesteguia, 2004; Martin et al., 2005; 1963; Crompton and Jenkins, 1979; Rougier Rougier et al., 2007), when Asfaltomylos et al., 1996, 2001; Cifelli et al., 1998; Ji et al., patagonicus from the Middle Jurassic 1999; Kielan-Jaworowska et al., 2004). Canãdon Asfalto Formation was described Amphilestidae is an assemblage of tricono- and other probably related forms as yet donts (Kielan-Jaworowska and Dashzeveg, undescribed were presented. Asfaltomylos has 1998; Sigogneau-Russell, 2003; Kielan- beendescribedasabasalmemberofarecently Jaworowska et al., 2004, Rougier et al., in erected group, the Australosphenida (Luo et press) that in most recent phylogenetic pro- al., 2001, 2002; Rougier et al., 2007), that posalsresultsinanonmonophyleticgrouping would encompass mostly Mesozoic groups (Jietal.,1999;Rougieretal.,2001;Luoetal., from the southern continents (Australia, 2001, 2002); however, Kielan-Jaworowska et South America, and Africa in particular) and al. (2004) recovered some of the traditional potentiallycouldrepresentthestemlineageof members of Amphilestidae and some of the monotremes (see Rich et al. [2002], Wood- traditional members of Triconodontidae as bourne [2003], and Woodburne et al. [2003] a monophyletic unit they dubbed Eutrico- for an opposite point of view). nodonta following earlier uses (Kermack et Triconodontsarerelativelywidespreadgeo- al., 1973). We think this arrangement unlikely graphically and temporally, being major com- and refer to amphilestids informally as those ponents of the Jurassic Holartic communities triconodonts traditionally included as such in and still important during the Early Cre- thehomonymous family, whichusuallyshows taceous (Cifelli et al., 1998; Rougier et al., three main cusps and two cingular cusps 2001; Li et al., 2003; Meng et al., 2003; Hu et arrangedfairlysymmetricallyandhaveaclear al., 2005). Occurrence of triconodonts in dominance of a cusp A/a (Simpson, 1928, a general sense (i.e., any mammaliaform with 1929; Patterson, 1956). As employed here, the a molariform crown dominated by a longitu- term has only practical reference value. dinal series of three major cusps) in South Systematic terms such as Mammalia, Theria, America’s Mesozoic has been proposed and others follow phylogenetic definitions 2007 ROUGIER ETAL.: SOUTHAMERICAN JURASSIC TRICONODONT 3 Fig. 1. Map indicating the location of the Queso Rallado locality, Chubut province, Argentina. Modifiedfrom Rougieret al.,2007. (Rowe, 1988, 1993; Rougier et al., 1998). Two subunits separated by a discordance Triconodont cusp nomenclature follows the were recognized by some workers within this convention proposed by Crompton and sequence (Musacchio et al., 1990; Proserpio, Jenkins(1968)andrecentreformulations,such 1987; Figari and Courtade, 1993); however, as Rougier et al. (2003). the passage from the lower to the upper part of the section is interpreted here as a lithological transitional change due to the prograda- GEOLOGICAL BACKGROUND tion of a fluvial system with a north-to- The Canãdoń Asfalto Formation (Stipanicic northwest direction over the lacustrine system et al., 1968), of probable Callovian-Oxfordian in the area of Cerro Cońdor village. age (Stipanicic et al., 1968; Tasch and The lower Las Chacritas Member (Silva Volkheimer, 1970; Musacchio et al., 1990), is Nieto et al., 2003), of approximately 250-m extensively exposed in several localities of thickness, is composed of carbonate deposits, Chubut Province, Argentina, along the middle biohermal bodies, and black bituminous valley of the Chubut River (fig. 1). Paleonto- shales developed in broad lacustrine basins. logical prospecting of this formation has been The sporadic intercalation of basaltic flows, centered around the village of Cerro Cońdor pyroclasticsediments, andmudflowsindicates where exposures are accessed relatively easily. the presence of contemporaneous but inter- The vicinity of Cerro Cońdor has become mittent volcanism, related to the evolution of aclassiclocalityfollowingBonaparte’spioneer- the sedimentary basin. ingworkinthearea(Bonaparte,1979,1986b). The upper Puesto Almada Member (Silva The lithological constitution of the Canãdoń Nieto et al., 2003) has a thickness of 270 m in AsfaltoFormationcombinesaseriesofcalcar- the Cerro Cońdor area. It is characterized by eous, silicoclastic, and volcanic deposits de- an association of sandstones, siltstones, and velopedduringtheriftingandfillingstageofthe tuffs intercalated by thin levels of limestones small Canãdoń Asfalto Basin (Figari and and conglomeratic lenses. This sedimentary Courtade,1993;Figarietal.,1996). succession is interpreted as a perilittoral flood 4 AMERICAN MUSEUMNOVITATES NO. 3580 plain and meandering fluvial deposits associ- small to mid-sized vertebrates. We think the ated with small, shallow, and transient lacus- mammalian specimens floated into the body trine bodies. The sporadic presence of pyro- of water as complete skeletons from the clastic material in the succession suggests the nearby area and sank to the bottom of the occurrence of intermittent ash fall episodes. small body of water where in most instances The Canãdoń Asfalto Formation deposits the skeletons were disturbed, resulting in have provided several vertebrates; among a preponderance of isolated elements over them, and besides the already mentioned relatively articulated skeletons. Asfaltamylos, are fishes (Tharria feruglioi Bordas, 1942; Oligopleurus groeberi Bordas, SYSTEMATIC PALEONTOLOGY 1942; and Luisiella inexcutata Bocchino, 1967); the sauropods Patagosaurus fariasi CLASSMAMMALIALINNAEUS,1758 (Bonaparte, 1979; Rauhut, 2003), Volkhei- ORDERTHERIIMORPHAROWE,1993 meria chubutensis (Bonaparte, 1979), and Argentoconodon, new genus Tehuelchesaurus (Rich et al., 1999); and the figures 3, 4 theropodsPiatnitzkysaurusfloresi(Bonaparte, TYPE AND ONLY SPECIES: Argentoconodon 1979) and Cońdorraptor currumilii (Rauhut et fariasorum, new species. al., 2002). Recent fieldwork in the area has ETYMOLOGY: Argento, from Argentina, the also provided isolated elements of anurans, country were the holotype was found; and con pterosaurs, and turtles. Invertebrates are odon, from the Greek ‘‘conical tooth’’, in represented by gastropods (Potamolithus reference to the conical aspect of the cusp of Musacchio, 1995) and freshwater bivalves the first described triconodonts, and now (Palaeomutela Turner, 1983). a common ending of triconodont names. The All of the mammalian specimens collected species name fariasorum is from Farias, after intheCanãdonAsfaltoFormation(Rauhutet Ricardo Farias and his family, who have al., 2002; Forasiepi et al., 2004a, 2004b; supported paleontological research on their Martin and Rauhut, 2005) were recovered landfordecades.Theyhavebeengracioushosts from the Queso Rallado locality, ca. 5.5 km who greatly facilitated our work. Our knowl- NW of the Cerro Cońdor village. The edge of the continental Jurassic in Argentina fossiliferous level is situated in the middle owesmuchtotheirlongstandingsupport. part of the Las Chacritas Member, ca. 110 m DIAGNOSIS: Generic and specific diagnoses from the base of the Canãdoń Asfalto are the same because only one species is Formation (fig. 2). The bone-bearing bed known. ‘‘Amphilestid’’ with a pentacuspid forms a subtabular and irregular 50-cm-thick lower molar consistent of three main cusps body intercalated in a thick, strongly de- b, a, c and small anterior and posterior cusps. formed succession of tuffs, tuffaceous rocks, All cusps are recurved to some degree and and thin basalt flows. The bone layer is asmallaccessorycuspispresentlingualtothe composed of thin interlaminated calcareous notchbetweencuspsaandcinthepositionof andtuffaceousdepositsrichinconchostracans g (Kuehneocone of morganucodonts). Cusps and intercalated by irregular opal veins. b and c are subequal in height. Accessory According to our observations, the bone- cusps e and d extend mesially and distally bearing deposits would have originated in (respectively)fromthecrownbase.Interdental a relatively small, shallow lacustrine body contact is in echelon. The crown is extremely placedinasupralittoralenvironmentadjacent compressed buccolingually. tothemainwaterbodyofthebasin.Acertain PROVENANCE: Theholotypeishousedinthe amountoftransportationisevidentinmostof Museo Paleonto´logico ‘‘Egidio Feruglio’’ the specimens, which in general are represent- (MPEF) in Trelew (Province of Chubut), ed by isolated elements; in a few instances, Argentina, and bears the collection number however, some association is preserved and MEF-PV 1877. The specimen was collected in several elements belonging to one individual March2003atthelocalschoolinCerroCońdor are found in close proximity to each other, by breaking assorted blocks from the Queso including occasionally partial skeletons of Ralladolocality(43u24933.550S,69u13950.10W), 2007 ROUGIER ETAL.: SOUTHAMERICAN JURASSIC TRICONODONT 5 Fig. 2. Reconstructed lithological section of the Queso Rallado locality (by A.G.), Las Chacritas Member,CanãdońAsfalto Formation, sensuSilva Nieto etal. (2003). 6 AMERICAN MUSEUMNOVITATES NO. 3580 South American Mesozoic mammals have consistently proven to be difficult to compare withmammalsfromotherregionsoftheglobe, and by the fact that the morphology of the molar has details that would be unusual in lower teeth, we consider it possible that MEF PV 1877 is in fact an upper molar instead of alowermolarasinterpretedhere. Themolar isrelativelylarge (seefig. 3A, B), closeto3 mminlength(seefigs. 3A,3B,5,and appendix 1), extremely compressed, and bears tall gracile cusps. The crown is dominated by threelargecusps(a–c)thatareflankedmesially anddistallybywell-definedcingularcuspseand d. Determination of the nature of the molariform(upperorlower,leftorright)isnotsimple. Therearevirtuallynocingula,andthecuspsare almost fully symmetrical in buccolingual view (fig. 3A, B). The main elements helping to decide these factors are: (1) there is a small amountofwearononesideofcuspb,butthis Fig. 3. Stereophotographs of Argentocondon couldalsobeasmallchipofenamel(fig. 3);(2) fariasorum (MPEF PV 1877) in labial (A) and thereisasmallcuspattheposteriorendofthe lingual (B)views. base of cusp a that can be interpreted as a remnant of a cingulum and is reminiscent of about 5.5 km west-northwest of the village of a cusp g, or Kuhneocone (Crompton, 1974; Cerro Cońdor (Bonaparte, 1979, 1986b; Sigogneau-Russell, 1983; Sigogneau-Russell Rauhut et al., 2002; Martin and Rauhut, and Godefroit, 1997); and (3) the position of 2005),inChubutProvince,Argentina. thecingularcusps(d,e)suggeststhatthefront ASSOCIATED FAUNA: Vertebrates at the of the tooth was slightly overlapped by the Queso Rallado locality mainly occur as preceding tooth, the overlap occurs buccally isolated elements of small to mid-sized ani- among the mammals known to us and there- mals; articulated or associated remains are fore suggests that this is the labial edge. These present,althoughscarce.Thevertebratefauna threeargumentssuggestthatthebuccalsideof of the Queso Rallado seem to represent the specimenistothe right,asseeninocclusal a composite of aquatic and terrestrial animals view. Cusp c is slightly asymmetrical, curving in agreement with littoral lacustrine sedimen- lightly toward the side identified as buccal by tary conditions inferred from the fossil-bear- the above arguments, which would be an ing strata at Queso Rallado. Small aquatic unusual circumstance. This cusp may be de- basal turtles, anurans, and crocodiles domi- formed or broken, but it is not evident (figs. 3 nate numerically; fish elements and other and 4). This feature raises doubts with regard aquatic vertebrates are far more scarce. to the interpretation of this tooth as a lower Terrestrial vertebrate elements are relatively molar. rare and are represented by sphenodontians, The main features of the tooth are the five pterosaurs, dinosaurs (teeth), and mammals. cusps aligned anteroposteriorly, identified here as cusps a–e. In occlusal view (fig. 4C), five aligned cusps (a–e) are clearly distin- DESCRIPTION guished; the accessory cusp (g), however, is Thespecimenisacompleteisolatedmolaror only a little bulge basal to cusp a, evident as molariform, interpreted here as a lower? right a triangular-shaped elevation between cusps tooth,ofalikelymid-rowposition;thatis,itis a and c. Cingular cusps (d–e) are placed neitherthefirstorthelastmolariform.Because slightly lingual to the main cusps a–c, 2007 ROUGIER ETAL.: SOUTHAMERICAN JURASSIC TRICONODONT 7 Fig. 4. Illustrations of Argentoconodon fariasorum (MPEF PV 1877) in lingual (A), labial (B), occlusal (C),distal(D),and mesial(E)views. Cusp nomenclature is afterCromptonand Jenkins(1968). although not enough to mask the essentially possible facet on the labial aspect of cusp b. linear arrangement of cusps. The lingual aspects of the major cusps are In labial view (fig. 4B), the major cusps are slightly more flattened than the labial slopes. well rounded, almost conical, and neither Cusp a is dominant, centrally located cingula or wear is evident, except for the between the two roots of the molariform, 8 AMERICAN MUSEUMNOVITATES NO. 3580 and pronouncedly recurved distally, with the base of the embrasure between them. This lingual slope slightly more vertical than the cuspmayrepresenttheremnantofacingulum bulging buccal side. Cusps b and c are of but it is not connected per se to a distinct similar height (cusp c is slightly taller), but cingulum. The position of this cuspule is cusp b is substantially more robust than cusp similar to the kuehnecone (g) of basal mam- c. Cusp b is separated from cusp a by a notch maliaforms and it is interpreted here as that is not carnassial and is placed in the a homologue structure. middle of the long axis of the tooth, and The molar has two fully separated roots therefore the occlusal view is symmetrical. that form a subcircular section, with the Cusp b has a thick base that projects more mesial root more robust and expanded than dorsally than the base of cusp a (that is, the the distal one. As preserved, both roots are valley between b and a is shallower that that subequal in length, but the tip of the anterior between a and c). There is clear cingulum root is broken, so it may have been longer borderingmesiallythebaseofcuspb,butitis than the posterior one. only slightly inflated. Cusp b is more erect than either cusps a or c, and it is almost DISCUSSION AND COMPARISONS parallel to the longitudinal axis of the tooth. Cusp c is very thin, pointed, and perhaps has The informal group of triconodonts is lostitsverytip.Aminuteamountofsediment usually regarded as a polyphyletic assemblage is still present on the lingual aspect of this of probable monophyletic subunits including cusp. Cusp c is recurved distally and is sharp Morganucodontidae,Amphilestidae,Tricono- and very thin. Two accessory cusps, d and e, dontidae, and a variety of other mammalia- are located at the posterior and anterior ends forms with dentitions dominated by the of the tooth, respectively; both of them are presence of three major cusps mesiodistally small and buccolingually compressed. Cusp aligned (Rougier et al., 1996, 2001, 2003; d is taller than cusp e and has a very peculiar CifelliandMadsen,1998;Kielan-Jaworowska outline in lateral view, hanging posteriorly andDashzeveg, 1998; Cifelli,2001; Luo etal., from the wall of the posterior root. The apex 2002; Sigogneau-Russell, 2003; Kielan- points posteriorly. Cusp e is very small, also Jaworowska et al., 2004). The comparisons basal, and, as with cusp d, is part of the below primarily address similarities and dif- interface between crown and root without ferencesofArgentoconodonwithtriconodonts. defining a conspicuous cingulum. The apexof The new specimen differs from Morgan- cusp e points mesially in a distinct way and ucodon and allies in the presence of a cusp alsoprojectssharplyfromthemesialaspectof b that is part of the crown and not cingular, the root. the lack of numerous well-developed cingular On the buccal aspect of cusp e there is cusps,andthepresenceofsimilarlysizedcusps a somewhat flattened surface that matches bandc.Allofthesetraitsarederivedfeatures a similar area on the buccal area of cusp d, shared by our specimen and more derived suggesting that the interlock between the mammaliaforms, in particular amphilestids successive molariforms was in echelon. This and derived triconodontids (Cifelli et al., interpretation is reinforced by the lack of 1998; Cifelli and Madsen, 1998; Kielan- grooves for interlocking of the roots, or Jaworowska and Dashzeveg, 1998; Rougier notched mesial and distal ends of the crown. et al., 2001). Exceptforthepossiblewearfacetonthetip Despite prima facie similarities, Argento- of cusp b, there are no clear wear facets conodon lacks any of the derived features of present on the molariform. later triconodontids (Triconodontidae sensu Asmallcuspuleisplaced between thebases stricto or eutriconodonts), in particular the of the cusps a and c, more closely related to Early Cretaceous representatives of this cusp a than to cusp c. This tiny cusp is borne group. Derived triconodontids have all prin- lingual to the principal ones and its develop- cipal cusps (a–c) and the posterior cingular ment does not exceed the base of cusps a and cusp (d) of similar height, and the molar c, being so low that its tip does not reach the interlocking is produced by a groove present 2007 ROUGIER ETAL.: SOUTHAMERICAN JURASSIC TRICONODONT 9 on the mesial face of the anterior root of the Argentoconodon is similar to the Bathonian molariforms that lodges cusp d of the pre- amphilestid Phascolotherium bucklandi in the ceding molar (Cifelli and Madsen, 1998; transverse cusp compression and in having Rougier et al., 2001; Luo et al, 2002, Kielan- cusps d and e of similar development. Jaworowska et al., 2004). Among more basal However, in P. bucklandi cusp b is similar in triconodontids, such as Priacodon (Simpson, height to cusp c, and a well-developed lingual 1929; Rasmussen and Callison, 1981; Krusat, cingulum is formed by a continuous thicken- 1989), the groove on the mesial aspect of the ing; these features are unlike those of molariform root is absent, and cusp d is Argentoconodon. Both Amphilestes and distinctively smaller than cusps a–c. Despite Phascolotherium show a basal labial bulging the plesiomorphic nature of Priacodon, this ofthebaseofcuspa,which ismissing orvery form is nonetheless a basal member of the poorly developed in Argentoconodon. Most triconodontid radiation (Simpson, 1925a, amphilestids show this bulging developed to 1925b, 1929; Rougier et al., 1996, 2001; Ji et a certain degree, and it has been regarded as al.,1999;Luoetal.,2002;Kielan-Jaworowska characteristic of the group (Simpson, 1928, et al., 2004). Specifically, lower molars of 1929). The asymmetry in the buccolabial Priacodon differ from our specimen in having section of cusp a created by this bulging is cuspbtallerthancuspc,inlackingcuspe,and what,inconjunctionwiththeocclusionmode, in having non posteriorly recumbent cusps hasledtotheconsiderationofamphilestidsas and a molar less buccolabially compressed. havingincipientlytriangular molariforms that A degree of uncertainty is unavoidable couldrepresentintermediatestagestowardthe when the material basis consists of a single full acquisition of triangular or ‘‘therian’’ isolated molariform; however, the affinities of molariforms (Vandebroek, 1964; Mills, 1971; thePatagonianspecimenclearlylieamongthe Starck, 1995). more derived triconodonts, amphilestids in The Patagonian tooth differs from the Late particular. Argentoconodon shares with am- Jurassic amphilestids from the Morrison For- philestid lower molars the following derived mation (United States) Comodon (Simpson, features: teeth pentacuspid and roughly sym- 1925b; Kretzoi and Kretzoi, 2000; Cifelli, metrical mesiodistally; cusps b and c of 2002) and Aploconodon (Simpson, 1929; subequal height and shorter compared to the Kretzoi and Kretzoi, 2000). In the former, principal cusp a; labiolingually compressed cusp e is lacking and in its place is cusp f; it molars in comparison to morganucodontids; has a lingual cingulid and cusp b is more cusp e present and large (subequal to cusp d); developed than cusp c, which are both very and lacking, or greatly reduced, lingual short compared to cusp a. Overall, Comodon cingulum and accessory cusps greatly reduced is similar to Tendagurodon (see below). or absent. Some of theses features, like the Argentoconodon is also different from relative height of the cusps are primitive Aploconodon comoensis, an amphilestid from characters and likely lack any phylogenetic the Late Jurassic of the United States, which information at this systematic level and un- hasnocuspsd–fexceptforthelastmolarthat derline the paraphyletic nature of ‘‘amphiles- shows cusp e. These Jurassic amphilestids tids’’ in general. from North America, Aploconodon and Compared to the Middle Jurassic Amphi- Comodon, with denudated crowns and simpli- lestes (Owen, 1871; Simpson, 1928; personal fied patterns seem to be related to later obs.),thetoothdescribedhere issimilarinthe Asiatic amphilestids from Asia (Rougier et generalarrangementoftheprincipalcuspsand al., 1999, 2001). in having cusps d and e of comparable height. Jeholodens jenkinsi was originally described On the other hand, Amphilestes (Simpson, as a triconodontid (Ji et al., 1999), but recent 1928, Sigogneau-Russell, 2003) differs from studies identify this form as a likely basal the Patagonian specimen in having a nonre- amphilestid (Rougier et al., 2001; Rougier et cumbentcuspa,symmetricalcuspsbandcthat al.,inpress).Jeholodensdiffersfromthemolar aremuchlessdevelopedthancuspa,andawell- describedhereinhavingcuspserectandnotas developedlingualcingulum. compressed as those of thePatagonianmolar. 10 AMERICAN MUSEUMNOVITATES NO. 3580 Jeholodens, as with most primitive tricono- Jurassic of India a variety of tricondonts has dontids,hasawell-developedcuspe(reported been described and variously attributed to as absent by Ji et al., 1999; see Rougier et al., MorganucodontidaeorAmphilestidae(Yadag- 2001) and, despite its juvenile condition giri, 1984; Datta and Das, 1996, 2001; Prasad (several antemolar elements are still in the and Manhas, 2002). Among the teeth de- process of eruption), shows a typical amphi- scribed as morganucodontids, Gondwanodon lestidalternateocclusion,somewhatsimilarto tapani (Datta and Das, 1996) shows, as does theonepresentinlatertherians,insteadofthe Argentoconodon, the relative reduction of the one-to-onemodecharacteristicoftriconodon- cingulum and Kuhnecone, as well as a subtle tids (Crompton, 1971, 1974; Crompton and recumbency of the main cusps. The morphol- Jenkins, 1979). ogy of this taxon is enigmatic and the The amphilestid Klamelia (Chow and Rich, attribution to morganucodontids is tentative 1984) from the Late Jurassic of China differs (Kielan-Jaworowska et al., 2004). The height fromthemolariformpresentedherebecauseit proportions of cusps a–d, however, differ hasasymmetricaltoothcrownswithcuspanot radically from Argentoconodon; the cusps are centered in occlusal view and a weak lingual also more robust and less compressed. Other cingulid. It is also different because of the taxa from India such as Paikasigudodon presence of a cingulum that includes a poorly (Prasad and Manhas, 2002), Indotherium developed cusp b. If our interpretation of the (Yadagiri, 1984), and Indozostrodon (Datta interdental contact of Argentoconodon is and Das, 2001) are more clearly related to correct, Klamelia and Argentoconodon share morganucodontids and megazostrodontids the partial overlapping or ‘‘echelon’’ contact (Kielan-Jaworowska et al., 2004) or, as in betweentwosuccessiveteeth.Thisconditionis Paikasigudodon, they are represented by ele- not widespread among triconodonts (see ments not comparable with Argentoconodon Kielan-Jaworowska et al., 2004). and do not warrant close comparison. Gobiconodontidsareaveryautapomorphic Previous to this report, there was a single group of triconodont mammaliamorphs that recognized triconodont genus in South have been considered to be related to amphi- America: Austrotriconodon Bonaparte, 1986a lestids (Trofimov, 1978; Jenkins and Schaff, from the Late Cretaceous Los Alamitos 1988; Kielan-Jaworowska and Dashzeveg, Formation, Argentina. This genus is the sole 1998) and, with reservations, to triconodon- member of the family Austrotriconodontidae tids (Rougier et al., 2001; Wang et al., 2001; Bonaparte,1992andisrepresentedbyisolated Luoetal.,2002;Mengetal.,2003).Themolar upper and lower teeth assigned to two described here shows many differences from different species: A. mckennai Bonaparte, Gobiconodontidae molariforms and closely 1986a and A. sepulvedai Bonaparte, 1992. relatedformssuchasRepenomamus(Lietal., Nevertheless, the atypical morphology of 2000; Wang et al., 2001; Meng et al., 2003), Austrotriconodon has prompted some doubts notwithstanding the fact that some of the with regard to the molar nature of some characteristicsthatdiagnosethisgrouparenot elements attributed to this genus (Kielan- available in our specimen (e.g., characters of Jaworowska et al., 2004) or their triconodon- the upper dentition and tooth formula). tan affinities (Rougier et al., 2002). Argentoconodon and gobiconodontids are dis- Argentoconodon shows many differences from similarinthatgobiconodontidspresentavery the published elements of Austrotriconodon distinctcuspf,possesscarnassialnotches,and (Bonaparte, 1986a, 1990, 1992, 1994). First, themaincuspspresent adistinctive lanceolate lower molariforms of Austrotriconodon have profile. Gobiconodontids lack cingular cusps crowns dominated by a principal cusp a, and do not have overlapping between succes- which is followed posteriorly by two small sive molars. additional cusps c and d. Cusp c can be Despite the paucity of the Gondwanan slightlylargerthancuspdbutitisalwaysvery record of triconodonts, these few specimens poorly developed. A rather robust cusp b is are particularly relevant for comparisons with present in most of the described teeth of Argentoconodon. From the Late Triassic and Austrotriconodon,andcingularremainscanbe