Great Basin Naturalist
Volume 55 Number 4 Article 2
10-31-1995
Additions to knowledge of Paleocene mammals from the North Horn Formation, central Utah
Richard L. Cifelli University of Oklahoma, Norman
Nicholas J. Czaplewski Johns Hopkins University School of Medicine, Baltimore, Maryland
Kenneth D. Rose
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Recommended Citation Cifelli, Richard L.; Czaplewski, Nicholas J.; and Rose, Kenneth D. (1995) "Additions to knowledge of Paleocene mammals from the North Horn Formation, central Utah," Great Basin Naturalist: Vol. 55 : No. 4 , Article 2. Available at: https://scholarsarchive.byu.edu/gbn/vol55/iss4/2
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ADDITIONS TO KNOWLEDGE OF PALEOCENE MAMMALS FROM THE NORTH HORN FORMATION, CENTRAL UTAH
Richard L. CifellP, Nicholas J. Czaplewsk;l, and Kenoeth D. Rose·
AIlf,-n\llCT.-111e distinctive lmt inade
Key words: Paleocene, North Hom Formation, Ptlercan, Thrrejollian, Dragon local fauna, Wagon Road local jatlna, Mwnmali. Paleocene mammals were first reported from Periptychus interval-zone), and Dragon to Tal the North Horn Formation, Emery and Sanpete (Periptychus I Tetraclaenodon interval-zone). counties, UT, by Gazin (1938). Further field Both Pu2 and Pu3 are interpreted to occur work resulted in the recovelY ofadditional taxa, within m.gnetic polarity chron 29N (Butler and interpreted as representing two faunas, from Lindsay 1985); the Dragon fauna is considered two main localities (Gazin 1939, 1941). In sub to lie within anomaly 27N (Tomid. and Butler sequent years, additional sites in the region 1980). , have yielded further specimens, including more The Paleocene mammals ofcentral Utah are taxa and a third faunal assemblage (Spieker of special interest in both temporal and geo 1960, Van Valen 1978, Toroida and Butler 1980, graphic contexts: they fall within a time inter Tomida 1982, Robison 1986, Archibald, Rigby, val not well represented elsewhere, and they and Robison 1983). Three assemblages are cur lie geographically between the classic sequence rently recognized, the Gas Tank, Wagon Road, of the San Juan Basin, NM, and faunas from and Dragon local faunas (Robison 1986). On more nOltherly parts ofthe Western Intelior (c£ the basis of the latter two, a "Dragonian" land Archibald et al. 1987: fig. 3.1). Mammals from mammal age was initially establisbed (Wood et the Paleocene of the North Horn Formation al. 1941). Later work, including magoetic are not, in general, well known. We describe stratigraphy and biostratigraphic compalisons, herein newly collected materials that provide suggests that the Gas Tank and Wagon Road further details on the morphology and system faunas al·e Puercan and the Dragon fauna Torre atics ofsome ofthe included taxa. jonian in age (Toroid. and Butler 1980, Toroid. The approximate locations of the major 1981, Robison 1986). Archibald et a1. (1987) mammal sites in the Paleoceoe part of the tentatively assigned the Gas Tank to Pu2 North Horn Formation, takeo from data pre (EctoconWJ / Tlwliclabis tluJensis interval zone), sented by Gazin (1941) and Robison (1986), Wagon Road to Pu3 (Taeniolabis taoensis I are given in FIgure 1. The materials described JOU1Jmm" MUfoOUm of N 304 1995] PALEOCENE MAMMALS, UTAH 305 DESCnIPTIVE ACCOUNTS Order Proteutheria Family Pantolestidae Cope, 1884 ?Propala.eosinopa sp. Figs.2A-B MATEHlAL.-OMNH 27681, fragment of right dcntary bearing the talonid of P4 (WTal = 1.5) and complete M1 (L = 2.8, WTri = 1.8, WTaI = 1.8). LOCALITY AN)) HORTZON.-OMNH V800, "Wagon Road" loeality (Gazin 1941, Robison 1986); Wagon Road local fauna, late Puercan (early Paleocene). Joes Valley Member, North Horn Formation, Emery County, UT. DESCRIPTION AND DISCUSSION.-Thc den tary fragment includes the anterior root of P4 and the anterior root of M2. The anterior root of P4 is bowed forward as in pentacodontids and most pantolestids, and its placement incli cates that P4 was relatively long, longer than Ml' The posterior mental foramen is large and is positioned between the posterior root of P4 Fig.!. Approximate locations of mammal-bearing sites and the anterior root of Ml' The talonid of P4 in Paleocene part of North Horn Formation, EmelY and includes a large hypoconid and a small entoco Sanpete counties, UTi data from Gazin (1941) and Robison (1986). Localities, Dragon local fauna: Dragon nid; these two cusps are united by a small, thin Canyon (1). Wagon Road local fauna: Wagon Road (2), postcristid, forming a small talonid basin. The Wagon Road Ridge (3). Gas Tank local fauna: Gas Tank apex of the hypoconid is on the midline of the Hill (4), Dairy Creek (5), Jason Spring (6), Ferron tooth, at the posterior termination of a cristid Mountain (7; prohably equivalent to OMNH V829), Blue obliqua that angles lingually toward the front; Lake (8), and Sage Flat (9). the postcristid is oriented almost perpendicu lar to the cristid obliqua. Posterior to the post herein were collected in 1993-94, through sur cristid and separated from it by a tiny trans face prospecting methods. With one excep verse basin, a small cuspule (hypoconulid?) is tion, all specimens are from the classic Dragon present; this cuspule is connected to the hypo Canyon (Dragon local fauna; ?To1) and Wagon eonid by a thin ridge. A tiny entoconulid, not Road (Wagon Road local fauna; ?Pu3) sites connected to the other cusps, is present at the described by Gazin (1941). The exception is a lingual base ofthe talonid basin. specimen assigned to Ectoconus ditrigonus The trigonid and talonid of M1 are of equal (OMNH 28111), collected by Jon Judd of Castle width; the trigonid is distinctly higher than Dale, UT, at a site south of Ferron Mountain. the talonid, though tbe tooth is moderately The site, OMNH V829, is probably the same worn. The protoconid and metaconid are both as Robison's (1986) Ferron Mountain loeality triangular in occlusal outline and of equal (Gas Tank local fauna; ?Pu2). occlusal area; the protoconid is the taller of the The following abbreviations are used for in two cusps. The paraconid is small, low, and stitutions eited in the text: BYU, Brigham Young transversely oriented. Anterior and posterior University, Provo, UT; OMNH, Oklahoma carnassial notches arc present in the para~ Museum of Natural History, Norman; USNM, cristid and protocristid, respectively. Because National Museum of Natural History, Washing of the transverse orientation of the paraconid, ton, DC. Measurements, in mm, are as follows: the paracristid forms an obtuse angle, with its L, anteroposterior length; W, transverse width; apex at tlle anterior carnassial notch. A short WTal, transverse width of talonid; WTri, trans anterior cingulum, which disappears at the verse width oftrigonid. anterolingual cornel' of the tooth, is present. 306 GREAT BASIN NATURALIST [Volume 55 Fig. 2. Proteutheria from the North Horn Formation. A, B, P4-Ml of Propalaeosirwpa sp. (OMNH 27681) in occlusal (A) and labial (B) views. C-G, Aphronorus simpsoni (OMNH 27667): C, D, right P4 in occlusal and labial views, respec tively; E, F, right P3 in occlusal and labial views, respectively; G, left p4 in occlusal view. Scale bar represents 2 mm; tooth roots and jaw fragments have been eliminated to improve c1mity. 1995] PALEOCENE MAMMALS, UTAH 307 The posterior wall ofthe trigonid is planar; the 1987). In this context, we note that several cristid obliqua meets the base of the posterior morphological details show the North Horn wall ofthe trigonid below the posterior carnas taxon to be distinct, at the species level at sial notch. Although it has been mostly obliter least, from described species; when better ated by wear, an entoconulid (or at least an ento known, it may prove to be generically separable. cristid) appears to have been present anterior to the entoconid. Family Pentacodontidae Of described species, OMNH 27681 most (Simpson, 1937) Van Valen, 1967 resembles the Torrejonian Pmpalaeosinopa di Aphmnorus simpsoni Gazin, 1938 luculi (which we tentatively regard as distinct Flgs.2C-G from P. albertemis following Rose 1981; see discussion in Van Valen 1967). However, the NEWLY REFERRED MATER1AL.-OMNH Utah taxon differs in several respects. The pos 27667, right dentary fragment with P3-4 (P3L terior mental foramen is more anteriorly located = 2.4, W = 1.4; P4L = 4.0, W = 2.5) and asso than in figured specimens ofP diluculi (Simp ciated left p4 (L = 3.3, W = 4.1). son 1936: fig. 3; Krause aod Gingerich 1983: LOCALITY AND HORlZON.-OMNH V799, figs. 8, 9). M1 of OMNH 27681 is long and "Dragon" locality Oocality 2 ofGazin 1941: p. 7, narrow relative to the corresponding tooth of fig. 1), Dragon local fauna, early Torrejonian P. diluculi: it slightly exceeds published size (early or middle Paleocene). Joes Valley Mem ranges (Simpson 1937a, 1937b, Krause and ber, North Horn Formation, Emery County, Gingerich 1983) in length but not width. In UT the Utah taxon the cusps of M1 are somewhat DESCRIPTION AND DISCUSSION.-OMNH more robust and the postvallid wall more 27667 differs from the type of A. simpsoni obliquely oriented with respect to the long (USNM 15539) in minor ways but is clearly axis of the tooth; the paracristid is higher, and referable to the species. P4 is slightly larger the metaconid lower, than in P diluculi.. The than in the type and differs in having a weaker talonid ofP4 is broader and more basined than anterior cingulum, which is barely indicated in P diluculi (or other species of the genus). on the anterolingual part of the tooth and is We regard the specimen from the North Horn completely absent labial to the keel extending Formation as representing a distinct species, down the anterior face of the protoconid. The but materials in hand are inadequate to proper minute ridge that extends down the posterior ly diagnose and circumscribe it. Gazin (1941) wall ofthe metaconid (to meet with the cristid briefly described two morphs, represented by obliqua) is lacking; however, the development upper molars, as generically undetermined of this ridge in the type may be due partly to pantolestids; both were from the Dragon local the advanced wear in that specimen. P4 of fauna. of these, he found pantolestid "au to OMNH 27667 bears a small but distinct ento compare favorably with Bessoecetor (= Propa conid; this region of the tooth is broken in laeosinopa), differing from "R. th01luumi" (=P. USNM 15539. The anterior end ofP4 in OMNH diluculi) in being slightly larger and in a few 27667 is slightly more developed downward morpbological details. It is possible that pan than in USNM 15539, vaguely recalling the tolestid "au and OMNH 27681 represent the more advanced condition seen in Pentacodon same species, although we point out that they (Simpson 1937a: 124). Unlike either species of derive from dilferent horizons in the North Pentaeodon, however, the P4 lacks a basal para Hom Formation. Differential representation conid, the protoconid is not as inclined poste precludes direct comparison with OMNH riorly from base to apex, and the talonid is bet 2768l. ter developed. Ifreferral ofthe newly recovered specimen P3 has not been previously figured or de to Propalaeosinopa is correct, it represents the scribed for Aphronorus simpsoni, though this oldest record of the genus and of the family tooth is known for A. fmudator (illustrated in Pantolestidae, a somewhat aberrant group of outline by Simpson 1937a, Gazin 1941). P3 of enigmatic affinities. The new occurrence is OMNH 27667 is more anteroposteriorly elon estimated to be late Puercan (Pu3) in age; the gate than in A. fraudatot: The tooth is distinct genus and family are otherwise first known 1y two-rooted and is much smaller than P4; from the late Torrejonian (1'03; Archibald et al. maximum width occurs just posterior to the 308 GREAT BASIN NATURALIST [Volume 55 protoconid. A small talonid basin is developed, Order Condylarthra with a minute hypoconid and a "cristid obliqua" Family?Arctocyonidae connected to a ridge running down the poste (Giehel, 1855) Murray, 1866 rior flank ofthe protoconid. A small, short ridge Desmatoclaenus hermaeus Gazin, 1941 and swelling on the posterolingual flank of the Fig.3A protoconid arc suggestive of a metaconid. A f~lint cingulum is present anterolingually. NEWLY REFERRED MATERIAL.-OMNI-l No associated upper teeth have been previ 27682, associated skull and jaw fragments with ously described for Aphronorus simpsoni, al broken right and left p4 (right p4L ~ 6.5), right though a few isolated specimens may belong MI-3 (MIL ~ 7.3, W ~ 8.6; M2L ~ 7.3, W ~ to the species (Gazin 1941, Rohison 1986). p4 11.0; M3L ~ 6.2, W ~ 8.7), left M2-3 (!vl2 bro ofOMNI-l 27667 is broken ncar the paraconule ken, L ~ 7.4; M3L ~ 6.0, W ~ 8.8), left M 1 (L and at the lingual edge of the tooth, between ~ 8.8, WTri ~ 7.2, WTal ~ 7.4), talonid of ~ ~ the cingulum at the base of the protocone and right M2 (W 6.4), trigonid of left Mz (W ~ the lingual root; the labial side of the meta 6.0), and talonid of right M3 (W 5.2). conid is also damaged. Three roots are pres LOCALITY A:-ID HORIZON.-OMNI-l V800, ent. The tooth, although similar to p4 of A. "Wagon Road" locality (Gazin 1941, Robison fiytudatm; differs in several respects. The para 1986); Wagon Road local fauna, late Puercan style is absent; a small paraconule is present; a (early Paleocene). Joes Valley Memhm; North metaconule as such is lacking, although there Horn Formation, Emery County, UI is a vague swelling of enamel in this position. DESCIUPTION AI\:D DISCUSSlON.-p4 has dis The basal protoconal cingula show no tendency tinct canules, with the paraconule being taller to develop cuspules, as they do in A. frauda than the metaconule. These cusps have not tor, and the metacone is much smaller in size, previously been noted for p4 of the species, relative to the paracone, than in that species. perhaps because of wear on the type specimen The labial cingulum of p4 in OMNI-l 27667 is (USNM 16202; sec Gazin 1941: fig. 19; West also less developed than in A. }i-audatac 1976; fig. 2). The upper molars have a labial Aphronorus simpsoni was diagnosed as dis cingulum that is continuous. Interruption ofthe tinct from the comparatively well-known A. edocingulum at the base of the paracone was cited as a generic character ofDesmatoclaenus. fraudator mainly on the basis of differences in However, the cingulum is complete in other proportions of P4 and the lower molars (Gazin specimens, such as BYU 3800 (Robison 1986: 1941). OMNI-l27667, which ineludes teeth pre pI. 2, fig. 10), and we regard this as a feature viously unreported for A. simpsoni, shows that that is intraspecifically variable. M3 bears a it is further distinct in having a somewhat more small but distinct cingular hypocone, another elongate P3; P4 has a narrower, smaller-basined character that is apparently variable in the talonid. p4 differs from that of A. in Faudatar species (Gazin 1941: figs. 19,20; Robison 1986). several respects, including the lack of a meta The only variation worthy of note in the lower conule and parastyle, and the much lesser de dentition of OMNI-l 27682 is the hypoconulid velopment of the metacone. Considering the of M 3, which apparently projected posteriorly specializations of the posterior premolars in as a distinct lobe, unlike the condition seen in pentacodootids (Simpson 1937a) and the pos USNM 16202 (Gazin 1941; fig. 19). sibility that they represent a relatively archaic Gazin (1941) originally descrihed two species group (Van Valen 1967), it is difficult to judge of Desmatoclaenus, D hel1naeus and D. para which conditions are apomorphous, although creodus, both from the Wagon Road fanna. West some ofthe states possessed by A. simpsoni (e.g., (1976) synonymized the two, a view apparent smaller P4 talonid; p4 with small metacone ly shared hy Tomida and Butler (1980), but and no metaconule) would appear-by com Robison (1986) recognized them as distinct parison to more primitive Eutheria-to be prim and reported additional materials of hoth itive. The Tiffanian species A orieli, known by species from other localities. In the original remarkably complete specimens (Gingerich et diagnosis (Gazin 1941), D. paracreadus was a!. 1983), appears to be considerably more said to be larger than D. hermaeus, with the advanced, with greatly expanded crushing sur lingual portion of upper molars more inflated faces (particularly the protocone) on p4. and with a relatively larger M3, bearing a better- 1995J PALEOCENE MAMMALS, UTAH 309 A 5mm ! ! B l developed hypocone. As shown by West (1976), genus with Tetraclaenodon and Protogonodon, these differences in size and morphology are as the latter taxon was then conceived (Matthew both minor and inconsistent. In this context, 1937, Simpson 1937a). Van Valen (1978) placed we note that MI-2 of OMNH 27682 arc rela "?P." protogonioides (cf. Matthew 1937) tively small (a supposed character of D. her originally referred (Cope 1882a), in part, to maeus), yet M3 is proportionately large, with a the genus Mioclaenus-in Desmatoclaenus, well-developed hypocone (characters cited for adding to the genus two additional species, D. D. paracrcodus). We follow West (1976) in rlianae and D. mearae; Protogonodon was syn regarding the species as synonymous. onymized with Loxolophus. We arc in agree In the original diagnosis and discussion of ment with these assignments; D. protogo Desmatoclaenus, Gazin (1941) compared the ni,oides is relatively well represented and adds 310 GHEAT BASIN NATURALIST [Volume 55 significantly to knowledge of the genus. Thus lingual base of the crown and enamel from the recognized, Desmatoclaenus is distinct from posterior margin of the tooth; its estimated L Loxolophus in having stronger protocones on is 3.1. This specimen is appropriate in size for p3-4; better-developed, morc lingually placed only two of the four species of Anisonchus re hypocone on Ml-2, with hypocone occasionally ported from the North Horn Formation (Gazin distinct on !vI3; and paraconid of lower molars 1941, Robison 1986); OMNH 27679 differs placed morc posterolingually and closely from M3 referred to A. athelae (ineluding A. appressed to the metaconid. Desmatoclaenus eowynae; Robison 1986) and is tentatively differs from Tetraclaenodon in having less referred to A. oligistus, for which M3 was not molarized premolars (a metacone is lacking on previously kno\ivn. Although the tooth is incom p3-4; the trigonid is poorly developed and a plete and worn, it can be seen that the anter talonid basin is lacking on P4), upper molars ocingulum was relatively weak and lacked a lacking mesostyle and with lesser develop pericone. Similarly, the hypocone was weak in ment of the hypocone; and lower molars with comparison to the condition in A. athelae, more distinct, anteriorly placed paraconid. being more similar to the larger A. dracus in Gazin (1941) considcred Desmatoclaenus to this respect. The pattern of wear suggests that be structurally intermediate between the archa both paraconule and metaconule were present, ic ungulate "Protogonodon" (then considered a placed near the base of paracone and meta creodont) and Tetraclaenodon, a primitive cone, respectively. phenacodontid; the differential comparisons presented above npbold this view. Snbseqnent Haploconus elachistus Gazin, 1941 workers have referred Desrnatoclaenus to the Figs.4B-F Arctocyonidae on the one hand (Van Valen 1978, Cifelli 1983) or the Phenacodontidae on the NEWLY REFERRED hlATERIAL.-O~1NH other (Simpson 1945, West 1976, Robison 27670, fragments of mandible with left M1-2 1986). The positioning ofthe upper molar hypo (M 1L = 3.8, WTri = 2.7, WTal = 2.8; M2L = cone somewhat more lingually in Desrnatoclae 3.9, WTri = 3.2, WTal = 2,9) and right M2 (L nus than in Loxolophus is vaguely reminiscent = 4.0, ,VTri = 3.1, WTaI = 3.0); 27713, frag of the presumably derived condition in the ments ofleft mandible with P3 (L = 4.5, W = Phenacodontidae; similarly, the low, bunodont 2.8) and a heavily encrusted molar; OMNH cusps bearing mainly flat, apical wear are sim 27680, right P4 (L = 4.5, W = 3.3). ilar to conditions generally obtained in mem LOCALITY AND HORIZON.-OMNH V800, bers of that family. Desrnatoclaenus may well "Wagon Road" locality (Gazin 1941, Robison he a transitional taxon, but in the absence of 1986); Wagon Road local fauna, late Puercan compelling evidence in the form of synapo (early Paleocene). Joes Valley Member, North morphies, we here tentatively retain it in the lIorn Formation, Emery County, UT Arctocyonidae. In this context, we note that the DESClUPTION AND DISCUSSION.-Available referred species D. protogonioides apparently lower premolars (OMNH 27680, 27713) are has a reduced anterior dentition, a condition too worn to determine whether a paraconid was shared with loxolophine arctocyonids (Cifelli present; Gazin (1941) reported the presence of 1983), this cusp on P3 but not P4 of Haploconus ela chistus. The protoconid is a large, inflated cusp, Family Periptychidae Cope, 1882 particularly on P4' A talonid crescent extends Anisonchus '?oligistus Gazin, 1941 posteriorly from the lingual base of the proto Fig. 41\ conid, curving labially at the posterior margin of both P3 and P4' The metaconid oflower NEWLY HEFERRED MATEHIAL.-OMNH molars is nearly as tall as the protoconid and is 27679, right M3. transversely aligned with that cusp; a weak LOCALITY AND HORlZON.-OMNH V800, paracristid descends anterolingually from the "Wagon Road" locality (Gazin 1941, Robison protoconid, terminating in a small paraconid, 1986); Wagon Road local fauna, late Puercan which lies in a median position. As described (early Paleocene). Joes Valley Member, North by Gazin (1941), the pre-entocristid is taller Horn Formation, Emery County, U'f. than the cristid obliqua, The entoconid forms DEscHwnoN,-OMN!-! 27679 is missing the a distinct pillar and projects somewhat on the 1995] PALEOCENE MAMMALS, UTAH 311 Fig. 4. Anisonchinae from the North Horn Formation, A, AnisQnchus ?oUgtstus (OMNH 27679, right M3 in occlusal view). B-F, Haploconu$ elachistus: B, left M1_Z (OMNH 27670) in occlusal vjew; C, E, left P3 (OMNH 27713) in occlusal and labial views, respectively; D, Ii; right P4 (OMNH 27680) in occlusal and labial views, respectively. Scale bar repre sents 2 mm; tooth roots and jaw fragments have been eliminated to improve clarity. 312 GREAT BASIN NATURALIST [Volume 55 lingual side of the tooth; the hypoconulid considered the species to be transitional be forms a fingerlike projection at the back of the tween Conacodon and more derived species of tooth and is somewhat lingual in position, an Haploconus. In retaining unreduced lower appearance emphasized in later wear stages. molar trigonids and relatively unspecialized Two species of Haploconus, H. angustus lower premolars, species of Conacodon are and the larger H. corniculatus, are recognized primitive with respect to Haploconus. In terms from the Torrejonian (To2; Archibald et ai. of characters that are probably derived within 1987) of the San Juan Basin, NM (Matthew the context ofCondylarthra, Conacodon, Haplo 1937). The apparent last record of Haploconus conus, and Oxyacodon have a lingually placed is represented hy a single molm~ of uncertain hypoconulid and hypertrophied postmeta specific alllnities, from Swain Quarry (T03?; cristid on lower molars, lingually placed hypo Archibald et ai. 1987), WY (Rigby 1980). The cone on upper molars, loss of protocone on p3, genus is othelwise known only from the North and, possibly, a columnar, lingually placed Horn Formation. Gazin (1939) described 11. entoconid on lower molars (not clearly seen in inopinatus from the Dragon fauna, later adding all species of Oxyacodon). Howevel; the exclu a second species, ?H. elachistus, fi'om the Wagon siveness ofthese characters and their potential Hoad (Gazin 1941). More recently, Robison status as synapomorphies remain to be estab (1986) has reported specimens of Haploconus lished. Archibald, Schoch, and Rigby (1983) sp. from the Gas Tank local fauna; these mate have shown that Conacoclon and Oxyacodon rials are of interest in documenting the first represent a distinctive subfamily, Conacodon appearance of the genus, but unfortunately tinae, whose relationship to other periptychids they are not specifically diagnostic. H. inopina is unclear; further investigation of the position tus, ofTol age, is similar in size to the later H. of Haploconus with respect to this clade is angustus hut differs from that species in pro clearly warranted. portions of the upper molars (Gazin 1939). 11. elachistus, the geologically oldest described Ectoconus ditrigonus (Cope, 1882) species, is smaller than the Torrejonian species Fig. 3D and, as noted by Gazin (1941), differs from them in a number of respects. In the lower NEWLY HEFEHHED MATEHIAL.-OMNH dentition, P3-4 are less inflated than in H. 28111, fragment ofleft maxilla with dp3--4 and angustus. Similarly, the trigonids oflower molars Ml (dp3L ~ 7.5, W ~ 7.0; dp4L ~ 7.5, W ~ in H. elachistus lack the inflated appearance 8.4; M1L ~ 9.6, W ~ 13.5). seen in Torrejonian species; a small paraconid LOCALITY AND HORIZOI\.-OMNH V829, is still present, whereas in remaining species the probably the same as Robison's (1986) Ferron paracristid forms a bladelike surface extending Mountain locality; Gas Tank local fauna, middle anteriorly from the protoconid and bears no Puercan (early Paleocene). Joes Valley Member, cusp. Lower molars of H. elachistus also lack North Horn Formation, Emery County, UT. the crenulated or striated enamel and promi DESCRIPTION AND DISCUSSION.-The decid nent labial cingulum seen in other species. As uous teeth, dp3--4, are markedly smaller than might be expected, the geologically older H. Ml; both have conspicuous parastylar and meta elachistus appears to be more primitive than stylar lobes. The third deciduous premolar has the Torrejonian species for the characters a roughly triangular occlusal profile and is cited. In this context the apparent presence of longer than it is wide. The paracone and meta a more derived species in the Gas Tank local cone are subequal in height; a large parastyle fauna (Robison 1986) is somewhat surprising. is present almost directly anterior to the para Haploconus is distinctive in the extreme cone. A prominent ridge extends lingually modification of lower molar trigonids (with from the parastyle to the protocone, which is reduction to loss of the paraconid) and in the nearly as tall as the paracone and metacone; unusual configuration of the talonid in posteri another ridge descends the labial slope of the or lower premolars (with a lingual rather than parastyle, continuing posteriorly as a weak ecto· labial crescent), characters that are both ex cingulum. Labial to the metacone, the stylar pressed in [-I. elachistus. The alllnities of the shelf broadens; a small CUSp, serially analo genus are puzzling; Gazin (1941), noting the gous (if not homologous) to a similar cusp on primitiveness of some features of H. elachistus, upper molars of Ectoconus clitrigonus (Osborn 1995] PALEOCENE MAMYIALS, UTAH 313 and Earle 1895), is present labial to the meta there is no basis for comparison with dp3--4 of cone. A salient postmetacrista descends pos Ec/oconus ditrigonus. terolabially from the apex of the metacone, extending to the posterolabial comer of the ACKNOWLEDGMENTS tooth. Weak paraconule and metaconule are present on the pre- and postprotocrista, We are especially grateful to Dale Harber respectively. Faint pre- and postcingulae are for the cooperation of the u. S. Forest Service. present on the lingual slopes of the protocone. We thank Jon Judd, Monte Swasey, and Scott The fourth deciduous premolar is more molar Madsen for help in the field; Dr. Scoll Russell, iform than dP3, differing from MI in having Noble Electron Microscopy Laboratory, for smaller conules and associated cristae, and in access to equipment and facilities; and Estelle the lesser development of the protocone Miller for preparing the SEM photographs. region. The parastyle of dp4 is more labially Drs. David W. Krause, J. David Archibald, and placed than on dp3, and the ectocingulum and Jeffrey G. Eaton provided invaluable com cingular cusp beller developed than on that ments that improved the manuscript. Field tooth; a small mesostyle is also present. The work was supported by grant number 5021-93 lingual cingulae are strong; pericone and hypo from the National Gecgraphic Society. cone are present. MI is typical of Ec/oconus and complete description is unnecessary. The LITERATURE CITED ectocingulum is strong and bears both a meso style and posterior stylar cusp. The laller is sub ARCHrBALD, J. D., P. D. Ge"CERlCH, E. H. Ll!\'OSAY, W. A. conical and is connected to the base of tbe CLEMENS, JEt, D. w: KRAUSE, AND K D. ROSE. 1987. First I orth American land mammal ages of the metacone by a low ridge. Paracone, metacone, Cenozoic Era. Pages 24-76 in .M. O. Woodburnc, and protocone are subeqnal in height; com"es editor. Cenozoic mammals of ~orth America: geo· are strongly developed and are only slightly chronology and biostratigraphy. University of Cali· lower than the principal cusps. fornia Press, Berkeley. Ectoconus ditrigonus, the type species, was ARCHIBALD. J. D., J. K. RIGBY, JR., AND S. F. ROBISON. 1983. Systematic revision of Oxyacodon (Condylarthru, first described on the basis ofmaterial from the Periptychidae) and a description of 0 ferronensis n. San Juan Basin, NM (Cope 1882b). Matthew sp. Journal of Paleontology 57: 53-72. (1937) reported a second species from the San ARCHIBALD, J. D., R. M. SCHOCH, AND J. K. RIGBY, }H. Juan Basin, E. majusculus, considered by Van 1983. A new subfamily, Conacodonlinae. and a new Valen (1978) to be synonymous with E. ditri species, Conacodon kohlbcrgeri, ofthe Peliptychidae (Condyl3orthra, ~t3ommalia). PostilLa 191: 1-24. gO"'/$. The genus is known from severallocali BUTLER, R. F., ..... ND E. H. LINDSAY. 1985. Mineralogy of ties, including both Pu2 and Pu3 horizons, in magnetic minerals and revised magnetic polarity that area (Archibald et al. 1987). Gazin (1941) stratigraphy ofcontinent:u sediments, San Juan Basin. described the species E. symbolus from the New Ylexico. Journal of Geology 94: 535-554. Wagon Road (?Pu3) fauna, North Hom Forma CIFELLI, R. L. 1983. The origin and affinities of the South tion. Robison (1986) described additional mate American Condylarthra and early Tertiary Litoptema (Mammalia). American Museum Novitates 2772: rials of E. symbolWi from localities of tbe Gas 1-49. Tank fauna, thereby extending the range of the COPE, E. D. 188230. Some new foons from the Puereo species to ?Pu2, and reported E. di.trigonus Eocene. American :-.J3ottualist 16; 833--834. from two Gas Tank localities. OMNH 28111 can · 1882b. Synopsis of the Vertebrata of the Puerco ---;;-Eocene epoch. Proceedings of the American Philo· be referred to the laller species on the basis of sophical Society 20: 461-471. size (larger than E. symbolus) and the pres GAZIN, C. L. 1938. A Paleocene mammalian fatuHl from ence of a relatively small posterior cusp, con central Utah. Journal of the Washington Academy of nected to the base of the metacone by a low Science 28: 271-277. Paleo~ ridge, on the ectocingulum of MI (Robison · 1939. A further contribution to the Dragon --cene fauna ofcentral Utah. Journal ofthe "Vashington 1986). Academy of Science 29: 2i3-286. Deciduous teeth of archaic ungulates have · 1941. TIle mammalian faunas of the PaL~nc of not been widely described or illustrated, a --c-e'ntral Utah, with notes on the geology. Proceedings notable exception being the deciduous premo ofthe United States National Museum 91: 1-53. GINGERICH, P. D., P. HOUDE, A)./D D. W KRAUSE. 1983. A lars of Phenacodontidae (West 1971). To our new earliest Tiffanian (late Paleocene) mammalian knowledge, deciduous teeth of Periptychidae fauna from Bangtail Plateau. western Craz.y Mountain have not been previously described, so that Basin, Montana. Journal ofPaleontology 57; 957-970. 314 GREAT BASIN NATURALIST [Volume 55 KRAUSI':, D, W, A.'l"D P. D. GINGF,R1CH. 1983. Mamnullian SPJF.KER, E. M. 1960. The Cretaceous-Tertiary boundary fauna from Douglass Quarry, earliest 'liffanian (lale in Utah. 21st International Geological Congress, Palcoecne) of the easteru Crazy Mountain Basin. Copenhagen 5: 14-24. Montana. Contributions from the Museum ofP-,ucon Tm.nD.-\, Y. 1981. "Dragonian" fossils from the San Juan tology. University of Michiwm 26: 157-H}6. Basin and status of the "Dragoman" land mammal MA"JTII1':W. \V. D. 1937. Palooccne faunas of the San Juan "'age." Pages 222-241 in S. G. Lucas, J. K. Rigby, Jr., Basin, New Mexico. Transactions of the American and B. S. Kues, edito~, Advances i.n San Juan Basin Philosophical Society, new series 30: 1-.510. paleontology. Uni\'er~ily of New Mexico Press, OSilOIl~, H. F, ANIl C. EAIILE. L89..5. Fossil mammals of Alhuquerque. the Puerco beds. Collection of 1892. Bull~tin of the __c;-' 1982. A new genus of picrodontid primate from American Museum of Natural History 7: 1-70. the Paleocene of Utah. Folia Primatologico 37: 37-43. HIGllY, J. K., In. 1980. Swain Quarry of the Fort Union TOM[J)A, Y., AND R. E BUTLEH. 1980. Dragonian mammals Formation, middle Paleocene (Torrejonian), Carbon and Palcocene magnetic polarity stratigraphy of the County, Wyoming: geologic setting and mammalian North I-lorn Formation, central Utah. American fl.mna. Evolutionary Monograph 3. 17811p. Journal of Science 280: 787-811. ROllISON, S. F. 1986. Paleocene (Pucrcan-Torrt::jonian) VAN VAliN, L. 1967. New Paleocene inst::ctivon::lS and mammalian faunas of the North lIorn Form~ltion, insectivore classification. Bulletin of the American central Utah. Brighalll Youn~ University Geology Museum of Natur-al History 135: 217-284. Studies 33: 87-133. -~o;-.' 1978. The beginning of the Age of Yiammals. RO:,E, K. D. 1981. The Clarkforhm land-mammal age :mcl Evolutionary Theory 4: 45--80. mammalian faunal compo~ition across the Pak:occnc W~ST, R. M. 1971. Deciduolls dentition of the early Eocene houndary. University of Michigan Papers on Tertiary Phcnacodontidae (Condylarthra, Mammalia). Paleontology 26: 1-196. American Mu.~eum ovitates 2461: 1-37. SIMI'SON, G. G. 1936. A new fauna from the Furl Union of _---,~;. 1976. The North American Phenacodontidae Montana. American Museum Novitatcs 873: 1-27. (Mammalia, Condylarthm). Contrihutions to Bio . 1.937a. The Fort Ullion of the Crazy Moulltain logical Ceology, Milwaukee Public Museum 6: 1-78. --~>C.·id·d, Montana, and its lllammalian faunas. Bulletin WOOD, H. E., n. R. W CHo\NEY, J. CLARK, E. H. COLBEln: ofthe United Srut<"'S Ni.ltionaJ Museum 169: 1-287. G. L. JI£PSI.L\', J. B. REKSIDE, In., A~D C. STOCK. --,e;:' 1937h. Additions to the upper Paleocene fuulla of 1941. Nomenclature and correlation of the North the Crazy Mountain Field. American Museum American continental Tertiary. Bulletin ofthe Geolog Novitates 940: 1-15. ical Society ofAmtlrica 52: 1--48. __ceo 194,5. The principles 01' classification and a classi fication of mammals. Bulletin of the Americlln Received 6 May 1994 ~llseliln of Natural History 8.5: 1-350. Accepted 12 Decembel'l994