ADDITIONS TO KNOWLEDGE OF PALEOCENE MAMMALS FROM THE NORTH HORN FORMATION, CENTRAL UTAH

11 Pages·1995·5.3 MB·English

by  Richard L Cifelli

GreatBasin Naturalist55(3), © 1995, pp.304-314
ADl^n IONS TO KNOWLEDGE OF PALEOCENE MAMMALS FROM
THE NOm HORN FORMATION, CENTRAL UTAH
II
Kichard L. C>itclli', NicliolasJ. Czaplewski', and Kenneth D. Rose^
—
Abstkact. The distinctive but inadeejuately known Paleocene faunas ofcentral Utah are significant in that they
sample a time interval not well represented l)y secjucnces in other areas. New materials from the Wagon Road (late
Puercan) and Dragon (earl\' Torrejonian) local faunas. North Horn Formation, provide additional information on the
composition ofthe assemblages and systematics ofincluded mannnal ta.xa. The proteutherian tPropalaeosinopa is
recorded, for the first time, from the Wagon Road fauna, indicating a significant extension for the enigmatic family
Pantolestidae,othei-wisefirstknown from theTorrejonian.Associatedpremolars oiAphnmorussirnpsoni,apentacodon-
tid proteutherian from the Dragon fauna, indicate that the species is more distinct from its Torrejonian congener, A.
fmudalor, than previousK' suspected. Newmaterials ofDesmatuclaenushermaeus uphold the synonymyofthis species
with D. paracreodus and permit moreadequatedefinition ofthegenus with respect to thearctocyonid Loxolophua and
thephenacodontid Tetraclaenodon;becauseDesinatoclaeniisappears tosharederivedmorphologywith Loxolophu.s,we
referittothebasalcondylarthfamilyArctocyonidae.TheperiptychidcondylarthHaploconus,representedintheWagon
Roadfaunabythegeologicallyoldestdescribedspeciesofthegenus,H. elachistus,isshowntobedistinctiveinthecon-
figuration oflower molars and premolars; H. elachistus appears to be more primitive than species known from the
Torrejonian ofNew Mexico. Some features oiHaploconus are suggestive ofthe Conacodontinae, a distinctive clade of
diminutiveperiptychids.
Kcij words: Paleocene, North Horn Fonnation, Puercan, Torrejonian, Dragon local fauna. Wagon Road localfauna,
Mainnuitiii.
Paleocene mammals werefirst reportedfi-om Periptyclws interval-zone), and Dragon to Tol
the North Honi Formation, Emery and Sanpete {Periptijchus I Tetraclaenodon interval-zone).
connties, UT, by Gazin (1938). Further field- Both Pu2 and Pu3 are interpreted to occur
workresulted in the recoveiyofadditional taxa, within magneticpolarit>' chron 29N (Butlerand
interpreted as representing two faunas, from Lindsay 1985); the Dragon faima is considered
two main localities (Gazin 1939, 1941). In sub- to lie within anomaly 27N (Tomida and Butler
sequent years, additional sites in the region 1980).
have yielded finther specimens, includingmore 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, Tomida 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 geographicallybetweenthe classic sequence
rently recognized, the Gas Tank, Wagon Road, of the San Juan Basin, NiM, and faunas from
and Dragon local faunas (Robison 1986). On more northerly parts ofthe Western Interior(cf.
the basis ofthe latter two, a "Dragonian" land- Archibald et al. 1987: fig. 3.1). Mammals from
mammal age was initially established (Wood et the Paleocene of the North Horn Formation
al. 1941). Later work, including magnetic are not, in general, well known. We describe
stratigraphy and biostratigraphic comparisons, herein newly collected materials that provide
suggests that the Gas Tank and Wagon Road further details on the moiphology and SNstem-
faunas are Puercan andthe Dragon faunaTorre- atics ofsome ofthe included taxa.
jonian in age (Tomidaand Butler 1980, Tomida The approximate locations of the major
1981, Robison 1986). Archibald et al. (1987) mammal sites in the Paleocene part of the
tentatively assigned the Gas Tank to Pu2 North Horn Formation, taken from data pre-
{Ectoconus ITaeniolahis taocnsis interval zone). sented by Gazin (1941) and Robison (1986),
Wagon Road to Pu3 {Taeniolahis taocnsis I are given in Figure 1. The materials described
OklaliDiiK.Mil )r\'atiinilllistiinandDrpartnicntofZiKiIdRv,UniversitynfOkhihoma.Norman,OK73019.
^Department(ilCellHiclciKyamiAnatomy,JohnsllopknisI niversil\ SelioolofMedicine.725North\\c
304
1
1995] Paleocene Mammals, Utah 305
Descriptive Accounts
Order Proteutheria
Family Pantolestidae Cope, 1884
?Propalaeosinopa sp.
Figs.2A-B
OMNH
Material.— 27681, fragment of
right dentaiy bearing the talonid of P4 (WTil
= 1.5) and complete M^ (L = 2.8, WTri = 1.8,
WTd =
1.8). —OMNH
Locality and horizon. V800,
"Wagon Road" locality (Gazin 1941, Robison
1986); Wagon Road local fauna, late Puercan
/— (early Paleocene). Joes Valley Member, North
Horn Formation, Emeiy County, UT.
—
Description and discussion. The den-
taiy fragment includes the anterior root of P4
and the anterior root ofM2. The anterior root
of P4 is bowed forward as in pentacodontids
and most pantolestids, and its placement indi-
cates that P4 was relatively long, longer than
Mj. The posterior mental foramen is large and
is positioned between the posterior root ofP4
M
Fig. 1. Approximate locations of mammal-bearing sites and the anterior root of j. The talonid ofP4
in Paleocene part ofNorth Horn Formation, Emeiy and includes alarge hypoconid anda small entoco-
Sanpete counties, UT; data from Gazin (1941) and
Robison (1986). Localities, Dragon local fauna: Dragon nid; these two cusps are unitedby a small, thin
Canyon (1). Wagon Road local fauna: Wagon Road (2), postcristid, forming a small talonid basin. The
\Vagon Road Ridge (3). Gas Tank local fauna: Gas Tank apex ofthe hypoconid is on the midline ofthe
Hill (4), Dairy Creek (5), Jason SOpMriNnHg (6), Ferron tooth, at the posterior termination ofa cristid
Mountain (7; probably equivalent to V829), Blue obliqua that angles lingually toward the front;
Lake(8),andSageFlat(9).
the postcristid is oriented almost peipendicu-
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; ?Tol) and Wagon conid b>' 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 lingualbase ofthe talonidbasin.
M
specimen assigned to Ectoconus ditrigoniis The trigonid and talonid of ^ are ofequal
(OMNH 28111), collectedbyJonJuddofCastle width; the trigonid is distinctly higher than
Dale, UT, at a site south of Ferron Mountain. the talonid, though the tooth is moderately
The site, OMNH V829, is probably the same worn. The protoconid and metaconid are both
as Robison's (1986) Ferron Mountain locality triangular in occlusal outline and of equal
(Gas Tanklocal fauna; ?Pu2). occlusal area; the protoconid is the tallerofthe
The followingabbreviations are used for in- two cusps. The paraconid is small, low, and
stitutions cited in the text: BYU, Brigham Young transversely oriented. Anterior and posterior
University, Provo, UT; OMNH, Oklahoma carnassial notches are present in the para-
Museum ofNatural Histoiy, Norman; USNM, cristid and protocristid, respectively. Because
National Museum ofNatural Histoiy, Washing- ofthe transverse orientation ofthe 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 the anterior carnassial notch. A short
WTal, transverse width oftalonid; WTri, trans- anterior cingulum, which disappears at the
verse width oftrigonid. anterolingual corner of the tooth, is present.
306 Great Basin Naturalist [Volume 55
Fig. 2. Proteutheriafrom tlie North Horn Formation. A, B, P4-M1 ofPropalaeosinopa sp. (OMNH 27681) inocclusal
(A)andlabial (B)views. C-G,Aplmmonissimpsoni (OMNH 27667); C, D, right P4inocclusalandlabialviews, respec-
tively; E, F right P3 in occlusal and labial views, respectively; G, left P"* in occlusal view. Scale bar represents 2 mm;
toothrootsandjawfragmentshavebeeneliminatedtoimproveclarity.
1995] Paleocene Mammals, Utah 307
The posteriorwall ofthe trigonid is planar; the 1987). In this context, we note that several
cristid obliqua meets the base ofthe 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
atedbywear, anentoconulid(oratleastanento- known, itmayprove tobegenericallyseparable.
cristid) appears to have been present anterior
to the entoconid. Family Pentacodontidae
OMNH
Of described species, 27681 most (Simpson, 1937) Van Valen, 1967
resembles the Torrejonian Propalaeosinopa di- ApJironorussimpsoni Gazin, 1938
luculi (which we tentatively regard as distinct Figs.2C-G
from P. albertensis following Rose 1981; see —OMNH
discussion in Van Valen 1967). However, the Newly referred material.
Utah taxon differs in several respects. The pos- 27667, right dentaiy fragment with P3^ (P3L
W W
teriormental foramen is more anteriorlylocated = 2.4, = 1.4; P4L =W4.0, = 2.5) andasso-
than in figured specimens ofP. diluculi (Simp- ciated left P^ (L = 3.3, = 4—.1)O.MNH
son 1936: fig. 3; Krause and Gingerich 1983: Locality and horizon. V799,
OMNH
figs. 8, 9). Ml of 27681 is long and "Dragon" locality (locality2 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 Gounty,
UT
Gingerich 1983) in length but not width. In —OMNH
the Utah taxon the cusps of M^ are somewhat Description and discussion.
more robust and the postvallid wall more 27667 differs from the type ofA. simpsoni
obliquely oriented with respect to the long (USNM 15539) in minor ways but is clearly
axis ofthe 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 aweaker
talonid ofP4 is broaderand 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 ofthe protoconid. The
but materials in hand are inadequate toproper- 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 ofthis ridge in the type may be due partly to
pantolestids; both were from die Dragon local the advanced wear in that specimen. P4 of
OMNH
fauna. Of these, he found pantolestid "a" to 27667 bears a small but distinct ento-
compare favorably with Bessoecetor {=Propo- conid; this region of the tooth is broken in
laeosinopa), differing from "J5. thomsom' {=P. USNM 15539. TheanteriorendofP4inOMNH
diluculi) in being slightly larger and in a few 27667 is slightly more developed downward
USNM
morphological details. It is possible that pan- than in 15539, vaguely recalling the
OMNH
tolestid "a" and 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 different horizons in the North Pentacodon, however, the P4 lacks abasal para-
Horn Formation. Differential representation conid, the protoconid is not as inclined poste-
OMNH
precludes direct comparison with riorly from base to apex, and the talonid is bet-
27681. terdeveloped.
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. fraudator (illustrated in
Fantolestidae, 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.fraudator. The tooth is distinct-
genus and family are otherwise first known ly two-rooted and is much smaller than P4;
from the late Torrejonian (To3; Archibald et al. maximum width occurs just posterior to the
.
308 Great Basin Naturalist [Volume 55
protocoaid. A small talonid basin is developed, OrderCond\larthra
withaminutehypoconidanda"cristidoblicjua Family PArctocyonidae
connected to a ridge running down the poste- (Giebel, 1855) Murray, 1866
riorflankof the protoconid. A small, short ridge Desniatoclaenushennaeus Gazin, 1941
and swelling on the posterolingual (lank of the Fig.3A
protoconid are suggestive of a metaconid. A
faintcingulum is presentanterolingually. Newly referred material.—OMNH
No associated upper teeth have been previ- 27682, associated skull andjaw fragments with
otuhsoluyghdeascfreiwbeidsofloarteAdphsrpoencoirmeunsssimianpysoibiei,loanlg- bMrlo-k3en(MrilgLht=an7d.3l,WefWt P^=(8r.i6g;htMP^^LL == 67..53),,Wrigh=t
to the species (Gazin 1941, Robison 1986). P^* 11.0; M^L = 6.2, = 8.7)W, left M2-3 (M^bro-
of OMNH 27667 is broken near the paraconule ken, L = 7.4; M^L = 6.0, = 8.8), left M^ (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 ofthe protocone and right Mo (W = 6.4), trigonid ofleft M2 (W =
the lingual root; the labial side of the meta- 6.0), and talonid ofright M3 (—WO=M5N.2)H."
conid is also damaged. Three roots are pres- Locality and horizon. V800,
ent. The tooth, although similar to P"* ofA. "Wagon Road' locality (Gazin 1941, Robison
fraudator, 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 Member, North
metaconule as such is lacking, although there Horn Formation, Emery County, —UT.
is a vague swelling ofenamel in this position. Description and discussion. P-* has dis-
Thebasal protoconal cingula show no tendency tinct conules, with the paraconule being taller
than the metaconule. These cusps have not
to develop cuspules, as they do in A. frauda-
tor, and the metacone is much smaller in size, previously been noted for P"^ of the species,
perhaps because ofwearon the type specimen
relative to the paracone, than in that species.
The labial cingulum ofp4 in OMNH 27667 is (USNM 16202; see Gazin 1941:'fig. 19; West
also less developed than inA.fraudator 1976: fig. 2). The upper molars have a labial
Aphronorus situpsoni was diagnosed as dis- cingulum that is continuous. Interruptionofthe
ectocingulum at the base ofthe paracone was
tinct from the comparatively well-known A.
cited as a generic charactero{Desmatodaenus
fraudator mainly on the basis ofdifferences in
However, the cingulum is complete in other
proportOioMnNsHofF_^ and the lower molars (Gazin specimens, such as BYU 3800 (Robison 1986:
1941). 27667, which includes teeth pre- pi. 2, fig. 10), and we regard this as a feature
viously unreported forA. simpsoni, shows that
that is intraspecifically variable. M'^ bears a
it is furtherdistinct in havinga somewhat more small but distinct cingular hypocone, another
elongate P3; P4 has a narrower, smaller-basined
character that is apparently variable in the
talonid. P'^ differs from that ofA.fraudator in species (Gazin 1941: figs. 19, 20; Robison 1986).
several respects, including the lack ofa meta- The only variation worthy ofnote in the lower
conule and parastyle, and the much lesser de- dentition ofOMNH 27682 is the hypoconulid
velopment of the metacone. Considering the ofM3, which apparently projected posteriorly
specializations of the posterior premolars in as a distinct lobe, unlike the condition seen in
pentacodontids (Simpson 1937a) and the pos- USNM 16202 (Gazin 1941: fig. 19).
sibility that they represent a relatively archaic Gazin (1941) originallydescribed tvvo species
group (Van Valen 1967), it is difficult to judge ofDesniatoclaenus, D. hennaeus and D. para-
which conditions are apomorphous, although creodus, both fiom theWagon Road fiiuna. West
someofthe states possessedbyA. simpsoni (e.g., (1976) synouNinized the two, a view apparent-
smaller P4 talonid; P^ with small—metacone ly shared by Tomida and Butler (1980), but
and no metaconule) would appea—r by com- Robison (1986) recognized them as distinct
paiisontomoreprimitive Eutheria tobeprim- and reported additional materials of both
itive. The Tiffanian speciesA. orieli, known by species from other localities. In the original
remarkably complete specimens (Gingerich et diagnosis (Gazin 1941), D. paracreodus was
al. 1983), appears to be considerably more said to be larger than D. hermaeus, with the
advanced, with greatly expanded crushing sur- lingual portion ofupper molars more inflated
faces (particularly the protocone) on P"*. andwidiarelativelylarger M'^, bearingabetter-
—
,
Paleocene Mammals, Utah 309
mm
5
t 1 ^ I
Fig. 3. ?Arctoc\oniclae and Periptychinae fioni the North Horn Formation. A, right P"*-M^ ofDesmatoclaenm her-
maeiis(OMNH 27682) fromthe North Horn Formation;baseofM-restoredfromcontralateraltoothofsamespecimen,
andmaxillaeliminatedtoimproveclarity-; B,leftdP^-^andMlofEctoconusditrigonus(OMNH28111)inocclusalview;
maxillaeliminatedtoimproveclarit)'.
developedhypocone. As shown by West (1976), genus with Tetraclaenodon and Frotogonodon,
these differences in size and morphology are as thelattertaxonwas tlien conceived (Matdiew
both minor and inconsistent. In this context, 1937, Simpson 1937a). Van Valen (1978) placed
we note that M^-^ ofOMNH 27682 are rela- "?F. " protogonioides (cf. Matthew 1937)
tively small (a supposed character of D. her- originally referred (Co—pe 1882a), in part, to
maeus), yet M-^ 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. paracreodiis). We follow West (1976) in diaiiae and D. mearae; Frotogonodon was syn-
regardingthe species as synonymous. onymized with Loxolophus. We are in agree-
In the original diagnosis and discussion of ment with these assignments; D. protogo-
Desmatoclaenus, Gazin (1941) compared the nioides is relatively well represented and adds
310 Great Basin Natur.\list [Volume 55
significantly to knowledge of the genus. Tlius lingual base ofthe crown and enamel from the
recognized, Desniatoclaenus 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
P*^^; better-developed, more lingually placed only two ofthe four species ofAnisonchus re-
hxpocone on \l'~-, with hypocone occasionally ported from the North Horn Formation (Gazin
OMNH
distinct on M'^; and paraconid of lower molars 1941, Robison 1986); 27679 differs
placed more posterolingually and closely from M'^ referred to A. athelae (including A.
appressed to the metaconid. Desmatoclaenus eowijnae; Robison 1986) and is tentatively
differs from Tetraclaenodon in having less referred to A. oligistus, for which M"^ was not
molarized premolars (a metacone is lacking on previouslyknown. Although the tooth is incom-
P'^""^; 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 ofthe 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) considered Desmatoclaenus to this respect. The pattern ofwear suggests that
be stmcturallyinteimediatebetween thearcha- both paraconule and metaconule were present,
icungulate "Protof^onodou' (then considered a placed near the base of paracone and meta-
creodont) and Tetraclaenodon, a primitive cone, respectively.
phenacodontid; the differential comparisons
presented above uphold this view. Subsequent Haploconus elachistus Gazin, 1941
workers have referred Desmatoclaenus to the Figs.4B-F
Ai^ctocyonidaeon theonehand (VanValen 1978, —OMNH
Cifelli 1983) or the Phenacodontidae on the Newly referred material.
other (Simpson 1945, West 1976, Robison 27670, fragments of mandible with left M^_2
1986). Thepositioningofthe uppermolarh)TDO- (MiL = 3.8, WTri = 2.7, WTal = 2.8; M2L =
cone somewhat more lingually in Desmatoclae- 3.9, WTri = 3.2, WTal = 2.9) and right M2 (L
noufsthtehapnriensLuomxaoblloyphduesriisvevdagcuoenldyirteimoinniisnctehnet m=en4t.0s,oWfTlrefit m=an3d.1i,blWeTawlith=P33.0();L 2=7741.35,,Wfrag=-
OMNH
Phenacodontidae; similarly, the low, bunodont 2.8) and a heavily encrusted molar;
W
cusps bearing mainly flat, apical wear are sim- 27680, right P4 (L = 4.5, =—3O.3)M.NH
ilar to conditions generally obtained in mem- Locality and horizon. V800,
bers of that family. Desmatoclaenus may well "Wagon Road" locality (Gazin 1941, Robison
be 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 Horn Formation, Emery County, UT—.
Arctocyonidae. In this context, we note that the Description and discussion. Available
(OMNH
referred species D. protogonioides apparently lower premolars 27680, 27713) are
has a reduced anterior dentition, a condition tooworn to detenninewhedieraparaconid was
shared with loxolophine arctocyonids (Cifelli present; Gazin (1941) reported the presence of
1983). this cusp on P3 but not P4 ofHaploconus ela-
chistus. The protoconid is alarge, inflated cusp,
Family Periptychidae Cope, 1882 particularly on P4. A talonid crescent extends
Anisonchus ?oligistus Gazin, 1941 posteriorly from the lingual base ofthe proto-
Fig.4A conid, curving labially at the posterior margin
ofboth P3 and P4. The metaconid of lower
—OMNH
Newly referred material. molars is nearly as tall as the protoconid and is
27679, right M'l —OMNH transversely aligned with that cusp; a weak
Locality and horizon. V800, paracristid descends anterolingually from the
"Wagon Road" locality (Gazin 1941, Robison protoconid, teniiinating 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 b\' Gazin (1941), the pre-entocristid is taller
Horn Formation, Emeiy County, UT. than the cristid oblicjua. The entoconid forms
Description.—OMNH 27679 is missingtlie a distinct pillar and projects somewhat on the
1995] Paleocene Mammals, Utah 311
Fig. 4. Anisonchinae fiom the North Horn Formation. A,Anisonclut.s 'fuli^istus (UMNH 27679, right M^ in occkisal
view). B-FHaploconuselachistus: B,left Mi_2(OMNH27670)inocclusalview;C,E,leftP3(OMNH27713)inocclusal
and labial views, respectively; D, F, right P4 (OMNH 27680) in occlusalandlabialviews, respectively. Scalebarrepre-
sents2mm;toothrootsandjawfragmentshavebeeneliminatedtoimproveclarit)'.
312 Gril\t Basin Naturalist [Volume 55
lingual side of the tooth; the inpoeonulid considered the species to be transitional be-
forms a fingerlike projeetiou at the baek of the tween Conacodon and more derived species of
tooth and is somewhat lingual in position, an Haploconus. In retaining unreduced lower
appearanceemphasizedin laterwearstages. molar trigonids and relatively unspecialized
Two species of Haploconus, H. angustus lower premolars, species of Conacodon are
and the larger H. coniictilaiiis, are recognized primitive with respect to Haploconus. In terms
from the Torrejonian (To2; Archibald et al. ofcharacters that are probably derived within
NM
1987) of the San Juan Basin, (Matthew tlie context ofCondylarthra, Conacodon, Haplo-
1937). The apparent last record ofHaploconm conus, and Oxyacodon have a lingually placed
is represented by a single molar, of uncertain hypoconulid and hypertrophied postmeta-
specific affinities, from Swain Quarry (To3?; cristid on lower molars, lingually placed hypo-
Archibald et al. 1987), WY (Rigby 1980). The cone on uppermolars, loss ofprotocone on P^,
genus is othenvise known onlyfrom the North and, possibly, a columnar, lingually placed
Horn Formation. Gazin (1939) described H. entoconid on lower molars (not clearly seen in
inopinatiLS fiom the Dragon fauna, later adding all species ofOxyacodon). However, the exclu-
asecond species, ?//. elachistm, fi-om dieWagon siveness ofthese characters and theirpotential
Road (Gazin 1941). More recently, Robison status as synapomoiphies remain to be estab-
(1986) has reported specimens ofHaploconus lished. Archibald, Schoch, and Rigby (1983)
sp. from the Gas Tank local fauna; these mate- have shown that Conacodon 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 otherperiptychids
they are not specificalh' diagnostic. H. inopina- is unclear; further investigation ofthe position
tiis, ofTol age, is similar in size to the later H. of Haploconus with respect to this clade is
angiistus but differs from that species in pro- clearlywarranted.
portions of the upper molars (Gazin 1939). H.
elachistus, the geologically oldest described Ectoconus ditrigonus (Gope, 1882)
species, is smaller than the Tonejonian species Fig.3B
and, as noted by Gazin (1941), differs from —OMNH
them in a number of respects. In the lower Newly referred material.
adnengtmittuiso.n,SiPmi3l_a4rha,retheletsrsigionnfildsatoefdlotwhearnmionlaHr.s 2M8l11(1d,pf3rLag=me7n.t5,WoWfle=ft m7a.0x;ildlPa-^wLit=h d7P.'5,^^Wan=d
in H. elachistus lack the inflated appearance 8.4; MlL = 9.6, = 13.5). —OMNH
seen in Torrejonian species; a small paraconid Locality and horizon. V829,
is stillpresent,whereas inremainingspecies the probably the same as Robison's (1986) Ferron
paracristid forms abladelike surface extending Mountain localit)'; Gas Tanklocal fauna, middle
anteriorly from the protoconid and bears no Puercan (early Paleocene). Joes Valley Member,
cusp. Lower molars ofH. elachistus also lack North Horn Formation, EmeiyGo—unty, UT.
the crenulated or striated enamel and promi- Description and discussion. The decid-
nent labial cingulum seen in other species. As uous teeth, dP'^~^, are markedly smaller than
might be expected, the geologically older H. M^;bothhave conspicuous parast\'larand 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 sube(]ual 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 ofthe paraconid) and in the nearly as tall as the paracone and metacone;
unusual configuration ofthe talonid in posteri- another ridge descends the labial slope ofthe
or lower premolars (with a lingual rather than parastyle, continuingposteriorlyas aweak ecto-
labial crescent), characters that are both ex- cingulum. Labial to the metacone, the stylar
pressed in H. elachistus. The affinities 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 ofsome features ofH. elachistus. upper molars ofEctoconus ditrigonus (Osborn
.
1995] Paleocene Mammals, Utah 313
and Earle 1895), is present labial to the meta- there is no basis for comparison with dP'^~l of
cone. A salient postmetacrista descends pos- Ectoconus ditrigonus
terolabially from the apex of the metacone,
extending to the posterolabial corner 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 ofthe U. S. Forest Service.
present on the lingual slopes ofthe protocone. We thank Jon Judd, Monte Swasey, and Scott
The fourth deciduous premolar is more molar- Madsen forhelp in the field; Dr Scott Russell,
iform than dP'^, differing from M^ 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 dP^ is more labially Drs. David W. Krause, David Archibald, and
J.
placed than on dP'^, and the ectocingulum and Jeffrey G. Eaton provided invaluable com-
cingular cusp better 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 andhypo- from the National Geographic Society.
cone are present. M^ is typical o{ Ectoconus
and complete description is unnecessaiy The Literature Cited
ectocingulum is strong and bears both a meso-
st)'le andposteriorstvlarcusp. The latteris sub- Archibald, J. D.. E D. Gingerich, E. H. Lindsay, W. A.
conical and is connected to the base of the Clemens,Jr., D. W. Krause,andK. D. Rose. 1987.
metacone by alow ridge. Paracone, metacone, First North American land mammal ages of the
Cenozoic Era. Pages 24-76 in M. O. Woodburne,
and protocone are subequal in height; conules editor, Cenozoic mammals ofNorth America: geo-
are strongly developed and are only slightly chronolog\' and biostratigraphy. University ofCali-
lower than the principal cusps. forniaPress,Berkeley.
Ectoconus ditrigonus, the type species, was Archibald,J. D.,J. K. Rigbv,Jr.,andS. ERobison. 1983.
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NM Peript\'chidae) and adescriptionofO.ferronensis n.
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Valen (1978) to be synonymous with E. ditri- species,Conacodonkohlbergeri, ofthePeript)chidae
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Wagon Road (?Pu3) fauna. North Horn Forma- ClFELLi, R. L. 1983. Theoriginandaffinities ofthe South
tion. Robison (1986) described additional mate- A(mMearmimcaalniaC)o.ndAymlaerrtihcraananMduesaerhu'mTerNtoivaiityaLtietsop2t77e2m:a
rials ofE. sijmbolus from localities ofthe Gas 1-49.
Tank fauna, thereby extending the range ofthe Cope, E. D. 1882a. Some new forms from the Puerco
species to ?Pu2, and reported E. ditrigonus Eocene.AmericanNaturalist 16:83.3-8.34.
from two Gas Tanklocalities. OMNH 28111 can . 1882b. Synopsis ofthe Vertebrata ofthe Puerco
Eocene epoch. Proceedings ofthe American Philo-
be referred to the latter species on the basis of
sophicalSociety'20:461-471.
size (larger than E. symbohis) and the pres- Gazin, C. L. 1938. A Paleocene mammalian fauna from
ence ofa relatively small posterior cusp, con- central Utah.Journal oftheWashingtonAcademv'of
nected to the base of the metacone b\' a low Science28:271-277.
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cenefaunaofcentral Utah.Journalofthe\^ashington
1986). AcademyofScience29:273-286.
Deciduous teeth ofarchaic ungulates have 1941. The mammalianfaunas ofthe Paleocene of
.
not been widely described or illustrated, a central L'tah,withnotesonthegeolog)'. Proceedings
notable exception being the deciduous premo- oftheLhiitedStates NationalMuseum91: 1-53.
lars of Phenacodontidae (West 1971). To our Gingenreicwh,earRliDe.s,t PTifHfoaunidaen,(laantedPDa.leWo.ceKnre.)4UmSEa.mm1a98l3i.aAn
knowledge, deciduous teeth of Periptychidae faunafiom Bangtail Plateau,westernCraz\-Mountain
have not been previously described, so that Basin,Montana.JournalofPaleontology'57:957-970.