New records of Middle and Late Miocene perissodactyla and artiodactyla from the western border of the San Joaquin valley Diablo Range, Fresno county, California

2008·24.6 MB·English

by  Thomas S Kelly

New Records oe Middle and Late Miocene
Perissodactyla and Artiodactyla erom the
Western Border oe the San Joaquin Valley,
Diablo Range, Fresno County, Calieornia
Thomas S. Kelly^ and D. Stewart^’^
J.
ABSTRACT. A mitigation project has resulted in the discovery of a highly significant new Miocene
vertebrate fossil locality in the Temblor Formation along Monocline Ridge, Diablo Range, Fresno
County, California. AdditionalMiocenevertebratefossillocalitieswerealsodiscoveredintheoverlying
Oro Loma Formation alongMonocline Ridge. These localities have yielded four superposed vertebrate
assemblages that range in age from the middle Miocene to the late Miocene (Barstovian through
Hemphillian North American Land Mammal Ages). Of the perissodactyls and artiodactyls recovered
during the project, the following taxa are identified and described: cf. Peraceras sp., Archaeohippus
mourningi, Desmatippus avus, ''Merychippus"' californicus, ''Merychippus” brevidontus, ''Merychip-
pus” cf. “M.” relictus, Hipparion tehonense, Neohipparion leptode, Dinohippus spp., Miolabis sp.,
Alforjas sp., Camelidae (medium-sized sp.), and Antilocapridae (Cosorycinae, gen. and sp.
indeterminate). Miocene horses and camels are useful in chronologic correlation because they are
abundant in the fossil record and, for most species, their geochronologic ranges are reasonably well
defined. This fact allows a chronologic framework to be proposed for the Temblor and Oro Loma
Formations based on the perissodactyls and artiodactyls.
INTRODUCTION caused by the construction of a new electrical
power line (Path 15) between the towns of Los
The eastern side of the Diablo Range, which Banos and Coalinga. The Path 15 route traverses
forms part of the western border of the San Monocline Ridge in a north-south orientation
Joaquin Valley ofcentral California, is composed along the east side of the Ciervo Hills, Diablo
primarily of marine sediments with minor terres- Range, Fresno County, California. The paleonto-
trial sedimentsranginginage fromthe Cretaceous logical impact portion of the project was led by
to the Fiolocene (Arnold and Anderson, 1910; J.D. Stewart and resulted in the discovery of a
Merriam, 1915c; Bode, 1935b; Woodring et al., new fossil locality that yielded highly significant
1940; Dibblee, 1975; Bartow, 1996). The first vertebrate fossil specimens. Four additional ver-
Miocene fossilterrestrial mammals to berecorded tebrate fossil localities near the project area along
from this area were found near the community of Monocline Ridge and one locality to the south,
Coalinga (Merriam, 1914, 1915c). Merriam near Domengine Creek, were also discovered.
(1915a) referred to this locality as the Merychip- Two localities consisted of bone beds with
pus Zone. Based on further collecting at the site sufficiently high concentrations of fossils to
by the California Institute of Technology, Bode warrant quarrying. The most productive quarry.
(1935a, b) provided a more detailed account of UniversityofCalifornia, MuseumofPaleontology
the taxa and stratigraphy of the Merychippus
locality V-99563, yielded over 1,200 vertebrate
Zone. Subsequently, a few other investigators fossils along with five Mollusca and one ostra-
have discussed the fauna from the Merychippus
code. Zaborsky (2004) provided a preliminary
Zone (e.g., Stirton, 1940a; Downs, 1961; Mac- faunal list for V-99563 based on the identifica-
nFaedwdesni,gni1f9i8c4a)n.t sSainmcpeletsheofintietriraelstdriisaclovveerriteesb,rantoe tions by a number of investigators (see Acknowl-
edgments section). Updated faunal lists for all
fossils have been recovered from the eastern
DiaDbulroinRgantghee ilnastovseerve7r0alyeyaerasr.s a program was locOalfittiehseafroessiplremsaenmtmeadlisn Traebcloveer1e.d, the perisso-
dactylsarerepresented byhorsesanda rhinoceros,
completed to mitigate the paleontologic impacts
while the artiodactyls are represented by camels
and a cosorycine antilocaprid. Because Miocene
Pal’eoRnetsoelaorgcyh, NAastsuorcailatHei,stDoreypaMrutsmeenutm ooffLVoesrtAenbgrealtees fossil horses are abundant in the fossil record and
County, 900 Exposition Boulevard, Los Angeles, Cali- have reasonably well-defined chronologic ranges,
fornia 90007 USA they are particularly useful for biostratigraphic
^ Stewart Paleontological Consulting, 107 Cedar correlation (MacFadden, 1984). Although their
Street, Pasadena, California 91103 USA taxonomy is notaswell defined as thatfor horses.
Contributions in Science, Number 516, pp. 1-29
Natural History Museum ofLos Angeles County, 2008
2 Contributions in Science, Number 516 Kelly and Stewart: Miocene Ungulates
Table 1 Vertebrate faunal lists from new fossil Table 1 Continued.
localities, Diablo Range, Fresno County, California. Neohipparion leptode
ABBREVIATIONS: indet. = indeterminate; undet. Dinohippus sp.
= undetermined Artiodactyla
UCMPV-99563,TemblorFormation,MonoclineRidge Camelidae
iansvseesmtbilgaatgoers(wmohdoifiideedntaifftieerdtZaaxbaorsseekyA,ck2n0o0w4le[dfogremliestntosf LLAACCMM7766A6l68f4,oraujnansdnas7pm6.6e7d,nOornomaLrionmeasFeodrimmaenttisono,faDnibdblee
section]; also see Tseng et ak, 2007; this paper). (1975), uppermost Oro Loma assemblage.
Amphibia Mammalia
Anura, sp. undet Perissodactyla
Eureptilia Equidae
Ophidia Dinohippus spp.
Colubridae
Masticophis or Coluber sp.
Testudines
camels can also be useful for biostratigraphic
Testudinidae
Hesperotestudo sp. ofthe H. osborniana- studies. Based primarily on the horses and camels,
orthopyga lineage three North American Land Mammal Ages are
Aves represented in the Monocline Ridge area (Barsto-
Anseriformes vian, Clarendonian, andHemphillian). Thisreport
Anatidae documents the perissodactyl and artiodactyl taxa
Branta cf. B. woolfendeni discovered during the course of this project and
anatid, sp. undet. providesa preliminarybiostratigraphicframework
Podicepidae
for the fossil localities.
Passeriformes, sp. undet.
Mammalia
Lagomorpha METHODS AND MATERIALS
Leporidae, sp. undet.
Rodentia, two undet. spp. All specimens from locality V-99563 were deposited in
Carnivora the Museum of Paleontology, University of California,
Felidae Berkeley. All other specimens were deposited in the
Bseudaelurus marshi Natural History Museum of Los Angeles County.
Mustelidae Detailed locality data are on file at these repositories.
Maries cf. M. glarea Measurements of teeth and appendicular elements
mustelid, new gen. and sp. were made tothe nearest 0.1 mmwith a verniercaliper.
Amphicyonidae Equid dental terminology follows Stirton (1941) and
Amphicyon ingens MacFadden (1984). All equid teeth were measured
Canidae followingthe standards set forth byMacFadden (1984).
Microtomarctus conferta All other specimens were measured at their greatest
Borophaginae, sp. undet. dimensions. Upper teeth are designated by uppercase
Perissodactyla letters and lower teeth by lowercase letters. Metric
Equidae abbreviationsanddentalformulaefollowstandardusage.
Archaeohippus mourningi All taxonomic identifications were determined by the
Desmatippus amts authors using published accounts and comparative
‘'Merycbippiis'' californicus material in the vertebrate paleontological collections of
''Merychippus'' breuidontus the Natural History Museum of Los Angeles County
''Merychippiis’' cf. “M.” relictus and the Museum of Paleontology, University of Cali-
Rhinocerotidae fornia, Berkeley.
cf. Peraceras sp
Artiodactyla ABBREVIATIONS
Antilocapridae
Cosorycinae, gen. and sp. indet.
Camelidae x^-P anteroposterior
Miolabis sp. Ar-Ar argon-argon
camelid, sp. undet. DPOF dorsal preorbital fossa
Proboscidea, sp. undet. K-Ar potassium-argon
LACM 7665, Oro Loma Formation, middle Oro Loma L left
assemblage. LACM Natural History Museum of Los Angeles
Mammalia County, Los Angeles, California
Perissodactyla If local fauna
Equidae Ma million years before present
Hipparion tehonense O.R. observed range
LACM 7666, Oro Loma Formation, upper Oro Loma R right
assemblage. ROC radius ofcurvature
Mammalia
s.l. sensu lato
Perissodactyla s.s. sensu stricto
Equidae TR transverse
Contributions in Science, Number 516 Kelly and Stewart: Miocene Ungulates 3
120«30’
Figure 1 Map showing the geographic location of study area and major vertebrate fossil bearing localities along
Monocline Ridge, Diablo Range, Fresno County, California. Base map: U.S. Geological Survey topographic map,
1:100,000 scale
UCMP University of California, Museum of Paleon- Temblor Formation (marine), (2) Big Blue Forma-
VU-TRL UtuopClpoeMgryP,tovBoeertrtkheebrlreoaywt,elCefaonlsgistfihlorlnoicaality tE(imtoacnrhieng(eom)ia,nri(nF4e)o)r,Jmaact(a3li)iotnoSsa(tnFetorarremstaMrtaiiarlog)na,r(i(6tt)earSreasFntorriJamolaa),tqiu(oi5nn)
clay (marine), and (7) Tulare Formation (marine).
Subsequently, Dibblee (1975) abandoned the
GEOLOGIC SETTING AND LOCALITIES names Jacalitos and Etchegoin formations for the
terrestrial sedimentsoverlyingtheTemblorForma-
ThePath 15routetraversesMonoclineRidgealong tion in this area and referred them to “unnamed
the eastern side of the Diablo Range, between nonmarine sediments.” Bartow (1996) provided
Panoche Creek in the north and Cantua Creek in the most recent geologic map of the Monocline
the south (Figure 1). Bode (1935b) provided a Ridge area, wherein he referred the “unnamed
correlation chart of several stratigraphic sections, nonmarine sediments” overlying the Temblor
includingtheMerychippusZone alongDomengine Formation to the Oro Foma Formation of Briggs
Creek, which is south of Path 15 at the southern (1953) (Figure 2). The marine Temblor Formation
endoftheDiabloRange.TheMerychippusZoneis inthestudyareaconsistsofcalcareouscementedto
consideredto occurinthe upperpartofthe marine friable, arkosic to lithic sandstone with occasional
Temblor Formation. The Cenozoic sediments in pebble conglomerate. The overlying nonmarine
this section were originally assigned to the follow- Oro Foma Formation consists of friable to locally
ing, from oldest to youngest (Bode, 1935b): (1) calcareous sandstone (commonly cross-bedded).
L
4 Contributions in Science, Number 516 Kelly and Stewart: Miocene Ungulates
N. SIDEOF ARROYO BETWEEN
CANTUA CREEK HONDO ARROYO CIERRO
SSE AND PANOCHE CREEK
NNW
NALMA VERTEBRATE
FOSSI
LOCALITIES
1LACM7664,7667,
7668
HEMP
—
LACM7666
CLAR —
LACM 7665
—
V-99563
BAR
Figure 2 SchematicstratigraphicsectionsofMonoclineRidgeareabetweenCantuaCreektothesouthandPanoche
Creek to the north, western border of San Joaquin Valley, California, with positions of vertebrate fossil localities.
Sections based on geologic map of Bartow (1996), vertical elevation not to scale. ABBREVIATIONS: FM =
formation; BAR = Barstovian; CLAR = Clarendonian; BBSMF = Big Blue Formation, Serpentinite-mudstone and
sandstone facies; HEMP = Hemphillian; NALMA = North American Land Mammal Age
Contributions in Science, Number 516 Kelly and Stewart: Miocene Ungulates 5
Figure 3 The rhinocerotid cf. Peraceras sp. from Temblor Formation, partial left dentary with three partial cheek
teeth, UCMP 167070, labial view. Scale = 10 mm
mudstone, claystone, and pebble conglomerate all the other localities along Monocline Ridge.
(Bartow, 1996). All ofthe fossils in the study area The fossils from these localities are referred to
were recovered from either the Temblor or Oro the uppermost Oro Loma assemblage. Another
Toma Formations. locality (LACM 7668) was discovered south of
The localities in the study area have yielded the project area, near the Mack Pumping
four superposed terrestrial mammal fossil as- Station, in the Domengine Creek area of the
semblages. The stratigraphically lowest locality, southern Diablo Range. This locality occurs in
V-99563, occurs on a small hill between the “unnamed nonmarine sediments” of Dibblee
Panoche Creek and Arroyo Cierro along Mono- (1975), which are a correlative of the Oro Loma
cline Ridge. The hill consists of landslide debris Formation along Monocline Ridge. The assem-
(Zaborsky, 2004) that came from the upper part blage from this locality is probably a correlative
of the Temblor Formation. This locality is an of the uppermost Oro Loma assemblage. Fig-
extensive bone bed that was quarried during the ure 2 provides three schematic sections of the
project and the fauna from it is referred to as the study area with the relative stratigraphic posi-
Monocline Ridge assemblage. Locality LACM tions of the vertebrate fossil-bearing localities.
7665, which occurs about 1.5 km south of V-
99563, is estimated to be about 640 to 740 m SYSTEMATIC PALEONTOLOGY
stratigraphically above V-99563 in the Oro
Loma Formation. The fauna from this locality Perissodactyla Owen, 1848
is referred to as the middle Oro Loma assem- Rhinocerotidae Gray, 1821
blage. Locality LACM 7666, which is also in Peraceras Cope, 1880b
geOarrsaotphioLcfoalmLlayACaFMboorvm7ea6t6ii5ot.n,aTnhodeccaufbraosuuntaab1of8ur0tomm0.L3sA3trCaktMim- cf. PeFrigaucreera3s sp.
7666 is referred to as the upper Oro Loma REFERRED SPECIMEN. From locality V-
assemblage. The other two localities occur to the 99563: partial left dentary with three partial
north (LACM 7664) and south (LACM 7667) of cheek teeth, UCMP 167070.
V-99563 along Monocline Ridge. Their relative DESCRIPTION. The partial dentary contains
stratigraphic positions are difficult to assess three well-worn partial lower cheek teeth. The
because of incomplete exposures in the area, anterior and posteriorcheek teeth are represented
but they occur in the uppermost part of the Oro by small portions of their occlusal surfaces and
Loma Formation, stratigraphically higher than their anterior and posterior roots, respectively.
6 Contributions in Science, Number 516 Kelly and Stewart: Miocene Ungulates
A
BCD
Figure 4 DesmatippusavusfromTemblorFormation.A,partialmaxillawithpartialRPl, RP2-M2,UCMP 166555;
B, RMl or2,UCMP 166863; C, Lp3 or4, UCMP 166883; D, Rml or2,UCMP 166697. All occlusalviews. Scale =
mm
5
Thesetwopartialteeth are missingthelingualand communication, 2007). However, due to the poor
labial enamel surfaces. The middle cheek tooth is preservation of UCMP 167070, it is only tenta-
missing the lingual enamel surface, whereas the tively referred to Feraceras.
labial enamel is partially preserved and exhibits a
distinct cingulum. It is difficult to determine Equidae Gray, 1821
which three lower teeth these represent because Desmatippus Scott, 1893
the lower premolars of Rhinocerotidae are mo- Desmatippus avus Marsh, 1874
lariform. ITowever, the occlusal wear pattern of Figure 4, Table 2
the middle tooth suggests that itmayrepresentp4
or ml. The A-P dimension of the middle tooth is REFERRED SPECIMENS. From locality V-
estimated at about 50 mm. 99563: partial left maxilla with P1-M2, UCMP
Although well worn, the middle tooth appears 166555; RMl or 2, UCMP 166863; Lp3 or 4,
to be lower crowned than those of Teleoceras UCMP 166883; Rml or 2, UCMP 166697.
Flatcher, 1894. Feraceras has strong labial and DESCRIPTION. The upper teeth are charac-
lingual cingula present on all lower cheek teeth terized bythe following: (1) moderatelylarge size,
(Prothero, 2005). Distinct labial cingula are also as compared with other parahippine horses; (2)
present on the lower cheek teeth of Aphelops moderately thick cement within the fossettes and
Cope, 1874, but the lingual cingula are not lophs, and a thin coat or none on the external
developed as in Feraceras. Because the lingual surfaces ofthe teeth; (3) simple crochet present in
enamel surfaces are missing in UCMP 167070, early wear extending to near the base of the
generic assignment of the specimen based on the protoloph (thecrochetisworn awayinlatewear);
presence or absence of lingual cingula cannot be (4) in early wear, protocone separated from the
determined. The size of the teeth in UCMP protoconule by a distinct constriction; (5) plica-
167070 appear too large to represent the Bar- tions present on the metaloph during early wear;
stovian Aphelops megalodus (Cope, 1873), Fer- (6) metaloph connected to the ectoloph; (7)
aceras hessei Prothero and Manning, 1987, or hypocone as large or nearly as large as the
Feraceras profectum (Matthew, 1899), but are protocone; (8) large triangular hypostyle; and
comparable in size to those of the Barstovian (9) well-developed anteriorcingulum extendingto
Feraceras superciliosum Cope, 1880b, and may the anterior labial aspect of the protocone. The
represent this species (D.R. Prothero, personal lower teeth are of typical parahippine morphol-
Contributions in Science, Number 516 Kelly and Stewart: Miocene Ungulates 7
Table 2 Measurements (in mm) ofDesmatippus avus 1987, 2004). In the type of P. brevidens and
from Temblor Formation. ABBREVIATION: a = ap- referred specimens, an internal cingulum is
lacking on the upper molars (Osborn, 1918;
proximate
Downs, 1956). Thus the presence or absence of
UCMP specimen internal and external cingula and cingulids on the
number Position/dimension Measurement upper and lower cheek teeth, respectively, does
166555 PI A-P 12—.5a not seem to be a reliable diagnostic character to
TR separate these species. Needless to say, the
P2 A-P 22.4a parahippines are in desperate need of revision.
TR 21.2 Based on size and all other dental morphology,
P3 A-P 21.4 the parahippine teeth from UCMP V-99563 are
TR 24.0
regarded as conspecific with the parahippine
P4 A-P 21.1
TR 23.5 material from North Coalinga and Mascall, and
Ml A-P 21.4 are referred to D. avus.
TR 23.5
M2 A-P 20.6a Archaeohippus Gidley, 1906
TR 23.5 Archaeohippus mourningi Merriam, 1913
PM21--4MA2-P 4600..67aa Figure 5, Table 3
166863 RMl or 2 A-P 22.0 REFERRED SPECIMENS. From locality V-
TR 24.3 99563: partial left maxilla with P3-4, UCMP
116666868937 RLpmT3lRoorr42AA--PP 111796...853 U16C6M50P8;16L6P6339o;rL4p,3UoCrM4,PUC16M6P5101;66R50M4l. or 2,
TR 13.7 DESCRIPTION. The upper cheek teeth are
characterized by the following: (1) moderately
large size, as compared with other species of
ogy. The lower premolar has much better Amractheadeomhiepspousst'y,le(c2)romwondehreaitghethiynpasobdaornetlyy w(eosrtin-
developed anterior and posterior cingulids than tooth is between 9 and 10 mm); (3) crochet
tmhaeylohwaevremeoxltaerndaenddairtoaupnpdeatrhsetehxattertnhaelcbiansgeuslidosf absent; (4) metaloph lacking plications; (5)
hypostyle large with deep pit in early wear,
theprotoconidandhypoconid, respectively. Inthe triangular in late wear; (6) hypocone well
lower molar the anterior and posterior cingulids
abreetwmeuecnhthweeapkreort,ocaolntihdouagnhdahycpiongcuolniidd.isAprmesoedn-t ccdehiveneeglkuolputemodo,ltahcaksihnalgsa;rgaaendwaes(a8k)plrnyootodcceeovmneeeln;otp.e(7dT)heeixnttleeorrwnneaarll
erately thick covering of cement is present on the cingulid and lacks cement.
lower teeth. DISCUSSION. The Archaeohippus teeth from
gy,DIthSeCUteSeStIhOfNr.omInUsCizMePanVd-9oc9c5l6u3salarmeorinpdhiostlion-- UmoCuMrnPingVi-9b9e5c6a3usearteheryefpeorsrseedsstoallAtrhcehadeioaghniopsptuisc
guishable from those of Desmatippus avus from characters of this species (Merriam, 1913; Os-
the Merychippus Zone from the North Coalinga born, 1918; Downs, 1956) and are indistinguish-
area of California and the Mascall Fauna of able from those referredtoA. mourningi from the
Oregon, except that the upper molars lack Barstow Formation, the Caliente Formation, and
internal cingula and the one lower molar lacks the Merychippus Zone of North Coalinga, Cali-
an external cingulid. Other investigators have fornia.
long noted that Desmatippus crenidens Scott,
1893, from Deep River, Montana, was very ""Merychippus"' s.l. Leidy, 1857
similar to D. avus (Gidley, 1907; Merriam and ''Merychippus" californicus Merriam 1915a
Sinclair, 1907; Downs, 1956). Downs (1956) Figures 6-9, Tables 4-5
noted that except for the lack of an internal
cingulum on the upper cheek teeth, lack of an REFERRED SPECIMENS. From locality V-
external cingulid on the lower cheek teeth, less 99563: partial skull with RP2-M3 and LP2-M3,
cement, and no ribs, all other characteristics of UCMP 166252; partial left maxilla with partial
the cheek teeth are as those in the type of D. Ml and M2-3, UCMP 166271; partial right
crenidens. The teeth from UCMP V-99563 differ maxilla with Ml-2, UCMP 166276; partial
from those of D. crenidens by having thicker maxilla with dP2-4, UCMP 166262; dRP4,
cement and better-developed parastyles and me- UCMP 166231; dLP3, UCMP 166295; three
sostyles. The material of Desmatippus from the associated cheek teeth, RM2 and LMl-2, UCMP
Merychippus Zone was originally referred to 166224; RP2s, UCMP 166213, 166214, 166225,
Parahippus brevidens (Marsh, 1874), which is 166238, 166310, 166483; LP2s, UCMP 166223,
now regarded as a junior synonym of D. avus 166229, 166245, 166289, 166318, 166338,
(Bode, 1935a; Downs, 1951, 1956;Tedfordetah. 166471; RP3s, UCMP 166234, 166241,
8 Contributions in Science, Number 516 Kelly and Stewart; Miocene Ungulates
Figure 5 Archaeohippiis mourningi from Temblor Formation. A, partial maxilla with LP3-4, UCMP 166508; B,
LP3, UCMP 166510; C, RMl or 2, UCMP 166639; D, lower left cheek tooth, UCMP 166504. All occlusal views.
Scale = 5 mm
166267, 166280, 166288, 166344, 166414; 166368; RM3s, UCMP 166222, 166233,
LP3s, UCMP 166305, 166319, 166463; RP4s, 166251, 166252, 166279, 166328; LM3s, UCMP
UCMP 166215, 166239, 166242; LP4s, UCMP 166261, 166379; left upper molar, UCMP
166220, 166228, 166253, 166258; RMls, 166243; partial right dentary with partial dp2-4
UCMP 166226, 166237, 166248, 166291, and ml-2, UCMP 166446; partial right dentary
166294, 166396, 166399; LMls, UCMP with iland p2-m3, UCMP 166917; partial right
166232, 166244, 166247, 166256, 166277, dentary with broken p2 and p3-m3, UCMP
166301, 166307, 166327, 166345, 166419; 166445; partial right dentary with partial dp2
RM2s, UCMP 166408, 166438; LM2s, UCMP andml, 166299; partialrightdentarywithpartial
166230, 166240, 166265, 166329, 166339, dp3 and dp4, UCMP 166455; partial right
dentary with dp4-ml, UCMP 166441; partial
rightdentarywithp2-m3, UCMP 166218; partial
UCMP
Tmaobulrenin3giMferaosmuTreemmebnltosr F(oirnmamtmi)onof Archaeohippiis rriigghhttddeennttaarryywiwtihthp3mo3r,4,UCMP 116666242876;;ppaarrttiiaall
UCMP right dentary with ml-3, UCMP 166260; partial
specimen right dentary with dp2-3, UCMP 166250; Rml,
number Position/dimension Measurement UCMP
166480; partial left dentary with dp2,
166508 LP3 A-P 14.4 UCMP 166469; partial left dentary with dp2 and
TR 13.9 partial dp3, UCMP 166216; partial left dentary
LP4 A-P 15.0 with p2, UCMP 166466; partial left dentary with
TR 14.2 p2-m3, 166315; partial left dentary with partial
116510 LP3 or 4 A-P 14.7 ml-2 and m3, UCMP 166306.
TR 16.6
166639 RMl or 2 A-P 13.4 DESCRIPTION. The sample includes a partial
TR 15.9 skull, three partial maxillae, 16 partial dentaries,
166504 LowercheektoothA-P 13.5 and numerous isolated cheek teeth. All positions
TR 11.0 and stages of wear are represented in the cheek
teeth including 12 specimens possessing decidu-
Contributions in Science, Number 516 Kelly and Stewart: Miocene Ungulates 9
-
B
Figure 6 ''Merychippus” californicus from Temblor Formation. A-B, partial skull with LP2-M2 and RP2-M3,
UCMP 166252: A, left side ofpartial skull showing position ofinfraorbital foramen (IF), ventral border ofanterior
portionofdorsalpreorbitalfossa (DPOF),anddorsoventraldepressionofboneabove facialcrest (FC) thatappearsto
represent the anterior portion of a shallow malar fossa and not a result of compression or distortion during
preservation; B, LP2-M2 and RP2-M3, occlusal view. Scale = 20 mm
10 Contributions in Science, Number 516 Kelly and Stewart: Miocene Ungulates
—
B
Figure 7 ''Merychippus” californicusfromTemblorFormation. A-B, partial leftmaxillawithpartialMl andM2-
3,UCMP 166271:A, labialview;B,occlusalview. Scale = 5 mm. Note: dorsoventraldepressionofboneabovefacial
crest (FC) that appears to represent the anterior portion ofa shallowmalar fossa and not a result ofcompression or
distortion during preservation
ous cheek teeth. One well-knowncharacteristic of coefficients of variation in the dental statistics,
horse upper and lower cheek teeth is that they especially in P3, Ml, and ml, where the samples
vary in length and width from the crown to the include very worn teeth and/or unworn teeth.
base (e.g., Downs, 1961; Eisenmann et ah, 1988). The sample of permanent upper cheek teeth is
At unworn or early wear stages, the A-P characterized by the following: (1) moderately
dimension at the occlusal surface is greater than complex occlusal fossette enamel plications in
theA-Pdimensionatthe base ofthecrown, which earlywearthat becomeprogressivelylesscomplex
results in significantly larger A-P measurements with wear, so that when they are about 50% or
for these teeth in comparison to teeth that are in more worn the occlusal pattern becomes simple;
moderate to late wear. Conversely at unworn or (2) prominent and relatively persistent plis proto-
early wear stages, the TR dimension is narrower conule present on P3-M3; (3) P3--M2 protocones
at the occlusal surface than at the base of the isolated from the protolophs until the teeth are
crown, so that the TR measurement increases worn by 50% or more; (4) oval P3-M3 occlusal
significantly with wear. This can result in higher protocone outlines with distinct spurs in early