The Sage Creek Mountain Local Fauna of the Bridger Formation Near Lonetree, Wyoming

Home , Brontotheriidae, Eotitanops, Hyaenodontidae, Limnocyon, Mesatirhinus, Miacidae

Brigham Young University BYU ScholarsArchive

Theses and Dissertations

1977-08-01

The Sage Creek Mountain local fauna of the Bridger Formation near Lonetree, Wyoming

Steven W. Barker Brigham Young University - Provo

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BYU ScholarsArchive Citation Barker, Steven W., "The Sage Creek Mountain local fauna of the Bridger Formation near Lonetree, Wyoming" (1977). Theses and Dissertations. 7620. https://scholarsarchive.byu.edu/etd/7620

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A 'lhesis

De_pe:r.tment of Zoology

Br1gham Young Universjty

In Partial Fulfillment

of the Requirements for the Degree Master of Science

August 1977 'I.Li_ s tLesls by Steven W Barker is accepted in its present

:fonr, bJ -Lbe Dep::i..Ttrr.ent of Zoolol::;y- o:r' Brigham Young University as satisf;yi1.tg the thed.s requi:remnit :fer the degree of Master of

ScienC€.

i:l A CKNOWLF:!DGBMRNTS

Grateful acknowledsement lr; made for the guidance and assistance given by the chairma.n of my a.clvisory com.mittee, Dr.

Wade E. Miller, and. the otba:r: ccmmi ttee members, Dr. J. Keith

Rigby Sr, and Dr. Clive D. Jorgensen. Acknowledgement i.s also given to Dr. J, Keith Rigby Jr, a.nd Dr, Robert M. West for their valuable suggestions and guidance.

I thank uy wi:fe, Holly, fo::c her inspiration, patience and

the help she gave me in the fleJ.d and. -.d.th preparation of thh: thesis,

iii 'I'.A:BIJiiO 1'' CONTF!NTS

Page

ACKNOWLEDGFJ.IENTS iii

LIST OF '.f:ABLES vi

LIST OF :B'IGURES• vii

INTRODUCTION 1

HIS'IORY O:B'INVES'rIGATION 2

METHODOLOGY. 4

Abbreviations Used in This Study. 6 GEOLOGY. 8

FOSSIL DISTRIBUTION • SYSTEMATICS. 16

Class Osteichthyes. 16 Class Reptilia . 17 Order Chelonia 17 Ord.er Crocodilia 18

Class Mammalia. 19

Order Creodonta. 19 Order Carnivor-~. 21 Ordei:· Primates 22 Order Rodentia 24 Ord.er Pantodonta 25 Order Condylarthra 26 Order Perissodactyla 28

AGE AND CORRELATIONS 35

CLIMATEAND ENVIRON111ENT• 37

iv Page CONCLUSIONS 38 LITERATURECI1ED. 39

APPENDIX 43

V LIST OF TABLES

Table Page

1. Cornposi tion of zones C and D of the Sage C..'reek i1ountain local Fauna • • • • • • ...... ~ . 1.5

vi LIS'l' OF F'IGURES

Figure Page

1. Index Map. The area of study is 9,7 kilometers north of Lonetree Wyoming, at the base of Sage Creek Mountain • • • • • • • • • • • • • • • • • • • • • • • 5

2. Area of study ( taken from the United States Geological Survey 7.5 1 maps of Lonetree and Reed Reservoir, Wyoming Quadrangles (1961+) Section 9, Township 13 North, Range 113 West) • . • • • • • • • • • • • • 7 J. The study area (viewed from the west) showing position o:f Bridger zones C and. D, and_ the Lone tree White I,a,yer . • • • . • • • .. • • '> • • • • • • • • • • • • 12

vii IN'J'RODUC'l'ION

The Bridger Formation in the Green River Basin has been divided into two members, the lower Black's Fork member and the upper T!,-d.n Buttes member. 'Ihe Black's Fork member is composed of' biostratigraphlc zones A and Band the Twin Buttes member is composed of biostratigraphic zones C, D and E. Recent workers have found that zones A and B contain the same fauna and therefore represent just one biostratigraphic zone (McGrew 1971, Robinson

1970). Future studies of the biostratigraphic zones of the 'fwin

Buttes member are necessary to determine if the C, D and E zones are valid. Some are currently being conducted,

In the present study fossils were collected from Section

9, Township lJ North, Range 113 W2st in the Green River Basin of southwest~,rn Wyoming. These fossils were critically examined and identified. in order to determine the biostratigraphic validity of zones C and D. Zone E was not present here.

Fossil fragmentation and paucity restrict the deg:ree of chrouologic precision.

1 HISTORY OF' INVESTIGATION

One of the earliest descriptions of Green River Basin features was written by Ball (18J5:3), who described it as c=i,n immense prairie with little vegetation upon which herds of buffalo fed, later, Fremont, enroute to Fort Bridger, collected and discussed a number of gastropods from near the fort which were later described by Hall in J:!"'remont's 1845 report,

A number of pre-Civil War geological surveys were conducted along various immigrant trails and wagon roads. During this period, beginning in 18 58 with a field survey :r-eported by lander, pale onto- logical investlgations began in the southern Green River Basin

(lander 1859), The first Green River Fossil fish were collected by Evans, and. later described by Leidy in 1856. 'l'he Bridger Formation was named by Hayden in 1869. At that time he wa.s conductiri.g territorial surveys concurrently w-ith Powell and Klng. Most of the work was done along the UJ,.ion Pacific H.ail:road's right-of-way, During one of these surveys Carter collected a fossil primate in the Grizzly Buttes near Fort Bridger, which was identified as Omomysby Leidy in 1869 (Hayden 1873). Cope also collected vertebrates in conjunction with the Hayden survey of

1872 and 1873. Early intensive explorations of the Bridger Formation were carried on for a number of years by Marsh of Yale

2 University, which resulted in a s0:rles of short papers between 1871 and 1875. 0ne of his most im:po.rtant papers was "Preliminary

Description;:; of New Tertiary Ma!itmals"(1872), later, Wortman (1901,

1903), Troxell (1930), and Wilson (19.38) conducted studies based on Marsh's explorations.

Detailed stratigraphic studies of the Bridger area began shortly af'te:r· the turn of the century (Veatch 1907, Schultz 1914).

In the early 192C's Bradley began a long study of the Green River fu.sin, which culrr..inated in his 1964 U.S. Geological Survey Professional Paper, the first complete study of the basin and adjacent areas.

Osborn (1902, 1929), Matthew (1909, 1910), Granger and Gregory (1917), Wood (1934) and Gazin (1959) all did extensive geological and vertebrate paleontologica~ research in the basin.

Their colleet:i.ons are now at Princeton University and the American

Museum of Natural History. Recently, many additional workers have been doing more detailed work and adding to the knowledge of the abundant :Bridger fauna, e.g., McKenna (1960), Simpson (1933),

Robinson (1957, 1966, 1967), and West (1969, 1970, 1972, 1973). MET'riODOLOGY

'Ihe study area is on the southwest, slopes of Sage Creek

Mounta:tn 9. 7 km north of Lonet-cee in the Green Hiver Basin of southwestern Wyoming (Fig. 1). 'Ihe topography consists of gently rolling hills with locally developed badlands at an average elevation in excess of 2,550 meters. Exposures are entirely of the Bridger Formation. Verte bra.te fossils, mostly mammalian, are relatively commonthroughout the area, although some stratigraphic zones yield more abundantly than others. 'l'he United Sta·tes Geological Survey 7. 5' topograph1c:J.l maps of the Ionetree, Wyoming Quadrangle and the Reed Reservoir, Wyoming Quadrangle of the 1964 series were used to determine location and areal extent of the study area, which consisted of Section 9, Township 13 North, Range 113 West, Uinta County, Wyoming. All vertebrate remains observed, with the exception of highly fragmented turtle sh0lls, were collected and their locations marked on an enlarged t-0pographic map (Fig. 2). Notes indicating stratigraphic position of each specimen, associations with other vertebrate fossils, sto ..te of preservation and condition were taken. Highly fragmented turtle remains are common. Fragmenta,tion is due to ice wedging and wandering livestock, 'Ihe lx-::st preserved turtle specimens

4 _____.,--- -- Fort Bridger {t~r--.---i -·---' Lyman 5 Kilometer~ _,,__M_i-11:-·v_r_n_er_- L M~~;~-1 View ~

...... ✓ ' I () (I) I I 3'.:..,o I I :r (t) (C I I • (1) (I) I ' ,.- I \ I \ I \ \ I. \ I Stuci'y,..,,, ~ Area NORTHi

WYOMING Lonetree II '·, ..---~-~---' '

Fig. 1. Index Map. T'ne area of study is 9,7 kilometers north of 1.one-t.ree Wyoming, at the oo.se of Sage Creek Mountain, were collectea, More productive locations were dry screened for smaller ve:cte brafos through 6 mm and 2.'ll.msieves, respect.i vely.

Fossi1B were identified as acc1u·ately as possible with reference matP.~d.als availabJe to the author. Measurements of small bones and. teeth were made with dlal ~alipers to the nearest tenth of a millimeter. The classificatlon used by West (1973) was adopted for use in this study.

'lhe rock uni ts present in the study area were examinect and identified in outcrop and hand samples. No petrographic or sieve analyses were conducted. Only gross sedimentary structures and textures were noted. For the most part Bradley's 1964 U.3. Geological Survey Professional Paper of the geology of the Green

River Bashi was followed for identification of the Bridger C and

D Meml::.ersa:nd locating the member boundaries.

Abbreviations Used in 'Ibis Study

AM-Amherst College, Massachusetts

BYU-Brigham Young University, Utah

USNM-U.S. National Museum., Washington, D.C.

ANMH-American Museum of Natural History, New York

YPM-Yale Peabody Museum, Connecticut ~ Scale l: 24,000 1,000 Feet i305 M5'tersl Contour Interval 50 Fe•H ( 12.2 Meters)

Fie;. 2 Area of' study (taken from the United States Geological Survey 7,5' maps of the Lonetree and Reed Reservoir, Wyoning Quadrangles (1964), Section 9, Township 13 North, Range 113 West). Tne numbers l through 27 represent fossil localities. (See apper!dix for J.ist of fossils recovered at each locality.) The· Lonetree White L.1.yer follows approximately the 7,500 foot contour line. l"ossil locations l--elow the Ionetree White Layer are in zone C. Those locations above the Lonetree White layer are in zone D. GEX)LOGY

Southwestern Wyomingwas an area of active tectonism during

Late Cretace◊us and. Early Tertiary times, with uplift occurring during the LaraJrd.de Orogenic pulses, and de:posi tion during and after periods of uplift. Iaramide block-faulting parallel to pre-Tertiary mountain ranges allowed down-warping of several basin floors, including the Green River Badn and the Washakie Basin. Tnis down- warping began in the Early Tertiary and continued more or less uniformly throughout the Eocene Epoch. It was primarily :responsible for the topogi--a:phic conditions which allowed continuous sedimentation in the Green Rive:c Basin (Bradley 1964). Several formations were deposited under fluvial, lacustrine and paludal conditions in the Green River Basin, including the Eocene Wasatch, Gre~n River and Bridger Formations. Volcanic ash and erosion of surrounding uplifted Late Cretaceous and Early Tertiary rocks and sediments :p:covided the source material (Bradley 1964). 'Ihe Green River Basin is a topographic as well as structural spoon-shaped, symmetrical, synclinal basin. It is bounded by the Granite Mountains, Wind River and Gros Ventre Ranges to the north, by thP. Uinta Mountains on the southi by the Rock Springs uplift on the east, and by the WyomingRange on the west. The major axis of

8 the bas:i.n trends northward "roughly parallel to the strik-~ of.' folded pre-Tertiary r0eks east and west of the area" (Bradley 19611-:AlO).

Low strea,:li gradients between the ba.sin region and the ocean during the Late Cretaceonn a.rd Early 'I'ertia.ry apparently prevented the margins from being cut down (Bra.cllr:;y 1964:A15). In the central region of the Green River Basin rocks are virtually flat, not exceeding angles of one and one half degrees. Beds become more steeply inclined near surround.ing mountain ranges at the basin margins. In the area of study the beds are virtually horizontal.

Af-Ler t.he Ia te Paleocent: uplift of the middle Iararn.ide

Orogeny, thick wedges of elastic material washed out into the Green.

River Basin d.eposi ting sediments of the Wasatch Foma tion (Eardley

1959:194). The lower part of this formation interfj_ngers basinward with the Lu.i11anTongue of the 1acus trine Green River Formation

(Wingate 1961). Pulses of uplift during Paleocene and Eocene caused fluvial ana_ lacustrine deposits to fluctuate in all areas except the center-most part of the basin where the undifferentiated L:=mey

Shale member of the Green River Formation and lower units of the

Bridger we:re deposited. In the Middle Eocene the predominantly fluvial Br:'Ldger Fomation began filling the basin. 'Ihis formation laterally bounds and overlies the thick lacustrine Ianey Shale

Tongue (Uest 1969) of the Green River Formation in a gradational and uncertain contact at the margins of the basin (Bradley 1961.1-:Al8).

Bridger sediments gradually filled the lake and subsequently the entire basin by the end of the middle Eocene (West 1973).

Due to erosion the total origiml thiclmess of the Bridger

Formation is not known, and the original upper surface is evldently no lor,ger prem,nt. A maximu.'Tlmeasured tM.ckness of 670 meters for this formati0n has been reported. in the area of Sage Creek Mountain

(Koenig 1960), just north and east of the present study area. (Fig.

1). 'Ihis exposure :is truncated by the Miocene Bishop Conglomerate.

Near the Uinta. ~ountains the eroc.ed :Bridger top is capped with a conglomeTate of the Fowkes Forma,tion of the Uinta Group (Wingate

1961). Tnrough most of the Green River fusin the Bridger Formation is the outcrop:pin..g ln:forrr..ation and typically forms badland topography.

R1.sJaward, the Bridger sediments become finer grained, interfingering with and overlying the Ianey Shale member of the

Green River .F'on1ation. These sediments alternate from predominantly tuffaceo"..ls sa,ndstones and sa.ncly tuffaceous mudstones, rangiug in color from light gray to greenish gray to grayish brown in weathered exposures (Brn,dley 1964:A.49). Clastic uni ts contain rounded quartz and calcite grains, with some orthoclase, bioti te, rhyoli t.e and glass shards identifiable in hand sample. Thin beds of volcanic ash are locally common, and widely separated, thin-bedded limestone and rnarlstone layers form conspicuous, often laterally extensive, benches in the Bridger badland topography,

'Ihe Bridger Formation is divided into two members, the lower

Blacks Fork Member and the upper Twin Buttes Member. 'The boundary between these members is recognized :primarily on the basis of vertebrate faunas and are separated by the Sage Creek White I.ayer (Gazin

1959). Originally, Matthew (1909) had llivided the Bridger into five units, A, B, C, D and E, which are still retained as biologic units. Zones A and. 13 a.re within the Blacks Fork Member and C and D are in

the Twin B'.1ttes Hembcr ( Bradley 196'--1,,Gazin 19 59, Wood 19J4) .

In t!-10 study area (section 9, Township 13 North, Ra11.ge113

West) the 'I'win Buttes Member is represented by zones C and. D as

recogri,ized by Wocd (193'-1-:241-24;~). These zones are separated by

the prominent L:>netree Whi.te Iay-er at an elevati.on of approximately

2,286 meters (Fig. 2 and Fig. 3). This white layer forms the upper- most unit of zone C (Koenig 1960). It is composed of a chalky white marlstone with alternating hard and soft layers ranging in thickness

from approximately one meter to five meters. It is persistent only in the southwestern portion of the Green River Basin (Koenig 1960).

Zone C contains numerous beds of bentonitic mudstones that are

loosely CE'mented and erode rapidly in outcrop, as is evidenced by

the locally developed badland topography. These erosional processes expose numerous vertebrate fossils. The beds of this zone range in

color from tan, to reddish-brown, and gray-green to gray on weathered

surfaces. Scattered throughout the Green River Basin are resistant

channel sands composed of fine to medium-grained q_uartz grains with abundant calcareous cement. These channel sands often appear bright green in weathered outcrops.

Zone D appears very much like zone C, At the upper boundary of the Lone tree Whl.te Layer it weathers to a slightly darker brown

than the layers of zone C immed.iately below. If the Lonetree White

Layer were absent, a zone boundary at that point would be difficult

to establish. Higher in the section zone D weathers lighter tan, and fo::..-insmore resistant ridges and steeper slopes. Near the top of Zone D

lonetree White lC!iyC'r ( 7500' Elevolion= 2286 metNs-See figure L.)

Zone C

Wyoming State . Highway '114

I-' Fig. J. The study area (viewed from the west) showing tile position of Zones C a,nd D ' N and the Lc•netree White Layer. Sage Creek Mountain, one half mHe to the northeast of the study area, the Upper \fr)-U.e layer outcrops and can be trci,ced only a short

d:tstance before it becomes ohsCtlr'3. This unit is composed of a

tuffa.ceous marlstone i:hat is distinctive from the L:rnetree wbi te

Layer by a g::.:-:-ea.te:r.·ash content, gritty texture lower d.ensi ty, and whiter appearance on weathered surfaces. The upper half of zone D weathers to~ light tan with local areas of darker material and

increasing amounts of ash. Overall, zone D is generally lir.;hter

colored than zono C and contains Maller amounts of da.. rk green-gray

sands.

'Ihroughout the southern porticn of the bas~.n and. within the

study area discontinuous lenticular-shaped white marlstone units

occur which have a maximum thickness of only a few feet. Tnese whl te laye:n; form benches due to their slightly greater resistance

to erosion. F08$1L DIS'I'RIIJUTION

The initial collection was made by systematically collecting exposed fossils in the entire study section. Areas with relatively abundant fossil~, were screened.. Locations were not discovered which were suitable for extensive q_uarrying. Fossils were found throughout the areas of exposed outcrops. In zone C fossil material was fairly a·bundant except in 2. 6 meter zone immediately below the

Lonetree White layer. From the ba.se of the Lonetree White layer up to approximately the lowest 3 meters of zone D, fossil material was abundan+.. Fossils were scarce in the rest of zone D. No environmental reason is evident for such fossil distribution.

According to Dr. Robert M. West (pers. Comm. May, 1975) fossil distribution follows the same pattern throughout the entire southern

Green River Basin where the Lonetree White Layer is seen (Fig. 3). Fossils from the area are well-preserved by perminerali- zation and replacement, but the majority are fragmented. They do not show abraded surfaces, indicating limited transportation before burial. However, frost-wedging along with wetting and drying of expandable sediments such as clays could have contributed significantly to fragmentation.

14 TABLE 1

COM.POSITION OF ZCNES C AND D OF THE SAGE CHEE'.{ MCU:NTAIN LOCAL 1'1Af.mA

Paunal composition Zone C Zone D cf. Lepidosteus X X

Testudinidae X X cf� Trionyx X X

Crocodilidae X

Hyaencdontid.s.e X X

Pseudocreodi X

Niacidae X

Hemiaccdon cf. lh, gr2.cilis X

Microparamyinae X

Coryyhodontidae X

X X

Brontotl::eriidae X X

Te1matheriun1 sp. X SYSTh~MA'I'I CS

'Ihe following is a discussion of the fossil vertebrates found in the study area. No representatives of the Amphibia and

Aves are present in the Sage Creek Mountain local Fauna. 'Ilie following discussion is not intended to be a review or revision of the middle Bridgerian fauna of the southern Green Rive:::- Ba,sin.

Instead it is a presentation of add..i t.ional vertebrate fossil material.

Class - OSTEICHTHYES

Infraclass - HOLOSTEI

Suborder - LEPISOS'IOIDEI

Family - LEPISOSTEIDAE

cf. Lepidosteus (Lacapede, 1803)

Material. BYU 1137, BYU 1139, BYU 1140, BYU 1141, BYU 1145,

BYU 1147, nUJTJ.erousfish scales; BYU 1142, one small amphicoelus vertebra.

Discussion. These fish scales are all ganoid and rhombohed...... -.-a_l(diamond) in shape. They ·,ary in size according to the location on the body and size of the fish. When these fish scales were compared with BYU 0929, identified as Lepidosteus, no differences -were observed. BYU llll-2 (amphicoelus vertebra) was

16 collected in association with numerous scales from a gar (BYU1140) and probabJy belongs to the same individual. Transversely, it is 8 mm in diamete,:-c, well within ti:1e size range of 1€nidost.eus. On the ventrolateral marg:i.n are two processes for rib attachment, one on each side, Dorsolaterally two small fossae are elongated antero- posteriorJ.y for attachment of the neural arch. These features place this vertebra in the anterior portion of the axial skeleton.

Class - REP'fILIA

Subclass - ANAPSIDA

Orel.er - CifilLONIA

Super family - 'IESTUDINOIDEA.

Family - TESTUDINlDAE,Gen. et Sp. indet..

M~ter.ial. BYU1127, BYU 1128, BYU1129, BYU1130, proximal ends of humeri; BYU1132, distal phalanyx; numerous shell fragments that may belong to Testudinidae.

Discussion. Humeri of the above specimens possess a nearly spherical head with large, dorsally placed tubercles extending laterally. 'l'he d..i.stal phalanx is claw-shaped and the bone is porous. Proximally the articulation surface has two concavities to accomoda,te the distal condyles of the next phalanx. R. M. West (11ers. ccmm. 1975) and Auffenberg (1964) stated that the present fossil turtle classification is outdated and in need of 0xtensive redefinition. later (1974), Auffenberg (1974) revised the classification of the family Testudinidae. Present specimens are similar to each other with the main difference arising due to size. 'Ihese specimens may represent a species of Stylemys which has been :reported as common:'i.!1 the ti t:-j,nothcre beds of Wyomingand Colorado

(Auffenber 0 1962, 1974).

Family - 'I'RIOI\TYCHIDAE

?Tri o.ny:x: ( Cope 1851) !'.!_~t~ria~. BYU1114, BYU1118, BYU1119, BYU1120, BYU1121,

BYD1122, BYU 1123, BYU1124, BYU 1126, shell fragments. p1~cussion. Tbe present specimens all show shell ornamentation characterized by discont:tnuous, rambling ridges with raindrop- like'impressions scattered throughout, Comparisons with specimens of

Trlor:Y_x_crassa on display at the Cleveland Natural History Museum yielded no dlfferences in the shell ornamentation pattern types. Cope (1884) and Hay (1908) illustrated shell ornamentation of

Trionyx which also compared favorably with the present specimens. However, J. H. Hutchison (pers. corru~. 1977) stated that the trionychids are in a "hopeless mess" and need extensive revision.

He further ~tated that there are at least two valid genera, Plastomenu~ and Trionyx. As a conseq_uence, generic and. specific classificaUon of the present specimens is uncertain.

Subclass - ARCHOSAURIA Order - CROCODILIA

Family - CROCODIItlDAE,Gen. et Sp. indet.

Material. l3YU1144, one small conical tooth. Discus8ion. This tooth measures 5 mmin height, and J mm in diameter at the base. It is vertically striated from the base to the crown with two larger ridges, one mid-anterior and one mid-poste"L"lor. Th:ts tooth is very slightly curved posteriorly, and may have broken off from approx1ma.Lely the middle region of the

maxilla, a :cegion that, Co:pE-1 tc!.111::; as the premaxillary (1884, plate

'Jl13 :present specimen ma.y belong to a species of Crocodylus o:r.· .Il2:-achyuranoc:hampsa_, both having been described from the middle

Bridgerian Sc:diments of Grizzly Buttes, the Washakie beds of Wyoming and the U5.nta. Basin o:f Utah (Mook 1962, Zangerl 1944, Cope 1882).

Class - MAMMALIA Subclass - THERIA

Infraclans - EUTHERIA

Order - CREODONTA

Family - HYAENODONTIDAE

MaJ£?=:ial. :BYU 0929, distal end of the left femur, proximal

end of right tibia, distal end of left third phalanyx, innominate

bone, three lumbar vertebrae r a right pelvis fragment containing

the acetabulum. Bl'U 0934, right femur head and medial condyle of

right femur, glenoid cavity of a scapula, left mandibular fossa,

four thoracic and four lumbar vertebrae, one distal end of a femur.

Diflcussion. Elements munbered BYU 0929 were collected in ·

association, indicating the possibility of a single individual. I:f creodont poot-cra:nial skeletal elements are not collected in

association with more diagnostic cranial elements, classification

at the generic level is difficult to obtain. No teeth or cranial

elements were found associated with the present specimens. 'l'hree

genera of the family Hyaenodontidae have been recorded from the

Bridger Formation, These are Ll.mnocyo!!, Thinocyon and Patriofelis. Dennison (19J8) described and lllustrated these three generA-, From his descript::tons e.nd illustrations, BYU 0929 compared best with

Limnocycn. '.I.he distal end of t,he femur of Limnocyon has a process on the lateral cond.yJe which is d:istinct5.ve. The lateral margin of this process and. the lateral platellar ridge form a "V" with the apex pointing ciistally. Pa triofelis and Thinocyon possess the same process ·but to a much f.';maller extent and it does not form a

"V". When the femu:c is compared with one from Patriofelis and

Thinoc:von, Llmnocyon is smaller and not as sto·,1t. The innominate bone does not show a strong, well-developed lateral ridge on the ilium as in Patriofe::;_is and Thinocyon. This is due to weaker gluteal r.mscles in Limnocyon as compared to Pat.riofelis and

'Ihinocyon. Tne cotyloid notch in the a.cetabulum of Patriofelis opens up ventrally. In cursorial individuals the cotyloid notch is deep and na.rrow; in a.11bulatory and especially aboreal types, it is relatively shallow and wider, allowing freer motion (Dennison

1938:?2.8). In these respects Limnocyon resembles Felis. The present specimens compare with Limnocyon and may represent that genus. Elements numbered BYU 0934 were collected in association, again ind:'Lcating a single individual and were identified from Dennison's (1938) descriptions and illustrations, When BYU 0934 was compared with Limnocyon and Thinocyon they were found to be larger and more robust than either of these genera.. 'Ihe femur head is spherical with the fossa for the ligmentum teres posteriorly placed, essentially marginal, and somewhat elliptically shaped, agreeing more completely with Pa triofelis than with either Limnocvo~ o:r 1.'t~Y£!l· Features of the medial condyle of the right femur such as the depressions on the lateral border and the shape also ind.icate that these specimens may ·belong to Patriofelis.

Superfa.rnily -· PSETJDJCREODI, Incer tae se::dis

Mater:ia.l, BYU10_58, canine tooth. ------Discussion. The term Pseudocre0di is used here as Ma t·'Ghew (1909) and Dennison (19J8) used it. BYU 1058 measures 4,0 mm wide at the base of the enamel and 8 mm long from the base of the enamel to the tip. In the pr€sent specimen the root is missing and it has anterior and poGterior ridges. These features are shown in Oxya~ and Limnocyon. Ia.ck of adequate material TGakes a more d.efini te identification uncertain.

Order - CARNIVOP.A

Suborder - FISSIPEDIA

Family - MIACIDAE, Gen. et Sp. indet.

Material. BYU 0999, lower jaw containing fragments of M1-J•

Discussion. The p:::-esent specimen is highly fragmented with partial cusps remaining on the M and M . Only the roots remain of 2 3 the M1. 'l'he M2 measures approximately 6.0 nun in greatest length and lLO r.1111in greatest width, while the M3 measures approximately 8.0 mm in greatest length and J.O mm in greatest width. The condition of the present specimen does not allow a definite genus classifiecktion. Gazin (1962) and West (1973) described and illustrated va:r1ous genera of the Miacidae and according to their illustrations the present specimen may belong to Miacis or Vulpavus. According to Cope• s (1884) dencript:lons of the Miacidae, the two mentioned. genera a.re similar and occur widely in the Green River

Basin. Due to tho cond.ition of BYU 0999 a definite genus j_dentifi- cation is uncertain.

Order - PRIHATF.S

Sub:'.)rder - PROSIMII

Snperfa,miJ.y - OMOMYOIDEA

Family - OMOMYIDAE

Hemiacodon cf. ..!!• gracilis (Marsh 1872)

!1a:.tcri...?,l. BYU 0918, lower right jaw fragment containing P , M _ ; BYU 0925, lower left jaw fragment containing M ; BYU 0986, 4 1 2 2 left maxillary fx-a.gment with M.�.

Discussion. Hemiacodon is closely related to .Q_momy§_; how ever, teeth of J-Iemiacodon generally have a more rugged or less delicate appearance, with :rugose enamel ( Gazin 1958: _54)• In Omomys the P is relatively a little broader and has a higher, better 4 The hypoconulid of the M developed. mctaconid. 2 in Q� is scarcely observable. BYU 0918 has a well-defined hypoconulid and has a more rugged appearance than illustrations of Omomys (Gazin

1968: plates 6, ?), In those respects the present specimen com pares well with Hemiacodon. Over 160 specimens of!!_. gracilis are known. Gazin (1958) measured 85 of those specimens and plotted the results, one plot using the length measurements and another usir,g the width measurements. He found that they both formed a normal curve. , 2,5 mm wide and BYU 0918 measurements are as follows: P4 3,0 mm in length; M1, 3.0 mm wide and J.6 mm in length; M2, J,0 mm wide and J.7 mm in length, The size of this specimen falls within

the curve plotted by Gazin (1958:56). The present specimen was also compared with cast::: of the ·type (YPM 11806 and Y.PM 12987-1) and was

found to com:pare extremely well, On the basis of these com1Jarisons

1 and the above descriptions the present specimen is oolieved to belong

to H, gracilis. BYU C92.5 measures _5,0 mm greatest length and 4.5 mm g:r.-eatest

width. This M is larger than the M of BYU 0918, Cusp :placement 2 2 and proportion of the tooth is identical to BYU 0918 and casts of

the type (YPM 11806 and YPM 12987-1) of Hemiacodon gracilis. BYU

092.5 is 0.8 :mm larger in width than measurements given by Gazin

(19.58:56) of He:niacodon gracilis, At present, size distribution is

not entirely clear, Of 160 specimern3 of !!_, gracilis known in 19.58,

Gaz:tn measured 85 of them. Of those 160 sp13cimens for which horizon

information is available, they are from the Bridger C and D and

represent Hemiaccdon gracilis (Gazin 1958:56), Gazin continued by

stating that he found no criteria by which a second or more species

might be defined, Since this specimen is lal'ger and size distribution

is currently uncertain, the present specimen has been identified as

Hemiacodon cf, H, gracilis, 2 BYU 0986, a left M-, in good condition, though worn, measures

5,0 mm in greatest width and 4,0 mm in greatest length, falling within

measurements given by Gazin (1958:57) for Hemiacodon gracilis. This

tooth is triangular-shaped and contains a worn metacone and paracone,

'Ihis protocone is considerably worn and is now a continuation of the

preprotocrista and the postprotocrista, ThG paraconule is still

present but the metaconule has been, for all practical purposes, worn away. C0mparlsons show +.hat the present specimen i.s simiJ.ar to species of O�omys, except that in Hem::.acodon the precingt1lwn ls expanded forming a ::;mall flange externling anteriorly from the protocone. In Om(w1ys this feature ls not well developed. The present ::;pecimen compares with Hemiacodon gracilis illustrated by

Gazin (19.58: plate 8, no. 3) and has been classified as Hemiacodon

cf. !!_. r£.E_acllis,

Order - RODENTIA

Subfamily - ?MICROPARAMYINAE, Gen. et Sp. indet.

:Material. BYU 1066, proximal half of a radius. Discussion. 'The radial head measures 6.0 mm in diameter, resembling the head of a "golf tee". It is one quarter the size of

Para.1J1ys and. Le:ptotomus but otherwise appears much like both genera.

The epiphysis is solidly fused and accordingly this specimen repre sents an adu.lt. Wood (1962:157) stated that the subfamily Micro paramyinae was wldespread in the Eocene of Western North America and the lower Eocene of Europe, but not well known, prol:ably due to its sma.11 size. Although the present specimen is well preserved, limited reference material makes identification difficult. Accord ing to Wood's (1962:157-170) illustrations and descriptions, the prtsent specimen procably represents the subfamily Microparamyinae. Order - PANTO:OONTA

Superfa.miJ.y - COHYPHODO:NTOIJJEA

K·vnily - OORYPHODON1.'IDAE

_t1ate_:ria1. BYU0988, lower left P3. Discussion. This specimen includes just the paraconid, protoconid., metacon.td and the trigonid basin, all in good condition.

Measurements were taken from the midpoint of one conid to the midpoint of another conid. F'rom the paraconid to the protoconid is

12.J mm; from the protoconid to the metaconid. is 11.9 mm; and from

the metaconid to the paraconid is 11. 7 mm, The above r.ientioned

conids form a triangle around the trigonid basin which opens lingu- ally. Smo,11 ridges extend from the paraconid and the metaconid into

the center of the trigonid basin. The present specimen compares

favorably with illustrations by Robinson (1966) of Coryphodon

(ANMH5654.3) of Wasatchian age. West (1973:126) stated that the

chronologic range of Coryphodon was not known to extend into the

B-~idgerian of the Green River Basin; however, Simons (1960:15)

stated that Coryphodon has been recorded in middle Eocene deposits

from China which are equivalent to the Bridgerian. Possibly by the middle Eocene in the Green River P-asin, Cory:phodon had become a rare

taxon. Sj_mons (1960) also stated that comparisons of Paleocene and

Eocene Coryphodon specimens show no features which would allow

separation. Consequently, the present specimen is presumed to

represent C.Jryphodon or possibly a closely related genus. Order - CONDYI.AHTHRA Family - HYOPSODONTIDAE _,,______Hyo1x;odus cf. -H, ---·marshi (Osborn 1902) Ma/~32.:?:.l· B:;:U0917, lower right jaw fragment with M _ BYU 1 2; 0919, lower left jaw fragment with M: BYU 0923, right P _; BYU 1_z"i 4 0924, lower :eight jaw fragment with P _ , M ; BYU 0996, left M . 3 4 1 2 Discussion. All the above specimens are in relatively good condition. However, the hy:pocone is missing from the M1 of BYU 0917. BYU 0919 and BYU 0921-1-are highly worn. Speeimen measurements are as follows: BYU 0917, the M1 is 4,5 mm in greatest length and 3.5 mm in greatest width, and the M2 is 5.0 mm in greatest length and 4,0 mm in greatest width; BYU 0919, the M1 is 4,1 mm in greatest length and 3 . .5 mm in greatest width, and the M2 is 5,1 mm in greatest length arid l+.5 mm i:.1 5-reatest width; BYU 0923, the Pq: is 3,0 mm in greatest length and 2.3 mm in greatest width; BYU 0924, the P3 is 3,0 mm ln greatest length and 2.0 mm in greatest width, the P4 is J.2 mm in greatest length and 2,8 mm in greatest width, and the M1 is 4-.0 mm in greatest length and 3.4 mm in greatest width; BYU 0996 is .5,3 m.min greatest width and 4,9 mm in greatest length,

'i1le trigonid portion of the lower molars in the present specimens consists of two cusps, the protoconid and metaconid. The hypoconid is the same height as the protoconid and the crista obliq_ua extends from the hypoconid directly to the metaconid, 'Ihese lower molars tend toward a selenodont pattern. 'The P4 of BYU 0923 has 2 prominent conids on the anterior portion of the tooth with the labial conid. being larger than the lingual conid, From the larger of the ti1·0 r�entioned. conids a rldgG extends to the medial border of the :posterior :po:d,ion of the tooth where a much s,11aller distinct conid arises. �he ?4 compai�z ext�emely well with the P4 of BYU 0924 and is belfovcd t.o represent the same species. In BYU 0996 the trigon basin is absent, with the paracone and metacone being the most prominent features of the tooth. Comparisons with cast of ANMH 16194 of fuopsodus mi ticulus show that this specimen may belong to the same ge1ms. Cusp placement and. cusp proportions are the same, with the exception that BYU 0996 is larger than AMNH 16194. Gazin

(1968) described species of Hyopsodus as typically having the above characters.

Gazin (1968:16) and Gingerich (1976:1) stated that specimens of Hycpso9-us are separated ba,sicly on size differences. Gingerich

(1974a:107) further stated that, each Hyopsodus lineage underwent gradual but significant size changes that were sufficient to justify time-successive phyletic species. He further stated that sympatric species of Hyopsodus can only rarely be diagnosed by morphological differences in their cheek teeth, though species usually differ significantly in size (Gingerich 1976:107). Gingerich (197L�h:895) studied cheek teeth of closely related species and found that they often cannot be distinguished by form alone and in such cases size differences are important in diagnosing the species. Gazin (1968) statistically �nalyzed species of Hyopsodus ba.sed on the length of the M 2 and illustrated the computed di.stribution histogram of Hyopsodus species from the Bridger C and D which formed a trimodal distribution pattern. !!_. lepidus was the smallest species, !!_. d.espiciens the intemecliate sized species and H. marshi the largest.

BYU0917 and Bl1J 0919 would pJ.o t. cJ.03e to the 50%range of H. marshi on Gazin's col:lpc;;;ite histogra,m (1968:28). Since BYU0923, BYU0924 and BYU0996 do noi contain an M2 tho species cannot be directly compared wl th Gazt:ri.'s computations a,nd the species identifi.cc:1,tion is uncertain..

Order - PERISSODACTYIA Suborder - Hil~POMORPHA

Subfamily - BRON'IOTHERIOIDEA Family - BRON'IDTHERIIDAE

Material. BYU1011, fragmented. lower jaw with teeth roots present; BYU1012, M2 fragment; BYU0174, BYU0945, BYU0949, BYU 0951, BYU1101, astragli; BYU0982, BYU1010, BYU1097, proximal ends of radil; BYU1069, distal rad..i..al end; BYU0955, BYU0957, BYU0982, BYU1047, distal ends of femora; BYU1053, ulna; BYU1009, BYU1081, proximal ends of calcanei; BYU0958, BYU1096, distal ends of humeri; BYU0983, proximal end of humerus; BYU1055, distal end of a tibia; BYU0946, BYU0948, BYU0950, BYU0974, BYU1001, BYU 1052, BYU1072, BYU1084, BYU1090, BYU1094, BYU1099, BYU1100, metapodials.

Discussion. Postcranial skeletal material of the family Brontotherioidea is presently not well defined at the generic level.

Unless cranial Il'.aterial is found associated with postcrctnial elements, a generic classification is uncertain. Unfortunately, the

cranial material mentioned above is fragmented so that insufficient detail remains for a generic clas8ification. By far the largest number of irK1lvtdual specimens founcl represent the family Bronto theriidae.

Osborn (1929) wrotr;; t:w volumes concerned with the ti tano theres of Wyoming, Dakota, and Ne brc.zka during the Tertiary. For the most part his descriptions, illustrations and classification have been followed. More recent articles have been published on various titanothe:res, mainly in response to geological and areal d.istribu Hons and. descriptj_ons of new material. Tnese articles treat crarLi.al e:.ements almost exclusively. Robinson (1966: 65) recogn.tzed that parts of Osborn's (1929) work are out of date, as is the cla.ssificati.on of the ti tanotheres. Osborn also (1929) treated much of tbe postcranial skeletons of the titanotheres described ia his two volumes and in many instances his work is still followed, Conseq_uently, the Perissodactyla :postcra.nial skeletal elements in this study have, for the most part, been identified. using Osborn's (1929) work.

Of the Perissodactyla, Lambdotherium, Eotitanops and.

PaleosyoEs have been reported as being common and widespread during parts of the middle Eocene. The present specimens are all similar.

When the same skeletal elements are compared, the major differences arise due to size variations. When these specimens were compared to various other genera of Perissodactyla, such as Mesatirhinus and

Manteo ceras, it was found that they compared best with La.mbd.otheri um,

Eotitanons and Paleosyo:E_s. The postcranial skeletal elements of these J genera are separated maiPiy on size and geological occur rences. Of those genera lrunbdotherium was light bodied, about the size of a. coyote. It was curzori::-,1, a.nd. smaller than the subcur sori.al _!i:c,t,11::§-E.ze...:c;_, :Paleosyops was rnuc:h larger than Eoti tanops.

BYU 0174, 13YU 09��9, BYU 0970, BYU 0945, BYU 0951, BYU 0946,

BYU 09li,8, BYU 0950, BYU 1001, BYD 1:) 52, BYU 1072, BYU 1094, BYU

1084, BYU 097l.J-, BYU 0982, BYU 1069, BYU 1081, BYTJ 0983, BYU 1047 and Bl'U 1053 were found to be larger than Iambdotheriwn, yet smaller than !'§,leosyops. There are four species of Eotitanops that Osborn

(1929) s+.,a,tGd. are common in Bridger sediments. These are�- bore alis, �- ri.regory, E· princeps and IJl. major. The four species are so close in :::�ize, and the differences in the :postcranial skeletal elements are so slight, that separation is accomplished mainly by comparisons of tooth structures a:nd size groupings, �-· gregoryi is the smallest, �- 1�:dnceps and �. oorealis are of intermediate size, and�- major is the largest of the four species, 'Ihe present specimens vary in size between!• Gregoryi and�. major, Osborn

(1929:593) stated that !• oorealis and �-• princeps are so closely related that their skeletal elements may be described under a. single heading, Present specimens will not allow clear identifications between the species of Eotitanops until more comparative material is available.

BYU 1096, BYU 1097, BYU 1098, BYU 1099 and BYU 1100 were found associated and probably belong to the same individual. Com par1sons show that they probably belong to a species of Limnohyops.

'Ihe closely related Paleosyops skeletal elements are all more heavily constructed, Limnohyo�s skeletal elements are narrower and more slender showing more adaptive resemblances to Mesatirhinus (Osborn 1929: 611..;,). However, th'3 hwneral trochlea for the ole cranon process is deeper :'Ln Mesatirbi1~~£, and in Limnohyops the olecranon fossa is spherica11y shaped, The other elements are not as distinctive but compare favorably with _!g.__mnohyops. Due to their associations and f'avorable comparisons it is believed they belong to the same indi vi.dual and also to the genus Limnohyops.

'Ihe femora of Eocene paleosyopines and manteoceratines are similar, In tbe manteoceratines the external patellar ridge, and the medial epicondyle is also sir..aller than the lateral epicondyle.

In the paleosyopines the knee is straighter than in the manteoceratines (Osborn 1929: 610), This is reflected in t,he angle formed by the long axis of the femora with the platellar facet, In the manteoceratines the angle is greater than in the paleosyopines, In these features BYU 0955 and BYU 0957 agree with the manteoceratines.

Also, the size is readily comparable, Comparisons show that these are the most similar to Manteoceras and Mesatirhinus. Femur comparisons between Manteoceras and Mesatirhinus shows the former to be stouter. The present specimens are stouter than illustrations of

Mesatirhinus (Osborn 1929:609-635) and are believed to be of the genus Manteoceras. BYU 1101, an astragalus, shows j_ts closest affinity with the manteoceratines in possessing a relatively br:oad neck, broad cuboid facet, and a sustentacular facet which forms a broad "L" with the cuboid facet. Distinctions between the astragali of Manteoceras and Mesatirhinus are that in Mesatirhirms the neck is relatively narrower and the internal keel of the trochlea is sharper; since the condyle is missing those features cannot be compared and the present spec:i.r,,en is tenta ti vo1y grouped with Manteoceras.

J3YU0982, BYU 098J, BYU1009, BYU1010, BYU1011, BYU105J,

BYU1055, al] post.cr.ud.al sko.letal elements, a:ce signif:i.cant:i.y larger

·than any of the species· of Perissodactyla. discussed to this point.

Paleosyous first appeared in Bridger A zone and became extinct during Bridger D time. Specimens of' this genus are larger than the conternpora ..neous Eoti tanops. Paleosyops appears abunda.nt.ly in the

Bridger f'aur.as and is dif'ficult.. to separate at the specific level due to many intergrading charP..cters (Osborn 1929: 229) • Also, many similar characters are shared between Paleosyops and LlmnohyoEs•

Separation is achieved based on the f'ollowing characteristics

(Osborn 1929:302): upper and lower teeth of Paleosyops are larger, more rounded, and more robust than in Li~~ohyops; nasals in Paleo- syops taper towards the extremities, whereas in Limnohyo-ps -'chey are essentially parallel. In Paleosyovs the cranium is convex, and in

Limnohyop~ :i.t is concave, 'Ihe postcranial skeleton in Paleosyops is more robust than in Limnohyops. The present specimens are more robust than illustrations and measurements given by Osborn for the same elements of Limnoh~. Distal ends of the femur show small depressions on the lateral border of the lateral condyle and enlarg- ment of the medial condyle. 'Ihe latter structure is offset medially and comparer.: favorably with Paleosyo~. BYU1010, BYU1011, BYU

1012 were associated when collected and were identified according to this association, BYU1053, an ulna, shows an elongate radial notch. The olecranon process is slightly curved posteriorly and the trochlear notch wraps around n.s a continual articulation surface. 13YU 1009 shows a well developed rugosity on the proximal end of the ca.lcaneus. It is significantly stouter than any of the measurements or illustrations g:iven by Osborn for Limnol:wops. From the size of this oor.e and. the well <}.evelo:ped. rugos:i.ty, a larger species of PaJ-eosyops such aG P, robustus i.s indicated,

Telmathe:dum sp. (Marsh 1872)

Material. 13YU 0175, upper right jaw fragment containing 4 somewhat fra.:::,01J1ented P1 - ,

Discussion, 'Ihe P� measures 2.4 cm in greatest length and

J,O cm in greatest width. 1he p2 measures 2,1 cm in greatest length /J, and 2,4 cm in greatest width, The p..:. shows a well-developed paracone and meta.cone, The protocone is missing. N"o evidence exists for a protoconule or hypocone. The pd shows a paracone and rnet.a,cone with a less well-developed protocone. No hypo cone is :present. It con tains a small bulge in the position of the protoconule, Comparisons show a similarity with Paleosyops, except that the pd of the present specimen shows a less-developed cingulum and appears more complicated than Paleosyops, The same applies to the P�. Also, the present specimen is more quadrate than Paleosyops. The above characters are present in TeL11atherium validum and in those respects the present specimen compares well with that species, 1, cultridens is similar but lacks the small fold in the position of the protoconule on the p2 and P� that is present in BYU 0175, In T. ultimwn a small hypocone is evident that is absent in the present specimen, Conse quently, the present specimen compares best with T. vaJ.idum, However, at this time the va:dab:lli ty of the above mentioned char acters is not ce:rta.:tn and the spf�eies identification is not entirely clear.

' • AGEAND CORP.ELATIONS

Sediments of the Bridger zones C and Dare verJ similar,

In the st.udy area, boundary definition is accomplished by using the location of the wnetree White layer, As this layer is not continuous in the northern part of the Green River Basin, zones C and D are distinguished. on the basis of vertebrate paleontology. Matthew

(1909) used the Lonetree White Layer as the bounda~--ybetween zones

C and D and in the study area this layer is evident.

McGrew (in Robinson 1970) demonstrated that the Bridger A bed contains a Bridger B fauna. Apparently, just a single biost.rat- igraphic zone should be recognized. Therefore, the member name,

Black's li'ork, becomes the Black's Fork Fauna found in the Bridger

A and B beds (Robinson 1970:87), Robinson (1970) continued by say- ing that a re-analysis of the faunas in the Twin Buttes member of the Bridger Formation is necessary to determine if Bridger zones C and D contain the same fauna, If so, the member name, 'lwin Buttes, would be more valid as the Tuin Buttes Fauna in the Bridger C and

D beds, Faunal distinctions were not evident between zone C and zone D. Regional studies may show this to be occurri11g throughout the Green River Basin.

Robinson (1957:126) found that Manteoceras manteoceras,

!:!.r2J?.sodusJ.epidus and Telmatherium cultridens are diagnostic of Late

35 Bridgerian 1..tge. Gazin (1968:28) reported Hyopsodus leuidus,

Hyopsodus des,12ic_tenG and ,!!yops�du� marsM. restricted to late

Bridgerian time. Osborn (1929), McGrew (1971) and West (197_3) stated that Eoti tanops and Lambdothcrhun occurred earlier than

Bridgerian, and that Paleosyops and. Llmnohyol?.§_ occurred in the

Bridgerian. McGrew (1959:126) found that specj_mens collechid from the Mo:rrow Creek member of the Green River Formation in the 'l'aber nacle Buttes area of northeastern Green River fusin represented both Early Brid.gerian and To.te Bridgerian time. Stratigra:phically, the Morrow Creek rnember underlies the Tw:i.n Buttes memr.x3r of the

Bridger Formation and is earlier in time. Robinson (1966) stated that the titanothere classification is presently in need of revi sion; conseg_uently, faunal zones established on various titanotheres are uncle3..r, Present1y, establisr.i.ment of late Bridgerlan time from the specimens in this study is inconclusive. However, the litho logic zones from which they were recovered have been identified by

Bradley (1964), Koenig (1960), West (1973), McGrew (1959) and

Robinson (1966) as representing Late Eridgerian time. None of the specimens recovered during this study are abraded, indicating they had not been transported far; conseq_uently, they are :probably time equivalent to the sediments from which they were recovered, CLIYiA'l'EAND ElNIRONMENT

Coarse-grained stream channel sands can be traced throughout

the Bridger sediments. Where they are exposed on the surface they

appear to meander widely. Surrounding these chan.~els are essentially horizontal beds of fine and mediwn-grained sediments that were

deposited as flood plain deposits when the streams became choked

with ash derived from adjacent volcanism (Koenig 1960).

McGrew (1969, 1970), Robinson (1966), West (1973) and Bradley (196l!-)stated that the terrain during the Eridgerian was

flat, swav1pyand heavily forested with abundant streams and ponds

in a semi-tropical climate. In the present study, spe::!imens of

crocodiles, turtles and Leuidosteus indicate the presence of streams

and somevrhat permanent bodies of water in a mild cli.mate. Prima.tes

such as Hemiacodon indicate the presence of forested areas (Robinson 1966:12), Relative abundance of large mammals infers that open country may have existed, We may picture the middle Eocene of the

Green River Basin as somewhat open, partly forested countryside with many rivers and small lakes with a mild climate,

37 CONCLUSI01IS

Zones C and D could not be distinguished faunally in the study area. However, the presence of the Lonetree White I.ayer li th- ologiec1.lJ.y separates the two zones. The absences from zone C of

Crocodilidae, and from zone D of Miacid.ae, Hemiacodon, Tviicropara- m.yina,e and Telmatherium do not provide sufficient evidence to establish a dis-Linction between these zones (Table 1).

1be recovery of a left PJ (BYU 0988) representing a cory- phodontid, extends the chronoJ.ogic range of that family in the Green

River Basin from J.ate Watsatcbian (Early Eocene) to Late :Bridgeria,n

(Middle Eocene).

In contrast to findings of other workers (Dr. Robert M. West, pers, comin, 1975; Dr. J, Keith Rigby Jr,, pers, comm, 1977), the

Lonetree White layer was not found to be more fossiliferous than other beds in the study area,

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(Fossils fou.ncl from sites 1 through 27 referenced from map of study area, text page 5,)

S:i.·te Fossils recovered 1 ...... Brontotheriidae - BYU0174, BYU0945, BYU 0970, BYU1001, BYU1055. Telmatherium s:p. - BYU0175,

2 • • • • • • • Hyopsod'Js cf. !!_. marshi, BYU0917.

Coryphodontidae, BYU0988. 3 ...... Hyopsodus cf, g. marshi, BYU0918, BYU092J. Hyaenodontidae, BYU0929, Brontotheriidae, BYU1072,

cf. T.don~, BYU 1124, BYU1126. Testudinidae, BYU1130.

4 ••.•••. Hyaenodontidae, BYU0934, BYU1096, BYU 1097, BYU1099, BYU1100. 5 . •••••. Hyaenodontidae, BYU0929. cf. Iepidosteus, BYU1137, 6 •••••.• Hemiacodon cf.~. gracilis, BYU0925, Micro:paramyina,e, BYU1066.

7 • • • • • • • Brontotheriidae , BYU0948, BYU09 58, BYU 1118.

43 S:i.to __f.'ossi1s, __ ~ recovered. 8 , . , . . . . Brontothcriid.ae, BYU091.J-9, BYU 0983, BYU 1010, BYU1011.

cf, l,epirlos teus, BYU1140. 9 . . . . Brontotheriidae, BYU0950. 10...... Brontotheriidae, BYD0951, 11 • ...... Brontotheriid.a.e, :SYU0955. Testndinidae, BYU1132. 12...... Brontotheri.id.ae, BYU09 57, BYUl0l1-7. 13...... Brontothcriidae, BYU0974, BYU 0982. . . . . Hemiacodon cf. _!i. graci1is, BYU 0986.

15. ~ . . . . . Hyopsodus cf, g,, marshi, BYD0996, Miacidae, DYU0999, cf. IB_pidosteus, BYU1145, 16 • . . . Brontotheriidae, BYU1090, 17...... Brontotheriidae, BYU1009. 13 • • . . . Brontotheriidae, BYU1052, cf, Iepido?teus, BYU1147, BYU1142, Crocodilidae, BYU1144. 19...... Pseudocreodi, BYU1058. 20. ' . . . . . Brontotheriidae, BYU1069, BYUl09lJ- 21...... Brontotheriid.ae, BYU1084. 22 • . " . . . . cf. Trionyx, BYU1114, 23...... cf. Trionyx, BYU1120, BYU1121. 21-1-• • . . . cf. Trionyx, BYU1122, BYU1123 25 • ...... Testudinidae, BYU1127, BYU1128, BYU1129. Fossils recovered

26. f " t • • • cf. I0pidosteus, BYU 11J9.

27 ••• , , • , cf, J€u::tdnsteus, BYU 1141. '.IHJ•� SAGE CREEK M0Ull1AIN LOCAL FAUNA OF THE BRIDGER

FOm1ATION NEAH LONET.REE, WYOMING

Steven W Barker

Dey;u,rtr,1.ent of Zoolo67 M. S. Degree� August 1977

ABSTRACT

Ta,xa in the present study area include representatives from the followlng orders: Semionotiformes, Chelonia, Crocodilia, Insectivora, Creodonta, Carnivora, Primates, Rodentia, Pantodonta, and Perissodactyla. The latter order was the most taxonomically diverse; that is typical for Bridger deposits. Fossils were common throughout i:.he study area, and most abundant in the lowermost zone C and iinmedJ.a:tely above and below the Lonetree White LaJer.

Faunal distinctions in the study area were not evider.t between zone C and zone D. Recovery of a left F3 representing Coryphodonticlae, extends the chronologic rarge of th&:t family into the L3..te Bridgeria.n,

Fi.ne-gra..i.ned sediments; sh·eazo. channels and. abundant remains of titanotheres, gar-like fish, and crocodiles indicate a ;ilild, well-watered climate with abundant plant cover. FaumJ. evidence based on the presence of Hyopsodus and TeJ.Jn.atherium suggest a, late :SridgeI'ian age.

COMMIITEE APPf1\1VAL: