FIELDIANA Geology Published by Field Museum of Natural History VOLUME 29 GEOLOGY AND MAMMAUAN PALEONTOLOGY OF THE NEW FORK-BIG SANDY AREA, SUBLETTE COUNTY, WYOMING ROBERT M. WEST MARCH 23, 1978 FIELDIANA: GEOLOGY A Coutinuation of the GEOLOGICAL SERIES of FIELD MUSEUM OF NATURAL HISTORY VOLUME 29 FIELD MUSEUM OF NATURAL HISTORY CHICAGO, U.S.A. GEOLOGY AND MAMMALIAN PALEONTOLOGY OF THE NEW FORK-BIG SANDY AREA, SUBLETTE COUNTY, WYOMING FIELDIANA Geology Published by Field Museum of Natural History VOLUME 29 GEOLOGY AND MAMMALIAN PALEONTOLOGY OF THE NEW FORK-BIG SANDY AREA, SUBLETTE COUNTY, WYOMING ROBERT M. WEST Department of Biology, Adelphi University Garden City, New York MARCH 23, 1973 PUBLICATION 1161 Patricia M. Williams Managing Editor, Scientific Publications Library of Congress Catalog Card Number: 72-9UU19 PRINTED IN THE UNITED STATES OF AMERICA BY FIELD MUSEUM PRESS TABLE OF CONTENTS PAQR Introduction 1 General Geography 1 History of Investigation 3 Methodology 10 Acknowledgements 11 General Geology 13 Eocene Stratigraphy 18 Wasatch Formation 18 New Fork Tongue 20 Cathedral Bluffs Tongue 27 Bridger Formation 32 Upper Laney Shale Member of the Green River Formation and Lower Bridger Formation Combined 32 Green River Formation 36 Fontenelle Tongue 36 Middle Tongue 38 Laney Shale Member 40 Summary of Depositional History 43 Structural Geology 48 Wind River Thrust Fault 48 Continental Fault 51 Pinedale Anticline 54 Occurrence of Fossil Material 55 Collecting 55 Preservation 55 Fossil Production 56 Vertebrate Faunal List 57 Fossil Mammal and Reptile Localities 59 Systematics 78 Order Marsupicarnivora 80 Order Insectivora 81 Order Creodonta 87 Order Carnivora 92 Order Primates 95 Order Rodentia 108 Order Tillodontia 125 Order Taeniodonta 125 Order Dinocerata 126 Order Pantodonta 126 vii viii FIELDIANA: GEOLOGY, VOLUME 29 PAGE Order Condylarthra 128 Order Perissodactyla 137 Order Artiodactyla 148 Geochronology 153 Faunal Correlations 156 New Fork Tongue 156 Cathedral Bluffs Tongue 159 Bridger Formation 163 Conclusions 165 References 168 Appendix — Measured Sections 177 INTRODUCTION General Geography The New Fork-Big Sandy area, about 430 sq. miles in extent, is located in the northeastern Green River Basin of Wyoming (fig. 1), It is entirely east of the Green River, and is crossed by two major tributaries of the upper Green River, the New Fork River and the Big Sandy River. To the east are the Wind River Mountains, while lower country bounds the area in the other directions. Pinedale, the Sublette County seat, is 6 miles north of the northwest corner. Big Piney about 10 miles west of the southwestern corner, and Farson about 27 miles south of the southern boundary. Most of the area is made up of gently rolling plains with an aver- age elevation in excess of 7,000 ft. Occasional badlands areas occur, usually at the infrequent sharp changes in relief. The maximum relief is along the streams and at the edge of the Mesa, a flat eleva- tion at the northwestern edge of the New Fork-Big Sandy area. Granitic knobs, such as Fremont Butte, with an elevation of 7,875 ft., form prominent highs. The Paleozoic rocks of Steele Butte project to 7,408 ft., and Ross Butte, in the southwestern corner, is 7,475 ft. in elevation. The locations of these features are noted on the geo- logical map of the New Fork-Big Sandy area (fig. 2). The New Fork and Big Sandy Rivers meander extensively. A major tributary of the New Fork, the East Fork River, flows gener- ally northwestward across the area, receiving water from Muddy, Cotton, Silver, and Scab Creeks. This part of the Green River Basin has a pleasant summer cli- mate, with daily high temperatures in the high seventies and low eighties, and nighttime lows in the forties and fifties. The average total annual precipitation is about 9.5 in. The growing season is short, averaging 60 to 80 days between killing frosts. The last spring freeze usually occurs about mid-June, and the first fall freeze in late August. The short duration of the growing season limits most fonns of agriculture. Land unsuited for growing hay is devoted to range for cattle and sheep. 1 Tetc Cou Miles 10 20 >f WIND RiVER BASIN Fig. 1. Index map of southwestern Wyoming. The areas of Tertiary expo- sure are unshaded, except for the sand dune area, indicated by dots. The areas of pre-Tertiary rocks are represented as follows: crosshatching — Precambrian; hori- zontal lines — Paleozoic and Mesozoic; vertical lines — Cretaceous only. The New Fork-Big Sandy area is outlined. WEST: NEW FORK-BIG SANDY AREA 3 Vehicle access to most of the area is good. U. S. 187 bisects tho area north-south, Wyoming State Secondary Highway 1801 goes west from U. S. 187 across the southwestern part of the area toward U. S. 189 and Marbleton and Big Piney, and Wyoming State Second- ary Highway 1804 is paved for 20 miles east and south of Boulder, almost to the Big Sandy Junction. This then continues south as a graded dirt road, the "Lander Cutoff Road," across the Big Sandy River at Buckskin Crossing. At that point it turns eastward and follows the flank of the mountains to join Wyoming State Highway 28 near South Pass and the Sweetwater River. A western branch goes almost due south from Buckskin Crossing, past Elk Mountain, and meets Wyoming 28 a few miles east of Farson. In addition to the numbered paved roads and their continuations, there are several primary graded dirt roads, maintained by Sublette County. A fine network of trails permits pickup truck access to most of the New Fork-Big Sandy area. History of Investigation In June, 1832 John Ball (1835, p. 3), accompanying William Sublette's Rocky Mountain Fur Company supply caravan, wrote of his impressions of entry into the Green River Basin via South Pass: Standing on the dividing ridge between the Great Ocean.s at an eleva- tion ... of about ten thousand feet, you look down East upon the granite mountains already passed, and then to the N.W. upon the snowy Wind- river mountain, rising probably, five thousand feet above the place where you stand. To the South on the height of the land, stretches an immense prairie as far as the limits of vi.sion, with little variation of surfaces, on which are feeding herds of buffaloes; and far to the West, extends north and south, a range of mountains of apparently great elevation. He then picked his way northwestward along the flank of the Wind River Mountains among the "gi'anite boulders, which showed con- clusively the character of that mountain" (Ball, 1835, p. 3). This is the earliest description of any geological features of the Green River Basin area. On August 7, 1842, Captain John G. Fremont crossed South Pass and headed northwest. He stopped on the Big Sandy on August 9, noting the "parti-colored sand, exhibited in escarpments fifty to eighty feet high" (Fremont, 1845, p. 61). He camped that evening along the East Fork at the base of what is now called Fremont Butte, spent a week in the high country, returned to the East Fork camp on August 17, and recrossed South Pass on August 19. Fre- R. i09w. LEGEND =>w£lSTQC£\E A\0 HECENT 1 Qol ] Quaternary Alluvium [ Qd 1 Sand Dwi«s I Qp ] Pinedoie Tin I QW I Bull Lake T.lt I Qt I Htgh Terrace Gi-oveis EOCENE 1 TM I Loney Shale Member - l.o*«er B^idger Formotion Undivided { Tiocb j Cothedrol Bluffs Tongue of Wosotch Formotion 1 Twifwj Western Facies ot New Fork Tongue of Wosalch Formation [ Twnfo 1 Arkosic Focies of New Fork Tongue of Wosotcfi Formotion [ Tgl j Loney S'lole Member of Green River Formotion j Tgm i M^dle Tongue of Green River Formation [ Tgf [ Fonieneiie Tongue of Green River Formotion GEOLOGICAL UNITS PALEOZOIC Cm Mississippon-Modison Limestone I Dd ) Devonion- Dorby Limestone i Ob j Ordovicicn- S;4tiorn Dolo.T>iTe I Cu j Cambrian Undivided -Quartzlte, sandstone, sha!e and limestone PRECAMBRiA.'j 1 FC j Granites, gneisses end schis's MAP SYMBOLS f-'oved hf^nway Graded dvt rood MOjOr troil Wyoming state secondory h^gtvfoy ~j S highway Perennial streom Infermif'ent strecm Stock tonk Formotion boundory cuit lity GEOLOGICAL MAP OF THE NEW FORK -BIG SANDY AREA. SUBLETTE COUNTY. WYOMING Robert M.West Scoi* 2 3 Fig. 2. Geological map of the New Fork-Big Sandy area. 5 6 FIELDIANA: GEOLOGY, VOLUME 29 mont observed the geology as well as the flora and fauna, and made special mention of the highly weathered granite in the Fremont Butte vicinity. Fremont visited the basin again in 1843, travelling to Ft. Bridger. At this time he collected a number of gastropods which were de- scribed by James Hall in Fremont's 1845 report. A number of pre-Civil War surveys were conducted pertaining to the various immigrant trails and resultant wagon roads, but these reports paid no attention to the local geology. A typical one of these is F. W. Lander's 1859 "Preliminary report . . . upon . . . explora- tions west of the South Pass, for a suitable location for the Fort Kearney, South Pass, and Honey Lake wagon road." During this period scientific work began in the southern part of the basin, espe- cially near Ft. Bridger. The first Green River fossil fish was collected in 1856 by Dr. John Evans and described by Joseph Leidy in 1857. After the Civil War, both the government and the Union Pacific Railroad encouraged systematic exploration. The territorial sur- veys, directed by Powell, Hayden and King, produced a wealth of information. Most of the work was focused along the Union Pacific right-of-way, but the Hayden Surveys of 1877-1878 concentrated on the area between latitude 41°45'N and 43 °N, which included the northern half of the basin. Hay den's 1877 survey included the geology of the "Green River Division" by A. C. Peale, and the "Sweetwater Division" by F. M. Endlich. Peale's division covered all but the eastern edge of the Green River basin. He observed the vast amounts of Tertiary sedi- ments in the northern Green River Basin, and established a fine framework for future studies. Endlich barely crossed South Pass, and only briefly visited the areas of the Big and Little Sandy Rivers. E. D. Cope collected vertebrates in conjunction with the southern portion of the Hayden Survey, continuing the legendary feud with 0. C. Marsh. One of the best of the other government surveys was Comstock (1874), which covered the area between Ft. Bridger and South Pass, as well as the eastern side of the Wind River Mountains and the Yellowstone region. Other groups working in the Green River Basin at this time included both Yale and Princeton in the Ft. Bridger vicinity. Cope continued his collecting work after the termination of his connection with the government surveys. <-r-T 1 UJ X h- tn en o X o < < UJ 'CD cc I < 00 >- Jt5 < '< cn 1 < o 03 to 1 z v: g 1— g o UJ 0) UJ z lC =) t— o 3 CE 8 ; ^ 1 - •1 >- 3 ^ CD. >> •a c CO n o n § I CO d 8 FIELDIANA: GEOLOGY, VOLUME 29 Detailed stratigraphic work commenced shortly after the turn of the century, initiated by A. C. Veatch's fine paper on the Evans- ton-Kemmerer area in 1907. A. R. Schultz (1914) continued Veatch's work, and also surveyed the Rock Springs Uplift area (1909, 1910, 1920). In the early twenties W. H. Bradley began his long and successful career as a student of the Green River Basin. His 1964 U.S. Geological Survey Professional Paper 494-A brings together his knowledge and experience in the basin and adjacent areas. More recent work has been concentrated on the establishment of areal stratigraphic relations and paleontologic faunal studies. Work pertinent to the study of the northern part of the basin (fig. 4) began with R. L. Nace (1939) in the Oregon Buttes area near South Pass. This work was carried northwestward by J. R. Berman (1950) at Tabernacle Butte and Elk Mountain and J. M. Hummel (1955) along Pacific Creek. These latter two papers were summarized by P. 0. McGrew and others in 1959, with the addition of the description of Bridgerian faunas. In 1964 H. D. Zeller and E. V. Stephens of the U. S. Geological Survey published a series of quadrangle maps covering the area to the south and west of South Pass, and a synthesis of their work appeared in 1969. H. B. Stewart, Jr., of Princeton University, wrote a senior thesis in 1945 dealing with a small area southeast of the New Fork-Big Sandy area, later discussed by Brad- ley (1964). To the west, A. J. Bertagnolli mapped in the LaBarge area in 1941. J. H. Donovan worked a large area along the Green River, extending north of Big Piney, in 1950. Both S. S. Oriel and N. C. Privravsky of the U. S. Geological Survey mapped smaller areas in 1963, Oriel at Fort Hill and Privravsky west of Big Piney, and Oriel published on the Fort Hill Quadrangle in 1969. Until about 20 years ago, paleontologic work was concentrated in the spectacularly productive beds in the southern part of the Green River Basin. C. L. Gazin of the U.S. National Museum opened up the northern end of the basin by discovering two levels of early Eocene fossils along the northwest side of the basin, north as far as 12 miles north of Big Piney (Gazin, 1952, 1962). McGrew et al. (1959) included a report on middle to late Bridgerian faunas from Berman's area at Tabernacle Butte, and M. C. McKenna and G. G. Simpson (1959), Simpson (1959), McKenna, P. Robinson, and D. W. Taylor (1962), and R. M. West and E. G. Atkins (1970) have reported additions to the later fauna. Teton County .mimmm^mt .1 Sublette County J. L I r I d I .: Sweetwater County WYOMING o I Colorado 10 20 30 40 Miles Fremont County 1 4 i — ,..,. .1. 6 I a I M ' 7 I • Fig. 4. Mapped portions of the northern Green River Basin. 1 — -Richmond, 1945; 2 - Privravsky, 1963; 3 Oriel, 1963, 1969; 4 Donovan, 1950; 5— New Fork-Big Sandy area; 6 McGrew et al., 1959; 7— Hummel, 1955; 8 — Nace, 1939; 9 -Zeller and Stephens, 1964; 10 -(dotted line) northern boundary of Bradley, 1964. 10 FIELDIANA: GEOLOGY, VOLUME 29 To the north, J. A. Dorr, Jr. (1952, 1958) has worked out the detailed stratigraphy of the Hoback Basin, and has studied Eocene mammals from the Pass Peak Formation (Dorr, 1969) . Recent work (Steidtmann, 1969) has extended south of the Hoback Rim into the area where the Hoback and Green River Basin units merge. In 1945 G. Richmond mapped a structurally complex area at the northwest end of the Wind River Mountains. Love (1950) described the Paleozoic units near Boulder, while the stratigraphy and paleontology of the Tertiary rocks within the New Fork-Big Sandy area have been discussed in five preliminary papers by me (West, 1968, 1969a, b, c, 1970). The paleontological possibilities of the New Fork-Big Sandy areas were first recognized by Dr. Paul 0. McGrew in September, 1956 when he found the Fault locality along the Big Sandy River. He visited it several times, but was unable to carry out any systematic exploration of the exposures along the Big Sandy. In 1965 he sug- gested to me that I use his locality as a starting point in my work. I visited the area for two weeks in August, 1965, and found in- triguing geology and vertebrate fossils. The entire summers of 1966 and 1967 were then devoted to geologic and paleontologic field work in the New Fork-Big Sandy area. Methodology The areal geology was mapped initially on U.S. Geological Survey 732 min. advance proof quadrangle sheets, U.S. Forest Service plani- metric maps, and aerial photographs. For the purposes of synthesis, the geology was transferred to a base adapted from the 1967 edition of the Sublette County Highway Map published by the State of Wyoming. Sections were measured by means of a Brunton compass and steel tape. I found a number of fossil localities (in addition to McGrew's initial find), 25 of which have produced identifiable fossil mammals. All areas of badlands exposures have been investigated, on hands and knees when necessary. In several places I was able to apply the washing technique outlined by Black and Dawson (1966, p. 300). An estimated 24,000 lbs. (dry weight) of sediment was processed through burlap bags during the two full summers of field work. The rock units present in the New Fork-Big Sandy area were studied in outcrop and hand sample; no petrographic or sieve analy- ses were conducted. Gross sedimentary structure and texture were WEST: NEW FORK-BIG SANDY AREA 11 noted. This information, along with that obtained from the areal stratigraphic relationships, was applied to the interpretation of depo- sitional environments and sequences. The fossil material has been identified as well as is possible with fragmental specimens. Direct comparisons were made with material at the U.S. National Museum, Princeton University, the American Museum of Natural History, Yale University, and the Carnegie Museum, as well as Field Museum of Natural History. The mate- rials collected by McGrew during his visits to Fault locality prior to my study were loaned to me for incorporation with my fauna. These are designated by the prefix UW before the catalog number, while my material, deposited at Field Museum, has been given the prefix PM. Measurements of fossil teeth were made both with dial calipers calibrated to .01 mm. and with an eyepiece micrometer in a binocular dissecting microscope. Acknowledgements The three summers in Wyoming were greatly facilitated by travel funds gi*anted by Dr. E. C. Olson and the Committee on Paleozoology (Evolutionary Biology) of the University of Chicago. The 1968 trip to the eastern museums was supported by the Hinds Fund of the Division of Biological Sciences. Dr. Olson allowed me use of the Committee on Paleozoology pickup truck for the 1966 field season. Many people in Wyoming aided the field effort, including Mr. and Mrs. John Arambel of Midland Land and Livestock, Rock Springs; Mr. and Mrs. Leonard Priebe of Boulder; and Mr. and Mrs. Perry Binning of Pinedale. Dr. Steven S. Oriel of the U.S. Geological Survey, Denver; Dr. John A. DoiT, Jr., of the University of Michigan; and Dr. James Steidtmann, now of the University of Wyoming; and I spent several days during the summer of 1967 conferring on common problems of the Green River and Hoback Basins. Dr. W. B. Clapham, Jr., now of Case- Western Reserve University, analyzed a pollen sample, and Dr. William P. MacLean III, now of the College of the Virgin Is- lands, helped by identifying the lower tetrapod fauna. During my museum visits I was cordially received and assisted by Drs. C. Lewis Gazin, U.S. National Museum; Glenn L. Jepsen, Princeton University; Malcolm C. McKenna, Frederick S. Szalay, and Giles T. Maclntyre, American Museum of Natural History; 12 FIELDIANA: GEOLOGY, VOLUME 29 A. W. Crompton, Yale Peabody Museum; and Mary R. Dawson, Carnegie Museum. Dr. Paul 0. McGrew of the University of Wyoming, who initially suggested the project, has offered helpful advice throughout, and visited the New Fork-Big Sandy area in August, 1967. Drs. Leigh Van Valen and Leonard B. Radinsky of the Committee on Evolu- tionary Biology of the University of Chicago were of great assistance in the overall consideration of early Tertiary faunas. Drs. Ralph G. Johnson and Alfred M. Zeigler, also of the Committee on Evolu- tionary Biology, offered encouragement and assistance on the tech- nical matters involved in manuscript preparation. My University of Chicago advisor, Dr. Everett C. Olson, now of the University of California, Los Angeles, must be sincerely thanked for his encourage- ment and help in so many facets of my graduate education at the University of Chicago. Lastly, I thank my wife, Jean, for her inspiration and patience. She helped with the field work all three summers, and became a competent fossil collector in the process. The last two years of work on this project were carried out during the tenure of a two-year National Science Foundation Graduate Fellowship. GENERAL GEOLOGY The northern Green River Basin is a faulted Laramide downwarp filled by Paleocene and Eocene sediments derived largely liom the lithologically variable bounding mountains (see fig. 1). The Over- thrust Belt along the western side is made up primarily of Paleozoic and Mesozoic marine sedimentary rocks. To the northeast, the Wind River Mountains are essentially all Precambrian igneous and metamorphic rocks. Far to the north the Gros Ventre Mountains contain both Paleozoic and Mesozoic sedimentary units. Most of the Tertiary sediments exposed in the northern Green River Basin are of Eocene age. The Eocene sedimentary rocks are of both fluvial and lacustrine origin. The center of the basin is filled with an irregular lens of lacustrine sediment, the Green River Formation, which is bounded beneath and laterally by the fluvial lower Eocene Wasatch Forma- tion and laterally and above by the fluvial middle Eocene Bridger Formation. The Wasatch Formation is represented, in the northern Green River Basin, by the New Fork Tongue and the Cathedral Bluffs Tongue. The older New Fork Tongue is divided, within the New Fork-Big Sandy area, into the arkosic facies along the Wind River Mountains and the western facies farther toward the Over- thrust Ranges. The Cathedral Bluffs Tongue overlies the arkosic facies at several localities in the eastern part of the area. Bridger Formation sediments are exposed only in the southeastern part of the New Fork-Big Sandy area, in a graben controlled by the Con- tinental Fault. Three Green River Formation subunits are present: the Fontenelle and middle tongues lie below and above the western facies of the New Fork Tongue in the western part of the area, and the Laney Shale Member interdigitates with and overlies the Cathe- dral Bluffs Tongue along the Big Sandy River. Each of these sedimentary units will be discussed in detail below, so no further description is presented here. Pleistocene glacial deposits obscure much of the earlier material along the flank of the Wind River Mountains, and the modern topography has been strongly affected by glacial runoff. 13 14 FIELDIANA: GEOLOGY, VOLUME 29 Fig. 5. Precambrian inlier to the north of Fremont Butte in NW J^ sec. 7, T. 32 N., R. 107 W. Pre-Tertiary. — Precambrian and Paleozoic rocks are present in the eastern part of the New Fork-Big Sandy area. No Mesozoic units have been located; their absence is largely structurally con- trolled. Many of the Precambrian exposures are inliers surrounded by Eocene and/or Pleistocene sediments (fig. 5). The most prominent is Fremont Butte, 5 miles east of Boulder. Other exposures of Pre- cambrian rocks are near the Big Sandy River. The lack of distortion of the surficial Eocene at these localities indicates that the Precam- brian material was thrust into position and eroded to approximately the present configuration prior to late-early Eocene time. In many places this unconformity between the Precambrian and the Eocene cannot be seen because of the heavy Pleistocene debris cover. The Precambrian within the New Fork-Big Sandy area is granitic with some separation into gneissic bands. The exposures are too limited for any large-scale trends to be detected, but de Laguna (1938, cited in Holmes and Moss, 1955, p. 632) recognized two zones WEST: NEW FORK-BIG SANDY AREA 15 in the Precambrian between the Big Sandy Openings and Mt. Bonneville. Fragments of Precambrian rocks occur in the Eocene sediments immediately adjacent to the Wind River Mountains, and are also included in the various Pleistocene deposits along the mountain front. The Paleozoic inliers in the Boulder vicinity have been studied by J. D. Love (1950, pp. 25-27). The largest Paleozoic exposure is Steele Butte (fig. 6), a prominent knob about 1 mile southwest of Fremont Butte, which includes units of Cambrian, Ordovician, Devo- nian, and Mississippian age. Four small exposures one-quarter mile west of Steele Butte are at least partly Devonian in age, on the basis of their marine fossil content. Two miles north-northwest of Steele Butte two low hills of Cambrian rocks are close enough to a Pre- cambrian inlier for an approximate contact to be located. Several miles north of Boulder are several small exposures of Pennsylvanian and Permian_age. Fig. 6. Steele Butte viewed from the south. The beds are dipping to the southwest at about 70°. Cambrian sediment is exposed at the right side of the picture, and Mississippian at the left. See Figure 27 for a cross-section of Steele Butte. 16 FIELDIANA: GEOLOGY, VOLUME 29 Southeast of the New Fork-Big Sandy area along the flank of the Wind River Mountains there are no surface exposures of either Paleozoic or Mesozoic units. To the northwest, the entire Paleozoic section, lacking only the Silurian, and a virtually complete Mesozoic section, is present near the Green River Lakes. Pleistocene. — A considerable volume of Pleistocene material oc- cupies the eastern part of the New Fork-Big Sandy area. Glacial till surrounds and overlaps some Precambrian knobs and obscures much of the Precambrian-Eocene unconformity. At least five glacial advances are recorded on the southwestern flank of the Wind River Mountains, remains of two of which are found within the New Fork-Big Sandy area. The oldest advance, the Buffalo, is not present in the area. The next two, the Bull Lake and Pinedale advances, are well documented within the area. The last two advances, the Temple Lake and Little Ice Age, occurred only high in the mountains. Terraces were formed by the meltwater runoff after each of these advances. Holmes and Moss (1955) have related most of these terraces to moraines, especially in the valley of the Big Sandy River. Of considerable interest are a series of granitic gravel and cobble terrace veneers. A thick layer of this material caps the Mesa, and Holmes and Moss (1955, p. 633) believed that it "antedate(s) the oldest till in the area, but may represent earlier glacial stages." Ross Butte, only 3 miles from the Mesa, has practically no capping cobble veneer. This suggests that the pre-Buffalo advance did not extend as far as Ross Butte. Cobbles also blanket the land surface around and to the west of Square Top. This zone is not flat like the Mesa top, and the cobble layer is only a few feet thick. No physical cor- relation can be made between these two areas to ascertain any pos- sible temporal relationships. The oldest till definitely identified within the New Fork-Big Sandy area represents the Bull Lake glacial advance. Bull Lake de- posits make up the irregular land surface near the Big Sandy River southeast of Buckskin Crossing, and almost all the hills in the vicinity of Big Sandy Junction. Bull Lake material is distinguished from the younger Pinedale by its more advanced weathering state. The Pinedale moraine, characteristically irregular and boulder- strewn, is well developed around Boulder Lake north of the New Fork-Big Sandy area, and also in the vicinity of Silver and Cotton- wood Creeks. The slight weathering of the Pinedale Till is reflected in the almost total lack of clay minerals. WEST: NEW FORK-BIG SANDY AREA 17 An area of recognizable sand dunes is located on the north side of the Big Sandy River about 1 mile upstream of Buckskin Crossing. Holmes and Moss reported stabilized sand sheets 1 3 ft. thick along the East Fork River near Boulder. The sand was originally derived from sandy flats on the Bull Lake and Pinedale outwash plains, and accumulated to the leeward (east) as influenced by the prevailing Pleistocene winds. Far to the south, east of Eden, the Kilpecker dune field extends some 60 miles into the Red Desert. EOCENE STRATIGRAPHY The classic interpretation of Eocene sedimentation in the Green River Basin is that so well expounded by Bradley (1964), and shown in Figure 7. His basic thesis involves a symmetrical basin; that is, it expanded and contracted in all directions essentially simultan- eously and with essentially equal expression. Among the assump- tions based on this model is the temporal equivalence of lake-bound- ing Wasatch Formation units, including the New Fork Tongue and the Cathedral Bluffs Tongue. In general, Bradley's model fits well the known stratigraphic picture of the Green River Basin. However, in peripheral areas along the margins of the lacustrine Green River Formation sequence this neat picture does not hold true uniformly (fig. 8). Within the New Fork-Big Sandy area it is apparent that the New Fork Tongue and the Cathedral Bluffs Tongue (as here interpreted) of the Wasatch Formation are not temporal equivalents; likewise, lacustrine units such as the Fontenelle Tongue of the Green River Formation are absent in some places. This latter condition reflects, at least in part, the limits of lacustrine expansion, but it also suggests that local situations in various parts of the Green River Basin, such as the New Fork-Big Sandy area, add unexpected complexities to Bradley's reconstruction. Ensuing discussions point out the relationships of the various early and middle Eocene units as they are developed in the northern Green River Basin. Wasatch Formation The Wasatch Formation is generally considered to include sedi- ments deposited throughout early Eocene time. The type section (Hayden, 1869, p. 90) is a series of conglomeratic exposures in Echo and Weber Canyons, Utah. The name has been, frequently with very little justification, extended to include many early Eocene inter- montane basin sediments. Logically the Wasatch Formation should be restricted to the early Eocene sediments of the Green River Basin, the depositional sequence including the type section. 18 WEST EAST Fig, 7. Bradley's (1964, p. A18, fig. 6) reconstruction of the probable sedi- mentary relationships of the Green River Formation and the bounding early and middle Eocene fluvial units. Key: Tw Wasatch Formation; Twn -Niland Tongue of Wasatch Formation; Twcb Cathedral Bluffs Tongue of Wasatch Formation; Twnf — New Fork Tongue of Wasatch Formation; Tb - Bridger Formation; Tglu — Lumen Tongue of Green River Formation; Tgt — Tipton Shale Member and Tongue of Green River Formation; Tgf Fontenelle Tongue of Green River Formation; Tgw— Wilkins Peak Member of Green River Formation; Tgl - Laney Shale Member of Green River Formation. '(MVXUOC)/' ■■■..■'.■■,y'.K.:'..y<^ ---^■> >■: Fig. 8. Digrammatic cros.s-section of stratigraphic relationships at the northern end of the Green River Basin. The center segment represents the New Fork-Big Sandy area; the left (west) segment is adapted and slightly expanded from Oriel, 1962, p. 2,163; and the right (east) segment is based upon estimates of the probable situation beneath the glacial debris along the flank of the Wind River Mountains. The various units of the Wasatch Formation are indicated by the unshaded areas; the various units of the Green River Formation by horizontal lines; and the Bridger Formation by dots. The older rocks are Mesozoic units of the Wyoming Ranges on the west and the Precambrian core of the Wind River Mountains on the east. Compare the relative developments and positions of the sedimentary units with Bradley's interpretation shown in Figure 7. 19 20 FIELDIANA: GEOLOGY, VOLUME 29 Wasatch Formation sediments are usually variegated mudstones, predominantly grayish with variable amounts of red (Bradley, 1964, p. A21). Coals and sandstone lenses are locally important, and con- glomerates frequently indicate rapid deposition along the flanks of mountain ranges. The maximum thickness of the unit is in excess of 4,000 ft. (Bradley, 1964, p. A22). A number of mappable tongues of the upper Wasatch Formation interfinger with the lacustrine Green River Formation. Several of these, as discussed below, occur in the New Fork-Big Sandy area. New Fork Tongue Donovan (1950, p. 64) described the New Fork Tongue of the Wasatch Formation as a sequence of variegated clay shales, arkosic conglomerates, and cross-laminated sandstones, with the type area near the confluence of the Green and New Fork Rivers. Bradley (1964, p. A27) extended Donovan's New Fork Tongue 80 miles farther southwest, and Oriel (1961, p. 107) included some fluvial beds in the New Fork Tongue which Donovan had originally placed in the Fontenelle Tongue of the Green River Formation. This study extends the exposure area of the New Fork Tongue into the north- eastern part of the Green River Basin, along the flank of the Wind River Mountains. Arkosic Facies The informal term "arkosic facies of the New Fork Tongue" is introduced here to designate a thick sequence of multi-colored sandy mudstones along the western flank of the Wind River Mountains. A typical exposure of this sequence is on the south bank of the Big Sandy River in the center of sec. 21, T. 30 N., R. 105 W., where 175 ft. of sediment are present in a high face. These sediments are re- ferred to simply as Wasatch Formation on the 1955 Geologic Map of Wyoming, as well as by Love (1950). Nace (1939, p. 17) regarded these banded mudstones as the Cathedral Bluffs Tongue of the Wasatch Formation. McGrew et al. (1959) called them Wasatch Formation, although Berman (1950) considered the possibility of the upper portion belonging to the Cathedral Bluffs Tongue. The present study has led to the conclusion that the variegated beds are older than the Cathedral Bluffs Tongue, and are assigned an infor- mal name for the purposes of reference and coiTelation. Exposures. — The arkosic facies of the New Fork Tongue is the lowermost Wasatch unit exposed in the New Fork-Big Sandy area, WEST: NEW FORK-BIG SANDY AREA 21 Fig. 9. Arkosic facies of the New Fork Tongue of the Wasatch Formation exposed along the East Fork River in SW '4 sec. 11, T. 31 N., R. 107 W. Note the irregular color bandings. and is by far the most extensive. Excellent exposures of this unit are present in stream cuts along the Big Sandy and East Fork Rivers, and on a long slope south of the East Fork near U.S. 187. The total thickness of the arkosic facies is unknown, as the surface exposures are only a part of the total thickness. About 175 ft. of exposed arkosic facies have been measured along the Big Sandy, and approximately 300 ft. are exposed on the slope south of the East Fork River. McGrew et al. (1959, p. 128) estimated a total expose sec. 2. T 26 N.. R. 101 W.) Nace (1939. pp. 37-39) measured 755.5-763.5 ft. of upper and lower Bridgei* Forma- tion combined. In the Tabernacle Butte area (McGrew et al., 1959, p. 128) 357 ft. of upper Bridger Formation sediment is present. About 300 ft. of lower Bridger Formation is exposed in the New Fork-Big Sandy area, giving a total of more than 650 ft. of Bridger Formation sediment in the northern Green River Basin. Lithologies. — The lower Bridger Formation is variable within the New Fork-Big Sandy area. This range of lithologies indicates a large amount of local environmental variation. Conglomeratic lenses, remnants of wandering stream channels, are relatively common. Resistant sandstones are plainly visible as elevations, while others occur as lenses or irregular beds in dissected areas and stream cuts. Most are not calcareous, or only slightly so, and are composed almost entirely of quartz with variable amounts of feldspar and little biotite mica or other ferromagnesians. Little evidence of current action is apparent, as few of these deposits dis- play current cross-bedding, graded bedding, or well-developed laminations. The finer clastic sediments make up the bulk of the lower Bridger Formation in the New Fork-Big Sandy area (fig. 14). The colors tend to be more pastel than those of the fluvial Wasatchian sediment. Buflf and brown are the most common colors and the overall range is from white to gray, green, and pink. The materials recognizable in hand sample are crystalline quartz, orthoclase feldspar, and mica, as well as particles of rhyolite and other acidic volcanics. The darker levels contain a greater proportion of ferromagnesian min- erals, especially biotite mica and hornblende. There is little evidence of current action. 34 FIELDIANA: GEOLOGY, VOLUME 29 Fig. 14. Typical exposure of the lower Bridger Formation along the Big Sandy River. The ledges are more calcareous and more resistant than the interbedded mudstone. Gray-green to brown sandy mudstones and intraformational mudstone conglomerate are abundant. Most of this sediment is blocky to rubbly in appearance, but some levels are almost shaley. The amount of calcium carbonate varies without apparent pattern. Recognizable grains in hand sample include quartz, biotite, and muscovite mica, ferromagnesians, rhj^olite, granite fragments, and sherds of volcanic glass. The abundance of volcanic derivatives is indicated by the presence of bentonite, detected by its characteristic hygroscopic action. Dense buff to dark gray siltstone makes up the remainder of the clastic sediments. These contain virtually no particles identifiable in hand sample, and vary considerably in the degree of calcareous- ness. Many are laminated, and some are almost fissile. Some tuffs are present, marked by their light blue-white weather- ing. Plant impressions were found in a tuff bed in the NW I4 sec. 4, T. 29 N., R. 106 W. The lower Bridger Formation continues the trend established in the underlying Laney Shale Member of the Green River Formation and becomes more tuffaceous upward. WEST: NEW FORK BIG SANDY AREA 35 Calcium carbonate is present in the form of crystal veins. Such veins are common at Hawk locality (SW ' |. NK ' , sec. 18, T. 29 N., R. 106 W.), while wider veins with poorly formed geodes of crystalline calcite occur in NE '., sec. 31, T. 30 N., R. 106 W. Crystals derived from weathered calcite geodes occur in the Fish Hill area (SW ' , sec. 5, T. 29 N., R. 105 W.). Gypsum crystals have been found in NW ^4 sec. 4, T. 29 N., R. 106 W.. possibly indicating some aridity and evaporation of sulfate-rich lake and pond waters. The last expansion of Lake Gosiute, represented by the Laney Shale Member of the Green River Formation, did not terminate abruptly, but ended slowly under various conditions at various places. Lacustrine sedimentation gradually gave way to more subaerial deposition in the Bridger Formation. At the same time as the lacustrine condition was disappearing, a greater amount of airborn pyroclastic debris came in from nearby active volcanic areas, probably the Yellowstone-Absaroka Plateau of northwestern Wyoming (Love. 1939, pp. 109 110). Thus, with time, the Bridger Formation fluvial deposits came to be dominated by pyroclastics. Such deposits are well exposed on the flanks of Tabernacle Butte south of the study area. lielatiouships. Although the sediment here assigned to the lower Bridger Formation is geogi-aphically isolated from the type region of the Bridger Formation, it is lithologically and faunally similai'. The New Fork-Big Sandy area lower Bridger Formation is strati- graphically below the upper Bridger Formation described by McGrew et al. ( 1959) in the Tabernacle Butte area, and conformably overlies the Laney Shale Member of the Green River Formation within the New Fork-Big Sandy area. The composition of the included fauna also indicates a younger age than that of the Wasat- chian units. The lower Bridger P^ormation exi)osure area is bounded almost everywhere by branches of the Continental Fault system. The dips within this downdropped block are mostly to the west and .south- west, although areas near the fault zones show fault-distorted dips which reflect the relative movement of the sediments. The strati- gi'aphically highest lower Bridger Formation .sediment within the New Fork-Big Sandy area is near the middle of the lower Bridger Formation exposure area. Unfortunately, the fault system obscures the Laney-Bridger transition zone. Paleontology. The lower Bridger Formation in the New Fork- Big Sandy area produces a diverse fauna, representative of the lower 36 FIELDIANA: GEOLOGY, VOLUME 29 part of the formation, Bridger B. No amphibians have been recov- ered, although a variety of reptiles are common. Birds are repre- sented in the collection by a single vertebra. The mammalian fauna is dominated by the smaller forms, especially primates and rodents. Comparatively few large mammals have been found. Sediment from four localities has been washed, and this technique has greatly in- creased the relative numbers of small animals represented in the assemblage. Green River Formation The Green River Formation is the lens of lacustrine sediment occupying the center of the Green River Basin. Temporally it transgresses early and middle Eocene time, interfingering laterally with both the Wasatch and Bridger Formations. Its marginal fluctuations represent the successive advances and retreats of the lake, while the composition of the sediments in the continuous central portion reflect great variations in salinity associated with the size changes. The tongues of the Green River Formation are based upon the expansions and lateral relationships to the bounding fluvial sediments. Only the upper part of the Green River Formation is present in the New Fork-Big Sandy area. None of the lacustrine units are developed across the entire area; this adds to the complexity of interpretation of the relationships along the northern end of the basin. Fontenelle Tongue The Fontenelle Tongue of the Green River Formation was pro- posed by Donovan (1950, p. 63) to designate a sequence of "alternat- ing buff-brown sandstones and green and gray mudstones, which conformably overlies the Knight member of the Wasatch." The type locality is about one-half mile south of Fontenelle Creek in sec. 13, T. 24 N., R. 115 W. Oriel (1961, p. 151) has since separated mudstones of the lower portion of the New Fork Tongue of the Wasatch Formation from the original upper Fontenelle Tongue, so the Fontenelle Tongue is now a primarily lacustrine unit (see Dono- van, 1950, p. 63). Oriel's rearrangement places the New Fork Tongue between the Fontenelle Tongue and higher lacustrine units, while Donovan's original interpretation placed Laney Shale sedi- ment directly on top of Fontenelle Tongue material. Although Donovan stated that the Fontenelle Tongue disappears in the south- WEST: NEW FORK-BIG SANDY AREA 87 Fig. 15. Fontenelle Tongue of the Green River Formation exposed in a large roadcut along Wyoming State Secondary Highway 1801 in sec. 11, T. 30 N., R. now. west comer of T. 30 N., R. 110 W., it is apparent from this study that it persists for about 10 miles to the northeast of the point indi- cated on his map. Exposures. — The Fontenelle Tongue is exposed within the New Fork-Big Sandy area only along the New Fork River. The top is placed at the top of the highest heavy huflf sandstone underlying the bright blue-gray to blue-gi*een mudstone of the basal western facies of the New Fork Tongue of the Wasatch Formation. The base is not exposed within the New Fork-Big Sandy area. The maximum thickness exposed within the New Fork-Big Sandy area is approximately 90 ft. in a prominent cut along Wyoming Highway 1801 in sec. 11, T. 30 N., R. 110 W (fig. 15). This is nearly the total thickness, as the underlying Wasatch Formation is exposed nearby to the west. According to Bradley (1964, p. A34), the Fontenelle varies from a feather edge to 250 ft. in thickness. Lithologies. — The Fontenelle Tongue is composed of well-lami- nated buflf to gray fine calcareous sandstone, fine gray muddy lime- 38 FIELDIANA: GEOLOGY, VOLUME 29 stone, poorly indurated fine yellow sand, and calcareous gi'ay blocky mudstones and shales. Some sandy ostracodal limestone is present low in the unit. Black chert grit in the sandstone and mudstone suggest derivation from the Paleozoic and Mesozoic units to the west. The angular to subrounded sand grains are sorted into thin laminae, suggesting deposition below wave base. The sediment is coarser toward the top of the tongue, with current ripple marks and long cut-and-fill structures evident. This reflects a gradual transi- tion to a more fluvial environment. Exposures along the New Fork River show yellow, buff, and brown sandstone lenses cut down into the much finer laminated sandstones and apparently having a greater feldspar component. Relationships. — In the middle of T. 31 N., R. 109 W. the lacustrine Fontenelle Tongue merges laterally, along a fluctuating shoreline, with fluvial sandy mudstones of the arkosic facies of the New Fork Tongue of the Wasatch Formation. This transition can be seen in a poor outcrop on the south bank of the New Fork River in Sec. 15, T. 31 N., R. 109 W. The Fontenelle Tongue has been considered the lateral equivalent of the Tipton Tongue, which is not developed in the New Fork- Big Sandy area. Roehler (1968) has shown that the upper part of the Tipton Tongue discussed by Bradley (1959) should be assigned to the Wilkins Peak Member of the Green River Formation. The faunal ages of the New Fork Tongue and Cathedral Bluffs Tongue in the New Fork-Big Sandy area suggest that the Fontenelle may be significantly older than the Tipton Tongue- Wilkins Peak Mem- ber sequence to the south. In the New^ Fork-Big Sandy area the Fontenelle usually dips slightly southeast (basinward). It dips southwest along the west flank of the Pinedale Anticline, in T. 30 N., R. 109 W., and is absent on the east flank of the anticline because of the lateral merger into the Wasatch Formation. Paleontology. — The Fontenelle Tongue has not produced any fossil vertebrates. Fresh-water ostracodes occur, and some layers contain plant remains as carbonized zones and impressions. Locali- ties outside the area, however, contain invertebrate faunas (Oriel, 1969, p. M19). Middle Tongue Oriel (1961) referred to a lacustrine level along the western margin of the northern Green River Basin as the middle tongue of the WEST: NEW FORK-BIG SANDY AREA 39 Green River Formation. These beds were initially mapped as Laney Shale Member by Donovan (1950). Bradley (1959) determined that the type Laney Shale Member in the Washakie Basin was not cor- relative with what had been called Laney Shale Member in the Green River Basin. He reassigned the name Laney Shale Member to higher beds in the Green River Basin and gave the name Wilkins Peak Member to what had previously been called Laney Shale Mem- ber there. The Wilkins Peak Member of the Green River Formation, with its type section on Wilkins Peak in the southern part of T. 16 N., R. 106 W., represents a contracted stage of Lake Gosiute, replete with evaporite minerals. The beds discussed by Oriel may represent the initial post-Wilkins Peak northward expansion of the lake, preceding the far more extensive Laney Shale expansion. Exposures. — The middle tongue is present on top of Ross Butte (SW 3 4 sec. 13, and SE >4 sec. 14, T. 30 N., R. 110 W.) and caps Ross Ridge and the west end of Blue Rim. No more than 100 ft. of middle tongue is present on top of Ross Butte, and there is much Fig. 16. Middle tongue of the Green River Formation exposed on top of Ross Butte. The hammer is resting upon an algal limestone unit, which is overlain by a thin-bedded calcareous sandstone. 40 FIELDIANA: GEOLOGY, VOLUME 29 less on the lower rises to the south and east. Elsewhere within the area it has been removed by erosion. A small amount of the middle tongue is present northwest of the New Fork-Big Sandy area, on top of Grindstone Butte in sec. 13, T. 33 M., R. Ill W. (Oriel, pers. comm., 1967). Lithologies. — The middle tongue of the Green River Formation is composed of gray-white algal limestone, platy buff calcareous sand- stone, and massive buff limestone (fig. 16). The unit is resistant, providing a cap on the ridges. As studied in hand sample, the sand- stones are composed mostly of subangular to subrounded particles with calcareous cementing material. Relationships. — The middle tongue overlies the New Fork Tongue of the Wasatch Formation with a sharp contact of limestone over green sandy mudstone. The top is not present within the New Fork- Big Sandy area, but Oriel (1961, p. B151; 1969, p. M17) mentioned an upper tongue of the Wasatch Formation overlying the middle tongue of the Green River Formation in the Fort Hill area. To the west of the area, the middle tongue merges laterally into fluvial Wasatch Formation beds (Donovan, 1950, p. 64). Eastward, the Cathedral Bluffs Tongue of the Wasatch Formation presumably occupies the same relative stratigraphic position. The middle tongue may well be a northward expansion of lacustrine deposition immedi- ately following the Wilkins Peak contracted stage, although con- tinuous exposures do not exist for verification. Paleontology. — Much of the material in the middle tongue of the Green River Formation in the New Fork-Big Sandy area is algal in origin. No vertebrates have come from the small exposures considered in this study, nor have any invertebrates been seen, with the possible exception of some larval arthropod cases. Donovan (1950, p. 65) found fragmental fish and insects, and Oriel (1969, pp. M20-M21) found plant remains and insect cases in the upper zone of the middle tongue. Laney Shale Member In 1920 A. R. Schultz proposed the name Laney Shale Member of the Green River Formation for lacustrine beds exposed along the Laney Rim on the north side of the Washakie Basin. Bradley, in 1959, equated the Washakie Basin Laney Shale Member with the Morrow Creek Member of the Green River Basin, and substituted Wilkins Peak Member for what had been known as Laney Shale Member in the Green River Basin. WEST: NEW FORK-BIG SANDY AREA 41 Exposures. — The Laney Shale Member, the most extensive lacus- trine unit in the area, caps several prominent hills near Speedway Road, including Square Top in the NE '., sec. 24, T. 30 N., R. 107 W.. and appears along the upthrown side of the Big Sandy Limb of the Continental Fault. Exposures along the Big Sandy River provide the most nearly complete Laney Shale Member section in the New Fork-Big Sandy area. The base of the Laney Shale Member is readily defineablc as that level at which "structured" or bedded and laminated shales and sandstones appear, while the top merges imperceptibly into the overlying Bridger Formation. This transitional upper part of the Laney Shale Member is included with the Lower Bridger Formation, and the lower, readily differentiable Laney Shale Member is treated separately here. Incomplete measured sections of the Laney Shale Member are 137.6 ft. thick on the southwest flank of Cone (E ^ sec. 8, T. 29 N.. R. 105 W.) and 50.5 ft. thick on the west flank of Square Top (NE 14 sec. 24, T. 30 N., R. 107 W.). McGrew et al. (1959, p. 128) mea- sured 156 ft. of Laney Shale Member (then called Morrow Creeks near Tabernacle Butte, just south of the New Fork-Big Sandy area, and Bradley (1926, p. 131) recorded 324 ft. of "Morrow Creek" in sec. 17, T. 23 N., R. 102 W., near Steamboat Mountain in northern Sweetwater County. The maximum thickness of the Laney Shale Member within the New Fork-Big Sandy area may be as much as 200 ft. More than 600 ft. of Laney Shale Member sediments are present to the south, near Rock Springs. Lithologies. — Shale and fine shaley sand are common in the Laney Shale Member and range in color from almost black to gray-white, brown, and buff. When observed with a hand lens, much of the shale has sizeable amounts of fine sand sized particles, usually composed of quartz and feldspar as well as biotite and muscovite micas. "Paper shales" appear at two elevations in the southeastern part of the New Fork-Big Sandy area: Cone (E '■_, sec. 8, T. 29 N., R. 105 W.) and Table (S y^y sec. 4, SW }4 sec. 3 and N H sec. 9, T. 29 N., R. 105 W.). Laney Shale Member sandstones and poorly indurated sands are gray, gray-brown, brown, buff, and yellow. They are generally' rather fine-grained, and most are at least incipiently bedded. Some are quite marly, with CaCOs abundant in the cement, while others are siliceous or clayey. The resistant sandstones frequently form 42 FIELDIANA: GEOLOGY, VOLUME 29 small ledges. The sandstones in the Laney Shale Member tend to be more tuffaceous than those of the lower lacustrine units. An excellent exposure of several tuffaceous Laney sandstones is present just east of the Big Sandy Limb of the Continental Fault in SW ^ sec. 24, T. 30 N., R. 106 W. These sandy zones are suggestive of beaches along the fluctuating Laney shoreline. The tops of both Table and Cone are supported by a hard sili- ceous conglomerate bed. In hand sample this poorly sorted con- glomerate contains loosely packed angular to subrounded quartz and plagioclase and microcline feldspar grains. Ferromagnesian minerals are much less common than in the finer, softer sandstone. The conglomerate is cut randomly by siliceous veins. Gray to brown sandy mudstones are usually reasonably well consolidated, although not particularly resistant. The fine matrix makes up the bulk of the rock along with a varying amount of sand- sized particles of quartz and feldspar. Some layers are extremely marly, and aquatic fossils frequently occur in these. Several buff to white, resistant limestones occur on Square Top and nearby elevations. They range from massive to granular and porous, and are rich in aquatic fossils — algae, ostracodes, and molluscs. Rapid facies changes from this organic limestone occur at several places on Square Top, reflecting rather abrupt environ- mental changes. Relationships. — In the New Fork-Big Sandy area the Laney Shale Member is bounded above and below by fluvial beds, but farther toward the center of the basin it is the top of a continuous lacustrine sequence, overlying the Wilkins Peak Member of the Green River Formation. The Laney Shale Member, while generally overlying the Cathedral Bluffs Tongue of the Wasatch Formation, is in part contemporaneous with it. In the SW 3^ sec. 30, T. 30 N., R. 105 W., brown shales and fine sandstones of the Laney Shale Member interfinger laterally with greenish sandy mudstone of the Cathedral Bluffs Tongue. Paleontology. — The Laney Shale Member is much more fossil- iferous than other lacustrine units within the New Fork-Big Sandy area. Plants, invertebrates, and vertebrates have been recovered and fossil material is scattered throughout the unit. Pollen and spores from the carbonaceous shale on Cone have been examined and are indicative of a swamp environment (W. B. Clapham, Jr., pers. comm., 1967). WEST: NEW FORK-BIG SANDY AREA 43 Invertebrates found in the Laney Shale Member include abun- dant gastropods and pelecypods as well as ostracodes. The gastro- pods are both terrestrial {Helix, sensu Shrimer and Shrock, 1944, p. 521) and shallow water {Vivipariis, Goyiiobasis, and Planorbina sensu McKenna et al., 1962. pp. 6 10). The systematics of these gastropods is debated by malacologists. Those who work with modern forms (Hyman, 1967, p. 623) have determined that there are no indigenous members of the family Helicidae in North America. Paleontologists such as La Rocque (1960, pp. 44-45) prefer to retain a very large and poorly defined species group for Helix. The pelecy- pods of the Laney Shale Member are less distinct, but appear to be unionids. Vertebrate fossils from the Laney include garpike (Lepisosteus) scales, fish spines, and miscellaneous vertebrae, crocodile teeth, frag- ments of turtle shell, lizard fragments, and a small amount of un- identifiable mammalian bone scrap. The aquatic fauna also occurs in the bounding fluvial units, as most of these animals were also able to live in streams and ponds on the alluvial plain lateral to the lake. Summary of Depositional History A. Figure 17. Marginal uplift and regional downwarping, both absolute and relative, around the Green River Basin. Deposition of Paleocene sediments, which may be related to the Hoback Forma- tion. Movement along the Wind River Thrust Fault to the east (Berg, 1962). Paleocene. B. Figure 18. Development of the overthrust area to the west. Continued movement along the Wind River Thrust. Chappo and LaBarge members of the Wasatch Formation deposited on the west, undifferentiated Main Body on the east (Berg, 1962; Oriel, 1962). Early and Middle Wasatchian. C. Figure 19. Movement on thrust faults virtually complete. First development of Green River Formation lacustrine deposits as the Fontenelle Tongue. Arkosic facies of New Fork Tongue fluvial material being deposited on the east. Late Wasatchian. D. Figure 20. Fluvial material of the western facies of the New Fork Tongue covers Fontenelle Tongue on the west. Continued deposition of arkosic facies on east. Late Wasatchian. K. Figure 21. Middle Tongue of Green River Formation shows a second lacustrine sequence in the New Fork-Big Sandy area. w E M \v^^ PC P \v^ ^-~-._______^ Tfu _^^^ M ). Fig. 17. Fig. 18. Fig. 19. 44 Fig. 20. Fig. 21. Fig. 22. 45 46 FIELDIANA: GEOLOGY, VOLUME 29 Fig. 23. Fig. 24. Cathedral Bluffs Tongue of the Wastach is lateral to the Middle Tongue of the Green River on the east. Early Bridgerian. F. Figure 22. The large lacustrine unit, the Laney Shale Mem- ber of the Green River Formation, covers much of the basin. This overlaps the small Upper Tongue of the Wasatch on the west (Oriel, 1969). Early Bridgerian. G. Figure. 23. Fluvial Bridger Formation fills the basin after the disappearance of Lake Gosiute. Bridgerian. H. Figure 24. Present topography, with faulting omitted, dis- plays two sets of units, eastern and western, with the Bridger For- mation eroded away completely. WEST: NEW FORK-BIG SANDY AREA 47 Key to Figures 17 through 2U PC — Precambrian undiflferentiated P — Paleozoic undifferentiated M — Mesozoic undifferentiated Tfu — Paleocene Fort Union Formation (or Hoback Formation) undifferentiated Tw — Main Body of the Wasatch Formation Two — Chappo Member of the Wasatch Formation Twl — LaBarge Member of the Wasatch Formation Twnfa — Arkosic Facies of the New Fork Tongue of the Wasatch Formation Twnfw — Western Facies of the New Fork Tongue of the Wasatch Formation Twcb — Cathedral Bluffs Tongue of the Wasatch Formation Twu — Upper Tongue of the Wasatch Formation Tgf — Fontenelle Tongue of the Green River Formation Tgm — Middle Tongue of the Green River Formation Tgl — Laney Shale Member of the Green River Formation Tib — Upper Laney Shale Member of the Green River Formation and Lower Bridger Formation, undivided STRUCTURAL GEOLOGY The Laramide Orogeny and related events formed the present structural Green River Basin. Precambrian to Cretaceous rocks were folded, faulted, and uplifted into the present basin-bounding elevations: the Wyoming Overthrust Ranges to the west, the Uinta Mountains to the south, the Rock Springs Uplift to the southeast, the Wind River Mountains to the northeast, and the Gros Ventre Range to the north. Post-Laramide movement within the New Fork-Big Sandy area occurred along a thrust fault zone and a com- plex normal fault system as shown on Figure 25. Wind River Thrust Fault Considerable evidence points to the existence of a major thrust fault zone along the southwestern front of the Wind River Moun- .^', Gros Ventre \\ Mountains Fig, 25. Structural map of the western and southern flanks of the Wind River Mountains, showing the major structural trends and their relationships to the New Fork-Big Sandy area. Adapted from Love et al., 1955, and Berg, 1961. 48 WEST: NEW FORK-BIG SANDY AREA 49 tains (fig. 25). North of the New Fork-Big Sandy area Richmond (1945) mapped two large thrusts; the largest, called the Wind River Thrust Fault, has a horizontal displacement of as much as 7 miles with a throw of 10,000 ft. at Flattop Mountain (center T. 36 N.. R. 109 W.). Seven miles east of the Wind River Thrust is the White Rock Thrust Fault, with a throw of 3,000 ft. Berg (1961, p. 74) utilized data from the core of Gulf 1 Unit (sec. 5, T. 36 N.. R. 110 W.) to locate the concealed New Fork Thrust Fault, estimated to have a throw of up to 25,000 ft. All three of these large thrusts decrease in magnitude to the northwest, swing westward, and merge with the structures of the Gros Ventre Mountains. Southeast of the New Fork-Big Sandy area the large thrust fault has been delineated by several wells (Berg, 1962, p. 75; Zeller and Stephens, 1969, p. 27). The fault zone trends more easterly and may extend as far east as the southern flank of the Granite Mountains before losing its identity. Berg (1961. 1962) recorded the Wind River Thrust Fault by a seismic survey and several cores taken near the Big Sandy River in T. 29 N., R. 105, 106 W. This indicated the presence of a large wedge of crystalline Precambrian material thrust out over Paleozoic, Mesozoic, and early Tertiary sediments, and in turn lapped over by Eocene sediments. The schematic cross-section (fig. 26) illustrates NE r 10,000 FT. Fig. 26. Structure section through the thrust wedge of the Wind River Thruat Fault in the southeast comer of the New Fork-Big Sandy area. Cosden 1 State is located in sec. 16, T. 29 N., R. 105 W. The presence of the small area of sedi- mentary rocks bounded on the northeast by a small fault is based on gravity data only. Vertical and horizontal scales are equal. Adapted from Berg, 1961, p. 73. 50 FIELDIANA: GEOLOGY, VOLUME 29 sw Fremont Butte Steele Eocene ^^"'^^ Butte /^ ^~~"*"--..,,„^^ y j\t^ Cm bd Ob • ■Cu / ^^^^ Eocene ^^ Eocene ? / / Precombrion Poleocene \ ^^ -^ NORMAL V FAULT \ --^-JH^ RIVER ^ After Love , 1950 NE Fig. 27. Structure section of the Paleozoic inlier at Steele Butte. Cu — Cam- brian undifferentiated; Ob — Ordovician, Bighorn Dolomite; Dd — Devonian, Darby Formation; Cm — Carboniferous (Mississippian), Madison Limestone. This section is approximately two miles in length. Adapted from Love, 1950. this structure. The Cosden 1 State drill hole (sec. 16, T. 29 N., R. 105 W.) passed through 3,100 ft. of "Wasatch" above the crystalline Precambrian rocks. Seismic evidence indicated to Berg that a sheet of sediment 1,000 to 2,500 ft. thick lies below the granitic thrust wedge. This sheet is probably composed of Paleozoic and Mesozoic rocks overridden by the thrust wedge, dragged along with it and overturned. At the toe of the thrust wedge the dip is about 50° NE; this decreases to about 10° NE near the middle of the wedge and then steepens sharply into the root zone. At this locality the thrust fault has a vertical displacement of 30,000 ft. and a horizontal displace- ment of 48,000 ft., although the vertical displacement may have originally been greater, prior to erosion on the surface of the thrust wedge. The Wind River Thrust was active through a considerable period of time. Cores show that in late Paleocene time coarse detritus from Paleozoic and Mesozoic units poured westward into the basin where they interfingered with basinal fluvial mudstones and sandstones of the Hoback Formation (Berg, 1961, p. 78). Higher, the debris reflects a more granitic source, as the sedimentary rocks were eroded away to the granite of the thrust sheet. Quartz and feldspar are more abundant in the upper Paleocene sediments. The thrust con- tinued its movement throughout the Paleocene and possibly into the early Eocene time. By middle Wasatchian time, however, its WEST: NEW FORK-BIG SANDY AREA 51 movement had ceased and crystalline-derived detritus covered over the fault trace. The presence of only depositional and compactional basinward dips indicate that significant relative uplift of the Wind River Mountains had also ceased. This does not mean, however, that there was no more regional uplift; there is a considerable body of evidence that all of western Wyoming has risen several thousand feet since middle Eocene time. The peculiar exposures of Paleozoic rocks in the Steele Butte vicinity are related to movement along the Wind River Thrust Fault. Love (1950, p. 27) believed that a normal fault moved later than the major thrust fault, bringing Devonian rocks down to the level of the early Paleozoic units, which are resting on the distorted tip of the thrust wedge (fig. 27). He suggested that this activity may be re- lated to some post-01 igocene movement described by Nace (1939) near Oregon Butte along the Continental Fault. The lack of dis- turbance of the Eocene between Steele Butte and the small Devonian outcrops leads me to believe that if some faulting occurred there, it took place soon after the major Wind River Thrust Fault. Continental Fault The Continental Fault was initially traced by Nace (1939) in the Oregon Butte-Continental Peak Region. McGrew et al. (1959) traced the fault as far as the Big Sandy River to the west, and the 1955 Geologic Map of Wyoming showed it eastward to the vicinity of Pickett Lake. I have traced the Continental Fault and its sub- sidiary limbs for an additional 7 miles to the northwest of the Big Sandy River. Waterhole Draw follows the course of the main limb of the Continental Fault for about 3 miles northwest of the Big Sandy River; the fault then swings more northerly. The herein named Big Sandy Limb of the Continental Fault (figs. 25, 28) may be traced readily in stream cuts for about 4^2 miles from sec. 24, T. 30 N., R. 106 W. to sec. 8, T. 29 N., R. 105 W. A few useful outcrops south of Table and Cone allow this limb to be followed into sec. 16, T. 29 N., R. 105 W. Southeast of this point the country is featureless for several miles; a fault with the same relative movement was mapped by Berman (1950) as far as sec. 2, T. 28 N., R. 105 W., about five miles southeast of the nearest exposure of the Big Sandy Limb. Northwest of the river-cut exposures the Big Sandy Limb disappears into the sagebrush. Some trends can be detected on aerial photos; these may reflect the course of the fault although nothing is visible on the ground. 52 FIELDIANA: GEOLOGY, VOLUME 29 Fig. 28. Fine shaley sandstones and shales of the Laney Shale Member of the Green River Formation at the Big Sandy Limb of the Continental Fault in SW J^ sec. 24, T. 30 N., R. 106 W. Sediments of the Bridger Formation are on the right (downthrown) side of the fault. Northwest of the Big Sandy Limb and the main extension of the Continental Fault is another subsidiary fracture here named the Square Top Limb of the Continental Fault after the prominent eleva- tion Square Top. It is best exposed in N 14 NE \i sec. 13, T. 30 N., R. 107 W., on the north side of a small hill, while the only other exposure is in a dry tank in SW M NE i^ sec. 18, T. 30 N., R. 106 W. At its western end the Square Top Limb breaks into at least two NNW-trending branches. Lower Bridger Formation sediment ex- posed between these is contorted, with SE dips of 15° quite common. Northeast of the Square Top Limb the lower Bridger Formation dips up to 8° SW. These three limbs of the Continental Fault trend toward each other in a flat area in NW M SW M T. 30 N., R. 106 W. Presumably, they meet as shown on the geological map and isolate the area of the lower Bridger Formation exposures. There has been considerable movement along the eastern portion of the Continental Fault. Nace (1939, pp. 45-46) gave a minimum WEST: NEW FORK-BIG SANDY AREA 53 of 1,450 ft. and a maximum of 1,830 ft. for the throw at Oregon Buttes. In the Tabernacle Butte area (McGrew et al., 1959, p. 129) the throw is 250 to 300 ft. No measurements could be made within the New Fork-Big Sandy area because of poor exposures and lack of correlative horizons on either side of the fault. Estimates based on the approximate thicknesses of the units cut by the fault give a throw of about 250 ft. along the Big Sandy River and a similar amount where maximum displacement occurs along the Square Top Limb. The amount of displacement decreases northwestward. The fault plane of the Big Sandy Limb generally dips 50° to 60" to the southwest. The main limb of the Continental Fault in a cut near Waterhole Draw dips 65° to 75° to the north, with the north side downdropped (McGrew et al., 1959, p. 129). The Square Top Limb has the same sense of movement as the main portion of the fault, but measurements of the dip of the fault plane could not be taken. The overall effect of the Continental Fault system was to drop middle Eocene Bridger Formation sediments down to the level of the early Eocene Wasatch and Green River Formations and thus allow them to escape erosion and remain as an indicator of the former ex- tent of Bridger deposition. The lower Bridger Formation material mapped along the Square Top Limb of the Continental Fault is the farthest north yet reported. Thirteen fossil mammal localities are in the downdropped lower Bridger Formation, so the structural situa- tion is paleontologically fortunate. Since the faulting within the New Fork-Big Sandy area cuts the Bridger Formation, at least some movement occurred in post- Bridgerian time. Zeller and Stephens (1969, pi, 1) showed the Con- tinental Fault cutting beds of the Miocene South Pass Formation in sec. 3, T. 27 N., R. 102 W., so the final movement cannot be any older than Miocene and may be as recent as mid-Pliocene (Love, 1954, p. 1,311). McGrew (pers. comm., Aug. 12, 1967) has seen Eocene fault scarps in the Elk Mountain vicinity which indicate that the Continental Fault system was active then as well. Berg (1961, p. 73) interpreted the Continental Fault system as a "late normal collapse along the toe of the (major) thrust wedge." He regarded the correlation between the subsurface position of the thrust wedge and the surface expression of the Continental Fault as good evidence for this interpretation. Zeller and Stephens (1969, pi. 1) showed the Continental Fault on the mountainward side of the Wind River Thrust Fault, resulting from a normal fault within the 54 FIELDIANA: GEOLOGY, VOLUME 29 thrust wedge. There is general agreement that the Continental Fault is genetically related to the Wind River Thrust Fault, but the pre- cise relationship is as yet unclear. Additional evidence pertaining to the location of the thrust might also be provided by the normal fault just west of Steele Butte proposed by Love in 1950. PiNEDALE Anticline The Pinedale Anticline extends 45 miles parallel to the Wind River Mountains from T. 35, N., R. 110 W., to T. 29 N., R. 106 W. (fig. 25). It is approximately symmetrical, 6 miles wide, with a closure of more than 1,500 ft. (Jenkins, 1955b, p. 155). It is poorly indicated along the south bank of the New Fork River in T. 31 N., R. 109 W., where the Fontenelle Tongue of the Green River Forma- tion reverses its dip along the west flank of the anticline. As this is the location of the facies change into sediments of the arkosic facies of the New Fork Tongue, a similar change in attitude cannot be seen on the east flank where bedded lacustrine sediments are not present. Both facies of the New Fork Tongue appear unaffected by the anti- cline, which thus is not a mappable surface structure. The Fon- tenelle Tongue is the highest unit to be visibly affected by the anticline; if the New Fork Tongue was at all distorted by the Pine- dale Anticline it cannot be detected in available outcrops. Drilling and seismic work have revealed the structure of the Pinedale Anticline to a much greater extent than is visible on the surface (Berg, 1961, p. 71). Thousands of feet of relatively young sediment are involved in the anticline which does not appear to be present in the Precambrian basement. OCCURRENCE OF FOSSIL MATERIAL Collecting The initial collection at every locality was a surface collection. Promising areas in all units were searched by systematic walking. If the resultant collection was large enough and the area seemed rich enough, washing was attempted. The Cathedral Bluffs Tongue fauna was collected primarily by washing, and four Bridger Forma- tion localities were extensively washed. No localities suitable for quanying operations were encountered. Preservation Fossils from all levels are usually well-preserved although frag- mentary. This durability of the fossil material is the main reason for the success of the washing technique. Were the fossils fragile it would be next to impossible to recover any identifiable material from the washed concentrate. Most material is fragmentary; few jaws have as many as three teeth, and only three reasonably complete skulls were found during all the collecting. Some of the smaller broken specimens were undoubtedly frac- tured during the washing procedure. Much fragmentation, however, occurred prior to and during deposition and burial and many speci- mens undoubtedly fragmented during recent erosional processes. Abraded fractures are sometimes visible, but the amount of friction during washing is certainly inadequate to significantly abrade a freshly broken surface. Deterioration of the bone by pre-burial dessication is a result of post-mortem exposure to the elements prior to being covered by sediment. During this interval it is also possible that scavengers may have disarticulated the carcass, scattering the elements so that only one or a few were in a position to be preserved and later col- lected. Severe deterioration of the carcass left only the most re- sistant elements, the teeth, available for preservation. 65 56 fieldiana: geology, volume 29 Fossil Production The western facies of New Fork Tongue of the Wasatch Forma- tion produces fossils from the green-to-gray mudstone zones adjacent to the yellow channel sandstones at seven localities along the south- eastern face of the Mesa. Two other localities are in fine blue-green sandy zones along the Blue Rim. These, and the localities mentioned below, are indicated on the geological map. Fossils are not as concentrated in the arkosic facies. The two localities in the arkosic facies are large in areal extent. The finer sandy mudstones, not necessarily adjacent to channel sandstones, are the most productive zones. Aside from the two localities in the northern part of the New Fork-Big Sandy area, the arkosic facies is virtually barren. The Cathedral Bluffs Tongue of the Wasatch Formation is poorly fossiliferous. Bone has been found in only two places within the New Fork-Big Sandy area. A fragmentary stylinodontine tooth and nearly a dozen edentulous mammal jaws were found near the Big Sandy River, while the remainder of the Cathedral Bluffs Tongue in that area has yielded only well-worn unidentifiable scraps of bone. A small surface collection led to the development of a washing locality, which has yielded 65 specimens, near the Square Top Limb of the Continental Fault. Both of these Cathedral Bluffs Tongue localities are in greenish intraformational mudstone conglomerate. Remains of aquatic animals are well distributed through the Laney Shale Member exposures. Unidentifiable fragments of teleost fish and turtles are common, along with the omnipresent Lepisosteus scales. The darker, more carbonaceous, shales of the Laney Shale Member contain more fossil material than do the light brown sandy shales. The lower Bridger Formation is the most productive unit in the New Fork-Big Sandy area. The 13 localities in the lower Bridger Formation are sharply delineated, as they are small areas with rela- tively abundant fossil material, while the same levels a few yards away produce nothing, with little or no physical difference in the sediments across such a transition. VERTEBRATE FAUNAL LIST Class Osteichthyes Order Semionotoidea Family Lepisosteidae Lepisoaleua sp. Undetermined teleosts Class Reptilia Order Chelonia Family Testudinidae Undetermined genera and species Family Trionychidae Trionyx sp. Order Squamata (as determined by W. P. MacLean III) Suborder Lacertilia F^'amily Iguanidae Undescribed genus and species Family Agamidae Tinosaurtis sp. Family Teiidae Undetermined genus and species Family Amphisbaenidae Lestophis sp. Family Anguidae Glyptosaurus (three species) Xestopa sp. Dimetopisaurus sp. Satiina sp. Undetermined genus and species Suborder Ophidia Family Boidae Ogmophis n. sp. Duti noph is microechinus Calamagras prinius Boavus sp. 57 58 FIELDIANA: GEOLOGY, VOLUME 29 "iParaepicrates brevispondylus Coniophis carinatus Order Crocodilia Undetermined Gavialidae Class Aves Undetermined genus and species Class Mammalia — See Systematics and Table 1. FOSSIL MAMMAL AND REPTILE LOCALITIES IN THE NEW FORK-BIG SANDY AREA Fossil mammals have been recovered from 26 localities in four stratigi'aphic units. There are two localities in the arkosic facies of the New Fork Tongue of the Wasatch Formation, nine in the western facies of the New Fork Tongue of the Wasatch Formation, two in the Cathedral Bluffs Tongue of the Wasatch Formation, and 13 in the lower part of the Bridger Formation. Reptiles have been found at two additional localities. These localities are described below. The reptilian fauna has been provisionally studied by W. P. MacLean. The lizards and snakes occur in the same localities with the mammals, and apparently lived in the same environments as the various mammals. The various localities have the following relative positions: Young (Later) Laney Shale Member Bridger Formation B-2, B-7, B-11, B-8 B-3, B-5, B-10 B-1, B-4, B-6, B-9, B-12, B-13 Cathedral Bluffs Tongue L-1 CB-l, CB-2 Western Facies of the New Fork Tongue NF-1, NF-2 NF-3, NF-4, NF-6, NF-7. NF-8, NF-9 Arkosic Facies of the New Fork Tongue BS-1, BS-2 Old (Earlier) BS-3 Localities Bridger Formation B-L Fault (Big Sandy of the University of Wyoming). SE \i NE )4 sec. 25. T. 30 N.. R. 106 W.. and NW i^ SW »^ sec. 30, T. 30 N., R. 105 W. Middle of high bluffs on east side of Big Sandy 59 60 FIELDIANA: GEOLOGY, VOLUME 29 River. One 10 ft. layer of sandy mudstone, brownish and gray-green, about 15 ft. below a prominent chippy, buff-white siltstone which carries plant impressions. One-third mile long on east side of the river; small amount of fossil material at corresponding level on the west side. Approximately 7,700 lbs. of matrix washed. Fauna: 470 specimens of 37 mammalian species. B-2. White Hills. NW Y^ sec. 2, T. 29 N., R. 106 W. Five foot layer of tuffaceous sandy mudstone, buff to white, in a series of terraces to the south of the access road. Small amount of fossil material on north side of access road. Fauna: 41 specimens representing 14 mammalian species. B-3. Hawk. SW M NE 3^sec. 18, 29 N., R. 105 W. Large draw on northwest bank of Big Sandy River. Fossils found on flat just above a big rivercut, and at about the same level across the first draw upstream. Also a small area with mammalian material near the head of the main draw. Some CaCOs veins present here. Access to this area by abandoned seismograph trail. Approximately 1,900 lbs. of sediment washed. Fauna: 91 specimens representing 20 mam- malian species. B-4. Tree Road. N 3^ SE i^ sec. 31, T. 30 N., R. 105 W. Just west of Big Sandy Limb of Continental Fault on west side of Big Sandy River. Buff-brown sandy mudstone about 50 ft. below a heavy channel arkose on south-facing surface. Some material on south side of first ridge to the south. Road at base of locality. Approximately 4,250 lbs. of sediment washed. Fauna: 84 specimens representing 16 mammalian species. B-5. Wash. NE >i sec. 19, T. 29 N., R. 105 W. Actually south of area. Flat breaks on northeast side of long draw, first to the south of an intermittently-flowing stream. Fossils found primarily on one interstream divide — very little on other divides at same level. Sandy mudstone with some shaley and blocky sandy mudstone. Approxi- mately 2,550 lbs. of sediment washed. Fauna: 44 specimens repre- senting 10 mammalian species. B-6. Fish Hill. SW M sec. 5, T. 29 N., R. 105 W. East-facing broken area just to west of Big Sandy Limb of Continental Fault. Light-colored sandy mudstone with CaCOs crystals weathering out. Some material on small knobs and hillside; remainder is slightly lower on washed-over areas. Fauna: 7 specimens representing 4 mammalian species. WEST: NEW FORK-BIG SANDY AREA 61 B-7. Little White Butte. SE M SE H sec. 1, NE K NE H sec. 12, T. 29 N., R. 106 W. Light colored sandy mudstone and tuflfaceous light sandstone on prominent knob just east of road on west side of Big Sandy River. Fossils around knob itself, and in brown sandy area slightly to southeast which is about 25 ft. lower. Approximately 350 lbs. of sediment washed. Fauna: 8 specimens representing 5 mammalian species. B-8. 1375 #8. SW ^ NE % sec. 32, T. 30 N., R. 106 W. Low breaks facing north on north side of small elevation. Fossils in very blocky, rubbly, gray mudstone. Fauna: 12 specimens representing 7 mammalian species. B-9. Jean's Quarry. NE i^ SW K sec. 8, T. 29 N., R. 105 W. Breaks in steep draw overlooking Big Sandy River. Just west of Big Sandy Limb of Continental Fault. Fauna: 4 specimens repre- senting 3 mammalian species. B-10. S i-i sec. 20, T. 29 N., R. 105 W. Just east of Wash Locality, and also out of the New Fork-Big Sandy area. BufT sandy mudstone in north-south draw to south of major drainage. Fauna: 3 specimens representing 2 mammalian species. B-11. SW M sec. 36, T. 30 N., R. 106 W. Low exposures of sandy mudstone below arkose several hundred yards north of road to Fish Hill. North of fence line. Fauna: 2 specimens representing 2 mammalian species. B-12. West of Cone. NE ^sec. 17, T. 29N., R. 105 W. Breaks facing west overlooking large meander of Big Sandy River. West of Big Limb of Continental Fault. Access road on top of bank over- looking this locality. Fauna: 1 specimen of mammal. B-13. Sandstone Point. N ^ NE ^ sec. 25, T. 30 N., R. 106 W. Prominent tongue of sandstone directed ESE, just to west of Big Sandy Limb of Continental Fault. Fossils from flats near top of exposure. Access road about one-quarter mile to the west. Approxi- mately 200 lbs. of sediment washed. Fauna: 5 specimens represent- ing 5 mammalian species. Laney Shale Member of Green River Formation L-1. Scale Canyon. NW H sec. 30, T. 30 N., R. 105 W. Long draw directed WSW. Fossils, especially fish fragments, found in dark fissile shales and interbedded marly sandstones of the Laney Shale. Fauna: lower vertebrates only. 62 FIELDIANA: GEOLOGY, VOLUME 29 Cathedral Bluffs Tongue of Wasatch Formation CB-1. Green. SW \i sec. 17, T. 30 N., R. 106 W. Located on a north facing slope, just south of Square Top Limb of Continental Fault. Above a blue-white tuffaceous zone. East of access road which crosses low, wide Cathedral Bluffs exposure. Fossils come from a gray-green intraformational sandy mudstone conglomerate. Approximately 6,200 lbs. of sediment washed. Fauna: 65 specimens representing 15 mammalian species. CB-2. Fence X Road. SE i^ sec. 30, T. 30 N., R. 105 W. On south side of a long draw directed east on the east side of the Big Sandy River. One poorly productive zone about halfway up the slope, in an intraformational sandy mudstone conglomerate near some arkosic zones. Marginal Laney a few hundred yards to the northwest. Fauna: 1 specimen representing a mammalian species. Arkosic Facies of New Fork Tongue of Wasatch Formation BS-1. Steele Butte Breaks. Sec. 30, and N Yi sec. 31, T. 32 N., R. 107 W., and S Yi sec. 25, and N 3^ sec. 36, T. 32 N., R. 108 W. Large sequence of colored breaks overlooking East Fork River about XYi miles southeast of Steele Butte. Fossils produced throughout the locality, but concentrated in the middle in generally darker, finer-grained sediments. Fossils found through 200 ft. of vertical section. Fauna: 115 specimens representing 22 mammalian species. BS-2. East Fork Rim. Sec. 1, N Yi sec. 12, N Yi sec. 11, S Yi sec. 10, NE M sec. 15, and sec. 2, T. 31 N., R. 108 W. and S H sec. 36, sec. 35, and SE i^ sec. 34, T. 32 N., R. 108 W. Large area of colored breaks overlooking East Fork River to the west and south of Steele Butte Breaks. Generally high on the rim, but abundant material found in long, low draw which opens in sec. 34, T. 32 N., R. 108 W. Material found throughout locality. U.S. Highway 187 cuts across western side. Fossils found through 200 ft. of vertical section. Fauna: 124 specimens representing 23 mammalian species. BS-3. NW Yx sec. 14, T. 31 N., R. 109 W. Small broken area facing northwest over the New Fork River, just to the east of the facies change from the Fontenelle into the arkosic facies. Access road on west side. Fauna: lower vertebrates only. Western Facies of New Fork Tongue of Wasatch Formation NF-1. Blue Rim. NW Yx NW Y sec. 16, SW Ya sec. 9, and SE Yx sec. 8, T. 30 N., R. 108 W. At base of Blue Rim where WEST: NEW FORK-BIG SANDY AREA 63 crossed by oil company road. Just below tongue of arkosic facies which can be easily identified by color and texture. Fossils produced from muddy blue-gi'een poorly consolidated sandstone. Fauna: 43 specimens representing 13 mammalian species. NF-2. Piney Cutoff. SW > , sec. 34, SE > , sec. 33. T. 31 N., R. 108 W., and NE > , NE >., sec. 4, T. 30 N., R. 108 W. At base of Blue Rim where it is crossed by Wyoming State Secondary 1801 in well-dissected area to north of highway. Fossils found in muddy blue-gi'een poorly consolidated sandstone. Fauna: 14 specimens representing 9 mammalian species. NF-3. Blue Saddle. NW ' , SW '., sec. 31, T. 32 N., R. 109 W. Saddle on side of hill north of access road. Fossil production from bluish sandy mudstone. Approximately 800 lbs. of sediment washed. Fauna: 6 specimens representing 4 mammalian species. NF-4. Unnamed. NW i, sec. 5, T. 31 N., R. 109 W. On hill- side on northeast side of deep draw to southeast of Blue Saddle. Very steep slope, best approached from top. Best level in a coarse blue to gi'ay sandy mudstone. Approximately 500 lbs. of sediment washed. Fauna: 17 specimens representing 6 mammalian species. NF-5. Two Buttes. SE >4 sec. 13, NW 'i sec. 13, N "2 sec. 14, NE ' , sec. 15, and sec. 11, T. 32 N., R. 109 W. Long valley with hill called Two Buttes in the middle. Fossil production sporadic from marginal exposures. Fossils come from yellow sandstones and adjacent gi*ay-gi'een mudstones. Fauna: 37 specimens representing 13 mammalian species. NF-6. Twnf-H. SE 1., sec. 21, T. 32 N., R. 109 W. Breaks on nose on southwest-facing slope in greenish mudstone near yellow sandstone. Fauna: 2 specimens representing 2 mammalian species. NF-7. Twnf-E. SW •., sec. 18, T. 31 N., R. 109 W. Low east- facing breaks. Fossils from gi'ay-green sandy mudstones near small calcareous pond deposit. Fauna: 1 specimen of mammal. NF-8. Twnf-C. SE '., sec. 28, T. 32 N., R. 109 W. Breaks low on a very high face. Fossils found in gi'ay-green mudstone sur- rounding several yellow sandstones. Road crosses east end of local- ity. Fauna: 6 specimens representing 3 mammalian species. NF-9. Twnf-D. SW K SW • , sec. 36, T. 31 N., R. 110 W., and NW > , NW • , sec. 1, T. 30 N., R. 110 W. Fossils found in a poorly indurated yellow-orange sandy zone halfway dow^n the slope of a veiy high southwestern-facing exposure. Fauna: 3 specimens representing 2 mammalian species. 64 FIELDIANA: GEOLOGY, VOLUME 29 The remains of lower vertebrates are present at all of these localities, as well as many other places in the New Fork-Big Sandy area. No record was kept of the occurrence of turtles because of their abundance and generally fragmentary nature. Mammalian Faunal Composition 1,208 identifiable specimens representing at least 75 species of 51 genera of mammals have been recovered from the 26 localities in the New Fork-Big Sandy area. The Bridger Formation localities account for 772 specimens of 45 species of 33 genera, the Cathedral Bluffs Tongue localities for 66 specimens of 16 species and 12 genera, and 370 specimens of 33 species and 26 genera have been recovered from the upper Wasatch Formation localities in the New Fork Tongue and Big Sandy facies. Both the calculated minimum number of individuals and number of specimens assignable to each taxon at each locality is indicated in Table 1 and summarized in Table 2. These minimum numbers were determined by the age-spread minimum as discussed briefly by Van Valen and Sloan (1965, p. 745) and at greater length by Schram and TurnbuU (1970) . This involves consideration of the wear shown by each tooth as well as its position in the dentition. The collections made within the New Fork-Big Sandy area, at all the productive horizons, are from mechanical assemblages created during the deposition of the Eocene sediments. The moving water gathered together organic debris from many places and deposited it when carrying capacities dropped. It is essential that the artificiality of the assemblage be recognized. Any determination of the popula- tion composition of the life assemblages from which the recovered individuals were drawn must take this into consideration, as well as the possible biases discussed in detail by Clark (1967, pp. 114-120). flQ I •a o I z Jl 81 If si 9| a-JUAVj, 6-JN D-JUAVL 8-JN a-JUMX L-AK H-JUAVL 9^^N saima OMi s-JN pauisuun trJN aippBsania c-JN jjojno Xauij j-qN uiJH ania I-JN luiH MJoj i««3 c-sa s^vatq a J ma simJS I-sa pBOH X 93uaj t-ao uaajQ I -83 )U!0({ auo)spuBS €I-a auo3jo isaM J I -a 9€ MStr/i MS Il-a or aas t/l SOI-€ XJJBnQ s,uB3f 6-a 8 ON SZ.CI 8-a aima 9i!MM amn z,-a iHH ^«I 9-a «i««MS-a p«o>i aaji fr-a 5|MBH E-a «n!H »>! 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C 70 E a e 3 I O E 9 Z c4 ea I O 1*3 E 3 Ob a-JUMl 6-JN D-JUMj, 8-JN 3JUMJ. i-JN H-JUMl 9-JN sauna OMJ, s-JN paunuun trjN aippBs anig c-jn jjojno Xauid j-jn wiM ania I-JN m'H 1JOJ is«3 t-sa -I* s^BSJa aima aiaaiS I-Sfl !2h" pvo)| X aauaj ^-go uaajo l-aD |U|oa auoispues ci-a auoD JO jsaM Z I -a 9€ MSfr/i MS Il-a or aas j/i soi-fl XJJBnf) s.ueaf 6-a 8 ON SLZl 8-a aijna a)iqAva|un t-fl inH qsij 9-a qsBM S-€ pBo>i aaji fr-a 3(MBH €-a linej I -a fir* rl«s tl«s tl- ;?|2 -I- 2K f^ I- - 1- — I— f>K«i *lr» Ml- mIw E3 8| -I SI .1 1^ -I !§• o u a: ^ o ■S a: 71 B s c -a o 6 1 CT3 .S ■i-> "^ •2-1 o '^ ac Ea S.i a-JUMi 6-JN D-JUAVL 8-JN H-JUMi 9-jN sajjne OMj, S-JN pauiBuun f-JN aippBS anie ejN jjojna Xauij j-jN uiiy ania I-JN ui'H MJOJ JSBg j-sa s5iE3ja 3»ng apajs I-Sfl pEoy X 33uaj t-eo uaajo i-aO juioj auojspuBs ei-a auo3jo ;saM ci-a 9e -oasf/l MS u-a or 'oas j/i s oi-a XajBnf) s,uEaf 6-a 8 "ON SL£l 8-a a»na aJIMM ai«n L-Q IHH MSiJ 9-a iJSBM s-a pBo>i aaJi f-a 5IMBH £-a SH!H.3MMMt-a nnBj T-a tifo m|fO nl s: ^ I I I •■c ■■c o s "3 CO =^ 72 o I c 8 ^'1 83 81 D-JUMj. 8-JN a-JUMi t-JN H-JU-*^! 9- AH saung oaaj, S^^N paiueuun ^-AH aippeS ania e-JN jjojno Xauij CvIN uiiM ania \AH lUfM 1JOJ JS'53 C-Sa s^eajfi aijng aiaajs ISA p«o>i X aauaj cao uaajo I-aO juioj auoispucs CI -a auoojojsaM tig 9e MSf/i MS 11 -a oz MS z/\ soi-a XiJBnft s.ueaf 6-g 8 •o^4 SZ.CI 8-a a>»ng aiiqM 3|Jl!l t-a IHH M«!J 9-a qsBM S-a peo>| aaJi f-g jjMBH €-a sil'H aJIMM J-a l|n«dl I a 1 2K i Si 5 § •a -I- I "S. 4: !> S r«lr< •ol* 5^ rtlo ool>o ?|2 o — 78 TABLE 2. Summary of faunal composition at the four stratigraphic levels of fossil production within the New Fork-Big Sandy area. Numerator-Number of specimens; Denominator-Minimum number of individuals Bridger Fm. Wasatch Fm. Cathedral Arkosic Bluffs Fades Western Fades Peratherium sp. 1 1 P. innominatum 6 5 P. ci.P. marsupium 10 6 Palaeictops cf . P. pineyensis T Apatemys bellulus 1 1 .. Centetodon cf. C. pulcher 3 2 Myolestes cf. M. dasypelix 2 1 Scenopagus edenensis 28 8 S. prisons 1 1 Creotarsinae incerta6 sedis 4 1 Nyctitherium sp. 5 3 Didelphodus altidens 1 1 Oxyaena forcipata •• T 0. sp. •• 2 Oxyaenid T IPrototomus sp. •• T IProviverra sp. 1 1 Tritemnodon sp. •• f Thinocyon cf. T. velox 4 1 Didymictis altidens •• 2 2 2 2 Viverravus gracilis 3 2 .. V. sp. 1 1 • Miacis latidens 2 2 1 1 74 TABLE 2. Summary of faunal composition at the four stratigraphic levels of fossil production within the New Fork-Big Sandy area. Numerator- Number of specimens; Denominator-Minimum number of individuals-conn>iu0(/ Wasatch Fm. Bridger Cathedral Arkosic Western Fm. Bluffs Facies Facies Vulpavus sp. •• •• 1 1 •• Notharctus cf. N. nunienus •• •• 4 5 S J N. tenebrosus 12 7 •• • • •• Smilodectes gracilis 24 11 •• Omomys carteri 37 7 •• •• 0. cf. 0. carteri 2 T •• •• •• 0. cf. 0. sheai •• •• •• 1 T Washakius insignis 18 T •• •• •• W. near W. insignis " 1 1 •• Anaptomorphus aemulus 6 5 1 1 Microsyops scottianus •• •• 5 2 5 4- M. elegans 102 25 •• M. sp. 8 3 •• •• Sciuravus nitidus 246 54 5 •• S. sp. 1 1 •• •• Sciuravid •• •• 2 2 Tillomys cf. T. parvidens 1 1 Taxymys lucaris 5 •• Knightomys cf. K. senior T •• K. sp. •• 3 I Paramys dehcatus 13 T •• P. excavatus " 1 1 P. near P. excavatus 1 T 8 2 76 TABLE 2. Summary of faunal composition at the four stratigraphic levels of fossil production within the New Fork-Big Sandy area. Numerator-Number of specimens; Denominator-Minimum number of individuals-conrmued Bridger Fm. Cathedral Bluffs Wasatch Fm. Arkosic Facies Western Facies P. group 60 5 3 3 Y P. wyomingensis 12 2 1 Reithroparamys huerfanensis 3 3 1 1 R. delicatissimus 3 1 1 1 R. near R. delicatissimus •• 1 T Pseudotomus robustus 1 1 •• Microparamys minutus 7 2 M. sp. A. 3 2 •• M. sp. B. 3 1 •• Esthonyx acutidens 2 1 StyUnodontine 1 T 4 2 2 2 Bathyopsis fissidens •• 2 1 Coryphodon sp. •• 27 8 Hyopsodus miticulus •• 6 3 9 5 H. wortmani 3 2 1 1 H. minusculus 94 30 17 4 H. paulus 2 I •• Meniscotherium chamense 21 7 30 14 M. robustum •• 2 2 6 5 Phenacodus vortmani •• •• 2 2 3 2 P. pritnaevus •• •• 1 1 P. sp. •• •• •• 1 1 Hyracotherium vasacciense 64 9 35 13 79 TABLE 2. Summary of fauna! composition at the four stratigraohic levels of fossil production within the New Fork-Big Sandy area. Numerator- Number of specimens; Denominator-Minimum number of individuals-co/tr/ni/ec/ H. craspedotum Orohippus cf. O. pumilus Lambdotherium popoagicum Eotitanops horealis Pataeosyops fort tina lis Heptodon posticus H. calcicuhis Hyrachyus modestus Tapiroid Diacodexis cf. D. secans Antiacodon pygmaeus Microsus sp. Helohyus cf. H. plicodon Axtiodactyl incertae sedis TOTALS Wasatch Fm. Bridger Im. Cathedral Bluffs Arkosic Facies Western Facies •• •• 13 9 2 2 13 X 2 T •• •• 57 13 IS •• •• T 2 T 4 2 •• •• 5 I 1 1 3 3 2 1 1 1 1 T •• •• I 1 •• 2 2 3 3 21 T 1 1 •• •• I .. 2 2 1 1 •• •• 772 iS9 66 To 241 88 129 77 77 SYSTEMATICS The following is a discussion of the fossil mammals found in the New Fork-Big Sandy area. The locality data indicates the levels at which the particular specimens were found. This discussion is not intended as a review and revision of the late Wasatchian and early Bridgerian faunas of the northern Green River Basin. Rather it is a presentation of fossil mammals recov- ered over a brief span of time from a restricted area. The intention is to delineate the faunas from the various levels which are used as evidence in the stratigraphic synthesis. Measurements are presented for all specimens which are suffi- ciently complete. Coefficient of variation and standard deviation and their errors are computed when there are six or more specimens of a single tooth available. In cases of two to five specimens only the mean and observed range are recorded. Frequently it was impossible to distinguish between first and second molars; these are then tabulated in a separate column. Article 36 of the International Code of Zoological Nomenclature is followed in determining authorship of the suprageneric names. Asterisks (*) alongside numbers in the lists of materials indicate specimens that are illustrated. Abbreviations: Museums PM — Field Museum of Natural History, Chicago UW — University of Wyoming, Laramie AMNH — American Museum of Natural History, New York USNM— U. S. National Museum, Washington Standard abbreviations are used for tooth position and number Measurements Wtrig^ — width of lower molar across trigonid Wtal — width of lower molar across talonid 78 WEST: NEW FORK-BIG SANDY AREA 79 N- number of specimens OR — observed range M — mean V — coefficient of variation SD — standard deviation Order Marsupicarnivora Superfamily Didelphoidea Gray, 1821 Family Didelphidae Gray, 1821 Peratherium Aymard, 1850 Peratherium sp. Plate la. Ma/ma/.— Fault: 1 UW 1538.* Discussion. — One very large Peratherium M? was found at Fault locality. A specific reference to P. comstocki, a large Graybull didelphid, would be insecure because of possible differences in the upper molars. UW 1538, the largest Peratherium specimen in the study collection, is 3.7 mm. long, 2.1 mm. wide across the trigonid, and 2.3 mm. wide across the talonid. Peratherium innominatum Simpson, 1938. Plate lb, c, d. Ma/mo/.— Fault: 5 (Jaws: PM 15861, RP'-M^; PM 15862*, LM^-M^ PM 15320*, LMi-Mo or M.-Ms), PM 15322, 15343. Hawk: 1 (Jaw: PM 15866*, RM'-M-). Discussion. — Peratherium innominatum, known from throughout the Bridgerian, is the smallest Eocene didelphid. Aside from its small size, it is comparable in detail to other didelphids. TABLE 3. Measurements in millimeters of teeth of Peratherium innominatum. N OR M P» M* M* M* M« M, M.. L 1 IJZ W 1 0.7 L 2 1.6-1.7 1.65 W 2 1.4-1.6 1.5 L 1 1.7 W 2 1.5-1.7 1.6 L 1 1.4 W 1 1.7 L 1 1.1 W 1 1.3 L 1 1.7 Wtrig Wtal 1 1.0 1 1.1 L 4 1.4-1.7 1.55 Wtrig Wtel 4 0.8-1.0 .92 3 0.9-1.0 .93 80 FIELDIANA: GEOLOGY, VOLUME 29 Peratherium cf. P. marsupium (Troxell, 1923). Plate le. Material.— Fault: 8 (Jaws: PM 15864*, LM^-M^; PM 15865, RM-=-M^), PM 15010, 15321, 15323, 15853, 15863, 21181. Wash: 1 PM 15324. Hawk: 1 PM 21124. Discussion. — These ten specimens fall into a size range inter- mediate between P. marsupium and P. knighti. They are referred to Bridgerian P. marsupium for the following reasons: protoconule and metaconule of M- and M^ are not well developed; although the stylar cusps are low, all five are present and definitive, whereas only three are present in P. knighti; and the size is somewhat closer to P. marsupium as measured by McGrew et al. (1959, p. 148). ^eratherium cf . P. marsupium. SD V .12 ±.03 5.04 ±1.13 TABLE 4. Measurements , in millimeters of teeth N OR M M^ L W 3 3 2.0-2.5 2.1-2.7 2.3 2.47 M« L W 2 2 2.2-2.5 2.9 2.35 Mi-3 L W 6 3 2.2-2.5 2.0-3.0 2.38±.05 2.47 M,-3 L Wtrig Wtal 1 1 1 1.9 1.0 1.2 Order Insectivora Suborder Proteutheria Romer, 1966 Superfamily Tupaioidea Gray, 1825 Family Leptictidae Gill, 1872 Subfamily Leptictinae Gill, 1872 Palaeictops Matthew, 1899 Palaeictops cf. P. pineyenesis (Gazin, 1952). Plate If. Material.— East Fork Rim: 1 PM 15565.* Discussion. — This single Ps is similar to that of P. pineyensis from the LaBarge local fauna illustrated by Gazin (1962). The well-defined anterior capsule is characteristic, as are the overall size and elongate shape. P. tauri-cinerei (Jepsen, 1930, pp. 124-126, pi. Ill) also displays this morphology of P3, but this species is much smaller than P. pineyensis. The size of PM 15565, 3.7 mm. long and 1.5 mm. wide, fits well with Guthrie's (1967, p. 11) measure- ments of Lysite P. pineyensis. i PLATE I. Marsupials and insectivores. All specimens illustrated as stereo- pairs. The line beside the left member of each pair represents 1 mm. a. Pera- Iherium sp., UW 1538, RMi-,. b. Peratherium innominatum, PM 15320, LM,.,. c. Peratherium innominatum, PM 15862, LM'-M^ d. Peratherium innominatum, PM 15866, RM'-M». e. Peratherium marsupium, PM 15864, LM'-M*. f. Palaeic- tops cf. P. pineyensis, PM 15565, LP4. &. Apatemys bellulus, PM 15060, RM,. 81 82 FIELDIANA: GEOLOGY, VOLUME 29 Superfamily Apatemyoidea Matthew, 1909 Family Apatemyidae Matthew, 1909 Until recently, many authors placed the Apatemyidae in the primates (summarized by McKenna, 1963, pp. 2-11). Jepsen (1934, p. 305) agreed with Matthew's (1909, pp. 543-544) suggestion that they belong in the Insectivora. Van Valen (1967) placed the Apatemyidae in the Proteutheria (named by Romer in 1966 after the discussion by McKenna, 1960a), as is done here, and Szalay (1968, pp. 24-25) remarked on certain parallelisms between apatemyids and prosimian primates. I am at present preparing a review of the Eocene members of this family. Apatemys Marsh, 1872 Apatemys bellulus Marsh, 1872. Plate Ig. Material— Fault: 1 PM 15060.* Discussion. — Apatemys is represented by this single jaw fragment referable to A. hellulus. Mi is approximately the same size (L — 1.8 mm., Wtrig — 0.9 mm., Wtal — 1.2 mm.) as the A. bellulus material tabulated by Robinson (1966, p. 37), although PM 15060 is slightly narrower. Breakage gives the trigonid a falsely triangular shape. The protoconid and metaconid are approximately equal in size. An elevated hypoconid is visible on the posteroexternal corner of the talonid marginal crest; the area of the entoconid is missing. P4 is partially preserved, and is reduced and single rooted, as in referred specimens of A. bellulus (Matthew, 1909, pp. 544-545). Suborder Erinaceota Van Valen, 1967 Superfamily Erinaceoidea Fischer von Waldheim, 1817 Family Adapisoricidae Schlosser, 1887 Van Valen (1967, p. 272) regarded this basal group of the Erina- ceota as significantly different from the Erinaceidae, thus warranting a familial separation. Subfamily Geolabidinae McKenna, 1960b Centetodon Marsh, 1872 Centetodon cf. C. pulcher Marsh, 1872. Plate Ila. Material— Tree Road: 3 PM 15834-5, 15836.* WEST: NEW FORK-BIG SANDY AREA 83 Discussiov .- The overall form of the teeth, all lower fourth premolars, especially the single large cusp on the talonid, compares favorably with McKenna's (1960b, pp. 148 149) description of Hypacodoti praecursor, synonymized with Centetodon pulcher by McKenna et al. (1962, p. 22). The type specimen is from an un- known level in the Bridger Formation. Several variations, primarily that these teeth are more antero-posteriorly shortened and the paraconid is higher than indicated in McKenna's illustrations, necessitate a tentative specific identification. TABLE 5. MeasurementvS in millimeters of P4 of Centetodon cf. C. pulcher. N OR M L P4 L 3 2.0-2.2 2.1 Wtrig 3 1.1-1.3 1.2 Wtal 3 1.1-1.2 1.17 Myolestes Matthew, 1909 Myolestes cf. M. dasypelix Matthew, 1909. Plate lib. Ma/maZ.— Fault: 2 UW 1567, PM 15822.* Discussion.— \]W 1567 is slightly smaller than PM 15822, but both are in the size range of M. dasypelix (McKenna, 1960b, p. 147). Myolestes lower molars are characterized by a strong protoconid and metaconid, lingually directed paraconid ridge, and a strong hypo- conid. The entoconid and hypoconulid are close together and are joined by a ridge. This species is known from throughout the Bridger Formation, and was reported from the Lost Cabin by Guthrie (1967). TABLE 6. Measurements in millimeters of Mi-j of Myolesles cf. M. dasypelix. N OR M L Mi-t L 2 1.3-1.5 1.4 Wtrig 2 0.8-0.9 0.85 Wtal 2 0.7-0.8 0.75 Subfamily Creotarsinae Hay, 1930 Scenopagus McKenna and Simpson, 1959 This genus was initially recognized by McKenna and Simpson in material collected at Tabernacle Butte and called Scenopagus mcgrewi. McGrew et al. (1959, pp. 148 151) had earlier referred a lower jaw to Diacodon edenensis. In 1962 McKenna et al. (pp. 26-27) referred edenensis to Scenopagus, with priority over mcgrewi. Since the initial discovery of this genus at Tabernacle Butte, Robinson i #: PLATE II. Insectivores. All specimens illustrated as stereopairs. The line beside the left member of each pair represents 1 mm. a. Centetodon cf. C. pulcher, PM15836, RP4. b. Myolestes cf. M. dasypelix, PM 15822, LMi-o. c. Scenopagus edenensis, PM 15067, RM1-M3. d. Scenopagus edenensis, PM 15846, RM^. e. Scenopagus priscus, PM 15827, RM^. f. Creotarsinae, incertae sedis, PM 15830, LM»-2. g. Nyctitherium sp., PM 15810, LP4. h. Nyctitherium sp., PM 15821, LP,.P4. 84 WEST: NEW FORK-BIG SANDY AREA 85 (1966) has reporte M* M'-« M* M, M, M,-, M, L W 1 1 1.6 1.3 L W 1 1 2.1 2.8 L W 1 1 2.3 2.7 L W 5 5 2.0-2.2 3.0-3.3 2.12 3.1 L W 1 1 2.0 2.9 L W 1 1 2.0 3.1 L Wtrig Wtal 4 5 5 2.3-2.4 1.5-1.6 1.4-1.6 2.35 1.54 1.52 L Wtrig Wul 6 6 6 2.1-2.4 1.6-1.8 1.6-1.8 2.23 ±.04 1.72 ±.32 1.67 ±.32 .10±.03 .08 ±.22 .08 ±.22 4.48 ±1.29 4.50 ±1.30 4.64 ±1.34 L Wtrig Wtal 2 2 2 2.1-2.2 1.3-1.7 1.4-1.5 2.15 1.5 1.45 L Wtrig Wtal 4 4 4 2.2-2.5 1.3-1.6 1.3-1.6 2.32 1.48 1.45 86 FIELDIANA: GEOLOGY, VOLUME 29 Scenopagus priscus (Marsh, 1872). Plate lie. Material—Fault: 1 PM 15827*. Discussion. — Robinson (1966, pp. 29-30) referred Nyctitherium priscum Marsh to Scenopagus. This is a smaller species than S. edenensis, with the same dental morphology, and like S. edenensis, ranges through the Bridgerian. The single specimen in the study collection, an M'-, is 1.5 mm. long and 2.0 mm. wide. Both species are represented by single specimens in the Huerfano collection, while S. priscus is obviously uncommon in the Bridger B collection from the New Fork-Big Sandy area. Creotarsinae incertae sedis. Plate Ilf. Material— Fault: 4 PM 15065, 15806, 15826, 15830*. Discussion. — These four specimens may be assigned to either Talpavus or Entomolestes. These two genera are very similar to each other as well as to several other creotarsines. Robinson (McKenna et al., 1962) revived the genus Talpavus Marsh which had been included in Nyctitherium by Matthew in 1909, and considered Talpavus and Nyctitherium to belong to two different families (Robinson, 1968a, p. 4) . Entomolestes is believed to be more advanced than Talpavus on the basis of its single-rooted anterior incisors (if E. nitens is included in Scenopagus). He also pointed out that the best distinction between these two genera for the purposes of identifica- tion is the expanded paraconid on the lower molars of Eritomolestes, in contrast with the more narrow, compressed paraconid of Talpavus. The indeterminate creotarsine molars in the study collection are about the same size as those of Scenopagus priscus, although the upper teeth are stouter. The hypocone is joined to the protocone anterobucally, and the conules are larger than in nyctitheres. The cingula are more strongly developed than in the closely related Scenopagus. The single lower molar, Ms in PM 15065, is not definitive in the matter of paraconid development, so a positive identification is not possible. TABLE 8. Measurements in millimeters of teeth of Creotarsinae, incertae sedis. N OR M M»-2 L 2 1.2-1.5 1.35 Mi-2 M3 L 2 1.2-1.5 W 1.9 L 1.6 Wtrig 1.0 Wtal 0.9 L 1.6 Wtrig 0.9 Wtal 0.7 WEST: NEW FORK-BIG SANDY AREA 87 Family Nyctitheriidae Simpson, 1928 The status of this family is the current subject of intensive study. Robinson (1968b) believed that a reasonably coherent family can be assembled around NyclUherium, and McKenna (1968), utilizing Robinson's unpublished conclusions, added the genus Leptacodou to the Nyctitheriidae. Van Valen (1967, p. 262) did not feel that the nyctitheres are so independent, and placed them as a subfamily of the Adapiscoricidae. Nyctitherium Marsh, 1872 Nyctitherium sp. Plate Ilg, h. Mo/ma/.— Fault: 5 PM 15810*, 15816, 15818, 15820, 15821*. Discussion. — This poorly preserved material may be either of two Bridgerian species, Nyctitherium serotimum or A^. velox (P. Robinson, pars, comm., 1968). Unfortunately, the poor quality of the material and the lack of adequate molars limits the accuracy of the identifica- tion. Distinctive features of these specimens include double-rooted p.. and Pa in front of the complex P4. The mental foramen is located below P3 in three specimens, but seems to be located beneath P4 in PM 15816, a specimen with a single badly fractured tooth which may not be part of this group. P4 has a trigonid with a low paraconid ridge in front of the high metaconid and protoconid. The talonid is rather distinctive, as the cristid obliqua is directed toward the posterior surface of the meta- conid, making the area of the talonid basin quite small. Both entoconid and hypoconulid are present, and the individual talonid cones are not connected by a crest as in Myolestes. Order Creodonta Superfamily Palaeoryctoidea Simpson, 1931 Family Palaeoryctidae Simpson, 1931 Subfamily Didelphodontinae Matthew, 1918 Didelphodus Cope, 1882 Didelphodus altidens (Marsh, 1872). Plate Ilia. Ma/erm/.- Fault: 1 PM 15852*. Discussion. — Didelphodus altidens is a long-ranging species, pres- ent from the Lost Cabin through the Bridgerian. It has primitive 88 FIELDIANA: GEOLOGY, VOLUME 29 TABLE 9. Measurements in millimeters of teeth of Nyctitheriu N OR M Ps L W 1 1 1.1 0.5 P4 L Wtrig Wtal 4 3 4 1.4-1.6 1.48 0.7-0.9 0.8 0.7-0.9 0.83 Ml L Wtrig Wtal 1 1 1.4 0.9 upper molars, compressed anteroposteriorly, with a wide stylar shelf and a prominent ectoflexus separating the two stylar lobes. The single tooth present in the study collection, a RMS is in good condition except for a small missing area at the mesostyle. It is 3.4 mm. in length and 5.0 mm. in width. Superfamily Oxyaenoidea Cope, 1877 Family Oxyaenidae Cope, 1877 Oxyaena Cope, 1874 Oxyaena forcipata Cope, 1874. Plate Illb, c. Maiena/.— Steele Butte Breaks: 1 (Skull: PM 15081*, including R&LP-'-M-, R&LP3-M0) Discussion. — Oxyaena forcipata is a large species, well known through the Wasatchian (Denison, 1938, p. 169). Guthrie (1967, pp. 16-17) discussed the Wasatchian species of Oxyaena, and con- cluded that only 0. forcipata was present in the Lysite and Lost Cabin faunas of Wyoming, and Robinson (1966, p. 47) recognized 0. lupina in the late Wasatchian of the Huerfano Basin in Colorado. PM 15081 is considerably larger than the 0. forcipata from the Lysite, as well as larger than the type specimen of 0. ultima from the Lost Cabin Member. The M1/M2 length ratio criterion proposed by Denison (1938, p. 197) for 0. forcipata ranges from .77 to .86; PM 15081 has a ratio of .81. TABLE 10. Measurements in millimeters of teeth of Oxyaena forcipata, PM 15081. P3 P4 M, M2 L W L W L W L W R 17.7 10.5 21.2 12.4 18.2 10.8 22.3 1 13.0 L 16.8 10.0 20.6 11.6 18.9 11.0 23.4 13.2 P» p» ] P* Ml M^ L W L W L W L W L W R 13.8 9.3 21.9 14.6 22.6 21.5 23.8 18.2 18.9 8.1 L 13.5 9.4 21.1 15.2 22.9 21.5 26.5 17.4 19.0 6.0 :t: PLATE III. Creodonts and carnivores. All .specimens illustrated as stereo- pairs. The line beside the left member of each pair .serves as the scale: for a, the line represents the length of 1 mm.; for b and c it represents 10 mm.; and for d through li it represents 5 mm. a. Didelphodun altidenn, PM 15852, RM'. b. Oxyaena foTcipata, PM 15081, RPj-M;. c. Oxyaena forcipala, PM 15081, RP'-M'. d. Tritemnodon sp., PM 15607, LM«. e, Thinocyon cf. T. velox, PM 15858, RPjM.Mj f. Thinocyon cf. T. velox, PM 15083, RP«-M'. g. Didymictis altidens, PM 15563. RM,. 89 90 FIELDIANA: GEOLOGY, VOLUME 29 Oxyaena sp. Material.Steele Butte Breaks: 2 PM 15080, 15082. Discussion. — Two specimens, both consisting only of premolars, are referable to Oxyaena, but they are considerably smaller than 0. forcipata. Perhaps a smaller species, such as 0. lupina, is present in the upper Wasatch fauna from the Green River Basin. Alterna- tively, these three specimens (including PM 15081) of Oxyaena may cover virtually the entire size range of a single variable species. Gazin has not reported any Oxyaena material from the New Fork Tongue; these specimens plus PM 15081 are the first record of upper Lost Cabin zone Oxyaena in the northern Green River Basin. TABLE IL Measurements in millimeters of teeth of Oxyaena sp. PM 15080 PM 15082 R L P^ L 10.1 10.1 14.3 W 6.8 6.9 10.9 10.1 10.1 6.8 6.9 14.0 11.0 P^ L 14.0 17.1 W 11.0 13.0 Oxyaenid Material— East Fork Rim: 1 PM 21228. Discussion. — This partial P3 is small for a late Wasatchian oxyaenid, too small for Oxyaena. It may belong to Ambloctonus (Matthew, 1915a, pp. 59-63; Denison, 1938, p. 191), but the material is inadequate for more than a suggestion of this assignment. The overall shape is indicative of Ambloctonus, as the talonid is broad, wider than the anterior portion of the tooth. This tooth is 11.4 mm. long and 8,5 mm. wide. Family Hyaenodontidae Leidy, 1869 Subfamily Hyaenodontinae Leidy, 1869 Tribe Proviverrini Van Valen, 1966 Prototomus Cope, 1874 PPrototomus sp. Material.— Steele Butte Breaks: 1 PM 15606. Two Buttes: 1 PM 15624. Discussion. — Van Valen (1965, p. 639) rejected the genus Sinopa, placing the various species in Proviverra Rutimeyer, Prototomus Cope, Tritemnodon Marsh, and the new genus Arfia. Prototomus is the most primitive genus and includes most of the Wasatchian species WEST: NEW FORK-BIG SANDY AREA 91 previously assigned to Sinopa (Matthew, 1915a, p. 72). Prototomus was regarded by Van Valen as the stem genus for the family Hyaeno- dontidae. PM 15606 is a fragmental upper molar, resembling Prototomus in overall aspect. PM 15624 is a lower molar trigonid, possibly also of Prototomus by comparison with other, more complete specimens. Proviverra Rutimeyer, 1862 PProviverra sp. Mo/er/o/.— Fault: 1 PM 15849. Discussion. — This specimen is the labial portion of an upper molar, showing the external shelf, paracone, and metacone. These external cones are too far apart for Prototomus, and seem to fit the criteria for Proviverra, which has Bridgerian species. The specimen is so incomplete, however, that specific identification is impossible, and the generic assignment has to be tentative. Tritemnodon Matthew, 1906 Tritemnodon sp. Plate Hid. Ma/erm/.— Steele Butte Breaks: 1 PM 15607*. Blue Rim: 1 PM 15571. Discussion. — The M- from Steele Butte Breaks is heavily worn and missing the protocone. Nonetheless, the large stylar shelf and the elongate metastyle, combined with the closely appressed meta- cone and paracone, are indicative of Tritemnodon. The specimen is close in size to late Wasatchian T. agilis, but is somewhat smaller. There is a heavy wear facet along the posterior metastyle-metacone crest. Subfamily Limnocyoninae Wortman, 1902 Tribe Limnocyonini Wortman, 1902 Thinocyon Marsh, 1872 Thinocyon cf. T. velox Marsh, 1872. Plate Ille, f. Material.— Tree Road: 3 (Jaws: PM 15858*, RPj, M,-M,; PM 15860, RP,, M,), PM 15859. Little White Butte: 1 (Jaw: PM 15083*, RP*-M'). 92 FIELDIANA: GEOLOGY, VOLUME 29 Discussion. — The maxillary fragment (PM 15083) is referable to Thinocyon velox, the single lower Bridger Formation species discussed by Matthew. It is small compared with Matthew's (1909, p. 458) measurements, but a great deal of size variability is recognized in this species. The two lower jaws are quite different in size — PM 15860 is smaller than PM 15858, and fits well with Matthew's illustrated T. velox. The location of the mental foramen below Ps can be seen in both of these specimens. The isolated molar trigonid, PM 15859, is assigned to this taxon because of its similarity to the M2 trigonid on PM 15858. TABLE 12. Measurements in millimeters of teeth of Thinocyon cf. T. velox. N OR M M» Pi Ml M2 Order Carnivora Suborder Fissipedia Blumenbach, 1871 Family Miacidae Cope, 1880 Subfamily Viverravinae Matthew, 1909 Didymictis Cope, 1875 Didymictis altidens Cope, 1880. Plates Illg, IVa. Material— S>tee\e Butte Breaks: 1 (Jaw: PM 15563*, R&LMi- M2). East Fork Rim: 1 PM 15589. Unnamed: 1 PM 15570*. Two Buttes: 1 (Jaw fragments: PM 15572, LP2-P4, RP2, P4). Discussion. — These four specimens represent a large species of Didymictis. It is likely that they are individuals of Didymictis altidens, a species which apparently increased in size through the later Wasatchian (Gazin, 1962, p. 57, found that D. altidens from L W 1 4.1 L W 4.2 4.1 L W 2.6 1.1 L W 4.6 L Wtrig Wtal 2 2 2 5.3-6.4 3.3-3.7 2.5-3.2 5.85 3.5 2.85 L Wtrig Wtal 1 1 1 7.2 4.0 3.0 « 41, 0^1 PLATE IV. Carnivores and primates. All specimens illustrated as stereo- pairs. The line beside the left member of each pair represents 5 mm. a. Didymictis altidens, PM 15570, LM>. b. Viverravus gracilis, PM 15085, RP,-M,. c. Miacis latidens, PM 15566, LM'. d. Vulpavm sp., PM 15564, RM». e. Nothardus cf. N. nunienus, PM 15541, RM'. f. Nolharcltis cf. N. nutiietituf, PM 15.547, LMa. H. Nothardus tenebrosus, PM 15040, RMj. h. Smilodedes gracilis, UW 1514, RM'. 93 94 FIELDIANA: GEOLOGY, VOLUME 29 TABLE 13. Measurements in millimeters of teeth of Didymictis altidens. N OR M p4 L W 16.9 11.4 Ml L W 8.6 10.7 P2 L W 9.6 4.0 Pa L W 11.8 5.7 P4 L W 16.0 7.5 M, L Wtrig Wtal 15.9 9.6 8.2 M2 L 2 9.1-10.4 9.75 Wtrig 2 5.8- 6.0 5.9 Wtal 2 4.9- 5.6 5.25 the New Fork Tongue is significantly larger than that from the LaBarge horizon). Viverravus Cope, 1872 Viverravus gracilis Cope, 1872. Plate IVb. Material— F2iu\t: 2 (Jaw: PM 15086, RP4-M1) UW 1553. Sandstone Point: 1 (Jaw PM 15085, RP4-M1). Discussion. — PM 15085 shows alveoli for only one tooth behind Ml, suggesting that these specimens are Viverravus rather than Didymictis. The size corresponds well to V. gracilis, a relatively common Bridgerian species, as can be seen in the measurements presented by Robinson (1966, p. 50). The lower molars of Viverravus differ from those of Didymictis in the wide separation between the paraconid and metaconid in Viverravus. TABLE 14. Measurements in millimeters of teeth of Viverravus gracilis. N OR M P4 L 2 5.0-5.2 5.1 Wtrig 2 2.4-2.5 2.45 Ml L 2 5.7-6.1 5.9 Wtrig 2 3.1-3.3 3.2 Wtal 2 2.5-2.8 2.65 Viverravus sp. Material.— Fault: 1 PM 15854. Discussion. — This single left P4 is probably referable to Viver- ravus, although it is not V. gracilis. Although the tooth shows the same morphology as V. gracilis, it is somewhat shorter and much WEST: NEW FORK-BIG SANDY AREA 95 more slender, being 4.8 mm. long and 1.8 mm. wide. It is impossible to make a specific assignment on such material. Subfamily Miacinae Trouessart, 1885 Miacis Cope, 1872 Miacis latidens Matthew, 1915. Plate IVc. Material.— East Fork Rim: 2 PM 15566*, 15568. Piney Cutoff: 1 PM 15629. Discussion. — Miacis latidens is represented by two upper first molars from East Fork Rim, complete PM 15566 and fragmentary PM 15568. They show the typical extended parastyle, large para- cone, and lack of hypocone. PM 15566 is 5.8 mm. long and 8.5 mm. wide. A third M', PM 15629, is a fragment including the paracone, metacone, and stylar area; it compares well with the other two I specimens. M. latidens is a Lost Cabin species. Vulpavus Marsh, 1871 Vulpavus sp. Plate IVd. Material.— East Fork Rim: 1 PM 15564*. Discussion. — This heavily worn M- appears most similar to V. asius, described by Gazin (1962, p. 60) from the New Fork Tongue. It has a narrow stylar shelf with an enlarged parastylar area. The parastyle is much larger than the metastyle, and a protoconule is present. A slight bulge on the postero-internal corner of the tooth may represent an incipient hypocone. The tooth is 5.5 mm. long and 7.6 mm. wide. Order Primates Suborder Prosimii Illiger, 1811 Superfamily Lemuroidea Gray, 1821 Family Adapidae Trouessart, 1879 There is some question as to whether the North American and European genera here included in the family Adapidae should be divided into two families, the Adapidae for the European genera and the Notharctidae for the North American genera. Gazin (1958, p. 31). argued for two families, and was hesitantly followed by Mc- Kenna (1967). I follow Simons (1963, p. 88), who placed all the genera in the single family Adapidae. Russell et al. (1967) consid- 96 FIELDIANA: GEOLOGY, VOLUME 29 ered the European early Eocene primate Cantius to be a notharctid, thus giving that family representatives on both sides of the North Atlantic. In all other respects they recognized two separate fam- ilies. Subfamily Notharctinae Trouessart, 1879 Notharctus Leidy, 1870 In 1957 Robinson reviewed middle Eocene Notharctus and de- lineated three basically size-determined species. In 1958 Gazin referred the smallest of Robinson's Bridgerian species to Smilodectes gracilis, leaving the larger species A^. tenebrosus of the Bridger B (and possibly C and D) and N. rohustus of the Bridger C and D as de- scribed by Robinson. Notharctus cf. N. nunienus (Cope, 1881). Plate IVe, f. Ma^erm/.— Steele Butte Breaks: 1 PM 15544. East Fork Rim: 3 PM 15546, 15547*, 15548. Blue Rim: 2 PM 15537-8. Two Buttes: 1 PM 15532. Twnf-C: 1 PM 15541*. Twnf-D: 1PM 15573. Discussion. — Comparison of the nine specimens listed above to Gazin's material (1962, p. 30) and the approximate measurements given by Granger and Gregory (1917, pp. 843-846) indicates that these specimens fall into the size range of Notharctus nunienus, a typical Lost Cabin species. The Ms, PM 15547, has the character- istic cristid obliqua conformation mentioned by Robinson (1957) for the Bridgerian species of Notharctus. TABLE 15. Measurements in millimeters of teeth of Notharctus cf. A^. nunienus. N OR M Mi-2 Notharctus tenebrosus Leidy, 1870. Plate IVg. Material— Fault: 8 UW 1734, PM 15040*, 15310, 15675, 15677, 15682, 15686, 15696. L 1 3.2 W 1 4.3 L 3 4.5-5.2 4.9 W 3 5.3-6.9 6.23 L 4 4.8-5.0 4.88 Wtrig 4 3.5-4.4 3.95 Wtal 4 3.9-4.5 4.12 L 1 6.9 Wtrig 1 4.0 Wtal 1 3.8 WEST: NEW FORK-BIG SANDY AREA 97 Hawk: 1 PM 15712. Washrl PM 15327. 1375 ^8: 1 PM 15746. SH sec. 20:1 PM 15044. Discussion. — Notharctus tenehrosus is the smaller of the two Brid- gerian species placed in Notharctus by Gazin. Robinson mentioned differences other than size that distinguish A', tenehrosus from the Smilodectus gracilis, including the large hypoconid on P3 and the cristid obliqua of Mj joining a ridge extending backward from the protoconid. The two Ma's of A", tenehrosus, PM 15040 and UW 1734, show the characteristic hook in the cristid obliqua. TABLE 16. Measurements in millimeters of teeth of Notharctus tenehrosus. N OR M p» L 1 3.5 W 1 3.9 M* L 2 5.3-5.7 5.5 W 2 7.0-7.1 7.05 P4 L 1 5.3 W 1 4.1 Ml L 1 6.2 Wtrig 1 4.3 Wtal 1 4.8 Mm L 5 5.8-6.4 6.0 Wtrig 5 3.7-4.9 4.1 Wtal 5 4.2-5.1 4.6 M, L 2 5.6-6.0 5.8 Wtrig 2 3.3-3.4 3.35 Wtal 2 3.1-3.6 3.35 Smilodectes Wortman, 1903 Smilodectes gracilis (Marsh, 1871). Plates IVh, Va. Ma/ma/.— Fault: 12 UW 1514*, 1527. 1541, 1548, 1570. PM 15005, 15062, 15256. 15329. 15335 6. 15697. Hawk: 2 PM 15314. 15783. Tree Road: 4 (Jaw: PM 15731. RP^ P*), PM 15737, 15740, 15743. Wash: 1 PM 15326. Little White Butte: 1 PM 15078. 1375 ^: 1 (Jaw: PM 15045. RM, M,). Jean's Quarry: 2 (Jaws: PM 15749*. LM, M.; PM 15750, RP,- SW 1^ sec. 36:1 PM 15752. 1 PLATE V. Primates. All specimens illustrated as stereopairs. The line beside the left member of each pair serves as the scale: for a the line represents 5 mm., and for b through e it represents 1 mm. a. Smilodedes gracilis, PM 15749, LM1-M2. b. Omomys carteri, UW 1320, RM1-M3. c. Anapiomorphus aemulus, PM 15661, LM'-M». d. Omomys of. O. sheai, PM 15337, RM2-M3. e. Washakius insignis, PM 15019, RP3-M2. 98 WEST: NEW FORK-BIG SANDY AREA 99 Discussion. — Smilodedes gracilis, common in Ihe Hridgerian col- lection, is distinguished from the slightly larger \'otharctus tenebrosuH on the basis of size, rectangular shape of M\ and configuration of the cristid obliqua on M3. Gazin's 1958 discussion of the middle and upper Eocene primates considers cranial differences between the two genera; cranial material is lacking in the study collection and thus is not useful here. Smilodedes gracilis is typical of the Bridger B, and is rare in the upper Bridger beds (P. Robinson, pers. comm., Dec. 20, 1968). TABLE 17. Measurements in millimeters and statistics of teeth of Smilodedes gracilis. N OR M SD V P» P« M>- M» P, P, P4 M, M, M,- M, Superfamily Omomyoidea Trouessart. 1879 Family Omomyidae Trouessart, 1879 Omomys Leidy, 1869 Omomys carteri Leidy, 1869. Plate Vb. Ma/ma/.— Fault: 25 (Jaws: UW 1320*, RMo M,; UW 1518. RP, M,), UW 1565, PM 15001 2, 15009, 15011, 15022. 15024, 15026. 15028, 15032, 15034, 15663 4. 15669. 15673. 15678 9, 15689. 15692. 15699 700, 15759, 15805. White Hills: 1 PM 15299. L 5 2.5-2.8 2.58 W 5 2.7-3.5 2.98 L 3 2.5-3.1 2.7 W 3 2.2-3.8 3.17 L 2 4.3-4.7 4.5 W 2 5.3-6.0 5.65 L 3 3.5-4.0 3.73 W 3 4.0-5.1 4.67 L 1 1.9 W 1 1.3 L 1 2.5 W 1 1.9 L 2 2.8 W 2 2.1-2.3 2.2 L T 4.6 Wtrig 1 3.0 Wtal 1 3.3 L 2 4.7-5.0 4.85 Wtrig 2 3.2-3.7 3.45 Wtal 2 3.5-3.9 3.7 L 6 4.8-5.4 5.07±.10 .24 ±.05 4.83 ±1.08 Wtrig 6 2.1-4.2 3.45±.32 .79±.18 22.90 ±5.12 Wtal 6 3.2-4.4 3.83 ±.18 .42 ±.09 11.22 ±2.51 L 1 6.0 Wtrig 1 3.1 Wtal 2 2.8-3.1 2.95 i 100 FIELDIANA: GEOLOGY, VOLUME 29 Hawk: 4 PM 15713 5, 15719. Tree Road: 4 PM 15724-5, 15736, 15745. Wash: 2 PM 15721-2. Green: 7 (Jaw: PM 15641, RP3-P4), PM 15531, 15637-8, 15640, 15643, 15645. Discussion. — Omomys carteri is a common Bridgerian species, with generalized, variable teeth. Weak conules and a lack of a mesostyle characterize the upper molars, although a small mesostyle bulge is infrequently present. The two-rooted, elongate P3 and P4 are present in UW 1518. The lower molars are simple teeth with prominent paraconids and deeply basined talonids. In 1958 Gazin named 0. Uoydi on material from the Powder Wash locality in the Green River Formation of the Uinta Basin. The basic differences between 0. Uoydi and 0. carteri are absolute size and relative size of M3. Some specimens of 0. carteri from the New Fork- Big Sandy area are small enough to be in the 0. Uoydi size range, but there is no indication in the size-frequency distribution that two different species are present. Ml M» M» Pj P4 Ml M2 M3 TABLE 18. Measurements in millimeters and statistics of teeth of Omomys carteri. N OR M SD V L 3 1.9-2.2 2.1 W 3 2.5-3.3 2.97 L 7 2.5-3.2 2.64 ±.10 .26 ±.07 9.81 ±2.62 W 4 3.1-3.3 3.25 L 2 2.2-2.6 2.4 W 2 3.4-4.1 3.75 L 4 1.6-2.2 1.9 W 4 2.5-3.3 2.95 L 3 1.4-2.2 1.93 W 3 1.3-1.5 1.4 L 8 2.1-3.0 2.61 ±.11 .32 ±.08 12.18±3.04 Wtrig 8 1.7-2.1 1.91 ±.06 .18±.04 9.58±2.40 Wtal 2 1.9-2.2 2.05 L 5 2.4-2.6 2.5 Wtrig 6 1.5-1.9 1.72 ±.07 .18±.05 10.70 ±3.09 Wtal 6 1.6-2.3 1.87±.10 .24 ±.07 12.89±3.72 L 12 2.1-2.7 2.45±.05 .17±.03 7.07±1.44 Wtrig 12 1.7-2.1 1.88 ±.04 .15±.03 7.87±1.61 Wtal 12 1.8-2.2 2.04 ±.03 .11 ±.02 5.37±1.10 L 4 2.5-2.8 2.72 Wtrig 4 1.5-1.9 1.68 Wtal 4 1.5-1.8 1.65 Omomys cf. O. carteri Leidy, 1869 Material.— Hawk: 1 (Jaw: PM 15710, LM^-M^. West of Cone: 1 (Jaw: PM 15084, RM^-M^). L 2 1.8-2.1 1.95 W 2 2.3-3.0 2.65 L 2 1.7-1.9 1.8 W 2 2.7-3.1 2.9 L 1 1.3 W 1 2.1 WEST: NEW FORK-BIG SANDY AREA 101 Discusstoft. — One badly broken maxillary fragment from the West of Cone locality and a better one from Hawk probably can be referred to 0. carteri. The buccal sides of all the teeth on PM 15084 are missing, but the lingual parts show the poorly developed cus- pules and internal cingulum of 0. carteri. This individual seems small, but with such a large portion of each tooth missing it is diffi- cult to determine the original size of the teeth. The molars of PM 15710 are relatively large, in contrast to most individuals of 0. carteri, in which both M' and M^ are relatively smaller than M-. However, with the great amount of variations observed in Omomys, it is likely that this specimen also belongs in 0. carteri. TABLE 19. Measurements in millimeters of teeth of Omomyn cf. O. carteri. N OR M M' M* M* Omomys cf. O. sheai Gazin, 1962. Plate Vd. Material.— B\ue Rim: 1 (Jaw PM 15536*, RM.-M,). Discussion. — In 1962 (pp. 31-32) Gazin described a new species, Omomys sheai, from the LaBarge local fauna. 0. sheai is smaller than the common Bridgerian 0. carteri (especially in M2), and is larger than the Lysite species 0. minutus. Gazin's single specimen, USNM 22384, shows a long M3 relative to Mg. PM 15536 shows this relationship of M3 to Mg, as well as the slight basining of the trigonid mentioned by Gazin. An anterior shelf, possibly homolo- gous to the normal paralophid, is present on the lower molars of PM 15536. A slight crest is also developed posterior to this, in the nor- mal position of the paralophid. This crest extends forward from the anterior face of the paraconid before curving toward the pro- toconid, so it makes up a larger proportion of the trigonid than in 0. carteri. TABLE 20. Measurements in millimeters of teeth of PM 15536 Omomys cf. O. sheai. M, M, Length 2Ji 2.8 Width trigonid 1.7 1.5 Width talonid L9 1.7 102 FIELDIANA: GEOLOGY, VOLUME 29 Washakius Leidy, 1873 Washakius insignis Leidy, 1873. Plates Ve, Via. Ma/ma/.— Fault :14 (Jaws: PM 15019*, RP3-M.2; PM 15027*, Lps-M''; PM 15055, RMi-M2; PM 15057, RP^-P^; PM 15687, RP3- Pi), UW 1533, PM 15004, 15036-9, 15061, 15670, 15674. White Hills: 3 PM 15068, 15703, 15707. Hawk: 1 PM 15072. Discussion. — Several dental specializations give Washakius a dis- tinctive appearance, although it is closely related to Omomys. The upper dentition of Washakius insignis is characterized by enlarged protoconules and metaconules on the molars, as well as prominent hypocones developed on the posterointernal cingula. PM 15038 shows another distinctive feature of Washakius, the twinned meta- conule. P3 and P4 have antero- and posterolingual crests from the primary cusp. The paraconid of Mi is lingual in position, and all the lower molars show development of a metastylid on the posterior slope of the metaconid. M3 has an anteroposteriorly compressed trigonid and a very large hypoconulid. TABLE 2L Measurements in millimeters of teeth of Washakius insignis. N OR M pa L 3 1.7-1.9 1.8 W 3 2.1-2.2 2.17 P4 L 3 1.8-2.0 1.87 W 3 2.3-2.5 2.43 Ml L 2 2.2-2.9 2.55 W 2 2.1-3.0 2.55 M^ L 2 2.1 W 2 3.2-3.4 3.3 Mi-2 L 1 2.1 W 1 2.7 M» L 1 1.8 W 1 2.8 P» L 2 1.5 W 2 1.3 P4 L 3 1.7-2.1 1.87 W 3 1.6-1.8 1.67 Ml L 3 2.1-2.2 2.13 Wtrig 3 1.6-1.8 1.7 Wtal 3 1.8-2.0 1.87 M2 L 5 2.1-2.4 2.22 Wtrig 5 1.8-1.9 1.88 Wtal 5 1.8-2.0 1.94 M,-2 L Wtrig Wtal 2.3 1.6 1.8 M3 L Wtrig Wtal 3.0 1.6 1.8 PLATE VI. Primates. All specimens illustrated as .stereopairs. The line beside the left member of each pair serves as the scale: for a through d and f the line represents 1 mm.; for e it represents 5 mm. a. Washakius insignis, PM 15027, Lp3-\fa 5^ Washakius near W. insignis, PM 15551, RMj.Mj. c. Anaptomorphus aemulus, PM 15041, RM'-M'. d. Anaptomorphus aemulus, PM 15684, RP4-M1. e. Microsyops scotlianus, PM 15535, LMj-Mj. if. Microsyops scoUianus, PM 15539, LP,. 103 i 104 FIELDIANA: GEOLOGY, VOLUME 29 Washakius, near W. insignis Leidy, 1873. Plate VIb. Material.— East Fork Rim: 1 (Jaw: PM 15551*, RM.-Ms). Discussion. — One specimen of Washakius, similar in size to W. insignis, has been recovered from the arkosic facies of the New Fork Tongue. In both M2 and M3 there is greater fusion of paraconid and metaconid than in molars of Bridgerian W. insignis, and the trigonid basin opens forward more prominently. The hypoconulid is slightly lower in M>, and in M3 it is narrower than in the Bridgerian speci- mens. However, these differences are minor in the face of many similarities, so it seems reasonable to refer PM 15551 to Washakius insignis, and extend its range back to the late Wasatchian. TABLE 22. Measurements in millimeters of teeth of Washakius near W. insignis, PM 15551. M2 M3 Length 2.1 2.6 Width trigonid 1.8 1.7 Width talonid 1.9 1.7 Family Anaptomorphidae Cope, 1883 Subfamily Anaptomorphinae Cope, 1883 Anaptomorphus Cope, 1872 Anaptomorphus aemulus Cope, 1872. Plates Vc, Vic, d. Material— Fault: 2 (Jaws: PM 15684*, RP4-M2; PM 15661*, LM>-M3). Hawk: 2 (Jaw: PM 15041*, RM1-M3), PM 15717. Tree Road: 2 (Jaw: PM 15739, LM2-M3), PM 15735. Wash: 1 PM 15043. Green: 1 PM 15882. Discussion. — The eight specimens of Anaptomorphus aemulus are a large assemblage of this uncommon early Bridgerian species. Gazin, at the writing of his 1958 paper on the middle and upper Eo- cene primates, knew of only the type specimen ; Szalay has additional material which will be included in his review of the Eocene prosimii. Ml and M2 are characterized as omomyid-like (Gazin 1958, pp. 74-75), but with a less well-defined paraconid on M2, short and poorly excavated talonid basins, and a generally rather bulbous appear- ance. P4 is short and broad, standing considerably higher than the trigonid of Mi and showing antero- and posterointernal crests off the main cusp as in Omomys. WEST: NEW FORK-BIG SANDY AREA 105 Mj is considerably narrower than M-.. and about as long. A para- conid bulge is present, joined to the metaconid, and slightly more medial. The protoconid is not connected by a crest to either in- ternal conid. There is no trigonid basin. The anterior end of the trigoid is a flat shelf and the posterior end opens into the talonid basin. The small entoconid is connected to the hypoconulid. The hypoconulid, though small, is larger than the entoconid and is not extended into a true heel. PM 15661, M'-M', is referred to A. aemulus (Szalay, pers. comm., 1970), and is the first record of upper molars for the species. M' is smaller than M-, and both have a prominent, cuspless, exter- nal cingular shelf. Low bulbous conules lie between the protocone and the paracone and metacone. The protocone is large, and on M- sends a strong crest anteroexternally toward the anterior cingulum. There is no hypocone on any of the molars. M' is small with a much narrower cingular shelf than in the anterior molars. While M' and M- are almost rectangular in outline, M' is distinctly triangular. TABLE 23. Measurements in millimeters of teeth of Anaptomorphus aemulus. N OR M M, M, M, Family Microsyopidae Osborn and Wortman, 1892 McKenna (1960a, pp. 76-79) revived the family Microsyopidae to include Cynodontomys, Microsyops, and Craseops of North Amer- ica, genera frequently previously included in the insectivore family Mixodectidae. Szalay (1969) reviewed the Microsyopidae, and pre- sented a summary (pp. 310-311) of the evidence for the primate affinities of the Microsyopidae. Microsyops Leidy, 1872 Microsyops includes what were formerly the separate genera Cy- nodontomys and Microsyops (Szalay, 1968, p. 26; 1969, pp. 248 249). L 1 2.2 Wtrig 1 2.2 Wtal 1 2.0 L 5 2.5-2.8 2.6 Wtrig 5 1.9-2.2 2.08 Wtal 5 2.3-2.6 2.4 L 2 2.7 Wtrig 3 2.0-2.3 2.17 Wtal 3 2.0-2.5 2.3 L 2 2.6-2.8 2.7 Wtrig 1 1.9 Wtal 1 1.7 106 FIELDIANA: GEOLOGY, VOLUME 29 They had long been recognized as two parts of a continuum, with the generic boundary drawn essentially at the temporal boundary be- tween the Wasatchian and Bridgerian zones. I follow Szalay in recognizing the Wasatchian and Bridgerian species as representa- tives of a single long-lived genus. Microsyops cf. M. scottianus (Cope, 1881). Plate Vie, f. Material.— Steele Butte Breaks: 3 (Jaw: PM 15545, RM2-M3), PM 15603-4. East Fork Rim: 2 PM 15550, 15555. Blue Rim: 2 (Jaw: PM 15535*, LM2-M3), PM 15539*. Unnamed: 1PM 15561. Two Buttes: 1 PM 15558. Twnf-H: 1 PM 15540. Discussion. — One species of Microsyops is present at six of the upper Wasatch localities. This material is near the size range of both M. scottianus and M. latidens. The single P4 present in the study collection, PM 15539, is primitive and somewhat similar to M. latidens. However, because of the overall robustness of the teeth I feel it is better to refer these specimens to Microsyops of. M. scot- tianus, a common element in middle and late Wasatchian faunas. Microsyops elegans (Marsh, 1871). Plate Vila, b. Material— Fsiult: 65 (Jaws: UW 1555, RM2-M3; PM 15654, Lp3_p4. PM 15660*, RM^-M^'; PM 15662, LP^-P^), UW P2, P3, 1510, 1517, 1522, 1524, 1529, 1530, 1535, 1544, 1551, 1557-8, 1560, 1719, 1723, 1726, 1739, PM 15003, 15006-7, 15013-8, 15023, 15025, 15030- 1, 15033, 15035, 15051, 15063, 15074-6, 15087, 15331, 15334, 15338, 15656, 15658, 15665-8, 15671-2, 15681, 15683, 15685, 15688, 15690, 15695. 15698, 15756-7, 15840, 15949. White Hills: 9 PM 15046-9, 15066, 15704-5, 15708, 21083. Hawk: 6 (Jaw: PM 15718, RP3-P,), PM 15071, 15073, 15709, 15716, 15720. Tree Road: 15 (Jaw: PM 15730*, LP^-M^, PM 15723, 15726-9, 15733-4, 15738, 15741-2, 15744, 15797, 21129, 21161. Wash: 1 PM 21226. Little White Butte: 3 PM 15042, 15069, 15077. 1375 #8: 1 PM 15747. Jean's Quarry: 1 PM 15751. WEST: NEW FORK-BIG SANDY AREA 107 TABLE 24. Measurements in millimeters of teeth of Mt icroayops «< N OR M M' L 3 3.8-4.8 4.27 W 8 4.4-5.4 4.9 M» L 1 4.0 W 1 5.0 P4 L 1 3.9 Wtrig 1 2.7 Wtal 1 2.9 M, L 3 3.9-4.2 4.03 WtrJK 3 2.5-3.1 2.77 Wtal 3 2.9-3.7 3.2 L 2 4.6-5.1 4.85 M, Wtrig 2 2.6-2.9 2.75 Wtal 2 3.0-3.1 3.05 Sandstone Point: 1 PM 21225. Discussion. — This is the most abundant primate in the study col- lection. The fourth premolars of Microsyops elegans, both upper and lower, are smaller and slightly more molariform than those of M. scottianns. The two external cusps of P* are equal in height, and the protoconid and metaconid are equal in Pi of M. elegans. The talonid is characterized by the proximity of the entoconid and hypoconulid. The canines are distinctive blade-like teeth with minor marginal serrations. M. elegans is a common early Bridgerian species. P» P« M> M* M'- M* P. P, M, M, M. TABLE 25. Measurements in millimeters and statistics of teeth of Microsyops eleg arts. N OR M SD V L 1 3.0 W 2 2.7-2.9 2.8 L 12 2.8-3.7 3.4 ±.08 .29 ±.06 8.59±1.75 W 12 3.0-4.0 3.72 ±.08 .27 ±.06 7.36 ±1.50 L 19 3.2-4.1 3.63 ±.06 .24 ±.04 6.70 ±1.09 W 19 3.2-4.7 4.28 ±.08 .36 ±.06 8.36 ±1.36 L 8 3.5-4.5 3.92±.13 .38±.10 9.64 ±2.41 W 8 4.3-5.7 4.79±.17 .49±.12 10.15±2.54 L 1 4.2 W 1 5.0 L 8 2.8-3.8 3.31 ±.11 .32 ±.08 9.52 ±2.38 W 8 3.2-4.8 3.85±,16 .46±.12 11. 97 ±2.99 L 1 2.0 W 1 1.6 L 10 3.0-3.7 3.47 ±.06 .20 ±.04 0.76 ±1.29 Wtrig 9 1.8-2.6 2.23 ±.08 .25 ±.06 11.16±2.63 Wtal 10 1.9-2.5 2.34 ±.05 .17±.04 7.31 ±1.64 L 16 3.2-4.0 3.71 ±.06 .24 ±.04 6.37±1.12 Wtrig 13 2.2-2.7 2.41 ±.05 .17±.03 7.10±1.39 Wtal 16 2.3-3.2 2.79 ±.06 .26 ±.04 9.14±1.61 L 13 3.4 4.0 3.70 ±.06 .20 ±.04 5.51 ±1.08 Wtrig 13 2.1 2.7 2.35 ±.07 .24 ±.05 10.05±1.97 Wtal 13 2.3 3.0 2.72 ±.06 .23 ±.04 8.61 ±1.69 L 3 4.2 4.3 4.23 Wtrig 2 2.3 2.4 2.35 Wtal 3 2.7 108 FIELDIANA: GEOLOGY, VOLUME 29 Microsyops sp. Plate VI Ic, d. Material— Green: 8 PM 15636, 15639, 15644*, 15646, 15647*, 15648, 21217, 21221. Discussion. — These specimens represent a robust species of Mi- crosyops, considerably larger than either M. cf. M. scottianus of the late Wasatchian fauna or M. elegans of the early Bridgerian fauna. Szalay (1969, pp. 263-267) discussed the very large late Wasatchian species M. lundeliusi; this species is probably too large to include the material from the Cathedral Bluffs Tongue. TABLE 26. Measurements in millimeters of teeth of Microsyops sp. P* Ml M2 P4 Ms L W L W L W L WtrigWtal L Wtrig Wtal N 11 11 11 111 111 OR 3.9 4.3 4.0 4.2 3.8 4.3 4.4 2.2 3.4 5.2 3.1 3.2 The P* metacone and paracone are not equal in height, a feature of M. scottianus. P4 has a nearly equal protoconid and metaconid, similar to M. elegans. It is possible that these teeth belong to two or more taxa, although this is unlikely. It is difficult to tell whether this represents a distinct species of Microsyops, a large variant of M. scottianus, or a very large variant of M. elegans. Order Rodentia Suborder Protrogomorpha Zittel, 1893 Superfamily Ischyromyoidea Wood, 1937 Family Sciuravidae Miller and Gidley, 1918 Sciuravus Marsh, 1871 Sciuravus nitidus Marsh, 1871. Plate Vile, f. Ma^maZ.— Fault: 147 (Jaws: UW P4, RP^-M^; UW P5, RP^- M2; UW 1325, LM2-M3; UW 1511, RP^-M^; UW 1571, RP^-M^; UW 1575, RP^'-M^; UW 1576, LP^-P^ UW 1548, RP^-M^; UW 1585, RP^-M^; PM 15094, RM^-M^; PM 15110, LM2-M3; PM 15910, LMi -M2; PM 15912, RP^-Mi; PM 15921, RMx-Ms; PM 21049, RP^- -M^; PM 21051, RM2-M3; PM 21062, RM1-M2, PM 21064, LP^-P^), UW P6-8, 1326-7, 1335-6, 1338, 1509, 1512, 1546, 1568, 1572-4, 1581, 1587, PM 15090-3, 15095, 15096-8, 15100-9, 15111-8, 15120, 15122, 15124-8, 15130-3, 15136, 15140-3, 15145, 15150, 15900, 15902-5, 15907-8, 15911, 15913-5, 15919-20, 15923-33, 15937, 15939-43, 15945-8, 15950-1, 15953-5, 15957-8, 15961-4, 15969-70, 15972-3, 15976-9, 21043, 21048, 21052a, 21053, 21056, 21058-9, 21061, 21065-6, 21068, 21196-7, 21198, 21200. PLATE VII. Primates and rodents. All specimens illu.strated as .stereopairs. The line beside the left member of each pair represents 1 mm. a. Microayops elegans, PM 15660, RM*-M». b. Microsyops elegans, PM 15730, LP<-M'. c. Microsyops sp., PM 15644, LP4. d, Microsyopa sp., PM 15647, RP«. e. Sduravus nitidus, PM 21079, LP*-M». f . Sduravus nitidm, PM 21 144, RP4-M1. ft. Sduravus sp., PM 15170, LM,-,. 109 110 FIELDIANA: GEOLOGY, VOLUME 29 White Hills: 7 (Jaws: PM 15156, RMi-M,, LMi; PMi 21079*, LF»-M3), PM 15159, 21075, 21077-8, 21082. Hawk: 17 (Jaw: PM 21106, RM1-M2) PM 15169, 15172, 21084- 5, 21087, 21089, 21091-2, 21098, 21101-2, 21104, 21107-8, 21110, 21113. Tree Road: 34 (Jaws: PM 21135, RM^-M-^; PM 21144*, RP4- M2; PM 21146, RM1-M2), PM 21133-4, 21137-8, 21140, 21146a, 21147-52, 21154-6, 21159-60, 21162-8, 21170, 21174-5, 21177-8. Wash: 30 PM 15176-92, 15194, 15196, 15342, 21114-9, 21121-3. Fish Hill: 1 PM 21130. Little White Butte: 2 PM 15166, 15175. 1375 #8:6 (Jaw: PM 21071, LP4-M2), PM 15152-4, 21070, 21073. SW M sec. 36: 1 PM 21126. Sandstone Point: 1 PM 15173. Green: 5 PM 21202, 21204, 21208-9, 21213. Discussion. — Sciuravus nitidus is the most abundant species in the fauna from the lower Bridger Formation localities in the New Fork-Big Sandy area. The teeth of these specimens agree with TABLE 27. Measurements in millimeters and statistics of teeth of Sciuravus nitidus. N OR M SD V P« L 3 0.7-1.2 1.0 W 3 1.0-1.2 1.1 P* L 22 1.6-2.0 1.80±.02 .11 ±.02 6.06±0.91 W 22 1.8-2.4 2.15±.03 .16±.02 7.30±1.10 Ml L 13 2.1-2.3 2.16±.02 .06±.01 2.94±0.58 W 13 1.9-2.5 2.22±.0o .17±.03 7.79±1.53 M2 L 6 2.1-2.2 2.18±.02 .05±.01 2.16±0.62 W 6 2.3-2.4 2.33 ±.02 .05±.01 2.02 ±0.58 Mi-2 L 72 1.8-2.5 2.20 ±.01 .12 ±.01 5.59 ±0.47 W 71 1.9-2.7 2.25±.03 .26±.02 11.60±0.97 M3 L 22 1.9-2.4 2.19±.02 .13±.02 5.94±0.90 W 22 1.9-2.3 2.15±.03 .14±.02 6.17±0.93 P4 L 15 1.8-2.4 2.05±.04 .16±.03 8.00±1.46 Wtrig 15 1.1-1.7 1.39±.05 .20±.04 14.53±2.65 Wtal 15 1.3-2.0 1.69 ±.06 .22 ±.04 12.84 ±2.34 Ml L 11 2.0-2.4 2.25±.04 .12±.03 5.56±1.21 Wtrig 11 1.5-1.9 1.75±.05 .16±.03 9.03±1.97 Wtal 11 1.5-2.1 1.96±.06 .19±.04 9.82±2.14 M2 L 11 2.1-2.5 2.14±.03 .11 ±.02 5.12±1.09 Wtrig 11 1.8-2.2 2.04 ±.03 .10 ±.02 5.14 ±1.10 Wtal 11 1.9-2.3 2.17±.04 .12 ±.02 5.39 ±1.15 Mi-2 L 61 2.0-2.5 2.29±.02 .18±.02 7.82±0.71 Wtrig 61 1.6-2.1 1.89 ±.02 .17 ±.02 8.84 ±0.80 Wtal 61 1.7-2.3 2.05±.02 .15±.01 7.41 ±0.67 M3 L 30 2.1-3.0 2.56 ±.04 .20 ±.02 7.62 ±0.98 Wtrig 30 1.7-2.3 2.03 ±.02 .14 ±.02 7.14 ±0.92 Wtal 30 1.7-2.3 1.96±.03 .18±.02 8.98±1.16 WEST: NEW FORK-BIG SANDY AREA 111 the descriptions of Wilson (1938, pp. 129-133) and Wood (1959. pp. 165-168). S. nitidus is well known throughout the Bridgerian. Considerable variability is present in the lower dentition, espe- cially in the development of the ectolophid and mesoconulid. The posterior parts of both upper and lower third molars do not show well-developed cusp and loph patterns, but rather are unpredictably variable areas with considerable cresting. Sciuravus sp. Plate Vllg. Mo/mo/.— Hawk: 1 PM 15170*. Discus&ion. — This single tooth, LP4, is approximately the same size as the correlative tooth in S. nitidus, with the length being 2.0 mm., the trigonid width 1.6 mm., and the talonid width 1.7 mm. It differs in having a much more prominent hypoconulid, virtually no ectolophid connecting the metaconulid with the protoconid and hy- poconid, and a very low anterior cingulum so there is no definitive trigonid basin. The talonid basin is proportionally larger than in S. nitidus. It is improbable that the range of variation of S. nitidus extends to include this specimen. Sciuravids. Plate VIII a, b. Ma/erio/.— Unnamed: 1 PM 15529*. Two Buttes: 1 PM 15526*. Discussion. — These two specimens from the New Fork Tongue demonstrate the presence of sciuravids in the later Wasatchian fauna of the New Fork-Big Sandy area. It is difficult to draw conclu- sions from them, as PM 15526 is a LP, and PM 15529 is a LM\ neither a particularly informative tooth. Both are the general size of S. wilsoni (Gazin, 1961; 1962, pp. 49-50). Tillomys Marsh, 1872 Tillomys cf. T. parvidens (Marsh, 1872). Plate VI lie. Ma/ma/.- Fish Hill: 1 (Jaw: PM 21128*, LM, M3). TABLE 28. Measurements in millimeters of teeth of ".sciuravids." PM 15529 PM 15526 M» Length 1.8 Width 1.8 P« Length 2.0 Trigonid Width 1.3 Talonid Width 1.5 PLATE VIII. Rodents. All specimens illustrated as stereopairs. The line beside the left member of each pair represents 1 mm. a. Sciuravid, PM 15526, LP4. b. Sciuravid, PM 15529, LM^. c. Tillomys parvidens, PM 21128, LM1-M3. d. Taxymys lucaris, PM 15123, RM'-^. e. Knightomys cf. K. senior, PM 15895, LM'-2. f. Knightomys sp., PM 15524, RM,-2. g. Knightomys sp., PM 15889, LMi-2. h. Paramys delicatus, PM 15337, RM'-^. i. Paramys delicatus, PM 21097, RM2. j. Paramys excavatus, PM 15528, LMi. k. Paramys near P. excavatus, PM 21076, RP^ 112 WEST: NEW FORK-BIG SANDY AREA 118 Discussion. — PM 21128 is heavily worn, so much of the detail of the tooth surfaces is unavailable. It is about 20 per cent smaller than S. nitidus and about 10 per cent smaller than the Tillomys senex material described by Wood (1959, pp. 168-169). The transversely elongate mesoconid, posteriorly prolonged metaconid, and shape of the posteroloph are characteristic of Tillomys (Wilson. 1938; Wood, 1959). TABLE 29, Measurements in millimeters of teeth of Tillomys cf. T. parvidens, PM 21128. M, M, M, Length 1.8 1.8 2.0 Trigonid Width 1.8 1.7 1.7 Talonid Width 1.6 1.7 1.5 There is a similarity to the upper Bridger T. senex in the complete anterior cingulum. On the other hand, the size and nature of the metaconid and mesoconid indicate a similarity to early Bridgerian T. parvidens. The affinities are probably with the latter species, although the amount of detail obscured by wear makes this assign- ment tentative. PM 21128 is a fragmentary jaw, and a few features of the man- dible are visible. The masseteric fossa ends below the posterior end of Ml, while the scar extends forward below Mi. No foramina are visible beneath the molars. Taxymys Marsh, 1872 Taxymys lucaris Marsh, 1872. Plate Vllld. Material.— Fault: 4 UW 1586, PM 15099, 15123*, 15960. Sandstone Point: 1 PM 21227. Discussion. — This small sciuravid is distinguishable from Sci- Mroints nitidus by its small size, very strong cresting on the upper molars, small hypocone, closer connections between conules and paracone and metacone, lower anterior cingulum, and transversely straighter lophs. Taxymys lucaris has been found previously only at upp)er Bridger localities, so its appearance at these lower Bridger localities extends its temporal range. TABLE 30. Measurements in millimeters of teeth of Taxymys lucaris. N OR M M'-« L 4 1.7-2.8 1.75 W 4 1.8-1.9 1.82 M» L 1 2.0 W 1 2.0 114 FIELDIANA: GEOLOGY, VOLUME 29 Taxymys (known only from upper teeth) and Tillomys (known only from lower teeth) are similar in size and are both sciuravids. It is possible that they are in reality a single genus. Until upper and lower teeth are found in unequivocal association, however, I con- tinue to regard them as separate genera. Knightomys Gazin, 1961 Knightomys cf. K. senior Gazin, 1961. Plate Vllle. Ma^ma^.— Green: 1 PM 15895*. Discussion. — In the absence of published descriptions of the up- per dentition of this species, PM 15895, a first or second upper molar, is compared with the Lysitian species Knightomys depressus (Wood, 1965, pp. 127-132). PM 15895 shows Knightomys generic characters such as small size, good separation of protocone and hy- pocone, convex lophs, and no mesocone. In contrast to K. depressus, PM 15895 has no ectoloph, and has an obliquely oriented mesostyle. The tooth is slightly longer than wide, being 1.7 mm. in length and 1.6 mm. in width, another difference from K. depressus. This specimen can be tentatively placed in K. senior on the basis of size, cusp separation, and stratigraphic occurrence. If the assign- ment is correct, this is the first record of an upper tooth of Knight- omys senior. Knightomys sp. Plate Vlllf, g. Material— Green: 3 PM 15524*, 15887, 15889*. Discussion. — These three Knightomys specimens are much larger than the material referred to K. senior. The lower molar, PM 15524, has a very small trigonid basin, deep and closed in all directions. A small bulge represents the hypoconulid, which is virtually continu- ous with the hypoconid. The entoconid is isolated, though it sends a weak crest toward the posterior side of the hypoconid. The meta- conid is large and somewhat extended anteroposteriorly. A low mesoconid is present, lacking connections to either the protoconid or the hypoconid. In the upper molars the posterior cingulum is much stronger than the metaloph, which is interrupted between the metaconule and the metacone. The metaconule of PM 15889 gives off a low ridge to- ward the protoloph, which ends in the central basin. The protoloph is stronger than the anterior cingulum, and the protoconule is only a slight bulge. The well-formed hypocone is smaller than the proto- WEST: NEW FORK-BIG SANDY AREA 115 TABLE 31. Measurements in millimeters of teeth of Knightomys sp. PM 15524 PM 15887 PM 15889 M»-» Length 2.1 2.1 Width 2.2 2.3 M|.t Length 2.2 Trigonid Width 2.1 Talonid Width 2.3 cone and is separated from it by a deep gi-oove. There is no con- nection between the protocone and metaconule. This species seems to be intermediate in development between Knightomys and Tillomys, and is probably closer to Knightomys. It is placed in Knightomys as an indeterminate species. Family Ischyromyidae Alston, 1876 Black (1968) placed the Oligocene genus Ischyromys in the fam- ily called the Paramyidae by Wood, thus reviving the familial name Ischyromyidae used earlier (see Simpson, 1945). Subfamily Paramyinae Simpson, 1945 Paramys Leidy, 1871 Paramys delicatus Leidy, 1871. Plate Vlllh, i. Ma/mo/.— Fault: 6 PM 15134, 15337*, 15339-40, 15916, 15918. White Hills: 1 PM 15162. Hawk: 4 PM 15168, 21095, 21097*, 21103. S »2 sec. 20:PM 15164-5. Discussion. — Paramys delicatus is a medium to somewhat large Bridgerian ischyromyid. It is separable from other ischyromyids TABLE 32. Measurements in millimeters of teeth of Paramyn delicatus. N OR M M' M* P* M,-, M, L W 3.7 4.8 L W 4.1 4.6 L W 4.1 4.7 L Wtrig Wtal 4.0-4.3 2.8-3.2 3.3-4.1 4.1 3.08 3.75 L Wtrig Wtal 3 3 4.5-4.6 3.9 4.2-4.3 4.53 3.9 4.27 L Wtrig Wtal 3 3 3 5.3-5.9 4.1-4.2 4.0-4.2 5.63 4.17 4.1 116 FIELDIANA: GEOLOGY, VOLUME 29 on a size-frequency distribution, although other taxa may overlap the small end of its size range. P. delicatus is distinctly smaller than Pseudotomus and Ischyrotomus (if these are separable). The diagnosis by Wood (1962, pp. 30-33) adequately describes Paramys delicatus. A great deal of variability is present in the sur- face crenulation, especially in unworn and slightly worn teeth. Paramys excavatus Loomis, 1907. Plate VIIIj. Material— Blue Rim: 1 PM 15528*. Discussion. — PM 15528, the single specimen definitely assigned to early and middle Eocene Paramys excavatus, is a LMi. P. excava- tus is one of the smaller species of Paramys, and is generally primitive in the lack of enamel crenulations. This tooth has a large metaconid, small posteriorly opening trigonid basin, and is 2.6 mm. long, 2.2 mm. wide across the trigonid, and 2.4 mm. wide across the talonid. These measurements place it in the size range of Wood's subspecies P. e. excavatus from the Lysite and Lost Cabin zones. This is the only ischyromyid from the upper Wasatch in the study collection that falls into this size range. Paramys, near P. excavatus Loomis, 1907. Plate Vlllk. Material— White Hills: 1 PM 21076*. Green: 8 PM 15888, 15898, 21201, 21205-7, 21219, 21222. Discussion. — These nine specimens fall into the Paramys excavatus size range, but are not definitely assignable to this taxon. The P"*, PM 21076, fits Wood's 1962 description of P^ of either P. excavatus or P. copei. The lower teeth from the Cathedral Bluffs Tongue are less certainly P. excavatus, largely because of the greatly reduced TABLE 33. Measurements in millmeters of teeth of Paramys near P. excavatus. N OR M P4 Mi- M2 Ms L W 1 1 2.4 2.8 L Wtrig Wtal 2 2 2 2.7-3.0 1.4-1.6 2.4-2.5 2.85 1.5 2.45 L Wtrig Wtal 3 8 3 2.9-3.2 2.6-2.9 2.7-2.9 3.03 2.73 2.8 L Wtrig Wtal 1 1 1 2.8 2.8 2.7 L Wtrig Wtal 2 2 2 3.1-3.4 2.7-3.0 2.6-2.8 3.25 2.85 2.7 WEST: NEW FORK-BIG SANDY AREA 117 TABLE 34. Measurements in millimeters and statistics of teeth of Paramys ufyomingensis. N OR M SD V L 2 2.9 W 2 24-2.6 2.5 L 7 2.1-2.6 2.3 ±.06 .16±.04 7.13±1.91 W 7 2.1-2.7 2.46 ±.09 .24 ±.06 9.72 ±2.60 L 2 1.9-2.3 2.1 Wtrig 2 1.5-1.6 1.55 Wtal 2 1.7-1.9 1.8 L 1 2.3 Wtrig 1 2.0 Wtal 1 2.0 L 2 2.5 Wtrig 2 1.9-2.0 1.95 Wtal 2 1.9 M»-« P4 M,-, M, mesoconid and ectolophid. P. copei is also a small species, and these rather indeterminate teeth might also be placed in that species. Paramys wyomingensis (Wood, 1959). Plate IXc, d. Ma/mo/.— Fault: 5 UW 2363, PM 15936, 15966, 21041, 21044. Hawk: 5 PM 15171, 21086, 21090, 21093-4. Tree Road: 1 PM 21173. 1375 #8: 1 PM 21072. Green: 2 PM 15890*, 21214*. Discussion. — Wood described this species as Microparamys iryomingensis in 1959 (p. 163) on three teeth from the upper Bridger Formation at Tabernacle Butte. West (1969a) determined that the species should be assigned to Paramys on the basis of the large size relative to most microparamyines, the large parastyle on P^ and the distinct round metaconule on the cheek teeth. The lower molars referred to Paramys iryomingensis are placed in this group because of their size, although this is an uncertain association. This occurrence in the Cathedral Bluffs Tongue extends the range of the species through all of Bridgerian time. "Paramys" group. Plate IXa, b. Ma/ena/.- Fault: 42 (Jaws: UW 2361*, RP4-M,; UW 2364, RP-M'; UW 2365*, RM'-M^; PM 15975, RP4-M,; PM 21042, LM'-M-), UW 1538-9, 1552, 1577-80, 1582-3, 2362, PM 15119, 15121, 15129, 15135, 15138, 15146-8, 15151, 15901, 15906, 15909, 15917, 15935, 15944, 15952, 15968, 15971, 15974, 15980, 21046, 21050, 21054-5, 21063, 21067, 21069. White Hills: 7 PM 15157-8, 15160-1, 21074 21080-1. 118 FIELDIANA: GEOLOGY, VOLUME 29 TABLE 35. M easurementi 3 in millimetei rs of teeth of "Paramys" i N OR M p4 L 5 3.1-3.6 3.28 W 5 3.8-4.7 4.06 Ml L 4 3.1-3.5 3.32 W 4 3.1-4.0 3.60 M2 L 3 3.2-3.6 3.43 W 3 3.7-4.2 3.97 Mi-2 L 16 3.0-3.9 3.38 W 16 3.5-4.6 3.78 M« L 3 3.1-4.4 3.80 W 3 3.2-3.9 3.53 Fi L 6 3.0-4.0 3.48 Wtrig 6 2.0-2.9 2.57 Wtal 6 2.3-3.7 3.03 M: L 4 3.6-4.1 3.82 Wtrig 4 3.0-3.2 3.12 Wtal 4 3.3-3.5 3.4 M., L 19 3.5-4.3 3.83 Wtrig 19 2.9-3.8 3.41 Wtal 17 2.8-3.9 3.51 Ml-2 L 2 3.6 Wtrig 2 3.0-3.2 3.1 Wtal 2 3.4-3.5 3.45 Ms L 16 4.0-4.8 4.34 Wtrig 15 3.1-3.6 3.37 Wtal 16 3.1-3.5 3.27 Hawk: 6 (Jaw: PM 15167, RMi-M.,), PM 21088, 21096, 21105, 21109, 21111. Tree Road: 3 PM 21132, 21136, 21172. Fish Hill: 2 PM 21127, 21129. Green: 5 PM 15525, 15883, 15891, 15894, 15897. Steele Butte Breaks: 1 PM 15174. East Fork Rim: 2 PM 15522-3. Blue Rim: 1 PM 15527. Discussion. — This is an artificial group, as it includes material which might be placed in Paramys delicatior, Thishemys plicaius, and perhaps Paramys copei. However, with the material on hand, I cannot separate any seemingly consistent groups from this large assemblage of medium-sized ischyromyids. Variability is con- tinuous, without any coherent gi^oupings. The variables include amount of surface enamel crenulation, depth of the valley between the metaconid and the entoconid, individuality of the entoconid and hypoconid, shape of the mesostyle, degree of development of the hypocone, and degree of development of the conules. Wood (1962) had large numbers of specimens when he divided the ischryomyid rodents into several taxa. It is probable that at PLATE IX. Rodents. All specimens illustrated as stereopairs. The line besides the left member of each pair serves as the scale; for a, b, and f it represents 5 mm., and for c through e and g it represents 1 mm. a. "Paramys" group, UW 2361, RP4-M,. b. "Paramys" group, UW 2365, RM»-M*. c. Paramys wyomingen- sis, PM 15890, LM'-'. d. Paramys wyomingensis, PM 21214, LP*, e. Reithro- paramys delicatissimus, PM 15163, RM'. f. Reithroparamya huerfanensis, UW 1328, LP4-Mi. g. Reilhroparamys near R. delicatissimus, PM 15893, LMi-j. 119 120 FIELDIANA: GEOLOGY, VOLUME 29 least some of those taxa are present in "Paramys" group, although I cannot recognize them. Subfamily Reithroparamyinae Wood, 1962 Reithroparamys Matthew, 1920 Reithroparamys huerfanensis Wood, 1962. Plate IXf. Ma/enaZ.— Fault: 2 (Jaw: UW 1328*, LP4-M3), PM 21047. White Hills: 1 (Jaw: PM 15155, RM1-M3). Green: 1 PM 21215. Discussion. — Lower molars of Reithroparamys huerfanensis are characterized by a ridge from the entoconid into the talonid basin. The masseteric fossa and scar teiTninate below Mi, rather than below the posterior molars as in other species of Reithroparamys. Both dentaries show this configuration of the masseteric fossa. UW 1328 is about 25 per cent smaller than the type specimen (Wood 1962, p. 137), from the Huerfano B. TABLE 36. Measurements in millimeters of teeth of Reithroparamys huerfanensis. N OR M P4 Ml M2 Mi-2 M3 Material.— White Hills: 1 PM 15163*. Tree Road: 1 PM 21139. Jean's Quarry: 1 (Jaw: PM 21125, LM2-M3). Green: 1 PM 15885. Discussion. — Reithroparamys delicatissimus, known from the en- tire Bridgerian, is differentiated from R. huerfanensis by its somewhat larger size (about 30 per cent greater) and the posterior position of the masseteric fossa. Molars of both species have an entoconid crest L Wtrig Wtal 1 1 1 1.9 1.5 1.8 L Wtrig Wtal 2 2 2 2.2-2.5 1.7-2.2 1.9-2.4 2.35 1.95 2.15 L Wtrig Wtal 3 3 3 2.3-2.8 2.1-2.7 2.2-2.7 2.57 2.37 2.43 L Wtrig Wtal 1 1 1 2.1 2.0 2.1 L Wtrig Wtal Jelicatis! 2 2 2 simus (L 2.4-3.1 2.0-2.7 1.8-2.5 .eidy, 1873). 2.75 2.35 2.15 Plate IXe, L W 1 1 3.1 3.5 L W 1 1 2.9 3.2 L Wtrig Wtal 2 2 2 2.7-3.0 2.6-2.8 2.8-3.1 2.85 2.7 2.95 L Wtrig Wtal 1 1 1 2.9 2.6 2.5 WEST: NEW FORK-BIG SANDY AREA 121 TABLE 37. Measurements in millimeters of teeth of Reithroparamys delicatissimus . M OR M M>-» M, M: extending into the talonid basin. PM 21125 has heavily worn teeth; size is the major criterion for the taxonomic assignment. PM 15163, an upper molar, shows the double metaconule typical of Reithro- paramys. Reithroparamys, near R.delicatissimus (Leidy,1873). Plate IXg. Mo/ena/.— Green: 1 PM 15893*. Discussion. — The overall appearance of this lower molar is similar to that of R. delicatissimus, with a few somewhat primitive features: the metaloph is inteiTupted, the ectoloph shows very little develop- ment of a mesoconid, and the hypoloph is broken just posterior to the hypocone. The specimen is small, but still within the Reithroparamys range. This tooth is 2.7 mm. long and 2.4 mm. wide across both trigonid and talonid. Subfamily Manitshinae Simpson, 1941 Pseudotomus Cope, 1872 Pseudotomus robustus (Marsh, 1872). Plate Xa, b. Material. — Tree Road: 1 PM 15965*, one individual with com- plete upper and lower dentitions, parts of the skull and skeleton. DisctLSsion. — The dentition of Pseudotomus robustus is well de- scribed by Wood (1%2, pp. 171-179, 182-186). The large size is the most striking feature of this Bridgerian genus. PM 15695 is about 20 per cent larger than Wood's P. robustus material, and corresponds well to his description. With the small amount of P. robustus mate- rial currently available, there is no justification for any specific separation based on a size variation of this magnitude. Pseudotomus is similar to the slightly smaller Ischyrotomu^s and Wood indicated that several lower Bridger species could easily be referred to either genus. Wood (1962, p. 186) utilized the shape of 122 FIELDIANA: GEOLOGY, VOLUME 29 TABLE 38. Measurements in millimeters of teeth of Pseudotomus robustus, PM 15965. pa p4 M' M2 M3 LW LW LW LW LW R 2.8 3.3 5.8 6.5 6.5 6.9 6.1 6.6 7.0 6.0 L 2.7 3.1 5.7 6.4 6.4 7.0 6.2 6.6 6.9 6.2 P4 M, M2 M3 L WtrigWtal L Wtrig Wtal L Wtrig Wtal L Wtrig Wtal R 5.8 4.7 5.7 6.0 5.4 5.4 6.0 6.1 5.8 7.4 5.8 5.4 L 5.9 4.9 5.8 5.9 5.6 5.5 6.2 6.0 5.8 7.5 5.7 5.6 the incisors as one means for separating the two genera in the early Bridgerian. Based on this criterion, as well as the large size, PM 15695 is Pseudotomus robustus. It is likely that some of the large rodent incisors found at other localities belong to Pseudotomus and that it is a more common genus than is indicated here. Subfamily Microparamyinae Wood, 1962 Microparamys Wood, 1959 Microparamys minutus (Wilson, 1937). Plate Xc, d. Ma^maL— Fault: 3 PM 15137*, 15144, 21060. Tree Road: 4 PM 21156a*, 21158, 21171, 21176. Discussion. — These small ischyromyids have a distinct V-shaped arrangement of strong lophs on the upper molars. This is well dis- played on PM 21156a, the only upper tooth of M. minutus in the study collection. The hypocone is present as a bulge on the posterior cingulum. A mesostyle is present, and there is a slight expansion on the lophs in the positions of the conules. The lower molars are typically ischyromyid. They have strong trigonid basins, with antero-external drainage anterior to the protoconid. There is a distinct enlargement of the hypoconulid. Both the hypoconid and the protoconid have weak connections to the mesoconid. M. minutus is known from throughout the Bridgerian. TABLE 39. Measurements in millimeters of teeth of Microparamys minutiis. N OR M Mi-2 P4 M,-2 L 1.2 W 1.4 L 1.3 Wtrig 0.9 Wtal 1.1 L 5 1.2-1.3 1.28 Wtrig 5 1.0-1.4 1.18 Wtal 5 1.1-1.5 1.30 Wy •I Ws c ^[Fc PLATE X. Rodents. All specimens illustrated as stereopairs. The line beside the left member of each pair serves as the scale: for a and b the line repre- sents 5 mm., and for c through h it represents 1 mm. a. P»eudotomus robustus, PM 15965, LPoMa. b. Pseudotomus robmlm, PM 15965, LP'-M\ c. Micro- paramys minutus, PM 15137, RMi-j. d. Microparamys minulus, PM 21156a, RM'-'. e. Microparamys sp. A, PM 15139, RMi-;. f. Microparamys sp. A, PM 21131, RM'-'. ij. Microparamys sp. B, PM 15193, RM^ h. Microparamys sp. B, PM 15195, RM'-». 123 124 FIELDIANA: GEOLOGY, VOLUME 29 Microparamys sp. A. Plate Xe, f. Material—Fault: 1 PM 15139*. Tree Road: 2 PM 21131*, 21143. Discussion. — This is a large microparamyine species, larger than either M. lysitensis or M. cathedralis, the largest early and middle Eocene species discussed by Wood (1962, p. 163). PM 15139, a very worn specimen, is placed here on the basis of size and overall shape. PM 21143, a P4, is a robust tooth with somewhat inflated cones and a well-developed hypoconulid. The most distinctive tooth assigned to this taxon is PM 21131, an upper molar. It has the typical Microparamys strong V-shaped lophs, but shows a prominent interruption in the metaloph near the protocone. Both anterior and posterior cingula are strong, with small accessory cuspules on the posterior cingulum. There is no hypocone, and the mesostyle is weak. A protoconule is present, but the metaconule is absent. Microparamys sp. A is a distinctive species, but no suggestions can be made of its relationships with other species until better material is available. TABLE 40. Measurements in millimeters of teeth of Microparamys sp. A. PM 15139 PM 21131 PM 21143 M»-2 Length 2.1 Width 2.4 Ft Length 2.2 Width Trigonid 1.5 Width Talonid 1.8 Mi-2 Length 2.1 Width Trigonid 1.7 Width Talonid 1.9 Microparamys sp. B. Plate Xg, h. Material— Wash: 3 PM 15193*, 15195*, 21120. Discussion. — This species (if the material represents a single taxon) is intermediate in size between Microparamys sp. A and Microparamys minutus. PM 21120, M^ or M-, is quite worn, but shows the presence of a rudimentary hypocone and complete lophs with the metaloph lower than the protoloph. PM 15195, much less worn, has a somewhat divided metaloph and a much stronger pro- toloph than metaloph. M^ (PM 15193) is typical of Microparamys, with a strong protoloph and anterior cingulum. It also has a meso- style, lacking on either of the anterior molars. PM 15193 is not certainly related to PM 15195 and PM 21120, despite the similar size. WEST: NEW FORK-BIG SANDY AREA 125 TABLE 41. Measurements in millimeters of teeth of Microparamys sp. B. PM 15193 PM 15195 PM 21120 M»-» Length 1.8 1.6 Width 2.2 1.9 M» Length 1.8 Width 1.7 Assignments of these teeth to Microparamys cathedralis, the other known microparamyine of this size, would be conjectural be- cause the upper teeth of M. cathedralis are as yet unknown. The size is the only present reason for a relationship. Order Tillodontia Family Esthonychidae Cope, 1883 Subfamily Esthonychinae Cope, 1883 Esthonyx Cope, 1874 Esthonyx acutidens Cope, 1881. Plate XIa, b. Material.— East Fork Rim: 2 PM 15567*, 15574*. Discussion. — The only complete lower tooth, RM3 of PM 15574, has the elongate hypoconulid characteristic of Lost Cabin Esthonyx acutidens, and is the same size as AMNH 14783 (Gazin, 1953, p. 28). The lingual portion of LM- shows a hypocone and anterior cingulum. A weathered RM', along with fragments of other teeth and bone, makes up PM 15567. Although much of the detail of the tooth has been lost due to weathering, the pronounced ectoflexus, small pre- and postcingula, and large parastyle are apparent. TABLE 42. Measurements in millimeters of teeth of Esthonyx acutidens. M, Order Taeniodonta Family Stylinodontidae Marsh, 1875 Subfamily Stylinodontinae Marsh, 1875 Stylinodontine. Plate XIc. Materia/.— Fence X Road: 1 PM 15198. Steele Butte Breaks: 2 PM 15199, 15602. East Fork Rim: 2 PM 15200, 15590*. PM 15567 PM 15574 Length Width Length Trigonid Width Talonid Width 7.4 13.4 12.4 6.5 5.4 126 FIELDIANA: GEOLOGY, VOLUME 29 Blue Rim: 1 PM 15610. Piney Cutoff: 1 PM 15625. Discussion. — All the materials consist of fragmentary teeth, showing the enamel distribution pattern characteristic of Eocene stylinodontines. No further identification is possible. Order Dinocerata Family Uintatheriidae Flower, 1876 Bathyopsis Cope, 1881 Bathyopsis fissidens Cope, 1881. Plate Xld. Material— Steele Butte Breaks: 2 PM 15197*, 15608. Discussion. — Of the two lower molars of Bathyopsis fissidens in the study collection, only PM 15197 is reasonably complete and measureable; it is 17.3 mm. long, 13.6 mm. wide across the trigonid, and 12.4 mm. wide across the talonid. PM 15197 is longer than Mi of Cope's type specimen of B. fissidens (he failed to publish the measure- ments of M2), but is not large enough to place it in B. middleswarti. The cf . B. fissidens found by Gazin (1952, pp. 64-65) in the New Fork Tongue, USNM 19990, is also larger than Cope's type, AMNH 4820. The notable feature of Bathyopsis is the peculiar lophodont structure of the teeth, with a vestigial paraconid and paraconid ridge, a heavy portoconid-metaconid crest with the metastylid closely joined to the postero-buccal surface of the metaconid, a hypoconid crest extending antero-internally from the hypoconid, and a convex posterior talonid crest at the rear of the tooth, presumably made up of the hypoconulid and entoconid. Order Pantodonta Superfamily Coryphodontoidea Marsh, 1876 Family Coryphodontidae Marsh, 1876 Coryphodon Owen, 1846 Coryphodon sp. Plate Xle, f. MaterialSteele Butte Breaks: 13 PM 15262*, 15263-6, 15592, 15593, 21182, 21189, 21191-4. East Fork Rim: 14 PM 15267-70, 15587, 15591, 21183-8, 21190, 21195. Discussion. — There are at present 28 named species of Cory- phodon, most proposed by Cope. Simons (1960) revised the Paleo- ^b ii ^^^ PLATE XI. Tillodonts, taeniodont, dinoccratan, pantodonts, and condy- larths. All specimens illustrated as stereopairs. The line beside the left member of each pair serves as the scale: for a, b, and d it represents 5 mm., for c, e, and f it represents 10 mm., and for g, h, and I it represents 1 mm. a. Esthonyx acutidens, PM 15567, RM'. b. Esthonyx acutidens, PM 15574, RM,. c. Stylinodontine, PM 15590, C. d. Bathyopsis fissidens, PM 15197, RM'-^ e. Coryphodon sp., PM 15592, RM'. f. Coryphodon sp., PM 15262, C. ft. Hyopsodus miticulus, PM 15514, RM'. h. Hyopsodus miticulus, PM 15543, LMi-j. i. Hyopsodus worlmani, PM 15511, RM'. 127 Length Width 20.0 15.0 Length Width 33.0 41.6 128 FIELDIANA: GEOLOGY, VOLUME 29 cene Pantodonta, but stopped short of Coryphodon. The genus is in a state of taxonomic confusion, and is in need of a careful review. The genus is common in the Wasatchian, but is not known to have survived into the Bridgerian. TABLE 43. Measurements in millimeters of teeth of Coryphodon, PM 15592. Pi M^ The material available in the study collection is not suitable for specific identifications. The large incisors are the most frequently- encountered elements, but these are not diagnostic. Accumulations of tooth fragments can be assigned only to the genus Coryphodon on their general aspect. In addition to the specimens listed above, numerous miscellaneous postcranial fragments are so large that they are probably Coryphodon. Order Condylarthra Family Hyopsodontidae Trouessart, 1879 Subfamily Hyopsodontinae Trouessart, 1879 Hyopsodus Leidy, 1870 Gazin (1968) has recently reviewed the morphology, systematics, and paleoecology of Hyopsodus, long a problem to mammalian paleontologists. I use his classification (op. cit., pp. 13-30) for the specific names applied to specimens in the study collection. Gazin used parameters such as size and variability to differentiate sympatric species of Hyopsodus. Features such as the molarization of the premolars and incipient hypsodonty are also sometimes useful criteria. On the whole, however, it is difficult to distinguish the vari- ous species on the basis of isolated teeth and partial jaws. Hyopsodus is the smallest and most abundant condylarth in the study collection, and is the only condylarth to be positively identified in both upper Wasatch Formation and lower Bridger Formation deposits in the New Fork-Big Sandy area. Hyopsodus is more abun- dant in the Bridgerian than in the Wasatchian in the New Fork-Big Sandy area. It is the most common genus in many Bridgerian surface collections, although it is outnumbered by Sciuravus in the New Fork-Big Sandy area, a result of the washing process. WEST: NEW FORK-BIG SANDY AREA 129 Hyopsodus miticulus (Cope, 1874). Plate Xlg, h. Material.— Steele Butte Breaks: 2 PM 15305-6. East Fork Rim: 4 PM 15542, 15543*, 15549, 15552. Blue Rim: 2 PM 15520-1. Piney CutoflF: 2 PM 15518, 15627. Blue Saddle: 1 PM 15512. Two Buttes: 4 PM 15513, 15514*, 15515-6. Discussion. — Hyopsodus miticulus is the larger and more abun- dant of the two species of Hyopsodus present in the late Wasatchian levels of the New Fork-Big Sandy area. The specimens are all isolated teeth, so Gazin's criterion of premolar spacing cannot be utilized. All three lower molars of H. miticulus in the study collec- tion have a small metastylid on the posterior side of the metaconid, seen well on PM 15543. Gazin (1968, pp. 14, 17-18) included the material he called. H. mentalis in 1962 (p. 64) within H. miticulus, so this species is well represented in the earlier New Fork Tongue collection. TABLE 44. Measurements in millimeters of teeth of Hyopsodus m N OR M M> L 1 3.8 W 1 5.0 M» L 3 3.6-3.9 3.77 W 2 5.2-5.3 5.25 M'-« L 3 3.7-3.8 3.77 W 2 4.5-5.4 4.95 M* L 3.4 W 4.9 P4 L 4.2 Wtrig 2.7 Wtal 3.0 M, L 2 4.1-4.2 4.15 Wtrig 2 3.6-3.8 3.70 Wtal 2 3.6-3.9 3.75 M,., L 2 4.2-4.4 4.30 Wtrig 3 3.1-3.6 3.37 WUl 2 3.5-3.7 3.60 Hyopsodus wortmani Osbom, 1902. Plates Xli, Xlla. Ma/ma/.— Steele Butte Breaks: 1 PM 15511. East Fork Rim: 2 PM 15301, 15533. Piney Cutoff: 1 PM 15519*. Discussion. — This species is about two-thirds the size of H. miticulus and is much less common in the study collection. This same relative frequency of occurrence was noted by Gazin (1952, p. 8) in his early collection from the LaBarge local fauna. However, 130 FIELDIANA: GEOLOGY, VOLUME 29 TABLE 45. Measurements in mi limeter s of teeth of Hyopsodus N OR M Ml L W 2 2 2.5-2.7 2.6 3.0-3.2 3.1 P3 L Wtrig Wtal 2.6 1.7 1.8 P4 L Wtrig Wtal 3.2 2.3 2.4 Mj L Wtrig Wtal 3.7 3.0 2.9 his (1962, p. 64) later material from the New Fork Tongue showed H. wortmani to be more abundant than H. miticulus by a factor of 10: 6 in a small collection. The variations in proportions between Gazin's New Fork Tongue collection and mine are probably due primarily to small collection bias. The single lower molar of H. wortmani, PM 15519, does not have a metastylid as noted in H. miticulus, but the small sample reduces the significance of the observation. Hyopsodus minusculus Leidy, 1873. Plate Xllb, c. Material— Fault: 46 (Jaws: UW 1526, RMi-M.; UW 1569, LP3-P4; PM 15008, LP4, M2-M3), UW 1322, 1523, 1525, 1528, 1531-2, 1534, 1536-7, 1554, 1563-4, 1719, 1722, PM 15029, 15054, 15271-8, 15280-3, 15312, 15560, 15642, 15694, 15748, 15753, 15755, 15758, 15760, 15762-3, 15765, 15938, 21052, 21223. White Hills: 4 PM 15298, 15702, 15786-7. Hawk: 32 (Jaws: PM 15767, RM2-M3; PM 15775*, RP4-M2; FM 15780*, LP^-MO, PM 15284-97, 15297, 15313, 15766, 15769-70, 15772-4, 15776-8, 15781-2, 15784-5, 21099. Tree Road: 4 PM 15794-5, 15796, 15732. Wash: 3 PM 15309, 15316, 15788. Fish Hill: 3 PM 15790-2. Little White Butte: 1 PM 15300. 1375#8: 1 PM 15789. Green: 17 PM 15530, 15651-3, 15799, 15800-4, 21203, 21210-2, 21216, 21218, 21220. Discussion. — Hyopsodus minusculus is the smaller of the two early Bridgerian species, approximating H. wortmani of the late Wasatchian in size. It is virtually ubiquitous in the lower Bridger Formation collections in the New Fork-Big Sandy area. The lower PLATE XII. Condylarths. All specimens illustrated as stereopairs. The line beside the left member of each pair serves as the scale: for a through d it represents 1 mm., and for e and f it represents 5 mm. a. Hyopsodus worimani, PM 15519, RMi. b. Hyopsodus mintisculus, PM 15775, RMj-M.i. c. Hyopsodus minusculus, PM 15780, LP«-M'. d. Hyopsodus paulus, PM 15308, LM,. e. Meniscoiherium chamense, PM 15353, LPj-M,. f. Meniscotherium chamense, PM 15307, RP«-M'. 181 132 FIELDIANA: GEOLOGY, VOLUME 29 TABLE 46. Measurements in millimeters and statistics of teeth of Hyopsodus minusculus. N OR M SD M» M2 Mi-2 M' P4 Ml M, M, molars have the metastylid noted in H. miticulus. This lower Bridger species also shows the development of an entostylid on the anterior face of the entoconid, not seen in the Wasatchian material. Speci- mens from Green locality in the Cathedral Bluffs Tongue lack this small cuspule. The Cathedral Bluffs Tongue material differs from the Wasatchian H. wortmani, though, in having a metastylid. Hyopsodus paulus Leidy, 1870. Plate Xlld. Material— Fault: 1 UW 1745. Wash: 1 PM 15308*. Discussion. — Hyopsodus paulus, poorly represented in the study collection, is a larger, more robust species than H. minusculus from the same level. The single lower molar, PM 15308, has a small metastylid and no entostylid. The frequency of occurrence of this species is just about the op- posite of that noted by Gazin (1968, pp. 24-26) in his large Bridger B surface collection from the southern margin of the Green River Basin. There the Hyopsodus sample is made up primarily of H. paulus. Farther north, near the junction of Ham's Fork and Black's Fork, H. paulus and H. minusculus are about equally abun- L 3 2.2-2.8 2.53 W 3 2.9-3.2 3.0 L 7 2.0-2.7 2.47 ±.09 .23 ±.06 9.47 ±2.53 W 7 3.5-4.1 3.87 ±.07 .19±.05 4.96±1.33 L 19 2.6-3.7 3.26 ±.07 .29 ±,05 8.96±1.45 W 19 3.3-5.0 4.06±.ll .46 ±.07 11.38±1.85 L 25 2.3-4.0 3.43 ±.06 .28 ±.04 8.10±1.14 W 24 3.7-5.0 4.38±.08 .40 ±.06 9.22±1.33 L 4 3.5-3.6 3.58 W 3 4.2-4.5 4.37 L 16 2.7-3.3 3.01 ±.05 .20 ±.04 6.58±1.16 W 16 3.5-4.5 4.08 ±.08 .30 ±.05 7.37 ±1.30 L 2 2.7 W 2 2.0 L 9 3.2-3.6 3.40±.05 .14±.03 4.18±0.98 Wtrig 9 2.4-2.7 2.51 ±.04 .12±.03 4.66±1.10 Wtal 9 2.5-2.9 2.68 ±.04 .13±.03 4.86±1.15 L 13 3.2-4.0 3.49 ±.06 .23 ±.04 6.53 ±1.28 Wtrig 13 2.3-3.0 2.71 ±.06 .21 ±.04 7.75±1.52 Wtal 13 2.4-3.0 2.72 ±.05 .19±.04 7.06±1.38 L 12 3.4-4.2 3.73 ±.07 .24 ±.05 6.41 ±1.31 Wtrig 10 2.3-3.5 2.92 ±.03 .11 ±.02 3.80 ±0.85 Wtal 10 2.5-3.4 2.91 ±.08 .25±.06 8.49±1.90 L 6 3.6-4.4 4.02±.ll .26 ±.08 6.57±1.90 Wtrig 6 2.2-3.0 2.62±.ll .26 ±.08 10.00 ±2.89 Wtal 6 1.9-2.6 2.27±.09 .22 ±.06 9.78±2.83 WEST: NEW FORK-BIG SANDY AREA 183 TABLE 47. Measurements in millimeters of teeth of Hyopsodus paulus. UW 1745 PM 15308 M» Length 3.7 Width 5.2 Ml Length 4.2 Width Trigonid 2.9 Width talonid 3.0 dant. In the New Fork-Big Sandy area, at the same faunal level much farther north, the smaller species is much more abundant than the larger H. paulus. Family Meniscotheriidae Cope, 1882 Subfamily Meniscotheriinae Cope, 1882 Meniscotherium Cope, 1874 Gazin (1965b) reduced the number of valid species of Meni- scotherium to three (two of which are present in the study collection). He pointed out the apparent ecologic sensitivity of Meniscotherium; this reduces the value of the genus as a biostratigraphic indicator. Meniscotherium chamense Cope, 1884. Plate Xlle, f. Mafmo/.— Steele Butte Breaks: 4 (Jaw: PM 15307*, RP<-M=, LM'-M-), PM 15487 9. East Fork Rim: 17 (Jaws: PM 15472, LP', RM'; PM 15473, LM^ R&LM2; PM 15475, RM'-M-, LM'), PM 15302-4. 15317, 15474, 15476-81, 15483-4, 15586. Blue Rim: 12 (Jaws: PM 15391, LC, P,-Mj; PM 15399, RMi- M,), PM 15388-9, 15394, 15503, 15505 6, 15611-14. Piney Cutoff: 1 PM 15352. Blue Saddle: 3 (Jaw: PM 15500, RM,, LM,, LM»), PM 15499, 15635. Unnamed: 10 (Jaw: PM 15353*, LPj-Ma), PM 15359, 15490-7 Two Buttes: 1 (Jaw: PM 15501, LM'-M»). Twnf-E: 1 PM 15633. Twnf-D: 2 PM 15630, 15632. Discussion. — Meniscotherium chamense is an abundant species in the western facies of New Fork Tongue, and is also common in the arkosic facies. It is the moderate-sized species of the genus, and ranges from middle to late Wasatchian. Like all species of Meni- scotherium, it is not known to extend into the Bridgerian. 134 FIELDIANA: GEOLOGY, VOLUME 29 TABLE 48. Measurements in millimeters and statistics of teeth of Meniscotherium chamense. N OR M SD M' M'- M' P- P3 P4 M, M. M,-., M3 Meniscotherium robustum Thorpe, 1920. Plate Xllla. Ma^gna/.— East Fork Rim: 2 (Jaw: PM 15482, R&LP4-M1), PM 15486. Blue Rim: 2 PM 15504, 15396. Piney Cutoff: 3 (Jaws: PM 15350*, LM1-M3; PM 15351, RP3-P4, LM1-2; PM 15502, LP^-MO. Blue Saddle: 1 PM 15365. Discussion. — This species is less abundant than M. chamense, being represented by only eight specimens. They are rather small for M. robustum, but the size-frequency distribution for all speci- mens of Meniscotherium shows two definite groups, with the larger designated as M. robustum. The occurrence of M. robustum in the New Fork Tongue extends the range of the species upward. Gazin (1962, p. 68) noted the pres- ence of M. robustum only in beds below the Tipton and Fontenelle Tongues of the Green River Formation. L 2 5.9- 6.0 5.95 W 2 5.9- 6.7 6.30 L 4 6.6- 7.5 6.95 W 4 7.9- 8.9 8.50 L 6 7.5- 8.9 8.27±.20 .48±.14 5.76±1.66 W 4 8.0-11.0 9.92 L 2 9.0- 9.6 9.30 W 1 10.4 L 6 8.2- 9.5 9.00±.22 .54±.16 6.06±1.75 W 3 10.0-10.9 10.57 L 1 5.1 W 1 3.5 L 2 5.9- 6.0 5.95 Wtrig 2 3.2- 3.5 3.35 Wtal 2 3.9 L 3 7.1- 7.4 7.27 Wtrig 3 4.5- 5.1 4.83 Wtal 3 5.2- 5.7 5.50 L 10 7.5- 8.1 7.81 ±.06 .19±.04 2.47±0.55 Wtrig 10 4.6- 6.5 5.38 d=. 15 .47±.10 8.75±1.96 Wtal 10 5.0- 7.0 5.86±.16 .51i.ll 8.67±1.94 L 5 8.2- 9.3 8.82 Wtrig 5 4.6- 6.9 5.92 Wtal L Wtrig 7 5.4- 6.9 6.33±.19 .50±.13 7.91 ±2.11 1 5.9 Wtal L 3 9.1- 9.9 9.53 Wtrig 3 5.3- 6.2 5.70 Wtal 3 5.0- 5.6 5.27 L 2 7.5- 8.0 7.75 W •) 8.8- 9.2 9.00 L 1 9.7 W 1 10.6 L 1 9.8 W 1 12.0 L 1 6.5 W 1 4.0 L 2 8.0- 8.8 8.40 Wtrig 2 5.3- 5.4 5.35 Wtal 1 5.9 L 3 9.4-10.0 9.67 Wtrig 3 5.9- 6.2 6.03 Wtal 3 6.1- 6.4 6.23 L •> 10.0 Wtrig 6.2- 7.0 6.60 Wtal 2 6.4- 6.9 6.65 L 1 11.0 Wtrig 1 6.0 Wtal 1 5.7 WEST: NEW FORK-BIG SANDY AREA 185 TABLE 49. Measurements in millimeters of teeth of M eniscolherium robuslnm. N OR M P* M> M* Pi P* M. M, M, Family Phenacodontidae Cope, 1881 Phenacodus Cope, 1873 The largest condylarth in the study collection is Phenacodus, represented by two species. Gazin's extensive collecting in both the western facies of the New Fork Tongue and the LaBarge level has produced no specimens of Phenacodus. and the genus has not been found in the post-Lost Cabin Cathedral Bluffs Tongue in the Wa- shakie Basin. West and Atkins (1970) reported the occurrence of P. primaevus in the upper Bridger Formation at Tabernacle Butte, so the genus is no longer restricted to Tiffanian and Wasatchian beds in TABLE 50. Measurements in millimeters of teeth of Phenacodus vortmani. N OR M M* M* M. M, M,-, M, L 8.1 W 11.2 L 7.0 W 9.3 L 7.3 Wtrig 5.7 Wtal 6.3 L 7.6 Wtrig Wtel 6.9 7.0 L 2 7.6-7.8 7.70 Wtrig 3 5.8-6.7 6.40 Wtal 2 6.4-7.0 6.70 L 1 8.3 Wtrig WuT 1 6.4 1 5.5 PLATE XIII. Condylarths and perissodactyl. All specimens illustrated as stereopairs. The line beside the left member of each pair represents 5 mm. a. Meniscotherium robustum, PM 15350, LM1-M3. b. Phenacodus vortmani, PM 15956, RM^M^. c. Phenacodus vortmani, PM 15510, RM1-M3. d. Phenacodus primaevus, PM 15507, RM'M^M^ e. Hyracotherium vasacciense, PM 15447, LP3-M3. 136 WEST: NEW FORK-BIG SANDY AREA 187 North America. Guthrie (pers. comm.. 1970) reports the same two species in the type area of the Lost Cabin fauna that I have found in the Lost Cabin level of the New Fork-Big Sandy area. Phenacodus vortmani Cope, 1880. Plate Xlllb, c. Materia/.— Steele Butte Breaks: 2 (Jaw: PM 15510*, RMi-M,), PM 15605. Blue Rim: 2 PM 15508-9. Two Buttes: 1 (Jaw: PM 15956*, RM'-M^). Discussion. — Phenacodus vortmani is represented by five speci- mens, which fall into the size range of P. vortmani from the Lost Cabin as tabulated by Robinson (1966, pp. 53-54). The species ranges through the Wasatch ian. Phenacodus primaevus Cope, 1873. Plate Xllld. Ma/ma/.— Two Buttes: 1 (Jaw: PM 15507*, RM», M^, M'). Discussion. — The single specimen of Phenacodus primaevus is about 25 per cent larger than the P. vortmani material discussed above. These worn teeth are the first evidence of P. primaevus in the New Fork Tongue. TABLE 51. Measurements in millimeters of teeth of Phenacodus •primaevus, PM 15507. pj M» M» Length 11.0 10.6 10.8 Width 8.0 14.0 12.3 Phenacodus sp. Materia/.— Piney Cutoff: 1 PM 15575. Discussion. — This fragmental upper molar displays the rounded shape and low cusps of Phenacodus, but it is too incomplete for spe- cific assignment. It is large, and is probably P. primaevus. Order Perissodactyla Suborder Hippomorpha Wood, 1937 Superfamily Equoidea Gray, 1821 Family Equidae Gray 1821 Hyracotherium Owen, 1840 Hyracotherium flourished during the Wasatchian and evolved into the Bridgerian Orohippus. Late Wasatchian Hyracotherium is char- acterized by incipient molarization of the third and fourth pre- 138 FIELDIANA: GEOLOGY, VOLUME 29 molars, lophodont upper molars with conules still prominent, and the lack of a mesostyle. Kitts (1956) reviewed Hyracotherium from North America, leav- ing only H. angustidens, H. vasacciense, and H. craspedotum as valid species. Guthrie (1967, pp. 41-42) revived the species H. index for small individuals from the Lysite zone. Kitts assigned statistical subspecies to H. vasacciense, but the systematics of Hyracotherium discussed here will consider only species. Hyracotherium vasacciense Cope, 1872. Plates Xllle, XlVa. Material— Steele Butte Breaks: 30 PM 15206, 15206a, 15207-9 15211-9, 15319, 15403-6, 15408-13, 15430, 15471, 15594, 15598-9. East Fork Rim.: 32 (Jaws: PM 15417, LP2, P4; PM 15454, RP2, Ms), PM 15238, 15240, 15247, 15250, 15252, 15415-6, 15419, 15441, 15443-6, 15448-53, 15455-6, 15458, 15485, 15576, 15579-83, 15585. TABLE 52. Measurements in millimeters and statistics of teeth of Hyracotherium vasacciense. N OR M SD V pj P* Ml M* M>-2 M» P4 Ml M2 Mj-2 M3 L 1 6.5 W 1 7.4 L 5 6.9- 7.5 7.32 W 5 7.8- 8.8 8.26 L 17 7.6- 8.4 8.00 ±.06 .24 ±.04 2.95±0.51 W 16 8.3-10.5 9.26 ±.14 .58±.10 6.30±1.11 L 12 7.4- 9.1 8.33 ±.14 .47±.10 5.63±1.15 W 11 9.5-11.3 10.22±.15 .49±.10 4.79 ±1.02 L 2 8.4- 8.9 8.65 W 1 10.2 L 16 6.8- 8.7 7.87±.13 .52 ±.09 6.60±1.17 W 16 7.9-10.2 9.18±.17 .68±.12 7.46 ±1.32 L 10 5.9- 7.9 6.98 ±.20 .65±.14 9.33 ±2.09 Wtrig 7 3.6- 5.0 4.34±.19 .51 ±.14 11.75±3.14 Wtal 8 4.1- 4.9 4.50±.17 .47±.12 10.36±2.59 L 9 6.8- 8.5 7.63 ±.22 .65±.15 8.57 ±2.02 Wtrig 8 3.9- 5.7 4.92 ±.21 .59±.15 11.91 ±2.98 Wtal 7 4.6- 6.0 5.14±.25 .67±.18 13.02 ±3.48 L 7 7.1- 9.0 8.11 ±.28 .75±.20 9.25±2.47 Wtrig 7 4.7- 6.1 5.34 ±.18 .49±.13 9.23 ±2.47 Wtal 5 4.8- 6.1 5.38 L 2 8.5- 9.3 8.9 Wtrig 2 6.0- 6.4 6.2 Wtal 2 6.6- 7.1 6.85 L 2 8.3- 8.5 8.4 Wtrig 2 5.6- 6.2 5.9 Wtal 2 5.6- 6.4 6.0 L 6 10.6-12.3 11.42 ±.24 .58±.17 5.12±1.48 Wtrig 6 5.5- 6.1 5.83 ±.09 .23 ±.07 3.98±1.15 Wtal 6 5.1- 6.0 5.62±.15 .37±.ll 6.60±1.91 I * X. ^ . PLATE XIV. Perissodactyls. All specimens illustrated as stereopairs. The line beside the left member of each pair represents 5 mm. a. Hyracotherium vasacciense, PM 15385, RP'-M'. b. Hyracotherium craspedolum, PM 15407, LP*, c. Orohippus cf. O. pumilus, UW 1316, RP*-M». d. Lambdoiherium popoagicum, PM 15201, LPj-Ma. e. Lambdoiherium popoagicum, PM 15434, LM'. 139 140 FIELDIANA: GEOLOGY, VOLUME 29 Blue Rim: 9 (Jaws: PM 15385*, RP3-M3, LP^-M^; PM 15392 RM^-M''), PM 15398, 15400, 15615-6, 15618-9, 15634. Piney Cutoff: 3 PM 15347, 15349, 15628. Unnamed: 3 PM 15355-6, 15498. Two Buttes: 16 (Jaws: PM 15371, RMS LM-'; PM 15447*, LP,,- Ms), PM 15367-70, 15373, 15376, 15378-81, 15517, 15533, 15622-3. Twnf-C: (Jaw: PM 15360, LP3-P4, RM^), PM 15362-3. Discussion. — Hyracotherium vasacciense, a middle and late Wa- satchian species, is by far the more abundant of the two species pres- ent in the study collection. Differentiation between this species and H. craspedotum is made essentially on the basis of size, with atten- tion devoted to the molarization of P'' when it can be positively associated. Hyracotherium craspedotum Cope, 1880. Plate XlVb. Material— Stee\e Butte Breaks: 6 PM 15204-5, 15210, 15229, 15407*, 15414. East Fork Rim: 7 PM 15239, 15418, 15436, 15442, 15457, 15578, 15584. Blue Saddle: 1PM 15366. Two Buttes: 1 (Jaw: PM 15384, RP4-M1). Discussion. — Hyracotherium craspedotum is about 20 per cent larger than H. vasacciense and is not nearly so well represented in the study collection. Gazin (1962, pp. 73-75) recorded both species from the New Fork Tongue, and found H. vasacciense to be more abundant by a factor of 3:1. H. craspedotum is more common in the arkosic facies of the New Fork Tongue than in the western facies, although only 15 specimens have been found, and it is far outnum- bered by H. vasacciense in both units. Orohippus Marsh, 1872 Orohippus cf. O. pumilus (Marsh, 1871). Plate XIVc. Ma^maZ.— Fault: 9 UW 1561-2, 1316*, P9, PM 15254-5, 15258, 15873-4. White Hills: 1 PM 15259. Hawk: 1 PM 15878. Tree Road: 2 PM 15879, 15881. Green: 2 PM 15344-5. WEST: NEW FORK-BIG SANDY AREA 141 TABLE 53. Measurements in millimeters of teeth of Hyracotkerium craspedotum P* L W M» L W M>-» L W M» L W Pi L Wtrig Wtel P« L Wtrig Wtel N OR M 5 8.0- 8.7 8.42 5 8.9-10.7 10.2 1 9.9 1 12.1 1 9.5 1 12.5 1 9.6 1 11.5 2 8.5- 8.6 8.55 2 5.0- 6.4 5.7 2 5.4- 5.5 5.45 1 8.7 1 5.8 1 6.5 Discussion. — Orohippus is the Bridgerian descendent of Hyra- cotherium. It is much less common in the early Bridgerian than Hyracotkerium is in the late Wasatchian. Progressive features that distinguish Orohippus from Hyracotkerium, considering, of course, that the two genera are portions of a continuum, include the presence of a mesostyle on the upper molars and a hypocone on P' and P* of Orohippus. Kitts (1957) reviewed Orohippus and reduced the 12 named species to five valid ones, one of which is present in the study collection. Most of the equid material from the various Bridgerian localities satisfies the criteria listed above for separation from Hyracotkerium. A P^ with a good hypocone is shown on PM 15258, and a molar with TABLE 54. Measurements in millimeters of teeth of Orohippus cf.^ N OR M P< L 3 6.4-6.9 6.6 W 3 7.0-7.5 7.3 M' L 4 7.0-7.5 7.32 W 4 6.7-8.1 7.82 M* L 2 7.5-7.6 7.55 W 2 8.7-9.7 9.2 M«-» L 1 7.8 W 1 8.0 M» L 2 7.0-8.5 7.75 W 2 7.0-7.8 7.4 P, L 2 6.0-7.0 6.5 Wtrig Wtel 2 3.9-4.0 3.95 2 3.8-4.0 3.9 P4 L 2 6.2-7.0 6.6 Wtrig 2 4.5-4.6 4.55 Wtai 2 4.5 M, L Wtrig Wtel 7.1 4.9 5.2 M, L Wtrig Wtel 11.0 5.0 4.5 142 FIELDIANA: GEOLOGY, VOLUME 29 a mesostyle by PM 15344. The mesostyles are poorly developed on most of these specimens, and only barely visible on some. However, this is a feature which is progressively better developed through the Bridgerian, and individuals occurring higher in the Bridger Forma- tion show it more prominently. An inspection of the Orohippus material at the American Museum of Natural History showed the Bridger B specimens to be variable in this feature, while specimens from the Bridger C and D have it well developed almost invariably. TABLE 55. Measurements in millimeters and statistics of teeth of Lambdotherium popoagicum. p4 M* Mi-2 M^ P4 M, M, Ml-, M, N OR M SD L W 3 2 8.8- 9.5 11.4-12.0 9.13 11.7 L W 10 10 11.1-13.5 13.0-16.8 12.1 ±.26 15.12rfc.44 .82±.18 1.38±.31 6.74 ±1.51 9.09 ±2.03 L W 3 2 10.3-12.5 13.8-15.0 11.53 14.4 L W 10 10 10.2-11.8 14.0-16.0 11.28±.15 14.62±.19 .47±.10 .60±.13 4.19±0.94 4.08±0.91 L Wtrig Wtal 4 4 3 8.6- 9.9 4.6- 5.8 4.8- 6.6 9.12 5.12 5.50 L Wtrig Wtal 8 8 8 8.2-10.8 5.8- 7.0 5.9- 7.0 9.42±.18 6.31 ±.11 6.50±.10 .73±.26 .43±.15 .41 ±.14 7.76±1.94 6.80±1.70 6.37±1.59 L Wtrig Wtal 7 7 7 10.9-14.5 6.0-10.0 7.2-10.0 12.00±.24 7.87±.50 8.07±.36 .64±.17 1.32±.35 .96±.26 5.29±1.41 16.77 ±4.48 11.88±3.18 L Wtrig Wtal 6 6 6 11.4-12.6 8.1- 8.7 7.8- 8.9 12.03 ±.20 8.35±.12 8.27±.16 .50±.14 .29 ±.08 .38±.ll 4.16±1.20 3.42±0.99 4.56±1.32 L Wtrig Wtal 3 3 2 11.2-18.0 7.5- 8.5 7.8- 8.6 11.9 8.1 8.2 L Wtrig Wtal 10 10 11 14.3-18.0 7.6- 9.3 7.1- 8.5 6.22±.36 8.60±.16 7.80±.16 1.13±.25 .51±.ll .52±.ll 6.97±1.56 5.98±1.34 6.73±1.43 Superfamily Brontotherioidea Hay, 1902 Family Brontotheriidae Marsh, 1873 Subfamily Lambdotheriinae Hay, 1902 Lambdotherium Cope, 1880 Lambdotherium popoagicum (Cope, 1880). Plate XlVd, e. Material— Steele Butte Breaks: 35 (Jaws: PM 15201*, LP2-M3; PM 15203, RP4, M2-M3, LM3), PM 15202, 15220-8, 15230-3, 15402, 15420-9, 15431-3, 15466, 15595-7, 15600. WEST: NEW FORK-BIG SANDY AREA 143 East Fork Rim: 22 (Jaws: PM 15241. RP4-M,; PM 15439, R& LP3-M,; PM 15463. RP3-P4), PM 15243-6, 15249, 15251, 15253, 15434*, 15435. 15437-8, 15440, 15459 62, 15464 5, 21230. Blue Rim: 7 PM 15386. 15390. 15393. 15395. 15397. 15401. 15617. Piney Cutoff: 1 PM 15348. Unnamed: 1 PM 15354. Two Buttes: 5 (Jaws: PM 15382. RMi-Mz; PM 15383, R&LM3), PM 15372. 15377. 15620. Twnf-C: 1 PM 15361. Discussion. Lamhdotherium popoagicum is a medium-sized cur- sorial perissodactyl, more generalized than its larger, horned Oligo- cene successors. It is as abundant as Hyracotherium in the later VVasatchian. and disappears without persisting into the early Brid- gerian fauna. Neither direct ancestor nor descendent are known. Subfamily Palaeosyopinae Steinman and Doderlein, 1890 Eotitanops Osborn, 1907 Eotitanops borealis (Cope, 1880). Plate XVa. Material.— East Fork Rim: 1 PM 15609*. Discussion. — Eotitanops is known from throughout the Lost Cabin faunal zone, although only one individual was found in the New Fork-Big Sandy area. The W-shaped ectoloph and conical in- ternal cusps are indicative of its position in the titanothere lineage. The protoconule is developed, but there is no trace of a metaconule. Since the material in the study collection consists of only two upper molars, both of which are too small to be Palaeosyops (Robinson. 1966, p. 66). there is no way to compare the lower molars with Robinson's or Osborn's (1929, p. 290) descriptions. TABLE 56. Measurements in millimeters of teeth of Eotilanopn borealis, PM 15609. M' M' Length 18.8 21.9 Width 21.1 24.0 Palaeosyops Leidy, 1870 Palaeosyops fontinalis Cope, 1882. Plate XVb. Material.— FauM: 1 UW PIO. Hawk: 1 PM 15876*. 144 FIELDIANA: GEOLOGY, VOLUME 29 Discussion. — Palaeosyops of the early Bridgerian is recognized as a genus separate from, and probably derived from, Eotitanops. It is morphologically similar to E. horealis, differing only in the larger size. The M- of P. fontinalis in the study collection, PM 15876, is 27.0 mm. long, half again as large as E. horealis. Robinson (1966, p. 66) recognized the similarity, although he differentiated the two genera, as I do here, with reservations. Gazin pointed out the arbitrariness of the generic distinction when in 1952 (p. 76) he sug- gested the assignment of a Washakie Basin Cathedral Bluffs palaeo- syopine to Eotitanops based on his interpretation of a Wasatchian aspect to the rest of the fauna from the locality. Suborder Ceratomorpha Wood, 1937 Superfamily Tapiroidea Gill, 1872 Family Helaletidae Osborn, 1892 Radinsky (1963, 1967) has recently revised the family, and his suggestions on the systematics are followed here. Heptodon Cope, 1882 Heptodon is the characteristic helaletid tapiroid of the middle to late Wasatchian. It occurs in the Lost Cabin equivalent faunas in the study collection, represented by two species, but is not persistent into the known Bridgerian faunas. Heptodon posticus (Cope, 1882). Plate XVc, d. Material.— S,tee\e Butte Breaks: 3 PM 15234, 15235*, 15467. East Fork Rim: 1 PM 15469*. Discussion. — Heptodon posticus is the largest species of Heptodon. It is much less common than H. calciculus in the Wind River Basin Lost Cabin zone; the single specimen known from the Bighorn Basin Lost Cabin equivalent fauna is H. posticus (Radinsky, 1963, p. 38). Gazin has not found any H. posticus in his New Fork Tongue locali- ties and all four of the specimens in the study collection are from the arkosic facies of the New Fork Tongue. Heptodon calciculus (Cope, 1880). Plate XVe. Ma^ma^.— Steele Butte Breaks: 2 PM 15236, 15470. East Fork Rim: 3 (Jaw: PM 15468*, RP3-M1), PM 15242, 15248. Two Buttes: 1 PM 15621. c PLATE XV. Perissodactyls. All specimens illustrated as stereopairs. The line beside the left member of each pair serves as the scale: for a it represents 10 mm., and for b through f it represents 5 mm. a. Eolitanops borealis, PM 15609, LM». b. Paloeosyopn fontinallf, PM 15876, LM*. c. Heptodon posticus, PM 15235, RP«M;. d. Heptodon poKticua, PM 15469, LM1.M3. e. Heptodon calculus, PM 15468, RP,-M,. f. Hyrachyus modestus, PM 15261, LP«M,. 145 146 FIELDIANA: GEOLOGY, VOLUME 29 TABLE 57. Measurements in millimeters of teeth of Heptodon posticus. N OR M M' L 1 11.0 W 1 14.0 Pa L 1 8.4 Wtrig 1 5.0 Wtal 1 5.0 P. L 1 9.3 Wtrig 1 6.2 Wtal 1 6.4 M, L Wtrig 1 9.0 Wtal Ms L 2 13.3-14.5 13.9 Wtrig 2 8.0- 9.0 8.5 Wtal 1 8.3 M.-2 L Wtrig 1 8.0 Wtal Ma L 1 16.4 Wtrig 1 8.0 Wtal 1 8.1 Discussion. — Heptodon calciculus, the smaller species of Heptodon present in the study collection, is also uncommon. Gazin (1962, pp. 78-80) found it in the New Fork Tongue, calling it H. ventorum, a species which Radinsky (1963, p. 34) synonymized with H. calciculus. Gazin (1962, p. 79) proposed reference of some larger individuals from his New Fork Tongue collection to H. ventorum mut. posticus, but the material in my collection allows a clear differentiation be- tween H. posticus and H. calciculus in the fauna from the western facies of the New Fork Tongue. TABLE 58. Measurements in millimeters of teeth of Heptodon calciculus. N OR M M» L W 10.0 11.5 Mi-» L W 10.0 11.0 P3 L Wtrig Wtal 6.9 4.4 4.2 P4 L Wtrig Wtal 7.1 4.9 4.8 Ml L Wtrig Wtal 8.5 5.8 5.9 M,.2 L Wtrig Wtal 11.5 7.2 7.2 Ma L 2 14.6-14.8 14.7 Wtrig 2 7.3- 7.9 7.6 Wtal 2 7.1- 7.2 7.15 WEST: NEW FORK-BIG SANDY AREA 147 Subfamily Hyrachyinae Osborn, 1892 Radinsky (1967). as a part of his re-examination of the early Tertiary perissodactyls, recently reviewed the genus Hyrachyus from North America and Europe. He (1967. p. 21) reduced the Hyra- chyidae to a subfamily and transferred it from the Rhinocerotoidea to the Tapiroidea, placing it in the Helaletidae. He felt that the hyrachyines are traceable to and not much different from the earliest Heptodon (early or middle Wasatchian), and that Hyrachyus thus belongs in the tapiroid line. Hyrachyus Leidy, 1871 Hyrachyus modestus (Leidy, 1871). Plates XVf, XVI a. Material.— F3iu\t: 1 PM 15872. Hawk: 1 (Skull: PM 15261*, LP--P', RP=-P\ LP,, P4, M2). Sandstone Point: 1 (Jaw: PM 15260, LM'-M-). Green: 2 PM 15346, 15569. Steele Butte Breaks: 1 PM 15237. Discussion. — This is the largest non-brontotheriid perissodactyl present in the study collection. Aside from a moderately well-pre- served skull from Hawk locality (PM 15261), it is represented only by fragmentary teeth. When the ectoloph of an upper molar is present, as in PM 15260, Hyrachyus is readily identifiable at the generic level. TABLE 59. Measurements in millimeters of teeth of Hyrachyus m N OR M P» L 2 10.5-12.7 11.6 W 2 16.2 P* L W 15.5 18.7 M> L W 19.8-20.0 18.0 19.9 M« L W 22.5-25.0 23.3 23.75 M'-« L W 15.8 22.0 M* L W 19.0 22.8 P. L Wtrte Wtal 12.5 8.0 8.2 P4 L Wtrig WuT 14.0 9.7 9.5 M,., L Wtrig Wtal 20.7 12.7 12.5 148 FIELDIANA: GEOLOGY, VOLUME 29 Radinsky's (1967) study stressed that the only valid criterion for separation of Bridgerian species of Hyrachyus is size, and that in the late Wasatchian H. modestus is the only species present. H. modestus is present in both Wasatchian and Bridgerian faunas in the study collection. The skull is large, with an M^-M^ length of 61.3 mm. Radinsky (1967, p. 3) mentioned two unusually large specimens of H. modestus with M1-M3 lengths of 63 and 65 mm., so PM 15261 falls readily within the observed range of this species. Indeterminate Tapiroid Ma^maZ.— Fault: 1 PM 15257. Discussion. — This fragmental tooth has the lophodont structure with transverse crests typical of tapiroids. It may be a representa- tive of the Bridgerian Helaletes, but the material is inadequate for even a familial identification. The tooth has an estimated length of 15 mm. and a talonid width of 6.7 mm. Order Artiodactyla Suborder Suiformes Jaeckel, 1911 Infraorder Palaeodonta Matthew, 1929 Family Dichobunidae Gill, 1872 Subfamily Diacodexinae sensu Gazin, 1955 Diacodexis Cope, 1882 Diacodexis cf. D. secans (Cope, 1881). Plate XVIb, c. Material— Y^^hite Hills: 1 PM 15706*. Steele Butte Breaks: 1 PM 15554. East Fork Rim: 1 PM 15556. Two Buttes: 2 PM 15557*, 15559. Twnf-H:l PM 15560. Discussion. — All the study collection upper Wasatch Diacodexis material is larger than the D. chacensis measured by Robinson (1966, p. 69), and falls close to the range of D. secans (op. cit., p. 70). The poor hypocone development and large conules on all the upper mo- lars are characteristic of Diacodexis. PM 15706, from White Hills locality, is the only specimen from the lower Bridger Formation assigned to Diacodexis. There is a close similarity to the late Wasatchian D. secans specimens. This occur- PLATE XVI. Perisaodactyl and artiodactyls. All specimens illustrated as stereopairs. The line beside the left member of each pair serves as the scale: for a it represents the length of 10 mm., for b through d and fH it represents 5 mm., and for e, f, and h it represents 1 mm. a. Hyrachyus modeittu«, PM 15261, RM'-M'. b. Diacodexis cf. D. secans, PM 15557, LM'. c. Diacodexis cf. D. secana, PM 15706, LMi-j. d. Antiacodon pygmaeus, PM 15655, RM'. e. Antiacodon pyg- maeus, PM 15676, LMi-j. f. Microsm sp., PM 15012, LMj. g. Helohyus cf. H. plicodon, PM 15875, RM,. h. Artiodactyl, incertae sedis, PM 15847, RP*. 149 L 1 4.1 W 1 5.1 L 2 4.2-4.5 4.35 W 2 5.6-5.8 5.7 L 2 4.6-4.7 4.65 W 2 5.2-6.0 5.6 L 1 4.5 Wtrig 1 3.9 Wtal 1 3.7 150 FIELDIANA: GEOLOGY, VOLUME 29 TABLE 60. Measurements in millimeters of teeth of Diacodexis cf. D. secans. N OR M M» M» M» rence is stratigraphically high for Diacodexis, as it is primarily a Wasatchian genus. Subfamily Homacodontinae Peterson, 1919 Antiacodon Marsh, 1872 Antiacodon pygmaeus (Cope, 1872). Plate XVId, e. Mafma^.— Fault: 16 (Jaw: UW 1519, LP4-M1), UW PI, 1516, 1520, 1545, 1556, 1721, PM 15279, 15330, 15332, 15655*, 15657, 15659, 15676*, 15691, 15693. White Hills: 2 PM 15325, 15701. Hawk: 3 PM 15711, 15768, 15771. Green: 1 PM 15798. Discussion. — This is the only artiodactyl in the study collection that is frequently encountered, and even it does not occur at all the well-represented localities. It is distinctive because of the reduced metaconid, close to the paraconid, the presence of a small hypocone TABLE 61. Measurements in millimeters and statistics of teeth of Antiacodon pygmaeus. N OR M SD V Ml L 2 4.3-4.5 4.4 W 2 5.8-5.9 5.85 M^ L 3 4.5-4.7 4.6 W 3 5.8-6.3 6.03 M3 L 5 4.1-4.5 4.3 W 5 4.4-6.0 5.24 P4 L 1 5.0 W 1 3.6 M, L 6 4.5-5.1 4.73±.08 .20±.06 4.11±1.19 Wtrig 5 2.7-3.4 3.1 Wtal 5 3.1-3.7 3.48 M.. L 4 4.7-4.9 4.82 Wtrig 4 3.1-3.6 3.38 Wtal 4 3.4-4.2 3.85 M3 L 2 5.2-5.3 5.25 Wtrig 2 3.3-3.5 3.4 Wtal 3 3.2-3.7 3.43 WEST: NEW FORK-BIG SANDY AREA 151 on M' and M-, and an incipient to small mesostyle on all the upper molars. The material in the study collection falls within the size range of Antiacodon pygmaeus from the Bridger Formation (Robin- son, 1966, p. 71), which is about 6 per cent smaller than the A. pygmaeus from the Huerfano B level, PM 15332 is a peculiar upper molar, as it shows a well-developed extra cuspule on the internal side of the protocone. Microsus Leidy, 1870 Microsus sp. Plate XV If. Material.— FsiuM: 1 PM 15012*. Discussio7i.~Th\s single lower third molar is referable to Bridger- ian Microsus on the basis of the lack of a paraconid and the relatively high cusps. It is larger than M. cuspidatus (Sinclair, 1914, pp. 288 289). Microsus is known too poorly for any further identification. The tooth is 3.7 mm. long, 2.4 mm. wide across the trigonid, and 2.0 mm. wide across the talonid. Subfamily Helohyinae Marsh, 1877 Helohyus Marsh, 1872 Ilelohyus cf. H. plicodon Marsh, 1872. Plate XVIg. Ma/erm/.— Fault: 1 PM 15871. White Hills: 1 PM 15875*. Discussion.— Two incomplete third lower molars form the sample of Helohyus cf. H. plicodon, a species known through the Bridgerian. Both are lacking the hypoconulid, but the area of breakage where the hypoconulid joined the main portion of the tooth is small, so pre- sumably the hypoconulid was also small. This, combined with the overall size and robustness of the tooth, suggests H. plicodon as the most reasonable assignment (Sinclair, 1914, pp. 281 283). TABLE 62. Measurements in millimeters of teeth of Helohyus cf. H, plicodon. PM 15871 PM 15875 M, Length 9.5 9.7 Trigonid Width 5.0 5.7 Talonid Width 5.0 5.5 Artiodactyl? incertae sedis. Plate XVIh. Ma^cnoZ.— Fault: 1 PM 15847*. Discussion. — This is a peculiar and interesting tooth, possibly referable to the Artiodactyla. It is probably a right P4, with a high 152 FIELDIANA: GEOLOGY, VOLUME 29 I protoconid and a lower metaconid. The paraconid is low and bicusped. The talonid is low and short, with a slight posterior crest. The tooth is 5.2 mm. long and 2.4 mm. wide. An additional possibility is that this specimen may be a somewhat aberrant premolar of Phenacodus, the condylarth genus recently re- ported from upper Bridger Formation beds at Tabernacle Butte (Westand Atkins, 1970). GEOCHRONOLOGY Table 63 provides a summary of the geochronologic positions of the various identified species from the New Fork-Big Sandy area. The lines indicate the known stratigraphic range of each species, and the x's indicate the horizons within the New Fork-Big Sandy area from which the species have been recovered. The Cathedral Bluffs materials from the Washakie and Great Divide Basins are not shown ; as pointed out in West (1969c) the precise identification of many of those specimens is uncertain. Nonetheless, Table 63, pp. 154-155, enables the reader to see readily the relationships between the New Fork-Big Sandy area faunas and the early and middle Eocene stan- dards. 153 WASATCHIAN BRIDGERIAN Groybull Lysite Lost Cabin Cathedral Bluffs Blacks Fork (?A, B) Twin Buttes (C.D) Peratherium cf. R innominatum f? marsupium Palaeictops pineyensis ^ Apatemys be/lulus Centetodon cf. C. pulcher Myolestes cf. M. dasypelix Scenopagus edenensis ^, S. priscus \ ] ^ Didelpfiodus alfidens ^, __ _. . .J Oxyoena forcipata ^, i j 1 Thinocyon cf. T. velox i X Didymictis alfidens i „ * Viverravus gracilis . ' — ^ — ! 1 Miacis Ictidens \ \ X Notharclus cf. N. nunienus \ \ i ^ 1 \ N. teneorosus \ 1 1 : X Smilodecles gracilis Onomys carferi X s/ 1 0. sheoi — X 1 1 Wcshckius insignis X ! Anoptomorphus aemulus X X Microsyops scottianus X M. elegans X X ^, Tillomys parvidens ' X Tcxymys lucoris X Knightomys cf. K. sen/or X Raromys deiicatus R eKcavatus ^, R wyomingensis X 154 WASATCHIAN BRIDGERIAN Groybull Lvsitu Lost Cothedrol '■^**' Cobin Bluffs 1 Black's Fbrk (?A.B) Twin Buttes (C.D) Rtitfroporamys hj0rfan«nsiS X (— ^ — R. tl«licotiSi:mu* X Pstudo'omus robust us X ' Esthonyt ocutidens X BathfCfi^s fissidtns X HyopSOduS miliculus X ! H, wcFtmon ^ i H. mirtuscuhjs X i^— X 1 H. poulus 1 — "" — 1 M«nscoif>e'njm chamense ^^ 1 H robustum ^, i Phtoocodus vortmani „ 1 ff primoems Hyncotherijm vcsocciens9 H. CrOSp*»rior«oiis X RokMosfOPS fontinolis X Haptodon posticus ^ H. COlCiCuluS ^ Hyrocfiyus modes tus X— . -^X— 1 Diocod0Mis ct. 0. seeofts ,, 1 X Aniiacodon p/gmotus X Hebhyus ef. H.plicodon 165 FAUNAL CORRELATIONS The intermontane basins of Wyoming, Colorado, and Utah con- tain a number of early and middle Eocene fossil-producing horizons. This period of time has been divided into a number of faunal zones: the early Eocene Wasatchian age includes the Graybull, Lysite, and Lost Cabin zones, and the middle Eocene Bridgerian age the Bridger A and B (Black's Fork) and Bridger C and D (Twin Buttes) zones. The late Wasatchian and early Bridgerian zones are of interest here. Figure 29 shows the presumed relationships between faunal levels in the New Fork-Big Sandy area and those in the above mentioned basins. Large animals are probably better than small ones for faunal cor- relations. First, they are more likely to range more extensively and to occupy available environments more rapidly than smaller animals, increasing the likelihood that they will be present in temporally equivalent localities in widely scattered areas. Secondly, due to their size and visibility, they are more frequently recovered, even in rather cursory prospecting. Smaller animals are badly under-represented or lacking in many surface collections because they are inconspicuous and are found often only by washing or quarrying. Larger forms, in- cluding perissodactyls, artiodactyls, condylarths, pantodonts, and dinoceratans form the primary basis for the faunal evaluation to fol- low, with evidence from the smaller mammals used when available. New Fork Tongue Late Wasatchian faunas are compared with the Wind River Basin Lost Cabin fauna, proposed by Sinclair and Granger (1911, pp. 105- 106). This fauna comes primarily from a relatively thin horizon, 40-50 ft. thick, about 200 ft. above the base of the Lost Cabin Member. Keefer (1965, pp. 69-70) presented partial measured sec- tions for the Lost Cabin Member of the Wind River Formation, giving it a firm stratigraphic status. The base of the Lost Cabin Member is placed at the level of the first occurrence of the primitive brontothere Lamhdotherium, the basis for the original description of 156 WEST: NEW FORK-BIG SANDY AREA 167 SOUTHERN a HKCSTFBN GBTFN RIVtR BASW NORTHEASTERN GREEN River BASIN WASHAKIE WIND RIVER MS*. BASIN BIGHORN BASIN HUERFANO BASIN o er.tf«*r CO Lipp*' Bi'tg*' iraiAatrf ii fauna % ,0.no s J i B'-dgrr B 'ouno LOmtf Bt'tf Fauna s 5 ? w ; Cotht^ol Biuttt CathtOrol Blullt TonQua fauna ? HUtrfOnp S Fauna « X * Ntw ferk ronju* rawM LOBorgt ytmb9r Nam fork Toitfa* Faunas 9 Dad Local Fauna Lesr Ca6>n Momtar Fauna Uffar WtllwOOd Fauna Hutrfano A Fouia Fauna Fig. 29. Relationships between faunal horizons of the New Fork-Big Sandy area and those of nearby productive basins. the unit as the "Lambdotherium beds," and presumably that genus did not survive the time represented by the Lost Cabin Member sediments. Other mammals characteristic of the Lost Cabin fauna include Eotitanops, Coryphodon, Bathyopsis fissidens, Phenacodus vortmani, P. primaevus, Meniscotherium chamense, Hyracotherium vasacciense, and Diacodexis. Most of these taxa did not persist into the Bridgerian. The late Wasatchian fauna from the New Fork-Big Sandy area (that found in the New Fork Tongue) is similar to the fauna from the Lost Cabin Member. Every taxon enumerated above is present in the arkosic facies, and only Coryphodon and Bathyopsis fissidens are missing from the fauna of the western facies. These two temporally equivalent facies show lithologic differences due to sediment prove- nance and minor environmental differences. Distinctions between their mammalian faunal compositions are shown in Figures 30 and 31. Coryphodon, the virtually ubiquitous pantodont of the Lost Cabin zone, is well represented in the arkosic facies (9 per cent of 88 individuals), while neither Gazin nor I have found it in the western New Fork Tongue western facies RODENTIA (?2) CONDYLARTHRA {?7) PRIMATES (3) TAENIODONTA (I) CARNIVORA (4) CREODONTA (3) ARTIODACTYLA (1) PERISSOOACTYLA (4) Fig. 30. Ordinal composition of the fauna collected from the various western facies of the New Fork Tongue localities in the New Fork-Big Sandy area. The number in parentheses indicates the number of species identified in each order. New Fork Tongue orkosic facies RODENTIA (?l) PRIMATES (3) TAENIODONTA (?l) .TILLODONTIA (I) CONDYLARTHRA (5) DINOCERATA (I) PANTODONTA (?l) CARNIVORA (5) CREODONTA (3) NSECTIVORA (I) ARTIODACTYLA (I) PERISSOOACTYLA (7) Fig. 31. Ordinal composition of the fauna collected from the two arkosic facies of the New Fork Tongue localities in the New Fork-Big Sandy area. The number in parentheses indicates the number of species identified in each order. 158 WEST: NEW FORK-BIG SANDY AREA 159 facies. It is such a large animal that, were it present, it would be difficult to miss, even if the remains were badly disarticulated and fragmented. Gazin (1962, p. 70) proposed that the absence of Coryphodon in the New Fork Tongue was due to its extinction at the end of the Fontenelle Tongue expansion of Lake Gosiute. The pres- ence of Coryphodon in the arkosic facies disproves that suggestion, and it is probable that the absence of Coryphodon to the west is due to ecological factoi-s. Gazin (1965, pp. 13-20) has discussed the en- vironmental sensitivity of Meniscotherium; the basic incompatibility of Meniscotherium and Phenacodus is also shown in the Lost Cabin equivalent faunas of the New Fork-Big Sandy area, as Menisco- therium is common while Phenacodus is quite rare. Most of the other differences between the faunules from the New Fork Tongue are probably due to small collection bias. Neither unit has yet produced a large number of specimens, so there are probably many elements of each fauna which have not yet been sampled. Cathedral Bluffs Tongue There is a temporal gap of uncertain duration between the time represented by the Lost Cabin fauna and that represented by the Green River Basin Bridger B fauna, the next higher well-defined assemblage. In the Wind River Basin this time may be represented partially by the poorly fossiliferous upper 750 ft. of the Lost Cabin Member, which might include some sediments of Bridgerian age. Matthew (1909, p. 296), when dividing the middle Eocene Bridger Formation in the southern Green River Basin, placed the poorly fossiliferous A horizon in this position. Robinson (1966) described two late Wasatchian faunas from the Huerfano Basin, and placed the latest, from the Huerfano B beds, in the Lost Cabin-Bridger interval. Composition of the Huerfano B fauna suggests that it is actually of Wasatchian age, probably late Lost Cabin, and should not be considered equivalent to Bridger A. C. Wood (1966) collected a small fauna from sediments of Bridger lithology near Opal, Wyoming, and referred these to the Bridger A. Woo , sec. 30, T. 30 N.. R. 105 W. Thickness (feet) 10. Siltstone, brown, fine-grained 11.5 9. Sandstone, gray-brown, fine-grained 0.2 8. Siltstone, brown, fine-grained; alternates with shale, dark brown to gray; well laminated 38.0 7. Sandstone, brown, coarse; ledge-former, with vague bedding 1.0 6. Sandstone, red, yellow and dark blue-gray, fine-grained 10.0 5. Mudstone, dark blue-gray, sandy; somewhat laminated near top and blockier near bottom.. 11.0 4. Sandstone, gray to orange, coarse-grained; locally well indurated 6.0 3. Mudstone, gray-green, sandy; unbedded 5.0 2. Mudstone, gray-brown to brown, sandy 13.0 1. Mudstone, gray-brown, sandy; to base of slope in sagebrush-covered area 10.0 + Total measured thickness 105.7+ feet Section 12 Laney Shale Member of the Green River Formation and Cathe- dral Bluffs Tongue and arkosic facies of the New Fork Tongue of the Wasatch Formation on the north side of Table in SE i:j sec. 4, T. 29 N., R. 105 W. Thickness Laney Shale Member (in part) : (feet) 3. Sandstone, siltstone and shale, brown and buff. Cathedral Bluffs Tongue: 2. Mudstone, drab gray-green, sandy; includes pebbles of igneous origin; some arkosic levels almost gravelly; vague color banding, mostly in shades of gray-green due to arkose content; quite uniform 60.5 192 FIELDIANA: GEOLOGY, VOLUME 29 Thickness (feet) Arkosic facies (in part) : 1. Mudstones, brightly banded, sandy Total measured thickness 60.5 feet Section 13 Laney Shale Member of the Green River Formation and Cathe- dral Bluffs Tongue and arkosic facies of the New Fork Tongue of the Wasatch Formation along the south bank of the Big Sandy River in S Yz sec. 19, T. 30 N., R. 105 W. Thickness Laney Shale Member (in part) : (feet) 5. Covered interval with shaley float 6.0 Cathedral Bluffs Tongue: 4. Mudstone, green to brown; sandy; some well- laminated shaley zones and some heavily oxidized zones; upper portion shalier 10.5 3. Sandstone, buff to yellow, coarse; merges down- ward into brown sandy mudstone; well-indu- rated gray arkosic channel sandstones present in this level 10.0 2. Mudstone, drab gray-green, sandy; vague color bands of purplish and yellowish mudstones along with light gray-green arkosic beds. Several arkosic sandstone lenses. The base is a three-foot thick cobbly zone 106.0 Arkosic facies (in part) : 1. Mudstones, brightly banded, sandy; to river level 10.0 Total measured thickness 142.5 feet Section 14 Bridger Formation at Big Sandy Fault locality, SE 34 NE i<4 sec. 25, T. 30 N., R. 106 W. Thickness (feet) 14. Covered interval 16.5 WEST: NEW FORK-BIG SANDY AREA 193 Thickness (feet) Bridger Formation (in part) : 13. Mudstone, gray; chippy, with clay pellets, ledge-former 4.5 12. Mudstone, brown, sandy; some bedding, grayer and more shaley toward base; some vertebrate remains found, but no mammals 35.0 11. Shale, light gray; well bedded, with rusty weathering; conspicuous impressions of vege- table remains, fish scales and assorted organic debris; good ledge-former 3.0 10. Mudstone, green to gray-brown, soft sandy. . . 5.5 9. Mudstone, dark brown, coarse-grained 8.0 8. Mudstone, gray-brown, sandy; somewhat bed- ded; contains a small amount of fossil ver- tebrate material 3.0 7. Mudstone, brown, sandy; poorly laminated, with irregular nodular material at base; con- tains a large amount of fossil vertebrate material 4.0 6. Mudstone, green to gray-green, sandy; chippy to somewhat shaley with some nodules; excel- lent producer of fossil vertebrates 4.5 5. Mudstone, light brown, sandy; conspicuous nodular zones near middle of unit; forms a steep slope below the nodular zone 30.5 4. Mudstone, dark brown, sandy 11.3 3. Mudstone, light gray-brown, sandy 1.0 2. Shale, light gray; chippy, forms a conspicuous white line on the outcrop 0.2 1. Mudstone, brown, sandy; has some hard, mas- sive zones and irregular greenish zones; forms occasional ledges; to water level 45.0 Total measured thickness 168.0 feet Publication 1161