Finding important fossil specimens usually takeshours of patient, tediousscraping and digging withtrowels, ice picks and

small paint brushes – the tools of the paleontologist. But in 1999, a

23-million-year-old fossil foundBruce Bailey, a paleontologist for theUniversity of Nebraska State Museum’sHighway Salvage Paleontology Program.At a highway construction site south of Gering, Bailey was walking behind a D-9 caterpillar pulling claw-like, steelteeth and tearing open the rocky soil.He was startled when a fossil snappingturtle tumbled down a bank and landedin the soft dirt at his feet.

“It was just lying there, both theupper and lower shells were complete.I put a plaster jacket on it for protection,but it was in great shape, a beautifulfossil from millions of years ago,”Bailey recalled.

Finding the fossil turtle was one ofmany exciting moments Bailey has hadat the site. Working there since the late-1990s, he and other paleontologistshave uncovered a world-class fossildeposit located in the highway right-of-way at the Wildcat Hills StateRecreation Area.

Because the importance of these discoveries first became apparent in1999, Bailey named the fossil deposit

Millennium’s End Quarry. Mammalfossils recovered so far include smallmoles, shrews, peccaries and rhinos, aswell as horses and hippo-like creatures.One of the quarry’s prize fossils is arare jaw from the powerful Miocenecarnivore, Ysengrinia, a type of beardog.Fossils of 24 species of small mammalsand 22 large mammals, including sevendifferent carnivores ranging from tinyweasels to the wolf-size beardog, havebeen found. Several fossils new to science, including a genus and speciesof beaver and a gopher species, havebeen recovered.

The first hint that important fossilswere buried by this ancient riveroccurred in 1968 when former highway salvage paleontologist King Arthur Richey discovered severalvertebrate fossil specimens weatheringout from nearly vertical road cuts madewhen Nebraska Highway 71 wasrealigned through the Wildcat Hills.On the stretch of highway that makesa scenic descent from the Wildcat Hillsinto the North Platte River Valley,Richey found the fossils at two distinctlevels along what he called the“Wildcat Grade.”

From the same area where Richeymade his discoveries, Bailey andRobert M. Hunt, Jr., a paleontologistwith the University of Nebraska StateMuseum, later collected several partialskeletons of the sheep-like oreodont,Merychyus, which is considered anindex fossil of early Miocene depositsin the Great Plains. They designatedthe Wildcat Grade a paleontologicallysensitive area. For more than 40 years,the state museum and the NebraskaDepartment of Roads (NDOR) havecooperated to salvage fossils from sensitive areas where highways areconstructed.

In the late 1990s, the roads

40 NEBRASKAland ● May 2005 NEBRASKAland ● May 2005 41

★

Millennium’s End Quarry is located in theNebraska Highway 71 right-of-way at

Wildcat Hills State Recreation Area10 miles south of Gering. Many of the

fossils found at the quarry are displayedin the recreation area’s Nature Center.

Bruce Bailey (top), Shane Tucker (center) and volunteer Ray Boice of Gering work in the northern endof Millennium’s End Quarry adjacent to Nebraska Highway 71.

Millennium’sEnd QuarryAncient River RevealsAncient WildlifeBy Bob Grier

An ancient river that once flowed along whatis now the Wildcat Ridge south of Gering isgiving up its secrets to paleontologists from theUniversity of Nebraska State Museum. Fossilizedbones of 46 species that lived 23 million years ago,including several new species, have been recovered.This fossil deposit is one of North America’s mostdiverse and significant discoveries of earlyMiocene mammals.

The upper shell of the snapping turtlefossil measured 8.5 inches.

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bed was excavated from the median tothe back slope with phenomenal results– more than 160 specimens were collected, a third of which were skullsor jaws!”

Bailey recalled, “The discovery wasbeyond my wildest dreams – a depositloaded with the tell-tale gravel of a

perennial river and the bones of fossilmammals; the mother lode, just a littledeeper than I had hoped to find it.”

The Ancient RiverAs a University of Nebraska-Lincoln

graduate student in the 1970s, geologist

Carl Vondra mapped river gravel andsand deposits along the Wildcat Ridgewhere pioneering geologist NelsonHoratio Darton had photographed spectacular gravel outcrops in 1899.Bailey colored Vondra’s geologic map,marking coarse gravel deposits of themain channel gray and fine-grainedsandstones of the ancient valley fill tan.The colored-coded map clearly showedthe river’s course along the spine of theWildcat Hills escarpment that extendsfrom Wyoming into Nebraska south ofthe North Platte River Valley. Followingthis map in the fall of 1999, Bailey tracedthe river’s cemented conglomerateswest of Nebraska Highway 71 and eastas far as Wright’s Gap, where gravelbeds that cap Big Haystack Mountainindicated the main channel was morethan 20 feet deep during high water.

Bailey described the ancient river:“About 23 million years ago a swift-flowing river carved a canyonover 200 feet deep and over a milewide, east out of the uplifted RockyMountains and onto the loess (wind-blown silt) plains of westernNebraska. Geologists call this type of

department notified the museum it planned to widen NebraskaHighway 71, a segment of the Heartland Expressway that linksInterstate 80 at Kimball to Interstate 90 at Rapid City, SouthDakota. Advance notice allowed Bailey and Heidi Mead, thenthe museum’s salvage preparator, to collect fossils before construction. NDOR opened a small test pit for exploration andBailey and Mead screened and sorted nearly a ton of gravel formicrovertebrate fossils. They found 16 species of insectivores,rabbits, and rodents, including the new gopher species. A bonusdiscovery was a complete, articulated skeleton of the small deerBarbouromeryx, which was named for Erwin Hinckley Barbour,a founder of the state museum. That find is probably a newspecies as well as the earliest occurrence of the group in NorthAmerica. They named the large and small mammal assemblagethe Stage Hill local fauna, for its location within the Wildcat Hills.

Some of the site’s earlier fossil bones, such as the oreodontMerychyus, were long-ranging species that gave the scientists a rough estimate of the deposit’s age, but the small mammal discoveries narrowed the age range to approximately 23 millionyears ago.

Significant Discoveries“We look forward to a project of this sort with great anticipation,”

Bailey said. “You might think heavy equipment and fragile fossilsare a combination to be avoided. Quite the contrary. Heavyequipment is the best way to remove tons of rock and reach the fossil treasures hidden beneath. I would often dream of discovering complete, articulated skeletons within the upperchannel sandstones.”

Road construction began during the spring of 1999. Baileyrecalled, “By mid-July the mechanical earth-moving monstershad transformed once familiar surroundings into a Martian landscape of bare rock and dust. Under these conditions the paleontologist resorts to walking the rubble wakes of D-9 ripper-cats, scrambling to carry sandstone blocks containing bonesout of harm’s way. In this fashion two of the prized big-gameanimals of the early Miocene were discovered: The extremelyrare four-horned deer Syndyoceras and Miotapirus, a tapir similarto modern forms found exclusively in tropical rain forests.”

That July the upper channel of the ancient river disappearedquickly and the paleontologists put their salvage operations onhold until excavation reached the river’s lower channel.

It was three weeks later, after the dirt crews moved their equipment into the area of the lower channel, when the fossilizedturtle tumbled in front of Bailey. At that time, he had noticedlarge, granite pebbles in the bottom of the channel – the firstindication that a through-flowing river with its headwaters in theRockies, 100 miles to the west, had deposited the sediments. The next day the earthmovers began to uncover the lower channeland Bailey first saw the significance of the site. His most optimisticdreams were exceeded when numerous, significant discoverieswere made during the first hours and days of excavation.

“As the fleet of a dozen scrapers neared grade to the north,they uncovered a veritable treasure trove of fossil bones,” Baileywrote in an article in Roadrunner (April/May 2001), a NDORpublication. “Platte Valley Construction Superintendent DennisGiesman instructed his crews to work around this area while weresorted to more conventional tools of the trade – namely shovels,trowels and paint brushes. During the next month, the entire bone

42 NEBRASKAland ● May 2005 NEBRASKAland ● May 2005 43

In 1999 bulldozers and scrapers remove the ancient river’s upper channel deposits (foreground) at the Wildcat Grade during thewidening of Nebraska Highway 71. In the background excavators are nearing the lower channel.

Shane Tucker draws a map showing the positons of the plaster-jacketed anthracotherebones along the base of the ancient river’s south channel wall.

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The right, lower jaw of the powerful beardog, Ysengriniaamericana, is 6.5 inches long.

This is the skull, measuring 3.5 inches long, and right, lowerjaw of a new genus and species of round-incisored beaver.

This left lower jaw of a young, adult, female Arretotheriumfricki measures eight inches long.

Associated hind limb fossils of the hippo-like anthracothere,Arretotherium fricki, in a 28-inch block.

the Oligocene, which had becomeextinct, and became the dominantcarnivore in the Miocene landscape.The beardog’s jaw, one of the quarry’sprize fossils, is on display at theWildcat Hills Nature Center.

The abundance of petrified woodand the discovery of a new genus ofround-incisored beaver kindled anotherline of speculation for Bailey: “It is anew kind of beaver found in NorthAmerica for the first time. They aremore closely related to the modernline of wood-chewing beavers thancontemporary burrowing beavers,such as the flat-incisored Paleocastor,which was responsible for the well-known “devil’s corkscrew”(Daemonelix) burrows. This beaver may have been acting like the modernCastor, cutting down trees anddamming watercourses. Of course we won’t know that for certain untilpetrified wood with gnaw marks is discovered.”

Compared to Agate Fossil BedsNational Monument, a similar-agedeposit located about 40 miles to thenorthwest, Millennium’s End Quarryhas yielded a greater diversity of mammal species. The most commonfossils at Agate are rhino bones. Onlytwo rhino specimens have been foundat Millennium’s End.

Located close to Highway 71’s northbound lanes, the Millennium’sEnd Quarry continues to be a working

paleontological site through the courtesy of the roads department and with security provided by theNebraska State Patrol. Over the pastfive years, Bailey and Shane Tucker,the current salvage preparator, haveworked river sediments across the mainchannel complex, which is 30 feet wideand 20 feet deep. During the past twoyears, they have recovered six perfectskulls and dozens of lower jaws fromforms, such as Zodiolestes, a weasel,Pseudoblastomeryx, a small saber-deer,and Archaeohippus, the collie-sizedthree-toed horse whose skull has beardog-size puncture wounds.

To date, workers have collectedand carefully mapped more than 500 large-mammal bones and well over athousand identifiable small-mammalspecimens, representing the 46 knownspecies. Over a third of the fossils represent partial to complete skulls or lower jaws. Few are articulatedskeletons. Many of the species areextremely rare, some are new to science, and some are seen in North America for the first time. The Stage Hill assemblage of mammalsis North America’s most diverse,single-site, Early Miocene fauna.

Paleontology CorridorRegional planners have proposed

adding this paleontology discovery siteto others, including Agate Fossil Beds,

Toadstool Geologic Park and theMammoth site at Hot Springs,South Dakota, in promoting a“Paleontology Corridor” roughly paralleling the Heartland Expressway.A fund-raising effort, primarily by theOregon Trail Foundation in westernNebraska, is underway to create artworkdepicting the ancient river’s landscapeand wildlife and to build displays at theWildcat Hills Nature Center.

Bailey said, “The site has tremendouspotential for educating students of allages. We are pursuing several avenuesto tell the story, including keeping aworking quarry open for trained volunteers and graduate studentresearch projects to learn more about thedeposit itself. This could be coupledwith a new, geologic and paleontologicinterpretive trail from the nature centerto the quarry. Additional fossil displaysare planned to supplement the strikingspecimens currently on display in thelower level of the nature center. Inaddition, we are contracting MarkMarcuson to paint a mural of the earlyMiocene landscape, reconstructing anumber of the animals we have foundfor the first time.” ■

NEBRASKAland ● May 2005 45

river entrenched because it cuts a deep,narrow, canyon through compactedrocks that confine the flow of water.In contrast to today’s slow-moving,shallow North Platte River, the rockdeposits left by the ancient WildcatHills river indicate a deep, narrow channel of swift-flowing water. A modern analogue would be the reach of the Niobrara River between Gordonand Merriman, where the modern riverhas cut a narrow, meandering canyonup to 200 feet deep. The ancient riverwas an energetic system that became araging torrent and physical barrier toanimal migration during flood events.”

Bailey explained why so many animalswere buried at the Millennium’s Endsite: “The river undercut the steepcanyon wall causing a bank collapseand introducing large boulders, one thesize of a Volkswagen, into the channel.This diverted the high-energy flow,allowing the deposition of fine gravel,sand, and silt which formed a point baron the inside bend of the river andquickly buried and protected fragilebones. At no other locality we have visited along this watercourse have we

encountered similar conditions, whichare necessary to produce fossil bonebeds. The high diversity of the riparian(stream-side) mammal community isdue to the river being the principalsource of water in the region 23 millionyears ago, which attracted the greatvariety of wildlife buried in the deposit.

“The ancient river cut almost completely through the lower part ofthe Arikaree Group into the salmon-colored sediments of the GeringFormation, which contain distinctive,white pumice fragments blown out ofa volcano in northeastern Coloradocalled Specimen Mountain and washedinto western Nebraska.”

In the millions of years since riversediments and bones were deposited,the Rocky Mountains and adjacentplains to the east have been uplifted onseveral occasions and then eroded byriver systems.

For several million years, the modernNorth Platte River has carved the locallandscape into a maze of canyons andoutlying buttes. The sediments of theancient Wildcat Hills river have beenpreserved along the spine of the ridge

more than 500 feet above the modernriver.

Jungle Fauna With BeardogsIn the state museum’s newsletter,

Mammoth, Bailey noted that 16 different large mammals have been discovered in the Millennium’s EndQuarry, including herbivores such asthe giant, clawed chalicothere, threevarieties of three-toed horses, tapirs,rhinos, two camels, peccaries, and threekinds of deer, as well as seven speciesof carnivores that fed upon them. Mostof the herbivores were low-crownedbrowsers, what legendary Nebraskapaleontologist Morris Skinner wouldhave called “jungle fauna.” The onlyhigh-crowned grazing herbivore of thetime, the slender camel Stenomylus, hasnot been found in this deposit, probablybecause it preferred open grasslands farfrom the forested river valley.

Monte Wegelin, a NDOR employeewho often volunteered to help Bailey,discovered the fossilized jaw of thebeardog, Ysengrinia. This wolf-sizespecies had replaced the large cats of

44 NEBRASKAland ● May 2005

Laterally accreted gravel caps Big Haystack Mountain in Wright’s Gap. The thickness of these deposits indicate a channel depthof more than 20 feet. David Fisher of Melbeta stands on the edge to provide scale to the photograph.

The Wildcat Hills SRA Nature Center has exhibits about the flora and fauna of the areaand displays some fossils from the Millennium’s End Quarry.

Visitors are invited view the paleontology and wildlife displaysat the Wildcat Hills SRA NatureCenter from 8 a.m. to 4:30 p.m.daily from April through Septemberand on weekdays from Octoberthrough March. A Nebraska ParkEntry Permit is required.

The 761-acre Wildcat Hills SRAand Big Game Reserve is located10 miles south of Gering onNebraska Highway 71. Wildlife inthe area include bighorn sheep,elk, deer and wild turkeys.

For more information aboutWildcat Hills SRA and its facilities,call (308) 436-3777, or go onlineto www.outdoornebraska.org.

Collection of vertebrate fossilswithin the Wildcat Hills StateRecreation Area is prohibited.Any fossils discovered should bereported to the Nature Center.For more information aboutMillennium’s End Quarry fossilsand other fossil sites in Nebraska,go the University of NebraskaState Museum web site atwww.museum.unl.edu.

Wildcat Hills SRAWildcat Hills SRAB

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