Intercontinental Migration of Neogene Amphicyonids (Mammalia, Carnivora): Appearance of the Eurasian Beardog Ysengrinia in North America

54 Pages·2002·2.5 MB·English

by  Robert M. Hunt

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3384, 53 pp., 24 figures, 6 tables December 27, 2002
Intercontinental Migration of Neogene
Amphicyonids (Mammalia, Carnivora):
Appearance of the Eurasian Beardog Ysengrinia in
North America
ROBERT M. HUNT, JR.1
CONTENTS
Abstract ...................................................................... 2
Introduction ................................................................... 2
Abbreviations ............................................................... 4
Early History of Amphicyonidae in North America ................................ 5
Early Neogene Amphicyonines .................................................. 6
History of Discovery of North American Ysengrinia ............................... 7
Geographic and Geologic Distribution of North American Ysengrinia ................ 8
Systematics ................................................................... 11
Ysengrinia Ginsburg, 1965 .................................................... 11
Ysengrinia americana (Wortman, 1901), new combination ...................... 14
Postcranial Osteology .......................................................... 26
Basicranial Anatomy ........................................................... 43
Dentition and Feeding .......................................................... 47
Acknowledgments ............................................................. 49
References .................................................................... 49
1Research Associate,DivisionofPaleontology,AmericanMuseumofNaturalHistory;Professor,GeologicalSci-
ences;andCurator,VertebratePaleontology,UniversityofNebraska,Lincoln,NE68588-0549.
Copyright(cid:113)AmericanMuseumofNaturalHistory2002 ISSN0003-0082
2 AMERICAN MUSEUM NOVITATES NO. 3384
ABSTRACT
At the beginning of the Neogene a remarkable faunal turnover occurred within the North
American carnivore community. The dominant larger Oligocene carnivores (creodonts, nim-
ravid cats, the amphicyonid Daphoenus) became extinct during the late Oligocene and were
replaced in the early Miocene by amphicyonine amphicyonids and hemicyonine ursids that
entered North America from Eurasia. During a five million-year interval from (cid:59)23 to18Ma,
large amphicyonines appear in late Arikareean and early Hemingfordian faunas of the North
American midcontinent. Although most fossils are from western Nebraska and southeastern
Wyoming, occurrences of amphicyonines at several sites in the eastern United States (Dela-
ware, Florida) indicate that they rapidly established a broad geographic distribution in North
America during the early Miocene.
This report describes and summarizesthe North American specimensoftherareimmigrant
amphicyonine Ysengrinia, the first large amphicyonine to enter the New World. Ysengrinia
exists in North America from (cid:59)23 to 19 Ma, becoming extinct at the end of the late Arika-
reean.AsinglespeciesofYsengriniaisrecognizedinNorthAmerica:Y.americana(Wortman,
1901), comb. nov., restricted to the late Arikareean of western Nebraska and southeastern
Wyoming. The North American hypodigm includes the only known complete skull of the
genus, associated with a mandible and partial postcranial skeleton. Because most Eurasian
occurrences of Ysengrinia are limited to mandibles or isolated teeth of single individuals,
intraspecificvariationinteethandskeletoninthesecarnivoreshasbeendifficulttodetermine.
The more complete North American specimens provide estimates of dental and osteological
variation in Ysengrinia, and suggest that the North American species is dimorphic. Skeletal
remains of early Miocene New World Ysengrinia are most often found in riparian and water-
hole environments.
INTRODUCTION prising large amphicyonine beardogs, hemi-
cyonineursids,anddiversespeciesoftheam-
Faunal turnover profoundly altered inte-
phicyonid Daphoenodon.
grated mammalian communities at various
The temnocyonine amphicyonids were the
times during the Neogene in both North
only major group of large carnivorans to
America and Eurasia. These turnover events
span the Paleogene-Neogene boundary in
produced changes in faunal composition
NorthAmerica,apparentlyunaffectedbythis
throughout the Holarctic region that eventu-
North American large carnivore turnover
ally influenced the southern continents, first
event (NALCTE). Temnocyonines first ap-
Africa in the early Miocene, and later South
peared in the early Arikareean ((cid:59)29–30Ma)
America in the Plio-Pleistocene.Oneachoc-
casion, extinction of multiple lineages was and diversified into several lineages (Hunt,
followed by the appearance of a new faunal 1998b) that attained their maximum size
association.Nowhereisthispatternmoreev- ((cid:59)40–80kg)inthelateArikareean.Thesub-
ident than in the turnover of large carnivor- family became extinct at the end of the late
ans during the Neogene of North America. Arikareean in North America.
Large carnivorans (cid:46)200 kg did notexistin By the mid-Miocene, creodonts were re-
the New World at the beginning of the Neo- duced to relict species in Africa, southern
gene. The largest carnivores of the North Asia, and Europe (Barry, 1980, 1988; Gins-
American late Paleogenewereanaggregation burg, 1980; Morales et al., 1998). Nimravids
ofdiverse,mid-sized((cid:44)100kginmostcases) were represented in the mid- to lateMiocene
nimravid cats, creodonts, and amphicyonids. of Eurasia and North America by a single
This carnivoran assemblage became extinct subfamily, the Barbourofelinae (Geraadsand
during the late Oligocene with the gradual Gu¨lec¸, 1997), of which only a few species
disappearance of Nimravinae, creodonts (Barbourofelis fricki, North America, to (cid:59)6
(Hyaenodontidae), and the daphoenine am- Ma; nimravid, Asian Siwaliks, to (cid:59)7.4 Ma;
phicyonid Daphoenus. In theearlyMiocenea Barry and Flynn, 1989) persisted to near the
newcommunityoflargecarnivoransappeared end of the epoch. The numerous genera and
in North America (fig. 1, NALCTE), com- species of late Eocene-Oligocene Nimravi-
2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 3
Fig. 1. Temporal ranges of large Oligocene and early Miocene carnivores in North America, dem-
onstrating the faunal turnover event at the Paleogene-Neogene boundary (Global Polarity Time Scale
from Berggren et al., 1995). Abbreviations: NALCTE, North American large carnivore turnover event;
GPE, last appearance in Great Plains; JDE, last appearance in John Day Formation, Pacific Northwest;
Ma, Mega-annum.
4 AMERICAN MUSEUM NOVITATES NO. 3384
nae found in North America and Eurasia toceneursid-felid-canidassociation(Huntand
were extinct by (cid:59)24–25 Ma, prior to the Tedford, 1993).
Miocene. This report is one in a series of publica-
By the end of the early Miocene, amphi- tions that explores the early Neogene radia-
cyonids and hemicyonines dominated niches tion of the Amphicyonidae in the New
for large carnivores on the northern conti- World. Earlier studies reviewed the Oligo-
nents (Hunt, 1998a, 1998b; Ginsburg and cene amphicyonids of North America (Hunt,
Morales, 1998). During the mid-Miocene, 1996, 1998b, 2001), the evolution of the
these were the first Neogene carnivorans to family in North America (Hunt, 1998b), and
attain sizes (cid:46)200 kg: among the largest of the intercontinental migration of the large
these arctoids were Amphicyon ingens of amphicyonine Amphicyon to the New World
North America, and the European Amphi- in the early Miocene (Hunt, in press). Here
cyon giganteus and hemicyonine Dinocyon I briefly review the early history of amphi-
thenardi. By the mid-Miocene several am- cyonids in North America (the temnocyoni-
phicyonids, including a large species of Am- nes and endemic daphoenines); describe the
phicyon, had entered Africa and rapidlypen- faunal turnover event (NALCTE, fig. 1) at
etrated to the southern limit of the continent the Paleogene-Neogene boundary when cre-
(Arrisdrift fauna, Namibia: Hendey, 1978; odonts,nimravinecats,Daphoenus,andtem-
Morales et al., 1998). nocyonines were replaced by immigrant am-
Amphicyonids and hemicyonines contin- phicyonines and hemicyonines; and place on
ued to dominate the carnivoran fauna of Ho- record the first of the large immigrant am-
larctica into the late Miocene. But withinthe phicyonines to appear in North America, the
late Miocene, during the Clarendonian land Eurasian beardog Ysengrinia.
mammal ‘‘age’’ of North America and the
Vallesian of Europe, both groupsbecameex- ABBREVIATIONS
tinct. Relict taxa of amphicyonids survived
Anatomical
in Africa at Lothagam (Kenya) to at least
(cid:59)6.5Ma(Werdelin,1999),andontheIndian A alisphenoid
subcontinent in the Siwalik Group to (cid:59)7.4 BO basioccipital
Ma (Barry et al., 1982: 112), but failed to eam osseous external auditory meatus
reach South America. After (cid:59)9 Ma, late gf postglenoid foramen
Miocene (Turolian, Hemphillian) faunas on h hypoglossal (condyloid) foramen
ips inferior petrosal venous sinus
the northern continents lacked amphicyonids
M mastoid process
and hemicyonines altogether; they were re-
me mastoid-exoccipital suture
placed by large ursids (Agriotherium, In-
p petrosal promontorium
darctos), felids, and canids—lineages that
pcf posterior carotid foramen
heralded the eventual rise to prominence of pg postglenoid process
these families in the Plio-Pleistocene. plf posterior lacerate foramen
Ecological roles occupied by amphicyon- pp paroccipital process
ids and hemicyonines on the northern conti- T ectotympanic
nents were eventually filled in the Pleisto-
cene/Holocene by ursine bears (Ursidae, Ur-
Institutional
sus, Thalarctos, Arctodus, Tremarctos), the
great cats (Felidae, Panthera, Smilodon, Di- ACM Pratt Museum, Amherst College, Mas-
nobastis), wolves (Canidae, Canis), and hy- sachusetts
enas (Hyaenidae, Crocuta, Hyaena, Para- AM Department of Mammalogy, American
MuseumofNaturalHistory,NewYork
hyaena, Pachycrocuta, Chasmaporthetes).
AMNH Division of Paleontology, American
Thus, the early to mid-Miocene interval in
MuseumofNaturalHistory,NewYork
North America is identified by a discrete as-
CM Division of Vertebrate Fossils, Carne-
sociation of large amphicyonids and hemi-
gie Museum of Natural History, Pitts-
cyonines that intervenes between the late Eo- burgh
cene-Oligocene creodont-nimravid-Daphoen- CNHM FieldMuseumofNaturalHistory,Chi-
us association and the late Miocene to Pleis- cago
2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 5
Fig. 2. Ysengriniaamericana (Wortman,1901),newcombination;holotypepalatewithleftP2–M2,
right P3–M3, YPM 10061, upper Arikaree Group, collected in 1875 by H.C. Clifford in northwest
Nebraska (see appendix 1). Scale bar, 1 cm.
F:AM FrickCollection,AmericanMuseumof (Hunt, 1996). The late Eocene to mid-Oli-
Natural History, New York gocene (Duchesnean–Chadronian through
FSL Faculte´ des Sciences, Universite´ de
Whitneyan)speciesallbelongtotheendemic
Lyon, Lyon
North American subfamily Daphoeninae,
MGL Muse´e Guimet d’Histoire Naturelle,
comprising four genera (Daphoenus, Da-
Lyon
NMB Naturhistorisches Museum, Basel phoenictis, Brachyrhynchocyon, Parada-
PaN Museo Paleontolo´gico de Valencia, phoenus). Daphoenus is the oldest New
Universidad de Valencia World amphicyonid, appearing in the Du-
SMNS Staatliches Museum fu¨r Naturkunde,
chesnean, and is the most plesiomorphic in
Stuttgart
dental, cranial, and postcranial features. The
UNSM University of Nebraska State Museum,
smallhypercarnivoreDaphoenictisisfirstre-
Lincoln
USNM DepartmentofPaleobiology,Smithson- corded in the later Duchesnean (Hunt, 1996;
ian Institution, Washington, D.C. fig. 2). Daphoenus, Daphoenictis, and Bra-
YPM Peabody Museum, Yale University, chyrhynchocyon all occur in the Chadronian,
New Haven and the latter two genera arenot knownafter
ZM Division of Mammals, University of
that time. Paradaphoenus is first certainly
Nebraska State Museum, Lincoln
known in the Orellan (early Oligocene) and,
EARLY HISTORY OF THE together with Daphoenus, it continued
AMPHICYONIDAE IN NORTH through the Whitneyan into the early Arika-
AMERICA reean (late Oligocene; Hunt, 2001). These
The first North American amphicyonids genera, then, comprise a New World amphi-
appear in the late Eocene at (cid:59)39–40 Ma cyonid assemblage characteristic of the late
6 AMERICAN MUSEUM NOVITATES NO. 3384
Eocene to late Oligoceneinterval,allsmaller theArikareeanNALMA(30Ma–(cid:59)18.8Ma,
carnivorans of less than 20 kg. MacFadden and Hunt, 1998; Tedford et al.,
In North America the only significantly 1996). Therefore, late Arikareean temno-
larger carnivores that occurred in this fauna cyonines, which are all younger than (cid:59)22.9
were the massive endemic Chadronian creo- Ma, are among the oldest Neogene amphi-
dont Hemipsalodon (Mellet, 1969; Gustaf- cyonids in North America. Temnocyonines
son, 1986) and the largest species of North (and species of Daphoenodon) are the most
American Hyaenodon, H. megaloides and H. frequently encountered New World amphi-
horridusoftheChadronianandOrellan,with cyonids in the earliest Miocene when the
skull lengths of 25–40 cm (Mellett, 1977). subfamily is represented by three lineages
These creodonts were the only species that (Temnocyon, Mammacyon, and an unde-
approached and, in some cases, exceeded scribed genus).
100 kg. A few early Arikareean nimravid In Europe, the haplocyonines are related
cats were of comparable size, with males to the Temnocyoninae, and evolvedsimilarly
possibly approaching 100 kg. However, the specialized dentitions in parallel at about the
small size of most carnivores at this time is same time (Bonis, 1973; Bonis and Guinot,
in marked contrast to the many large ungu- 1987).
lates (brontotheres, rhinoceroses, entelo- Near the Oligocene-Miocene boundary,
donts) in the late Eocene-OligoceneofNorth the beardog Daphoenodon appears in North
America. America (fig. 1). Early occurrences are pri-
By the beginning oftheArikareean((cid:59)29– marily in Florida where a small species, D.
30 Ma), the character of the amphicyonid notionastes, has been identified by fragmen-
faunahadbeguntochange.TheNorthAmer- tary remains coming from a number of Ari-
icantemnocyonineamphicyonidsfirstappear kareean fissure fills and karst sinkholes
in the earliest Arikareean (Hunt, 1998b), the (Frailey, 1979). This species is also known
most primitive species showing a resem- from east Texas, suggesting a restrictedGulf
blance to Daphoenus. The last record of Da- Coastal Plain range (Albright, 1996). Da-
phoenus ((cid:59)28.5 Ma in the GreatPlains,(cid:59)27 phoenodon, however, is better known from a
Ma in the John Day beds, Oregon) is almost succession of chronospecies from upper Ari-
concurrent with the first appearance of tem- karee and lower Hemingford Group sedi-
nocyonines at (cid:59)29.5 Ma in the John Day ments in western Nebraska and southeastern
Formation, Logan Butte, Oregon (fig. 1). Wyoming (Hunt, 1998b). These fossils are
Temnocyonines diversify and increase in found in fluvial, waterhole, and eolian sedi-
size throughout the Arikareean (fig. 1), but ments of a semiarid continental interior. The
are absent from earliest Hemingfordian fau- oldest of the Great Plains species is repre-
nas and are therefore presumed extinct by sented by an undescribed mandible from the
(cid:59)18.5 Ma. The largest species probably at- type area of the Harrison Formation, esti-
tained (cid:59)40–90 kg. They arebestrepresented mated at (cid:59)22–23 Ma, and hence close to the
intheArikareeGroupoftheGreatPlainsand Oligocene-Miocene boundary. It directly
JohnDaybedsofthePacificNorthwest,with precedes in time a population sample of the
rareoccurrencesfromFloridaandCalifornia. holotype species, D. superbus, from the wa-
Temnocyoninesaretheonlygroupoflarge terhole bonebed and carnivore dens at Agate
carnivorans that bridge the temporal hiatus National Monument (Peterson, 1910; Hunt,
that occurs between the Paleogene and Neo- 1990). The genus is known only from North
gene large carnivore associations in North America, and possibly is derived from the
America (fig. 1). They span the interval be- endemic North American Oligocene da-
tween the last occurrence of endemic Da- phoenine Daphoenus.
phoenus ((cid:59)27 Ma) and the first appearance
of Daphoenodon and immigrant amphicyon-
EARLY NEOGENE AMPHICYONINES
ines ((cid:59)23 Ma). The Oligocene-Miocene
boundary, placed at (cid:59)22.9–23.8 Mainwest- In the early Neogene three European am-
ern Europe (Steininger et al., 1989, 1996, phicyonine genera appear successivelyinthe
1997; Shackleton et al., 2000), occurs within New World at (cid:59)23 Ma (Ysengrinia), (cid:59)19.2
2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 7
Ma (Cynelos), and (cid:59)18.5–18.8 Ma (Amphi- tition (fig. 2), an upper canine, and a calca-
cyon). These North American first occur- neum of a young adult beardog, discovered
rencesareinterpretedasEurasianimmigrants in northwest Nebraska in 1875 by H.C. Clif-
because of their earlier presence in Europe ford, at that time in the employ of O.C.
and their more advanced stage of evolution Marsh of Yale University (appendix 1). The
relative to the earliest Old World species. amphicyonid palate was later designated the
There are no plausible ancestors for these holotypeof‘‘Amphicyon’’americanusbyJa-
amphicyonines among North Americanbear- cob Wortman (1901).
dogs. Cynelos and Ysengrinia have been re- Wortman’s (1901) published paper report-
ported previously from the latest Arikareean ed that the palate was found in the ‘‘Loup
of western Nebraska (Hunt, 1972, 1998b), Fork beds, Niobrara River, Nebraska’’ and
dated at (cid:59)19.2 Ma. Recently discovered ev- did not mention Clifford or the 1875 date of
idence of Ysengrinia in older lateArikareean collection, information recorded only in the
rocks of western Nebraska, estimatedat(cid:59)23 YPM catalogue. Casts of the palate which I
Ma, indicates an earlier entry into North had previously examined in various muse-
America. Amphicyon is the last of the three ums were poorly executed. In December
genera to appear, first known from early
2000, I examined the original specimen: its
Hemingfordian sediments in northern Colo-
exceptional preservation has prompted this
rado and northwest Nebraska at (cid:59)18.5–18.8
review of the genus in North America, sup-
Ma (Hunt, in press; MacFadden and Hunt,
plementing (andsupercedinginpart)myear-
1998).
lierremarks(Hunt,1998b).Becauseallother
Ysengrinia occurs in both the late and lat-
North American specimens of Ysengrinia
est Arikareean intervals in North America
discovered since 1875 can be attributed to a
((cid:59)23–18.8 Ma). Cynelos first appears in the
single species, Wortman’s (1901) species-
latestArikareean((cid:59)19.2Ma),representedby
group term serves as the name-bearerforthe
two teeth found in waterhole bonebeds at
hypodigm. Hence, the palate (YPM 10061)
Agate Fossil Beds National Monument,
becomestheholotypeoftheNorthAmerican
Sioux County, Nebraska (Hunt, 1972: fig.
species, Ysengrinia americana, comb. nov.
6B,D).CynelosandAmphicyonarealsopre-
Following Clifford’s discovery of the ho-
sent in theearly Hemingfordian,butarerare,
lotype, no new material of Ysengrinia came
whereas they are the common large amphi-
to light in North America until several foot
cyonines of the late Hemingfordian. The ro-
and limb bones were found in earlyMiocene
bust Cynelos idoneus is present in the late
upperArikareerocksofwesternNebraskaby
Hemingfordian Sheep Creek Formation of
O.A. Peterson from 1904 to 1908. These
western Nebraska where it is accompanied
were initially attributed to large canids by
by the even larger Amphicyon frendens.
Peterson (1910). Hunt (1972) later described
Thesetwogenerapersistaslargecarnivorans
isolated teeth, an edentulous mandible, and
in the early Barstovian. Cynelos is not found
somepostcranials(includingPeterson’sspec-
in the mid-Barstovian and is presumed to be
imens), recognizing them as amphicyonids
extinct. Amphicyon survives into the mid-
Barstovian at Horse and Mastodon Quarry, and referring them to (?)Ysengrinia Gins-
Colorado, but by (cid:59)14 Ma is also extinct. burg, 1965. Although Peterson (1910) and
Amphicyon and Cynelos are replaced in the Hunt (1972) initially attributed these fossils
late Barstovian by the amphicyonids Pseu- to the Harrison Formation, Hunt (1978,
docyon and Ischyrocyon (Hunt, 1998b), best 1985,1990)laterreferredthelocalitiestothe
represented at sites in the Great Plains and lower part of the overlying Upper Harrison
California. Both genera are no longer in ev- beds, based on lithostratigraphic revision of
idence by the end of the Clarendonian ((cid:59)9 the upper Arikaree Group in its type area in
Ma). Sioux County.
In 1937, collectors from the Frick Labo-
HISTORY OF DISCOVERY OF NORTH ratory (AMNH) discovered an associated
AMERICAN YSENGRINIA skull, mandible, and postcranials of a large
In North America the first record of Ysen- adult Ysengrinia in the Upper Harrison beds
grinia is a palate with nearly complete den- of southeastern Wyoming (fig. 3), but it re-
8 AMERICAN MUSEUM NOVITATES NO. 3384
Fig. 3. Ysengrinia americana,paratypecraniumandassociatedmandible,F:AM54147,UpperHar-
rison beds, 25 Mile District, latest Arikareean, Goshen County, Wyoming.
mained unidentified. This individual (F:AM Miocene waterhole environment in which
54147) demonstrates for the first time an as- scattered skeletal remains of a variety of
sociated upper and lower dentition, the form mammals were buried. The teeth and bones
of the skull,andadamagedbutlargelyintact of a large amphicyonid similar to Ysengrinia
basicranium, features unknown in OldWorld americana were intermixed with these re-
Ysengrinia. The postcranials were limited to mains. In a recent summary of amphicyonid
cervicalvertebraeandforelimbelements,but diversity in North America (Hunt, 1998b), I
nevertheless reveal a short-footed, robust allocated this large Bridgeport amphicyonid
skeleton, similar to the postcrania of Amphi- toYsengrinia.Discoveryoftheexceptionally
cyon (Ginsburg, 1961; Hunt, in press). No preserved palate and dentition of Wortman’s
completeskullisknownfromtheOldWorld; holotype of ‘‘Amphicyon’’ americanus dem-
the Wyoming skull is the first of its kind. onstrates that the early Hemingfordian
University of Nebraska excavations from Bridgeportcarnivoreisbetterallocatedtoan-
1974 to 1990 at Harper Quarry and other other taxon (Hunt, in preparation).
nearby latest Arikareean sites in westernNe-
braska produced additional remains of Ysen- GEOGRAPHIC AND GEOLOGIC
grinia (Hunt 1978, 1990). Ysengrinia was DISTRIBUTION OF NORTH AMERICAN
common in waterhole and riparian environ- YSENGRINIA
ments of this age. In addition to these latest
Arikareean fossils, a large collection of iso- All North American specimens of Ysen-
latedteeth,mandibles(mostedentulous),and grinia are from nonmarine sediments of late
unassociated postcranials were excavated by or latest Arikareean age in westernNebraska
the University of Nebraska State Museum and southeastern Wyoming (fig. 4). The ear-
from the early Hemingfordian Bridgeport liest North American record of Ysengrinia is
Quarries, Morrill County, Nebraska, during a mandiblewith p3–m2fromlateArikareean
1932–1940. These quarries sampled an early fluvial sediments at Wildcat Ridge, south of
2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 9
Fig. 4. Geographic distribution of Ysengrinia in the North American midcontinent. Localities 1–5,
latest Arikareean; locality 6, late Arikareean: 1, Harper Quarry; 2, University Quarry at AgateNational
MonumentandAmericanMuseum–CookQuarry;3,MoravaRanchQuarry;4,25MileDistrictofFrick
Laboratory, AMNH; 5, Lay Ranch beds (an Upper Harrison paleovalley) at Spoon Butte; 6, UNSM
Locality Sf-105; HC, the geographic area where H.C. Clifford collected the holotype (YPM 10061) of
Y.americana,possiblyfromMoravaRanchQuarry(appendix1).Alllocalitiesareinstrataoftheupper
Arikaree Group.
Gering, Nebraska (Harrison Formation, esti- Ysengrinia apparently was an important
mated age, (cid:59)23 Ma). scavenger-predator.
A latest Arikareean sample of Ysengrinia From higher stratigraphiclevelswithinthe
includes fossils from the waterholebonebeds Upper Harrison beds of latest Arikareean
((cid:59)19.2 Ma: University Quarry at Agate Na- age, only three occurrences are known—(1)
tional Monument, Hunt, 1972, 1990; Harper an associated partial postcranial skeleton
Quarry, Hunt, 1978; Morava Ranch Quarry, (USNM 186993) from the Lay Ranch beds
Coombs and Coombs, 1997; AMNH-Cook (Hunt, 1985) west of Spoon Butte, Goshen
Quarry, Hunt, 1972) that occur in the basal County, Wyoming; (2) isolated teeth and
Upper Harrison beds along the valley of the postcranials of one or two individuals from
Niobrara River in Sioux and Box Butte theLay Ranch bedseastofSpoonButte;and
Counties, Nebraska. If Clifford’s holotype (3)theassociatedskull,mandible,andpartial
palateofY.americanawasalsofoundatMo- skeleton (F:AM 54147, paratype of Y. amer-
rava Ranch Quarry, which seems probable, icana) from Upper Harrison beds, Goshen
itisofthesameage.Seventotenindividuals County,Wyoming,(cid:59)15miles(24km)north-
are known from these waterholes where west of Spoon Butte.
10 AMERICAN MUSEUM NOVITATES NO. 3384
Ysengrinia americana is accompanied by form, and a few phalanges (Hunt, 1972: figs.
other large carnivorans in the latest Arika- 8, 9,10A, 11).Thedepositionalenvironment
reean Upper Harrison fauna of western Ne- ofMoravaRanchQuarryfossilshasbeende-
braska and southeastern Wyoming. Ysengri- scribed by Coombs and Coombs (1997) as a
nia americana, Daphoenodon superbus, and waterhole in a fluvial setting. The diagnostic
atemnocyoninearefoundintheAgateQuar- M1 of Ysengrinia americana is known from
rieslocalfauna(Hunt,1985,1990),collected Morava Ranch Quarry and from American
from waterhole deposits and carnivore dens Museum–Cook Quarry (Hunt, 1972: fig.
at the base of the Upper Harrison in Sioux 10A, B). These molarsarenearlyidenticalto
County. At higher stratigraphic levels in the theM1oftheholotypeandparatype.Despite
Upper Harrison beds of southeastern Wyo- the lack of teeth in the Morava Ranch man-
ming, Y. americana and two large unde- dible, its deep-jawed, robust form, the size
scribed amphicyonid species are associated and spacingofthealveoli,andtheplacement
with faunas age-equivalent to the Niobrara of the mental foramina demonstrate a corre-
Canyonlocalfauna(Hunt,1985,1990).Also spondence to the mandible of the Y. ameri-
present in the Upper Harrison is the giant
cana paratype.
mustelid, Megalictis ferox (Hunt and Skol-
Although Ysengrinia is uncommon in Up-
nick, 1996), and two species of large tem-
per Harrison sediments (Lay Ranch beds,
nocyonine amphicyonids representing the
Hunt, 1985) filling the Lay Ranch paleoval-
terminal members of their respective lineag-
ley at Spoon Butte, the few scattered occur-
es. Both paleofelids (Nimravidae) and neo-
rences include an associated partialhindlimb
felids (Felidae) are absent from these assem-
that establishes the proportions of femur to
blages (Hunt and Joeckel, 1988), and con-
tibia, and provides insight into thefunctional
sequentlyseveralofthesearctoidcarnivorans
anatomy of the hindfoot. This partial skele-
apparently occupied the niches for large cat-
ton of a large individual, probably male,was
like predators.
discovered and excavated in 1972 west of
The Harper Quarry waterhole assemblage
Spoon Butte by R.J. Emry and M.F. Skinner
(Harper Quarry local fauna: Hunt, 1978,
for the Smithsonian Institution. In the same
1985, 1990) produced the most numerous
paleovalley east of the butte, a partial man-
postcranial remains of Y. americana—al-
dibleofamuchsmallerindividualwasfound
though at least four individuals are repre-
by UNSM in 1983, suggesting that sexual
sented, there were no articulated elements.
dimorphismwasanattributeofY.americana
No crania or mandibles have been found,
populations. Evidence of dimorphism occurs
only isolated teeth. Scavenging at the water-
not only in the Lay Ranch beds in south-
hole is everywhere evident, suggesting that
eastern Wyoming but also at Harper Quarry
skulls were fragmented and scattered.
in northwest Nebraska where marked size
Ysengrinia americana is present but rare
differences are evident in some postcranial
in the waterhole bonebeds in the vicinity of
bones.
Agate Fossil Beds National Monument
Finally, a large ‘‘canid’’ humerus (CM
(Hunt,1972).Arobustmetacarpalwasfound
2400) was reported by Peterson (1910: fig.
in the waterhole bonebed at University Hill
56) fromaquarry 8–10 mileseastoftheAg-
in 1904, but no remains have come from the
quarries at Carnegie Hill and the nearby car- ate Quarries. This humerus was later refig-
nivore den site (Hunt et al., 1983; Hunt, ured and described by Hunt (1972) and at-
1990). At the American Museum–Cook tributed to (?)Ysengrinia. Peterson’s quarry
Quarry waterhole, located a few kilometers hasneverbeenrelocated,andnootherfossils
north of the Agate waterhole bonebed, Ysen- from this quarry were identified in the col-
grinia is represented by a calcaneum and lections of the Carnegie Museum (Pitts-
M1. burgh), despite Peterson’s (1910: 262) state-
Fragmentary remains of Y. americana at ment that the ‘‘quarry ... contains a similar
Morava Ranch Quarry includean edentulous fauna to that of the Agate Spring Fossil
mandible (F:AM 25423), isolated M1, a par- Quarries’’. The anatomy of the distal humer-
tial innominate, distal humerus, ectocunei- us indicates referral to Y. americana.