Small Oligocene Amphicyonids from North America (Paradaphoenus, Mammalia, Carnivora)

20 Pages·2001·8.4 MB·English

by  R. O. B. E. R. T M. Hunt Jr.

2 AMERICAN MUSEUM NOVITATES NO. 3331
es from the Duchesnean to the early Arika- siomorphicmolarsthatresemblethoseofEu-
reean and is the most common North Amer- ropean Cynodictis from Quercy in France.
ican Paleogene amphicyonid. The Duches- The previously undescribed Whitneyan and
nean D. lambei is the smallest speciesofthis earlyArikareeanParadaphoenusfossils,rep-
lineage and is a likely ancestor to all later resented by only two mandibles and an un-
Daphoenus. After the appearance of Da- associated maxilla from Nebraska and South
phoenus in the early Duchesnean, Daphoen- Dakota,warrantthenamingofanewspecies,
ictis and Brachyrhynchocyon first occur in P. tooheyi.
the late Duchesnean and early Chadronian, A functional interpretation of the teeth,
respectively, coexisting with Daphoenus skull, and postcranial skeleton suggests that
throughout the Chadronian: all of these gen- Paradaphoenus was a small terrestrial om-
era are small, fox-sized carnivores ((cid:59)4–10 nivore lacking cursorial specializations, and
kg). Daphoenictis and Brachyrhynchocyon probably able to climb when necessary.
become extinct at the end of the Chadronian, These characteristics would be compatible
but Daphoenus persists into the Orellan(ear- with a wooded habitat, whether savanna or
ly Oligocene), and progressively increasesin riverine gallery forest. Its basicranial anato-
size during the Whitneyan. By the early Ari- my establishes it as a member of the Am-
kareean (late Oligocene), Daphoenus ap- phicyonidae (Hunt, 1998).
proaches the size ((cid:59)20–30 kg) of a small
wolf (Hunt, 1996). ABBREVIATIONS
Much less familiar to paleontologists is
another lineage of very small amphicyonids, Anatomical
Paradaphoenus Wortman and Matthew,
A alisphenoid
1899, entirely restricted to North America.
ac alisphenoid canal
The genus first appears in Orellan sediments BO basioccipital
of the Great Plains, continues through the BS basisphenoid
Whitneyan, and terminates in the early or ca pit for anterior crus of ectotympanic
mid-Arikareean. Members of this lineage in- E caudal entotympanic
crease only slightly in size over (cid:59)6 million F facet on petrosal promontorium for ec-
years, never exceeding 3–4 kg, and are the totympanic
gf postglenoid foramen
smallest New World amphicyonids.Theirre-
h hypoglossal (condyloid) foramen
mains were often placed in disparate taxa or
L middle lacerate foramen
went unrecognized in collections.
m mastoid
The North American hypodigm of Para-
me mastoid-exoccipital suture
daphoenus includes the remains of just 10 P petrosal promontorium
individuals (fig. 1), allocated to 3 species, P. plf posterior lacerate foramen
minimus (Hough, 1948a) and P. tooheyi, n. pp paroccipital process
sp., from White River and lower Arikaree ps basioccipital embayment for inferior
sediments of Nebraska and South Dakota, petrosal venous sinus
and a terminal species, P. cuspigerus (Cope, SQ squamosal
T ectotympanic
1878), from the John Day beds of Oregon.
x partial M3 alveolus
Fortunately,thegenusisrepresentedbythree
skulls with well-preserved teeth and basi-
Institutional
crania. Paradaphoenus cuspigerus is based
on two skulls from the John Day beds, one AMNH American Museum of Natural History,
of which (the holotype, fig. 2) includes both New York, NY
LACM Los Angeles County Museum of Nat-
mandibles of the same individual, demon-
ural History, Los Angeles, CA
strating a critical association between lower
UNSM University of Nebraska State Museum,
and upper teeth. The Orellan species, Para-
Lincoln, NE
daphoenus minimus, is oldest and is repre-
NMB Naturhistorisches Museum, Basel,
sented by a skull, severalisolatedmandibles, Switzerland
and the only known postcranial material at- SDSM South Dakota School of Mines and
tributable to the lineage; it has dentally ple- Technology, Rapid City, SD
2001 HUNT: OLIGOCENE AMPHICYONIDS 3
Fig. 1. Geographic distribution of Paradaphoenus in North America: all fossils are fromOligocene
sediments of the central Great Plains (White River and Arikaree Groups, P. minimus, P. tooheyi) and
Oregon (John Day Formation, P. cuspigerus).
SYSTEMATICS and early Arikareean of western Nebraska;
OrellanandearlyArikareeanofsouthwestern
ORDERCARNIVORABOWDICH,1821
South Dakota; early or mid-Arikareean of
DIVISIONARCTOIDEAFLOWER,1869 central Oregon.
FAMILYAMPHICYONIDAETROUESSART,1885 DIAGNOSIS: Smallest ((cid:44) 3–4 kg) North
American amphicyonid carnivorans with m1
Paradaphoenus Wortman and Matthew,
lengthsof8.3–9.4mm;rudimentaryauditory
1899
bulla formed by a slightly inflated ossified
TYPE SPECIES: Paradaphoenus cuspigerus ectotympanic that does not fully enclose the
(Cope, 1878). middle ear; dental formula 3-1-4-3/3-1-4-3;
INCLUDED SPECIES: Paradaphoenus cuspi- P4 length short relative to combined lengths
gerus, Paradaphoenus minimus (Hough, of M1-2 (P4L/M1-2L: Orellan, 80.8%; early
1948a), Paradaphoenus tooheyi, new spe- Arikareean, Great Plains, 77.6%; early or
cies. mid-Arikareean, Oregon, 67.7–73.2%); P4
KNOWNDISTRIBUTION:Orellan,Whitneyan, with abbreviated protocone relative to Da-
4 AMERICAN MUSEUM NOVITATES NO. 3331
Fig. 2. (A) Cranium and mandibles of the genoholotype of Paradaphoenus (P. cuspigerus, AMNH
6852) from the John Day Formation, Oregon (in lateral view); (B) stereophotographs of the same
individual, initially figured by Cope (1884, P1. 68, figs. 1–4) as Amphicyon cuspigerus. Scale bar in
this and all subsequent figures is 1 cm in length unless otherwise noted.
phoenus, Hesperocyon, and Cynodictis; M1 DISCUSSION: The fossilsofParadaphoenus
with well-developed meta- and paraconules fall into four samples of decreasing geologic
as in Cynodictis; M2 prominent and the cen- age: (1) an Orellan sample, comprising the
tralmemberofanuppermolarrowthatgrad- holotype cranium of ‘‘Daphoenus’’ minimus
ually diminishes in size from M1-3; m1 with Hough 1948a (fig. 3, AMNH 39099) from
basined talonid, m1 paraconid blade not an- near Scenic, South Dakota, and four isolated
teriorly extended (it is extended in Hesper- mandibles from western Nebraska (fig. 4,
ocyon); prominent rectangular m2 with ba- UNSM 25030, 25305, 26139; UNSM 25148
sined talonid and anterolabialswellingofthe not illustrated), all from White River sedi-
cingulum (m1-2 talonids are markedly en- ments; (2) an isolated Whitneyan mandible
larged with prominent basins in Whitneyan from White River sediments of western Ne-
and Arikareean species, less so in Orellan); braska (fig. 4, UNSM 26130, P. tooheyi, n.
postorbital/preorbital lengthratio(cid:59)2:1(table sp.), with its molar dentition evolvedbeyond
1). Lower molars become wider in younger that of the Orellan specimens, but not to the
species; upper molars are correspondingly degree observed in the early Arikareeanfos-
enlarged (table 2). sils;(3)amandiblefromlowerArikareesed-
2001 HUNT: OLIGOCENE AMPHICYONIDS 5
Fig. 3. Stereophotographs of the holotype cranium (in ventral view) of Paradaphoenus minimus
(AMNH 39099), Orellan, White River Group, South Dakota. For abbreviations in this and subsequent
figures, see p. 2.
iments, Wagner Quarry, Dawes Co., Nebras- the basined molar talonids), a character
ka (UNSM 6002-92, holotype of P. tooheyi, found in the younger species of the genus.
n. sp.), and a maxilla of the same species This broadening of the molars is first ob-
from the Sharps Formation of South Dakota served in the only Whitneyan specimen of
(LACM 21649, P. tooheyi, n. sp.), both of Paradaphoenus, a mandible with p2-m1
early Arikareean age(fig.5);(4)thecranium (UNSM 26130), and becomes most pro-
and associated mandibles (fig. 2, AMNH nounced in the lower molars of the Arika-
6852, genoholotype) of Paradaphoenus cus- reean mandibles (fig. 6). The Orellan fossils
pigerus(Cope,1878),andareferredcranium include the smallest individuals of the Par-
of the same species (AMNH 6853, holotype adaphoenus lineage, based on dental mea-
of ‘‘Amphicyon’’ entoptychi Cope, 1879) surements and the size of the only known
from the John Day beds, central Oregon, Orellan cranium (AMNH 39099, table 1,
both fossils unfortunately lacking exact basilar length (cid:59)8.8 cm). The plesiomorphic
stratigraphic data, but probably of late early features of the molars warrant retention of
to mid-Arikareean age. Geographic and Hough’s (1948a) species minimus fortheOr-
stratigraphic information for these fossils is ellan hypodigm.
presented in appendix 1. The early Arikareean fossils from South
The Orellan cranium and mandibles are Dakota and Nebraska include a maxilla with
the geologically oldest remains of the genus M1-2 (alveoli or broken roots of P3-4, M3)
and retain the most plesiomorphic dentition. from the Sharps Formation of southwestern
These mandibles show no transverse broad- South Dakota, and an isolated mandiblewith
ening of m1-2 (in particular, no widening of p4-m2 (alveoli of p1-3, canine root) from a
6 AMERICAN MUSEUM NOVITATES NO. 3331
Fig. 4. Mandibles of Paradaphoenus from the White River Group, western Nebraska: (A) Labial
view—top, P. tooheyi, Whitneyan, UNSM 26130; middle, P. minimus, Orellan, UNSM 25305; bottom
leftandright,P.minimus,Orellan,UNSM25030and26139.(B)Lingualview—top,P.tooheyi,UNSM
26130; middle, P. minimus, UNSM 25305; bottom left and right, P. minimus, UNSM25030and26139
(stereophotographs).
lower Arikaree channel fill (Wagner Quarry) 1981 (reported by J. R. Macdonald [1970]to
in northwestern Nebraska (fig. 5). The beequivalenttoSDSMLoc.V5359,nearthe
Sharps maxilla was discovered in the collec- middle of the Sharps Formation). The Wag-
tion of the Los Angeles County Museum, ner Quarry mandible was found in 1992 dur-
and is from LACM Wounded Knee Loc. ing a UNSM excavation of a basal Arikaree
2001 HUNT: OLIGOCENE AMPHICYONIDS 7
TABLE1
Preorbital, Postorbital, and Basilar Lengths of Paradaphoenus Crania (in mm)a
Taxon Museumno. Preorbital Postorbital Ratio Basilar
Paradaphoenuscuspigerusb AMNH6852 36.4 70.2 1.93 94.8
Paradaphoenuscuspigerus AMNH6853 (cid:59)38 68.3 1.80 (cid:59)100
Paradaphoenusminimusb AMNH39099 (cid:59)30 66.2 2.20 (cid:59)88
aPreorbitallengthismeasuredfromthetipofthepremaxillatotheanteriorborderoftheorbit;postorbitallength
ismeasuredfromthe anteriorborderoftheorbitto theoccipitalcondyle.
bHolotype.
fluvial channel fill cut into sediments of the or can be directly correlated with, the type
White River Group near Chadron, Nebraska; areas of the Orellan, Whitneyan, and Arika-
associated mammals included anthracothere, reean land mammal ages. The recent discov-
entelodont, rhinoceros, nimravid,andseveral ery and identification of the Whitneyan and
rodents. early Arikareean fossils from Nebraska and
Whitneyan and early Arikareean Parada- South Dakota allowed a more accurate age
phoenus fossils from Nebraska and South estimate for the John Day specimens, which
Dakota, although differing in age, are mor- previously were difficult to date. These new
phologically similar, and are placed in a new fossils also document successive evolution-
species, Paradaphoenus tooheyi (appendix ary stages in the Paradaphoenus dentition
2),intermediateintheformofm1-2between duringtheOrellantoArikareeanintervalthat
P. minimus and P. cuspigerus. The new spe- support the placement of the three known
cies is named for Dr. Loren Toohey of Mid- species in a single lineage.
land, Texas, who has contributed for over 60 Thisscenarioisbasedonanobservedpro-
years to UNSM field excavations in Nebras- gressivealterationintheformofm1-m2.For
ka, and participated in the 1992 Wagner example, the recently discovered Wagner
Quarry excavation that discovered the holo- Quarry mandible of P. tooheyi has an m2
type. morphologylikelytohavebeenderivedfrom
Fortunately, the Great Plains fossils of the plesiomorphic m2 of the Orellan P. min-
Paradaphoenus can be placed in established imus. In the Wagner Quarry m2, the trigonid
stratigraphicsequencesthateitherarewithin, is reduced and crowded to the front of the
Fig. 5. Stereophotographs of the maxilla (LACM 21649, Sharps Formation, South Dakota) and
holotype mandible (UNSM 6002-92, lower Arikaree Group, Nebraska) of early Arikareean P. tooheyi,
n. sp., known only from the central Great Plains. Note alveoli for well-developed M3 in maxilla.
8 AMERICAN MUSEUM NOVITATES NO. 3331
is apparently somewhat younger, possibly of
late early to mid-Arikareean age, based on
the observation that the amount of change in
the molar teeth between P. tooheyi from
Wagner Quarry and P. cuspigerus is rather
modest. Lower Arikaree sediments at Wag-
ner Quarry are probably time equivalent to
lower Arikaree fluvial rocks of the Gering
Formation at Wildcat Ridge in the southern
Nebraska panhandle, dated at (cid:59)28.1–28.3
Ma (Tedford et al., 1996; MacFadden and
Hunt, 1998). John Day P. cuspigerus would
necessarily postdate this interval, but the
amount of time involved is uncertain. Gray
tuffaceous siltstone adhering to the skulls
could have been derived from a number of
tuffaceous units within the upper John Day
Formation, but the exact horizon is indeter-
minate. A speculative upper age limit for the
Paradaphoenus lineage, based on the sumof
presentevidence,isestimatedat(cid:59)25–23Ma.
Fig. 6. Stereophotographs of the lower denti-
DENTITION
tion of holotypes of Paradaphoenus tooheyi (left,
UNSM6002-92)andP.cuspigerus(right,AMNH
Incisors: No specimens of the Orellan or
6852) in occlusal view. Note wider molars and
Whitneyan species of Paradaphoenus pre-
more anteriorly placed m2 trigonid in AMNH
6852. serve either upper or lower incisors. The an-
terior rostrum of the only known Orellan
skull (AMNH 39099) is missing, and none
tooth, and the talonid is widened and more ofthemandiblesretainstheanteriorpartwith
prominently basined, relative to the P. min- incisor alveoli.
imusm2,inwhichtheunreducedtrigonidoc- The early Arikareean Wagner Quarry
cupies theanteriorhalfofm2andthetalonid specimen preserves the anterior part of the
is not expanded. In the holotype mandibleof left mandible: although no incisors remain,
the John Day P. cuspigerus, the widening of there is a large i3 alveolus, but the part of
the molars observed in the Wagner Quarry the dentary with the i1-2 alveoli was lost.
mandible is even more pronounced (fig. 6): In the P. cuspigerus holotype mandible, a
the m2 trigonid of the John Day species re- partial, poorly defined i3 alveolus lies inter-
mains crowded to the anterior end of the nal to the canine root. However, the upper
tooth as in the Wagner Quarry mandible,but incisor row in the premaxillae preserves an
the m2 talonid is even more expanded. The intact acuminate I3, slightly recurved and
lower carnassial also is broadened, particu- without accessory cusps. I1-2 progressively
larly the basined talonid. The upper molars decrease in size internal toI3,butarebroken
of the two John Day crania (AMNH 6852, off at their roots.
6853) also demonstrate thistrend (fig.7),for Canines: No canines are preserved in the
they are enlarged and broadened relative to Orellan or Whitneyan fossils. The Wagner
the upper molars in the maxilla from the QuarryArikareeanmandibleretainsarobust,
Sharps Formation of South Dakota (fig. 5). slightly laterally compressedcanineroot(5.3
The John Day crania, then, are unlikely to (cid:51) 3.2 mm). The mandible of the P. cuspi-
be of earliest Arikareean age, because their gerus holotype also contains a robust, some-
molars are more derived than those in the what laterally compressed canineroot(5.5(cid:51)
Wagner Quarry mandible and Sharps For- 2.8 mm), but the crown was lost. The deli-
mation maxilla. The John Day P. cuspigerus cate upper canine of the holotype (AMNH
2001 HUNT: OLIGOCENE AMPHICYONIDS 9
6852) is laterally compressed (4.5 (cid:51) 3.3 whereas diastemata between the other pre-
mm), and although incomplete, shows the molars are negligible. There is a progressive
posterior and anterointernal longitudinal decrease in size from P3 to P1; this is also
enamel ridges typical of amphicyonids. seenintheArikareeanParadaphoenusskulls
Premolars: Only one Orellan mandible from the John Day beds (figs. 7B, 7C).
(UNSM 25305, fig. 4) retains any part of a P4 in all Paradaphoenus skulls (AMNH
premolar; all other mandibles are broken an- 39099, 6852, 6853) is a short, robust carnas-
terior to m1. UNSM 25305 retains the base sial, surrounded by a pronounced cingulum.
of p4 (for dental measurements, see table 2), P4 has a prominent but abbreviateprotocone
which suggests that the premolars in the Or- that in occlusal view is nearly confluentwith
ellan Paradaphoenus minimus were similar the medial face of the carnassial; the proto-
to the laterally compressed premolars in the cone is not strongly extended toward the
younger species of the genus. Theonly man- midline as in, for example, Hesperocyonand
dible of Whitneyan age (P. tooheyi, UNSM Daphoenus.
26130, fig. 4) retains p2-4 and a single-root- P2-4intheJohnDayskulls(AMNH6852,
ed p1 alveolus. Here p2-4 are elongate, lat- 6853, fig. 7) are very similar to these teeth
erally compressed teeth separated by very in the Orellan skull (AMNH39099).AMNH
short diastemata; each premolar has a rela- 6852, the P. cuspigerus holotype, preserves
tivelylowcentralcusp,anextendedposterior P1-4, the only complete upper premolar row
heel with a small posterior cingulum cusp, known in the genus. P1 is a small, laterally
and a slightly extended anterior cingulum; compressed tooth with an anteriorly placed
there is a small anterior cingulum cusp on main cusp. P4 retains the diagnostic shape
p2-4. seen in all other specimens; however,theen-
Although the Wagner Quarry mandible circling cingulum is even more pronounced.
(UNSM 6002-92, fig. 5) retains only p4, this Molars: Upper molars are present in the
tooth is somewhat taller and less elongate Orellan and Arikareean skulls of Parada-
relative to the Whitneyan p4 of UNSM phoenus (fig. 7), and also in the Arikareean
26130. Also, the dimensions of the p2-3 al- maxilla from the Sharps Formation (fig. 5).
veoli in the Wagner Quarry mandible indi- Inthesespecimensthemolarsarelargelyun-
cate that these premolars were not as elon- worn, with a well-defined cusp pattern;
gate as in the Whitneyan specimen. In fact, AMNH6853isanexception,withsomewhat
the Wagner Quarry mandible and the holo- worn molars. Both John Day skulls and the
type mandible oftheJohn DayP.cuspigerus Sharps Formation maxilla have three upper
(AMNH 6852, figs. 2, 6) share shorter pre- molars. M3 is actually present in AMNH
molars without evident diastemata, relative 6853, and this tooth is representedbyalveoli
totheWhitneyanmandible.TheJohnDayP. in the Sharps maxilla and in AMNH 6852.
cuspigerus mandible preserves p2-4: each In the Orellan AMNH 39099 an indentation
premolar has a principal cusp placed slightly in the posterior border of the left maxilla
forward of center descending to a posterior suggests M3 was initially present (fig. 3, x).
heel that increases in size from p2 to p4; a Thus, Paradaphoenus retained three upper
prominent, somewhat laterally placed poste- molars throughout its known range, and
rior accessory cusp occurs on p4 but is ab- Wortman and Matthew (1899:129) included
sent on p2-3. A fine enamel ridge descends the presence of M3 in their definition of the
the anterior face of each premolar: it is de- genus.
flected to the anterointernal margin of p2, In all the skulls and in the maxilla, the
less so on p3, and continues directlyforward molars diminish in size from M1 to M3.
to the anterior border of p4. However,thereisaproportionalsizeincrease
Only P3-P4 are adequately preserved in in M2 relative to M1 between the Orellan
the Orellan skull(AMNH39099,fig.7A).In and Arikareean species. This is particularly
lateral view, P3 is triangular, with a small evident in the John Day species, P. cuspi-
heel,butlackingaposterioraccessoryorcin- gerus, in which the M2 is conspicuously en-
gulum cusp. P2 is separated from P1 by a larged (fig. 7).
diastema 4.3 mm in lengthinAMNH39099, The distinguishing features of M1-2 are:
10 AMERICAN MUSEUM NOVITATES NO. 3331
Fig. 7. Stereophotographs of the upper dentition (palatal view) of (A) Paradaphoenus minimus
(AMNH 39099, holotype) from the Brule Formation, South Dakota, and (B, C) Paradaphoenus cuspi-