Paleontology and Geochronology of the Deseadan (late Oligocene) of Moquegua, Perú

2009·6.3 MB·English

by  Bruce J. Shockey

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3668, 24 pp., 8 figures, 5 tables November 30, 2009
Paleontology and Geochronology of the Deseadan
(late Oligocene) of Moquegua, Peru´
BRUCE J. SHOCKEY,1 RODOLFO SALAS GISMONDI,2 PHILLIP GANS,3
ANNIE JEONG,4 AND JOHN J. FLYNN5
ABSTRACT
SubsequenttoourinitialreportsofthediscoveryofDeseadanfossilsinsouthernPeru´,wehave
obtainednewdataregardingthepaleontologyandgeologyoftheuppermemberoftheMoquegua
Formation. These data include newly recovered fossil specimens and further analyses of those
collectedinourearlierfieldseasons.Wehavealsoobtainedanashdirectlyfromwithinthefossil-
bearingunitsnearthesummitofCerroPandeAzu´car.BiotitesfromthisSugarloafashgiveanage
estimate of 26.25 6 0.10 Ma, thus supporting our previous suggestion that these fossil-bearing
horizons are of late Oligocene age (Deseadan South American Land Mammal ‘‘Age’’) and
removing our query regarding a possible early Miocene age. Most of the fossils are of
notoungulates and most of these are trachytheriine mesotheriids. Remarkably, three distinct
mesotheriidtaxaappeartohavebeenpresentintheMoqueguafauna,noneofwhicharereferable
tothecommonTrachytherusalloxusofthenearbyandatleastpartlycontemporaneousSallabeds
of Bolivia. Other fossils documented here include postcranial elements of the notohippid
notoungulate,Moqueguahippus,amacraucheniidlitoptern(cf.Coniopternium),anosteodermofan
unnamedspeciesofarmadillo(Dasypodidae,cf.Dasypodinae),andaclawofaphorusrhacidbird.
Wealsodescribeadiminutivenewhystricognathrodent,Sallamysquispea,sp.nov.Itissimilarto,
but distinct from, S. pascuali of Salla. Indeed, despite the temporal and geographic proximity of
MoqueguatoSalla,noneofthetaxafromMoqueguathatcanbeidentifiedtospeciesareknown
fromSalla.Likewise,wehavefailedtofindanydasypodidsfromSallathathaveosteodermslike
that described in this work. Thus, it is appears that distinctive paleogeographic and
1Department of Biology, Manhattan College, New York, NY 10463. Research Associate, Division of Paleontology,
AmericanMuseumofNaturalHistory([email protected]).
2MuseodeHistoriaNatural,UniversidadNacionalMayordeSanMarcos,Lima,Peru´ ([email protected]).
3DepartmentofGeologicalSciences,UniversityofCaliforniaatSantaBarbara([email protected]).
4BiologyDepartment,BarnardCollege,NewYork([email protected]).
5Division of Paleontology and Richard Gilder Graduate School, American Museum of Natural History (jflynn@
amnh.org).
CopyrightEAmericanMuseumofNaturalHistory2009 ISSN0003-0082
2 AMERICAN MUSEUMNOVITATES NO. 3668
paleoenvironmentalconditionsinthelateOligoceneledtoaregionalbioticdifferentiationforthe
Moquegua areaofcoastal Peru´.
INTRODUCTION regarding the paleontology and geology of
these localities in the upper member of the
Upper regions of peaks west of the R´ıo Moquegua Formation. The new data include
Moquegua,nearthecityofMoquegua(fig. 1), additional specimens collected in subsequent
have yielded the first known fossils of the fieldwork, further analyses of previously
Deseadan South American Land Mammal collected material, and 40Ar-39Ar geochrono-
‘‘Age’’ in Peru´ (Shockey et al., 2006). Since logical analyses of an ash collected from
preparation of the initial report of this directlywithinthefossil-bearinghorizonsnear
discovery, additional data have been gathered the summit of Cerro Pan de Azu´car (fig. 2).
Fig. 1. Geologic map of the fossil localities of the upper Moquegua Formation. Based on: Bellido, E.
and C. Guevara. 1961 (Mapa Geolo´gico del Cuadra´ngulo de Clemens´ı, Carta Geolo´gica Nacional y
Instituto Geogra´fico Militar); Shockey et al., 2006: fig 1; and satellite images from Google Earth.
TrachytheriinelocalitiesofBoliviaareindicatedininsertmapatupperright:Salla(Trachytherusalloxus);A,
Lacayani (T. spegazzinianus);andB, R´ıoIru Pluma (T. subandinus).
2009 SHOCKEY ETAL.: THEDESEADAN OFMOQUEGUA, PERU´ 3
Fig.2. PhotoofthenorthfaceofthesummitofCerroPandeAzu´carillustratingthelowerregionofthe
upper Moquegua Formation, including the Sugarloaf ash. (The boundary between the lower and upper
MoqueguaFormationiscoveredatthislocale.)Notecrewmembershikinguptheslopesforanimpression
ofscale.
Most of the fossils recovered are of no- removing prior uncertainty regarding a possi-
toungulates. The present work describes post- ble early Miocene age for the fossil-bearing
cranial remains from three species of me- units (Shockey et al., 2006).
sotheriid notoungulates, including the nearly
completepesofthelargestofthethree(cf.,T.
BACKGROUND
spegazzinianus). This represents the first such
description of any mesotheriid pes. Also, we The Tertiary sediments in the Moquegua/
describe additional material of the notohip- Tacna Basin traditionally have been referred
pid notoungulate, Moqueguahippus glycisma to as the Moquegua Formation (Bellido and
Shockeyetal.,2006,andweexpandthefaunal Guerra, 1963) or Moquegua Group (Tosdal
list by reporting the remains of the only et al., 1981; Acosta et al., 2002), composed of
xenarthran (Dasypodidae, cf. Dasypodinae), the ‘‘formacio´n Moquegua inferior’’ and
and a diminutive new species of rodent, the ‘‘formacio´n Moquegua superior’’ (see
Sallamys quispea, closely related to but dis- Sempere et al., 2004, for discussion of
tinct from the Deseadan species S. pascuali nomenclature problems). These are separated
from Salla, Bolivia. by an angular unconformity (Acosta et al.,
As detailed below, the geochronological 2002; Sempere et al., 2004); in addition, the
analysis provides a date of 26.25 6 0.10 Ma ‘‘lower Moquegua Formation’’ consists of
for the ash that lies in the lower part of the finer sediments than the upper.
fossil-bearing sequence. This date strongly Work in progress (see Sempere et al., 2004)
supports the initial conclusion that the fauna may clarify the complex depositional history
collected is late Oligocene in age, thus of the Tertiary deposits of southern Peru´ and
4 AMERICAN MUSEUMNOVITATES NO. 3668
the resulting unstable geological nomencla- their 40K-40Ar geochronological analysis (see
ture. The strata of interest for our study 40Ar-39Ar Geochronology below).
involve the upper unit of the Moquegua The Moquegua Formation has generally
Formation (sensu Bellido and Guevara, been considered ‘‘nonfossiliferous’’ (Tosdal et
1963; Bellido and Landa, 1965; Tosdal et al., al., 1981). However, in 2002, Rossana Quispe
1981; equivalent to: ‘‘Formacio´n Moquegua and her classmates and instructor (Jorge
Superior’’ of the Moquegua Group [Acosta et Acosta) from the Universidad Nacional
al., 2002]; ‘‘Formacio´n Moquegua superior’’ ‘‘Jorge Basadre Grohmann,’’ Tacna, Peru´,
[Flores et al., 2004] or ‘‘Upper Moquegua found fossils in the upper Moquegua
Formation’’ [Shockey et al., 2006]; ‘‘Mo- Formation, at and just below the summit of
quegua C’’ [Sempere et al., 2004]; Moquegua Cerro Pan de Azu´car (Shockey et al., 2003,
Formation [Sa´nchez Fernandez et al., 2000]), 2006). This initial discovery motivated our
underlain by the lower unit of the Moquegua more intensive National Geographic–spon-
Formation (equivalent to: ‘‘Formacio´n Mo- sored fieldwork in the austral winters of 2002
quegua Inferior’’ of the Moquegua Group to 2004, with results detailed here.
[Acosta et al., 2002]; ‘‘Formacio´n Moquegua
inferior’’ [Flores et al., 2004]; ‘‘Moquegua B’’
MATERIALS, ABBREVIATIONS, METHODS
[Sempere et al., 2004]; Sotillo Formation
[Sa´nchez Fernandez et al., 2000]). For conve- Specimens collected from the Deseadan
nience, given this conflict among various aged localities of the upper Moquegua For-
stratigraphic assignments, we will refer to mation are curated in the MUSM (Depart-
the upper part of the Moquegua Formation amento de Paleontolog´ıa de Vertebrados,
as the ‘‘upper Moquegua Formation’’ and Museo de Historia Natural, Universidad
the lower part as the ‘‘lower Moquegua Mayor de San Marcos, Lima, Peru´). Other
Formation.’’ institutional abbreviations used in the text
Bellido and colleagues (Bellido and Landa, include: UF (vertebrate paleontology collec-
1965; Bellido and Guevara, 1963) character- tions, Florida Museum of Natural History,
ized the Moquegua Formation as continental University of Florida, Gainesville, FL,
siltstones, sandstones, and conglomerates. U.S.A.); AMNH (American Museum of
Conglomerates form the base of the upper Natural History, New York, NY, U.S.A.).
Moquegua Formation (fig. 2) with overlying Additional abbreviations used in this study
finer-grained lagoonal facies (Tosdal et al., include SALMA, South American Land
1981;Acostaetal.,2002).Thesearecomposed Mammal ‘‘Age’’; I, C, P, and M for upper
of clayey and fine-grained sandstones and incisors, canines, premolars, and molars,
mudstones,withpinkignimbriteintercalations respectively (lowercase notation for lower
(Acosta et al., 2002). The regionally extensive teeth).
lower Moquegua Formation locally uncon- The 40Ar-39Ar ages were obtained at the
formably overlies the late Cretaceous to early argon geochronology laboratory in the
Tertiary Toquepala Group (Tosdal et al., Department of Earth Sciences at the
1981; Marocco and Noblet, 1990; Acosta et University of California, Santa Barbara.
al., 2002; and fig. 1). Conventional stepwise-heating and plateau-
Tosdal et al (1981) obtained 40K-40Ar dates age analyses were conducted on biotite sepa-
(25.3 6 0.8, 23.3 6 0.8, and 22.7 6 0.8 Ma) rates (Sugarloaf biotites) obtained from the
from three widely separated ignimbrite expo- ash collected above the basal conglomerates
sures near the top of the upper Moquegua below the summit of Cerro Pan de Azu´car.
Formation, all east of the Moquegua River.
Our new dates (40Ar-39Ar) come from an ash
GEOGRAPHICAND GEOLOGICAL CONTEXT
westoftheMoqueguaRiver,nearthesummit
of Cerro Pan de Azu´car. This Sugarloaf ash The Tertiary Moquegua localities lie 50 km
lies just above the basal conglomerates, thus inlandfromthePacificinthecoastalplainsof
representing a stratigraphically older horizon southern Peru´, east of the Cordillera de la
than those sampled by Tosdal et al., 1981, for CostaandwestoftheCordilleraOccidentalof
2009 SHOCKEY ETAL.: THEDESEADAN OFMOQUEGUA, PERU´ 5
TABLE1
Analytical Data for40Ar/39Ar forthe SugarloafBiotitesof CerroPan deAzu´car
Sample: SB51-18,SugarloafBiotite, J50.0020807
T(uC) t 40(mol) 40/39 38/39 37/39 36/39 K/Ca S39Ar 40Ar* Age(Ma)
650 12 1.6e214 13.4769 1.9e22 0.1618 0.0284 3.0 0.03529 0.377 19.060.3
750 12 3.0e214 9.1264 1.8e23 0.0399 0.0082 12 0.13503 0.736 25.060.1
820 12 2.0e214 8.7735 3.5e24 0.0351 0.0057 14 0.20587 0.807 26.460.1
880 12 2.1e214 8.6844 0.0e+0 0.0176 0.0053 28 0.28003 0.821 26.660.1
940 12 2.3e214 8.8685 0.0e+0 0.0136 0.0061 36 0.36067 0.798 26.460.1
980 12 2.7e214 9.6360 5.8e24 0.0152 0.0085 32 0.44637 0.738 26.560.1
1020 12 3.2e214 9.4337 0.0e+0 0.0135 0.0081 36 0.55122 0.745 26.260.1
1060 12 4.0e214 8.6092 2.3e24 0.0102 0.0055 48 0.69330 0.810 26.060.1
1100 12 4.1e214 7.9361 0.0e+0 0.0111 0.0030 44 0.85017 0.887 26.260.1
1140 12 2.5e214 7.6858 0.0e+0 0.0133 0.0022 37 0.95080 0.916 26.260.1
1190 12 1.1e214 7.6572 0.0e+0 0.0476 0.0018 10 0.99326 0.929 26.560.2
1250 12 1.5e215 9.2983 0.0e+0 0.2417 0.0062 2.0 0.99821 0.802 27.861.3
1320 12 7.6e216 13.0247 1.2e23 0.2417 0.0229 2.0 1.00000 0.482 23.464.0
Total fusion age, TFA5 25.90 6 0.05Ma (including J); weighted mean plateau age, WMPA5 26.24 6 0.05Ma
(includingJ);inverseisochronage526.2160.17Ma.;(MSWD54.52;40Ar/36Ar5297.868.4);stepsused:820,880,940,
980,1020,1060,1100,1140,1190uC,(3–11/13or86%S39Ar);t5dwelltimeinminutes;40(mol)5molescorrectedfor
blankandreactor-produced40;ratiosarecorrectedforblanks,decay,andinterference;S39Ariscumulative,40Ar*5rad
fraction.
theAndes(fig. 1).Thesefossil-bearingbedsof 20 m above the upper Moquegua Fm./ lower
the upper Moquegua Formation are encoun- Moquegua Fm. contact (figs. 1: a on map; 2).
tered only at the summits of a series of peaks A sample of this ash was collected at
(Cerros Pan de Azu´car, Mono, and Santa S17u13.0169 and W71u0.7869 and a 2.3 mg
Ana) flanking the western banks of the R´ıo separate of biotites was subjected to a
Moquegua,whichregionallyrunsalongtheW stepwise-heating 40Ar-39Ar geochronological
71u longitudinal line in the Departamento de analysis. Each dwell time lasted 12 min at
Moquegua, Peru´. Cerro Pan de Azu´car is temperatures that ranged from 650u C to
located 9 km WSW of the city of Moquegua, 1300u C. Plateau temperatures occurred at
at S17u12.8719 and W71u0.6619 (elevation 820u, 880u, 940u, 980u, 1020u, 1060u, 1100u,
1663 m). Cerro Mono (elevation 1780 m) 1140u, and 1190u C.
stretches from 2 to 6 km SW of Cerro Pan Thesedataprovidedatotalfusionage(TFA)
de Azu´car, and Cerro Santa Ana (elevation of25.9060.05 Ma(including‘‘J,’’asummation
1790 m), S17u16.8669 and W71u2.7449, lies term for a series of variables, determined by
10 km SW of Cerro Pan de Azu´car. placinga‘‘fluxmonitor’’sampleofknownagein
Intensive prospecting for fossils in the vast, the reactor with the sample whose age is being
but accessible, area of outcrop of the lower determined, see table 1), a weighted-mean pla-
Moquegua Formation was entirely unproduc- teauage(WMPA)of26.2460.05 Ma(includ-
tive. All fossils found during our fieldwork ing J), and an inverse isochron age of 26.21 6
came solely from the summits of the moun- 0.17 Ma (see table 1 and fig. 3). These yield a
tainswheretheupperMoqueguaFormationis 40Ar-39Ar age determination for the Sugarloaf
exposed. For the most part, the fossils were ashof26.2560.10 Ma.ThislateOligoceneage
broken and scattered on the surface of the falls within the currently accepted time span of
heavily weathered sediments. the Deseadan SALMA (Flynn and Swisher,
40AR-39AR GEOCHRONOLOGY: A volcanic 1995;Kayetal.,1998),andisconsistentwiththe
ash (‘‘Sugarloaf ash,’’ in reference to its being occurrence of Deseadan SALMA fossils that
from Pan de Azucar [5 Sp. sugarloaf]) is were all collected within about 20 m above the
exposed on the north face of Cerro Pan de level of the ash or 10 m below, all within the
Azu´car, about 20 m below the summit and upperMoqueguaFormation.
6 AMERICAN MUSEUMNOVITATES NO. 3668
Fig.3. AragespectrafortheSugarloafbiotiteofCerroPandeAzu´car.TFA5totalfusionage;WMPA
5weighted mean plateauage.
This date of 26.25 6 0.10 Ma from 20 m thislargebirdhasbeenrecovered.Itspresence
above the lower/upper Moquegua Formation at Moquegua was previously noted (Shockey
boundary provides a radioisotopic age deter- et al., 2006) and we here provide a photo
mination within the lower part of the upper (fig. 4) of the single element from what must
Moquegua Formation. This date for the base have been a moderately large bird.
of the upper Moquegua Formation is congru- In terms of its size, curvature, and pres-
ent with the younger 40K-40Ar age determina- ence of lateral nutrient grooves, the avian
tionsofTosdaletal.(1981)fortheupperpart claw from Cerro Mono is similar to that of
of the upper Moquegua Formation, which the Santacrucian (middle Miocene) Pho-
ranged from 22.7–25.3 Ma. rorhacos (see Sinclair and Farr, 1932). It is
notreferredtoPhororhacos,however,asitisa
SYSTEMATIC PALEONTOLOGY little smaller and has a lower degree of
curvature. The material is inadequate to refer
CLASSAVESLINNAEUS, 1758 to any of the known Deseadan genera of
FAMILYPHORUSRHACIDAE AMEGHINO, 1889 phorusrhacid (e.g., Physornis, Andrewsornis,
or Psitopterus; see Alvarenga and Ho¨fling,
Genus and species indeterminate 2003).
Figure 4A
CLASSMAMMALIALINNAEUS, 1758
MATERIAL: MUSM 351, ungual phalanx,
collected in the upper Moquegua Formation, MAGNORDERXENARTHRA COPE, 1889
near the eastern summit of Cerro Mono (fig.
1: e on map). ORDERCINGULATA ILLIGER, 1811
COMMENTS: Despite many hours of pros- FAMILYDASYPODIDAE GRAY, 1821
pecting in the area where this avian ungual
phalanx of was found, no further material of CF. DASYPODINAE GRAY, 1821
2009 SHOCKEY ETAL.: THEDESEADAN OFMOQUEGUA, PERU´ 7
Fig.4. Miscellaneouspostcranialelements.A,phorusrhacoidclaw(MUSM351),inlateralandplantar
views; B, dasypodid osteoderm (MUSM 1604) from the articulating region of the carapace; C,
macraucheniid metapodial (MUSM 349) in dorsal, lateral, and plantar views; and D, right cuboid
(MUSM669) in dorsalandmedial views.
Genus and Species Indeterminate poorly defined. It was found in the upper
MoqueguaFormation,about20 mbelowand
Figure 4B
southeast of the summit of Cerro Pan de
MATERIAL: MUSM 1604, an isolated os- Azu´car, in the area where the holotype of
teoderm, the anterior portion of which is Sallamysquispeawasfound(fig.1:donmap).
8 AMERICAN MUSEUMNOVITATES NO. 3668
COMMENTS: MUSM 1604 is a movable- margins aresmooth,similartowhatisseenin
band osteoderm. It is rectangular, small, and the Astegotheriini. Vizca´ıno (1994) suggested
slender, measuring 16.0 mm long and 4.7 mm that in these animals the carapace was more
wide. The lateral margins are smooth and flexible than in modern Dasypodini where
fairly straight. The posterior border is slightly the scutes are fixed by spicules along their
rounded; it is partly damaged, but five pits, lateral margins. The osteoderms of archaic
likely sites for hair follicles, are recognizable. Astegotheriini and the Dasypodinae from
The central figure is delimited by two parallel Moquegua may have been bounded together
sulci connected anteriorly and reaching the by soft tissue.
posterior margin. Each sulcus presents two InmostAstegotheriinifromtheCasamayorian-
large nonaligned foramina and a number of Mustersan of Patagonia (e.g., Astegotherium)
dispersed smaller ones. The articulation zone the main figure is lageniform and the sulci do
is well defined by a transverse bevel. As in not reach the posterior margin (see Vizca´ıno,
some movable osteoderms of Dasypus novem- 1994). In Anadasypus hondanus from the
cinctus, some foramina are identified just Middle Miocene of La Venta (Colombia),
behind the bevel. parallelsulcidivergelaterallytoreachthesides
MUSM 1604 almost certainly represents a justbeforegettingtotheposteriormargin.Itis
new taxon of a small Deseadan dasypodid, considered the oldest member of the
similar in size to Dasypus hybridus. Unfor- Dasypodini because this pattern suggests the
tunately, the scarcity of well-documented derivedstateseeninextantspeciesofDasypus,
material of coeval taxa and the fragmentary in which the secondary keratin scutes are
conditionofthepresentrecord discouragesus triangular (Carlini et al., 1997). In the osteo-
from erecting a new species. It is probably a derms, the synapomorphy is revealed by the
Dasypodinae based on the surface design of divergent sulci that reach each posterolateral
the osteoderm. The longitudinal and parallel corner (Vizca´ıno, 1990). In the dasypodine
sulci imply the existence of overlapping scales from Moquegua, surface design of the osteo-
covering lateral areas of two adjacent scutes derm implies (1) secondary horny scales were
(secondary horny scales), an apomorphy for rectangular—not triangular and (2) each sec-
the Dasypodinae (Vizca´ıno, 1994; but see ondary scale took up the total length of the
Ciancio and Carlini, 2008). Its systematic visible surface of the osteoderm. This combi-
positionwithinthegroupisuncertain,though. nation of characters is not seen in the early
The Dasypodinae consist of the following membersoftheAstegotheriini,butitmayhave
tribes: Astegotheriini (including Stegotheriini; been attained and by a cluster of a pre-
sensu McKenna and Bell, 1997) from the DasypodiniduringtheOligocene.
PaleocenetotheMiocene(seeVizca´ıno,1994),
and Dasypodini from the Miocene to the ORDERRODENTIA BOWDICH, 1821
present (Vizca´ıno, 1990; Carlini et al., 1997).
Despite the vast expanse of time, general SUBORDERHYSTRICOGNATHA TULLBERG, 1899
shape, and outline of movable osteoderms
SUPERFAMILYOCTODONTOIDEA SIMPSON, 1945
show little difference between both tribes. As
in the Deseadan armadillo from Moquegua, GENUSSALLAMYS HOFFSTETTERANDLAVOCAT,
theyarethinandslenderinAstegotheriiniand 1970
Dasypodini (see Vizca´ıno, 1994; Carlini et al.,
1997). This conservative character was once Sallamys quispea, sp. nov.
used to diagnose the tribe Astegotheriini
Figures 5 and 6; table 2
(Vizca´ıno, 1994), but has since been regarded
as representing a primitive state in the Dasy- HOLOTYPE: MUSM 1404, jaw fragment
podinae evolution (Oliveira and Bergvist, with lower right dp4-m1.
1998). The phylogenetic significance of the REFERRED SPECIMENS: Known only from
suturesofthemarginsisambiguous,although the holotype.
they have implications regarding structural TYPE LOCALITY: The upper Moquegua
demands of the carapace. In MUSM 1604 the Formation, about 20 m below and southeast
2009 SHOCKEY ETAL.: THEDESEADAN OFMOQUEGUA, PERU´ 9
Fig.5. HolotypeofSallamysquispea,MUSM1404.Micrographsprovideviewsfromfourperspectives
(occlusal[A],lateral[B],medial[C],andmedialoblique[D])aswellascloseupsoftheocclusalsurfacesof
m1(E)anddp4 (F).
of the summit of Cerro Pan de Azu´car (fig. 1: brachydont; trilophate m1 with occlusal con-
d on the map). nection of the posterolophid to the hypololo-
ETYMOLOGY: Thespecificname,quispea,is phid, mesolophid extending from the ectolo-
given to honor Rossana Quispe of the city of phid; metalophid intersecting midpoint of
Moquegua, who discovered the first fossils anterolophid.Them1anterolophidhasaspur
known from the Moquegua Formation. She that with more wear would subdivide the
alsoparticipatedinallourfieldprojectsinthe fossetidintotwo.Them1issubquadrangular,
Moquegua Formation, during one of which whereas dp4 is more ovoid. Molariform dp4;
she found the holotype of this diminutive hypolophidwithasmall,posteriorlyextending
rodent. spur; anterolophid extends from protoconid
DIAGNOSIS: Smaller than all known around the anterior end of tooth to the
Deseadan and Santa Rosa local fauna (Peru´) metaconid, so that the anterolophid spur and
rodents, slightly smaller than the smallest metalophid tip join to form a figure eight–
known specimens of Sallamys pascuali; shaped fossetid.
10 AMERICAN MUSEUMNOVITATES NO. 3668
Fig. 6. Comparative anatomyof dp4and m1 of Sallamys spp. A,Right dp4 and m1 of S. quispea, sp.
nov.(holotype,MUSM1404),shownasaSEMmicrograph(left)andalinedrawing(right)toillustratethe
terminology used in the text. (Terminology based on Patterson and Wood, 1982; and Candela, 1999:
Abbreviations: hypf 5 hypoflexid; hyp-lophd 5 hypolophid; mesf 5 mesoflexid; post-lophid 5
posterolophid; prtcnd 5 protoconid.) B, is the right dp4 and m1 of PU 20909, Sallamys pascuali, in
whichthedp4reflectsthemorphologyofthatoftheholotype(HoffstetterandLavocat,1970).Cisaleftdp4
and m1 (digitally reversed to appear as right) of Sallamys, cf. S. pascuali, UF 114458, in which the
morphologyofthedp4isdistinctfromthatoftheholotypeandreferredspecimenPU20909(seePatterson
andWood,1982:fig.5d,andtextfordiscussion).PhotoofPU20909EYalePeabodyMuseumofNatural
History,New Haven,Connecticut.
DIFFERENTIAL DIAGNOSIS: Sallamys quispea pascuali, but with transverse dimension short-
differs from rodents of the Deseadan assem- er than all). Differs from Branisamys luri-
blage from Salla, Bolivia, in the following bayensis in its much smaller size (m1 mesio-
ways:Itismostsimilarinoverallmorphology distal dimension just a third of that of B.
to Sallamys pascuali, but with lower crown luribayensis); m1 having only three major
height;dp4notasmolariform,butsubequalin lophids, mesolophid not distinct or fully
size to m1 (just 3% longer than m1 in formed. Differs from Incamys bolivianus in
mesiodistal dimension), whereas dp4s of S. smaller size (linear dimensions 40%–65% of
pascualiarelarger(14%–25%longerthanm1); those of Incamys); labial hypolophid and
anterior lophid of dp4 continuous from posteriorlophidofm1closer,formingaunited
protoconid to metaconid, lacking the flexid crest with little wear (persistently separated in
that separates protoconid from anterior lo- Incamys); lingual spurs projecting from ante-
phid of S. pascuali and lacking a second rolophid of m1 with formation of an ante-
mesiolabial flexid; mesolophid of dp4 without rofossetid. Differs from Migraveramus beatus
connection to metaconid; less pronounced in having only three major lophids (mesolo-
recurvature of lingual extreme of posterolo- phidshort,notreachingthemetaconid),wider
phid of dp4 and m1; posterior spur at meta- and mesoflexids, and considerably
hypolophid-ectolophidjunctionofm1shorter. smaller size (m1 mesiodistal dimension less
Dental dimensions smaller than those of S. than 75% to those of M. beatus).
pascuali (mesiodistal dimension of dp4 just Sallamysquispeadiffersfromrodentsofthe
82%thatofsmallestdp4ofS.pascualiandm1 Deseadan of Patagonia: Differs from Platy-
mesiodistal dimension similar to that of only pittamys in more complex anterolophid, two
the smallest of individual sampled of S. anterofossetids.DiffersfromDeseadomysaram-