n^o
,50
^
FIELDIANA
GEOtOGYUBRARy
Geology
NEW
SERIES,
NO.
50
Notoungulata
and
Litopterna
of
the
Early
Miocene Chucal
Fauna,
Northern
Chile
Darin
A.
Croft
John
J.Flynn
Andre
R.
Wyss
CO
c\#CD
July
30,2004
Publication
1528
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UNIVERSITY
OF
ILLINOIS
LIBRARY
AT
U^SANA-CHAMPAIGN
FIELDIANA
GEOLOGY
LIBRARY
Geology
NEW
SERIES,
NO.
50
Notoungulata
and
Litopterna
of
the
Early
Miocene Chucal
Fauna,
Northern
Chile
Darin
A.
Croft
Departmentof
Anatomy
CaseWestern Reserve University
School ofMedicine
10900EuclidAvenue Cleveland, Ohio 44106 U.S.A.
DepartmentofGeology
Field
Museum
of Natural History1400SouthLakeShore Drive
Chicago, Illinois60605-2496
U.S.A.
John
J.
Flynn
DepartmentofGeology
Field
Museum
of Natural History1400SouthLakeShore Drive
Chicago, Illinois60605-2496
U.S.A.
Andre
R.
Wyss
Departmentof Geological Sciences
Universityof California—SantaBarbara
Santa Barbara, California93106
U.S.A.
Published July
30,2004
Publication
1528
©
2004
FieldMuseum
of Natural HistoryISSN
0096-265
1Table
of
Contents
Abstract
1Introduction
1Geographic
and
Geologic
Setting 2Materials
and Methods
2Abbreviations
4
Systematic
Paleontology
4
Notoungulata4
Toxodontidae
4
Nesodon
imbricatus 5Adinotherium
sp 8 Mesotheriidae 11 Altitypotheriumpaucidens
12 Altitypotherium chucalensis20
Eotypotheriuum
chico25
Hegetotheriidae 31Hegetotherium
cf. H. mirabile33
Litoptema
36
Macraucheniidae
36
Theosodon
sp. indet38
Phylogeny
of Mesotheriines
40
Age
and Faunae
Comparisons
42
Discussion
and
Conclusions
47
Acknowledgments
49
Literature Cited
49
9.
Upper
dentitionof holotype ofAltity-potherium
chucalensis,SGOPV
4100,a partial skull withportions ofall
pre-molars
and complete
molars 2110. Portionsof lowerdentition oi
Altity-potherium
chucalensis,SGOPV
4100
....22
11.
Holotype
ofEotypotherium
chico,SGOPV
5157,a partial right maxillaand zygomatic
arch withP3-M3
27
12.
Upper
dentitions referred toEotypo-therium chico
28
13. Partial left
mandible
withm2-3,
SGOPV
5158, referred toEotypothe-rium chico
29
14.
Comparison
ofthe degree offusionofthe tibia
and
fibulaamong
selectedSantacrucian typotheres
32
15. Isolated upper
cheek
teeth referred toHegetotherium
cf. H. mirabile34
16.
Lower
dentitions referredto Hegeto-therium cf. H. mirabile 35 17. Selectedpostcranialspecimens
referredto
Theosodon
sp. indet39
18. Strictconsensustrees of mesotheriinerelationships
43
List
of
Tables
List
of
Illustrations
1.
Geography and
geology oftheChucal
Formation
32. Partial skull of
Nesodon
imbricatus,SGOPV
4053
73. Bivariate plot oflower
molar
dimen-sions for
Adinotherium
and
Nesodon
84. Partial left ?i2 of Adinotherium,
SGOPV
4064
95. Relative sizes of mesotheriines
and
toxodontids
from
Chucal, as illustratedby
the sizeofthe ulna 10 6.Morphology
oftheproximal radius inmesotheriines
and Adinotherium
11 7.Holotype
of Altitypotherium paucidens,SGOPV
4038, a partial rostrum withleftII, left
P4-M3
and
rightP4-M1
.... 138.
Lower
dentitions referred toAltitypo-therium
paucidens
141.
Measurements
forChucal specimens
ofNesodon
imbricatus6
2.
Measurements
forspecimens
ofAltity-potherium paucidens
12 3.Development
of suborbital fossaand
sizeofinfraorbital
foramen
in selectedmesotheriines 19 4.
Measurements
forspecimens
ofAltity-potherium
chucalensis20
5.Measurements
forspecimens
ofEoty-potherium
chico26
6.Measurements
forChucal specimens
ofHegetotherium
mirabile37
7. List ofcharacters
and
character statesused in phylogenetic analysis of
me-sotheriine relationships 41
8. Character-taxon matrix for
phylogenet-ic analysis of mesotheriine
relation-ships
42
9. Ungulates ofmiddle-latitude early to
middle
Miocene
faunas of northernChile
and
Bolivia45
10. Ungulates ofselected low-, middle-, 12. Revised
taxonomic
list oftheChucal
and
high-latitudeMiocene
faunas ofFauna
47
South
America
46
13.Body
mass
estimates ofmesotheri-11. Ungulate faunal resemblance indices ines
48
(Simpson
coefficients)among
selectedlow-, intermediate-,
and
high-latitudeMiocene
faunas of SouthAmerica
47
Notoungulata
and
Litopterna
of the
Early
Miocene
Chucal Fauna, Northern
Chile
Darin
A.
Croft
John
J.
Flynn
Andre
R.
Wyss
Abstract
This study describes the notoungulates
and
Htopterns(endemic
SouthAmerican
ungulates)from
theChucal Fauna
of northern Chile. Eight species areknown
to date, including sevennotoungulates
and
one
litoptern.The
bulk of the toxodontid notoungulate material, including a well-preserved partial skull, is referred toNesodon
imbricatus.A
few
postcranial elementsand
a single partial tooth are referred toAdinotherium
sp. indet. Poorly preserved dentalma-terial
may
represent a third (indeterminate) toxodontid.Fragmentary
dentaland
postcranialremains are referred to
Hegetotherium
cf. H. mirabile (Hegetotheriidae).Theosodon
sp. indet.(Litopterna: Macraucheniidae) is recorded
on
the basis ofa variety ofdiagnostic limb bones,but dental remains of this taxon are not yet recorded at Chucal.
Three
new
species ofmeso-theriid notoungulates are described: Altitypotherium paucidens, Altitypotherium chucalensis,
and Eotypotherium
chico.The
largest, Altitypotheriumpaucidens, differsfrom
all previouslydescribed mesotheriids in the loss of an upper premolar (P3). Altitypotherium chucalensis is
represented
by
an associated skulland
mandiblesplus postcranial remains.Eotypotherium
chi-co, basedon
gnathic remains,isthesmallestmesotheriidknown.
Bracketingradioisotopic datesand
biostratigraphic correlationargueforreferraloftheChucal
Fauna
totheSantacrucianSouthAmerican
Land
Mammal
"Age"
(late early Miocene).The
forms
from Chucal
are the onlymesotheriids
known
forthis temporal intervaland
alsomark
theearliestknown
occurrence ofmesotheriines.
A
phylogenetic analysis places the three taxafrom Chucal
as early divergingmembers
ofthe Mesotheriinae, withEotypotherium
chico representing the outgroup to allre-maining
members
of the clade. In the presenceand
abundance
of mesotheriinesand
in theabsence ofinteratheriids, the
Chucal
Fauna
more
closely resembles geographically proximate (but younger) faunas in Boliviaand
the Precordillera of northernmost Chile than temporallycorrelative faunas
from
southernSouth
America. This pattern indicates significant faunalpro-vinciality in South
America
during the late earlyMiocene and
suggests that the intermediatelatitudes might
have
been
a center of diversification for mesotheriinesand
potentially othergroups of
mammals.
Introduction
Study
ofSouth
American
fossilmammals
hastraditionallyfocused
on
faunasfrom
thehighlat-itudes, especially Patagonian Argentina
(Patter-son &. Pascual, 1972;
Simpson,
1980).The
dis-covery
of faunas elsewhere inSouth
America
(e.g., Bolivia, Brazil, Chile,
Colombia)
hascon-tributed to
more
complete
understanding of theevolution of
South
American
mammals
but hasalso revealed unanticipated complexities (see
Flynn
«feWyss,
1998; Flynn, 2002).These
extra-Patagonian faunas demonstrate, forone, that
lat-itudinal provinciality characterized
South
Amer-ican
mammal
faunas formuch
ofthe Cenozoic,necessitating
sampling
of awide
geographicrange for
any
given time slice to gain a fuller understanding ofmammal
evolutionon
thecon-tinent (Pascual et al., 1985;
Wyss
et al., 1994;Madden
et al., 1997).Our
researchteam
hasbeen working
to un-coverand develop
fossilmammal
faunas ofious ages throughout the length of Chile.
The
Chucal Fauna
represents the northeasternmost ofthese fossiliferous localities.
The
first fossilver-tebrate
specimen from
this fauna, discovered in1992
during the course of geologicmapping
northeast ofSalar
de
Surire (Fig. 1), pertains toNesodon,
an earlyMiocene
toxodontidnotoun-gulate (Charrier, Mufioz,
Wyss,
et al., 1994).To
determine
whether
theChucal Formation
would
produce
other identifiable fossilmammal
re-mains, a return trip to the areawas
undertakenin July 1998. This expedition yielded a variety
of well-preserved specimens, including a
diver-sity of
endemic
ungulates, as well as the oldestchinchillinerodent (Flynn, Croft,etal., 2002).
A
second
expedition to the area in2001 produced
many
additionalspecimens and
atleast fivespe-cies not recorded previously (Charrier et al.,
2002).
The
present study provides descriptionsand
taxonomic
analyses ofthemost
diverseand
abundant
component
oftheChucal
Fauna, ofitsnotoungulates, as well as ofits single litoptern.
Prior to discovery of the
Chucal
Fauna, onlyisolated
Cenozoic
mammal
specimenshad been
reported
from
northern Chile.The
first, ameso-theriid
mandible
(MLP
86-VIII-lO-l),was
col-lected
by
D. Pacci in1969
in theareaofCaragua
(approx. 18° 25'S, 69°35'E) west ofthe
town
ofBelen.
The
second,a nearly complete mesotheriid skulland
mandibles with associated postcrania(SGOPV
4004),was
discovered in1989
(Salinaset al., 1991), probably
from
thesame
locality asPacci's specimen.
Both
specimenswere
collectedfrom
theHuaylas
Formation, aunitdemonstrablyyounger
(middle lateMiocene,
definitely<16
Ma
and
most
likely~
10.8-11.7Ma;
Flynn
et al., inpress) than the Santacrucian-aged horizons
de-scribed here.
The
two
mesotheriidspecimens from
Caragua
(and athird discoveredin thesame
areaby
ourteam
in 2001)have been
referred toanew
mesotheriine taxon (Flynnet al., in press).
Geographic
and
Geologic
Setting
Charrier et al., 2000, 2002;
Womer
et al., 2000;Chavez, 2001;
Bond
&
Garcia, 2002;Flynn,Croft,et al., 2002), including initial paleontological
re-ports, geochronologic analysis,
and
studies ofthesyntectonic depositionofthe fluviolacustrine
sedi-ments
of theChucal
Formation (Fig. 1).Fossilif-erous strataof the
Chucal
Formation are wellex-posed
on
both limbs of a major N-S-orientedgrowth
anticline (theChucal Anticline),which
doc-uments marked
thickness and facies variationon
eitherflank and at leastfour progressive erosional unconformities
(U1-U4
in Charrier et al., 2002;Fig. 1; see also
Riquelme
&
Herail, 1997, andRi-quelme, 1998).
As
detailed in Charrier et al.(2002), the Chucal Formation at Cerro
Chucal
isthickest
(—600 m)
on
its west-dipping (35-40°)western flank (informal
Members
W1-W4)
and isthinner
on
its steeplyeast-dipping (generally >50°)eastern flank (informal
Members
E1-E3),where
the syntectonic erosional unconformities are
most
pronounced.
Mammal
fossils aremost
common
inthe floodplain facies (and
some
lacustrine-influ-encedintervals) inthe lowerpartsof
Members
W3
and
W4
and the fluviatile facies ofMembers
El
and
E3
(Charrieret al., 2002).Unconformities separate the
Chucal Formation
from
the underlyingLupica
Formation
(earlyMiocene,
dated at 21.7±
0.8Ma
atChucal and
at
>18.5
Ma
elsewhere in the region)and
theoverlying
Quebrada
Macusa
Formation
(the base ofwhich
is datedat 17.5±
0.4Ma
atCerroChu-cal; Muiioz, 1991; Riquelme, 1998;
Bond
&
Garcia, 2002; Charrier et al., 2002).
The
Chucal
Formation,therefore,
was
depositedand
deformed
very rapidly (possiblyover considerably lessthan
4-5
million years); it isno
older than 22.5Ma
(possibly 18.5
Ma)
and
no younger
than about 17Ma.
Thus, basedon
both the biostratigraphicoc-currences
and
radioisotopic constraints,we
con-siderthe
mammalian
fossilsfrom
theChucal
For-mation
in this region to represent a single short-duration assemblage, theChucal
Fauna
(Charrieret al., 2002; Flynn et al., 2002).
Material described herein is derived
from
the<600-m-thick
Chucal Formation near CerroChu-cal, located
on
the Chilean Altiplano northwest ofthe Salar de Surire (18°43'S, 69°10'W). Several
earlierstudies havedetailed thegeology ofthis re-gion (e.g., Mufioz, 1991; Charrier, Mufioz,
&
Pal-ma-Heldt, 1994; Charrier, Mufioz,Wyss,
et al.,1994;
Riquelme
&
Herail, 1997; Riquelme, 1998;Materials
and
Methods
Upper
toothlociareindicatedby
uppercase let-ters (e.g., II, P2,Ml)
and
lower tooth lociby
lowercase letters (e.g., il, p2, ml); deciduousteethareindicated
by
a"D/d"
precedingthe toothposition.
Terminology
for toxodontidmolar
mor-phology
followsMadden
(1990). Allmerits
were
taken to the nearest O.Imm
using digital calipers.We
recognizethatmany
groups(e.g., Nesodon-tinae, Hegetotheriinae), as currently conceived,are likely paraphyletic.
Because
thesenames
arefamiliar to South
American paleomammalogists,
we
continue toemploy them
in their traditional sense until phylogenetic definitions and/oralter-nate
names
are proposed.Taxonomic names
that are potentially invalidbecause of
synonymy
(e.g.,Mesotherium
"angus-tirostmm")
are indicated throughthe useof quo-tation marks.To
ourknowledge, no
comprehensive
analysisofthe stratigraphic
and
geographic occurrences ofthe taxaconsidered in the present study has
been
published previously.
The
distribution cited foreach taxon therefore represents a preliminary ef-fort to detailthegeologic formationsin
which
that taxon isknown
to occur basedon
firsthandob-servations
and
summary
compilations ofBonde-sio et al. (1980), Marshall et al. (1983),
Savage
and
Russell (1983),Mones
(1986),Madden
(1990),
and
Marshalland Sempere
(1991).The
FriasianSALMA
remains controversial(Flynn
&
Swisher, 1995;Madden
et al., 1997; Flynn, Croft, et ai., 2002).We
distinguishbe-tween
Friasian in its traditional sense (Friasiansensu lato;
subsuming
theMayoan,
Colloncuran,and
Friasian sensu strictoSALMAs)
and
theterm's
more
restrictive definition (Friasian sensustricto; including only thetemporal interval
char-acterized
by
the typeassemblage
in southernChile,
and
correlative faunas), following Flynn,Croft, et al. (2002).
Abbreviations
AMNH,
American
Museum
of NaturalHistory,New
York;FMNH,
FieldMuseum
of Natural His-tory, Chicago;GB,
ServicioGeologico de
Bolivia (housed at theMuseo
Nacional de Historia Nat-ural,La
Paz);MACN,
Museo
Argentino deCien-cias Naturales,
"Bernardino
Rivadavia,"Buenos
Aires;
MLP,
Museo
de
La
Plata, Argentina;MNHN,
Museum
National d'Histoire Naturelle,Paris;
PU,
Princeton University Collection(now
housed
atYale University,New
Haven,
Connect-icut);SGOPV,
vertebrate paleontologycollec-tions,
Museo
Nacional de Historia Natural, San-tiago;Ma, megannum;
mm,
millimeter;cm,
cen-timeter; S.I., sensu lato; s.s., sensu stricto;
SAL-MA,
SouthAmerican
Land
Mammal
"Age";
C\,consistency index; RI, retention index;
RC,
re-scaled consistency index. Metacarpals
and
meta-tarsals areabbreviated
MC
and
MT,
respectively.Systematic Paleontology
Mammalia
Linnaeus, 1758
Notoungulata Roth, 1903
Toxodontia
Owen,
1853
Toxodontidae Gervais 1847
Nesodontinae
Murray,
1866
Diagnosis
—
The
Nesodontinae, as traditionallyconceived (e.g.,
Nesodon,
Adinotherium,Proadi-notherium, etc.), islikely a paraphyletic
group
of toxodontids lacking derived character statespre-sent in other toxodontid subclades
(Madden,
1990; Nasifetal., 2000).
Specimens from Chucal
are referred to the
Toxodontidae
basedon
largesize; presence of very
hypsodont
cheek
teeth;cheek
teeth with protoconeand hypocone
unitedearly in wear; upper molars with distinct
and
per-sistent firstcrista; lingual origin ofthe crochetin upper molars; triangular cross sectionof i1;
hyp-selodont, procumbent,
and
tusklike 13;and
re-duced
enamel
along the lingual portions of thelower molars
(Madden,
1990;Cifelli, 1993; Nasif et al., 2000). Nesodontines differfrom
othertox-odontids in absence of derived
mandibular
sym-physismorphology (Madden,
1990);unreduced
sagittal crest (Nasifet al., 2000); lack of hypse-lodont molars (although
M3
rootsform
only inold individuals;
Madden,
1990); absence ofsim-plified, straightectoloph(i.e.,lackingdistinct
par-astyle, paracone,
and metacone) on P2-4;
pres-ence oflingual folds
on
upper molarsthatbecome
completely isolated as fossettes;
and
presence oftwo
lingual folds plus an accessory fossettid inthe lower molars.
Nesodon
Owen,
1846
Type
Species—
Nesodon
imbricatus.Included
Species—
The
type,Nesodon
con-spurcatus,
and
Nesodon
cornutus.Diagnosis
—
A
nesodontine
differingfrom
Proadinotherium
in larger size; greaterdegree of hypsodonty; presence ofII withtrapezoidal crosssection (triangular in Proadinotherium); absence
of cingulae in II;presence of simple
and rounded
F3
fossetteon
upper molars; reduction oflingualenamel band on ml;
presence of flattenedand
sharply angled posterior external face of
ml
tal-onid;
and
presence of deep,wide
lingualgroove
on
molars (groove is shallow inProadinothe-hiim). Differs
from Adinotherium
in larger size(approximately twice as large in linear
dimen-sions),absence of angled posteroventralborder of
mandible, presence of II with trapezoidal cross
section (kidney shaped in Adinotherium),
pres-ence of
P2-4
lingual precingulae,presence ofrel-atively larger lower premolar
row (p2-p4
length>50% ml-m3
length inNesodon,
<50%
in Adi-notherium), absence ofanteriorand
entohypocon-ulid folds
on
p3, relativelylower-crowned
p4,re-duction of lingual
enamel
band on ml,
presenceofflattened
and
sharplyangled posterior externalface of
ml
talonid,and
distinct calcanealmor-phology
(see Scott, 1912). Differsfrom
nearlycontemporaneous Palyeidodon
(likely abasal tox-odontineand
not a nesodontine, fideMadden,
1990; Cifelli, 1993; Nasif et al., 2000) in
unre-duced
sagittal crest, presence ofmore
developed upper premolarparastyles, presence ofupperpre-molar
lingual precingulum, presence ofparastylesulcus
on
Ml,
presence of accessory fossetteon
upper premolars, presence of
F3
accessory fos-sette inupper molars, isolationof primary lingualfold as fossette in later
wear
stages inM2
and
M3,
presence ofmore
persistentF3
fold/fossettein
upper
molars,and
presence of accessory fos-settid in lower molars(Madden,
1990; Cifelli,1993; Nasifet al., 2000).
Distribution
—
SantaCruz
Formation, Patagon-ia, Argentina, late earlyMiocene
age,Santacru-cian
SALMA
(Scott, 1912;Madden,
1990);Chu-cal Formation, northernChile, late early
Miocene
age, SantacrucianSALMA;
Cura-MallfnForma-tion, south-central Chile, late early
Miocene
age,Santacrucian
SALMA
(Croft,Radic,etal.,2003);unnamed
formation (possibly equivalent toRio
Zeballos Formation), southern Chile, late early
Miocene
age, SantacrucianSALMA
(Flynn,No-vacek, et al., 2002).
Comments
—
Nesodon
is bestknown
from
therichlateearly
Miocene
SantaCruz
depositsalongthe Atlantic coast of Patagonia(Scott, 1912).
Re-cent studies suggestthat
Nesodon
may
serveas auseful index taxon for the Santacrucian
SALMA
(Croft, Radic, et al., 2003). Reports of
Nesodon
from
othertime periodsand
from
areas outsideofChile
and
Patagonia are poorly substantiatedand
are thereforenotincludedinthe
above
list(Flynn,Croft, et al., 2002; Croft, Radic, et al.,2003).
Bond
and
Garcia (2002) questionably referredthree poorly preserved
and
fragmentarytoxodon-tid teeth
from
the upper part of theChucal
For-mation to Palyeidodon, a taxon resembling
Ne-sodon
that occurs in slightlyyounger
deposits(early middle
Miocene
Friasian s.s.and
Collon-curan
SALMAs;
Madden,
1990).They
furthernoted that these teeth (all pertaining to a single
individual) possess a
mix
of features normallyfound
in thosetwo
taxa as well assome
distinctfeatures (autapomorphies) that indicate it
might
represent a
new
taxon.The
dental similarities ofNesodon
and Palyeidodon
make
them
difficulttodistinguish without sufficiently
complete
and
well-preserved specimens. Moreover,
some
ofthecharactersused
by
Bond
and
Garcia (2002)todif-ferentiate the
two
are ofambiguous
utility: theabsence ofa posteroexternal fossette in
M
1(char-acteristic of Palyeidodon) also occurs in
some
specimens
oiNesodon
(e.g.,FMNH
P10379), theMl
lingual foldbecomes
isolated withwear
inboth
Nesodon and Palyeidodon
(although this isnot thecase for
M2
and
M3;
Madden,
1990),and
it is
unknown
whether
the isolatedMl
theyde-scribed
would
eventuallyhave formed
roots(as inNesodon)
orwould have
maintainedopen
roots(as inPalyeidodon) later in life.Additionally, the
specimens
describedby
Bond
and
Garcia (2002) differ in several respectsfrom
bothNesodon
and
Palyeidodon: the parastylar region is
much
more
pronounced and
is deflected lingually instead of labially (as notedby
Bond
and
Garcia), theec-toloph is strongly
convex
instead of straight orslightly
concave
(alsonotedby
Bond
and
Garcia),and
the teeth (especiallyMl)
are significantlylarger than those of both
Nesodon
(Scott, 1912)and Palyeidodon (Madden,
1990). Itmay
there-fore represent a
new
toxodontid, butone
thatcur-rently is too poorly represented to be
named.
Pending
description ofmore
diagnostic material,we
consider these teeth to pertain to an indeter-minatetoxodontid.Nesodon
imbricatusOwen,
1846
(Figures2, 4, Table 1)
Referred Specimens
from
the
Chucal
For-mation
—
SGOPV
5073,partial skull with broken right ?I2, rightP2-M3,
isolated leftM2;
SGOPV
4043, fragmentary
and
poorly preservedskulland
rightmandible;
SGOPV
4027,leftpostorbitalpro-cess;
SGOPV
4054,incisor/canineand
other toothfragments (unprepared);
SGOPV
4066, leftM3;
Table 1. MeasurementsforChucal specimens ofNesodon imbricatus.
P2
P3
P4
Ml
M2
Upper
dentitionL
W
W
W
W
W
M3
W
SGOPV
5073(R)SGOPV
5073(L)SGOPV
4066(L)Lower
dentitionm2
19.8 25.2 21.6 28.3 31.4 27.6 ni3 45.1 44.0 34.5 34.4W
W
58.6 46.4 31.3 (26.6)SGOPV
4105 (R) 39.8 17.2SGOPV
4099 (L) (75) (22)SGOPV
5036, rightmandibular
fragment withportions of ?p3-4;
SGOPV
4105, rightm2;
SGOPV
4099, left mandibular fragment withm3;
SGOPV
5118,right?dp;SGOPV
4018
partial leftglenoid;
SGOPV
5225,lefthumerus
(see Charrier,Murioz,
Wyss,
et al., 1994);SGOPV
4044, prox-imal left ulna fragment;SGOPV
4040,fragmen-tary large postcranial bones, right metacarpal II,
and
rightmagnum;
SGOPV
4015, fragmentarypostcranial
bones
(associated withSGOPV
5036).Age
and
Distribution—
SantaCruz
Formation,Patagonia, Argentina, late early
Miocene
age,Santacrucian
SALMA;
Chucal
Formation,north-ern Chile, late early
Miocene
age, SantacrucianSALMA.
Diagnosis
—
Differsfrom
Nesodon
conspurca-tus inlargersize.Differs
from
N. cornutusinlow-erocciput
and
absence ofdermal
horn.Description
—
The
most
completespecimen
ofNesodon
imbricatus in theChucal
collections isSGOPV
5073, a partial skull withmuch
of theright toothrow preserved.
Although
thebone
isnot especially well preserved,
most
of the teethare in excellent condition.
The
skull is partiallyprepared,
and
the occlusal surfaces of rightP2-M3
have been
exposed, as has the entire length of an associated leftM2
(almost certainlyfrom
the
same
individual but displacedfrom
itsalveo-lus). Other teeth are present as "float" in the
block containingthe skullbutremain unprepared.
Dental
measurements
forthisand
otherspecimensreferred toN. imbricatusarepresentedinTable 1.
The
premolars ofSGOPV
5073
areall roughlyquadrangularin outline.
The
anteriorhalfofP2
isnot preserved, portionsofthe anterior
and
lingualfacesof
P3
are missing, butP4
isessentiallycom-plete.
The
ectoloph of each tooth includes apar-astyle
and
parastyle sulcus.These
structures aremost pronounced
inP2 and
less so inmore
pos-terior premolars. All three premolars
show
mod-erate wear,
and
the only occlusal featureremain-ing isthe central fossa.
The
fossa is avery smalloval in
P2 and
is largerand
more
elongatean-teroposteriorly in
P3 and
P4.A
noteworthy feature ofthe premolar series isthe variation in the level of the occlusal surfaces
ofthe teeth.
The
occlusal surfaceofP4
is at thesame
levelas the molars, whilethatofP2
ismore
dorsally situated, approximately 1.75
cm
nearerthe base ofthe tooth.
The
third premolar bridgesthis
gap
in occlusal surfaces;most
ofP3
is atthesame
level as P2, but the posterior quarter hasbeen
worn
such that itforms
an extremely steepdentine slope (ranging
from
45° to85° at thelin-gual
and
labial margins, respectively) that blendsinto the anterior face of
Ml.
As
inmany
othernotoungulates,
enamel
is absent along the labialportions of both the posterior face of
P4
and
theanterior face of
Ml
in this area, resulting in theconfluenceofthe
two
dentine surfaces.The
firstand
second upper molarsarebothtrap-ezoidal.
The
ectolophs are straight with littleev-idence ofa parastyle or parastyle sulcus.
Only
thecentral fossa is present
on
the occlusal surface ofMl.
InM2,
the bifurcate primary lingualenamel
foldhas
become
isolated asalarge,bifurcate,cen-tral fossa.
The
F3
fold ispresent as a small
fos-sette located almostdirectlyposteriorto the point
ofbifurcationofthe central fossa.
The
thirduppermolar
is nearly triangular in shapeand
displaysless
wear
than thetwo
anterior molars.Both
theprimary lingual
enamel
foldand
theF3
fold arepresent; the former has not yet
become
isolatedby
wear, whilethe latterrecently has.Specimen
SGOPV
5118
is apparently anun-erupted deciduous right lower
premolar
Its lackof wear, small size,
and
lack of roots suggest itwas from
a veryyoung
individual.The
anteriorFig. 2. Partial skullofNesodonimbricatus,
SGOPV
4053,including right?I2andP2-M3.
A.Rightlateralview.B. Occlusal view. Scale bars equal 5cm.
and
posterior faces converge slightlytoward
thebase (in lingual view), indicating that the tooth
would
nothave
increased in size with furtherde-velopment. Itis similarin overall
form
to thean-terior tooth of
MLP
12-245, a partial rightman-dible with
?dp4-ml
from
SantaCruz
referred toNesodon
imbricatus (pers. observ.).Relatively
few
postcranialbones
from Chucal
are referable to
Nesodon;
these include the lefthumerus
found in 1992(SGOPV
5225), a partialleftglenoid
(SGOPV
4018), aproximal leftulnarfragment
(SGOPV
4044),and
some
fragmentarylarge long
bones
associated with a rightMC
IIand
rightmagnum.
Comments
—
The
size differencebetween
Ne-sodon
imbricatusand
N. conspurcatus ispro-nounced, implying that the validity of the
two
species is well
founded
(Croft, Radic, et al.,2003); in this regard,
specimens
from
Chucal
compare
wellwithN. imbricatus(Fig. 3).The
sta-tus of N. cornutus is less certain; the species isrepresented only
by
the holotype (a nearlycom-pleteskullwithheavily
damaged
teeth)and
isdis-tinguished
from
other speciesby
skullproportions3.0-Fig. 4. Partial left ?i2 of Adinotherium,
SGOPV
4064,in labialview. Scalebar
=
5mm.
Comments
—
Although
Scott (1912) noteddif-ferencesin the vertebral
column,
scapula,and
an-kle of
Adinotherium and Nesodon,
morphologicalcharacters currently used to distinguish the
two
taxa are all craniodental
(Madden,
1990; Nasifetal., 2000).
The
limbbones
of toxodontidsarefair-lyeasytodistinguish
from
thoseofotherendemic
South
American
ungulate clades (e.g., litopterns,astrapotheres, pyrotheres)
and
othercontempora-neous
notoungulates(e.g., mesotheriids, hegetoth-eriids).Given
the significant metric differencesbetween Adinotherium and Nesodon,
postcranialspecimens of the
two
Santacrucian toxodontids can be discriminatedon
the basis of size alone (Scott, 1912; Croft, Radic, et al., 2003). Sinceonly a single toothof
Adinotherium
(a partialin-cisor. Fig. 4) has
been
collected at Chucal,refer-ence ofpostcranialelementsto thistaxon isbased
on
their similarmorphology
—
butmuch
smaller size—
compared
toNesodon
(Fig. 5).Adinotherium
sp. indet.(Figures
4-6)
Referred Specimens
from
Chucal
—
SGOPV
4064, partial ?left i2, partial right articular
con-dyle, various ?mandibular fragments (Fig. 4);
SGOPV
4012,leftunciform, proximal leftMC
IV,left
MC
V, dorsal half of rightmagnum,
many
otherpartialhand/foot
bones
and bone
fragments;SGOPV
5035, phalanx,many
smallbone
frag-ments;
SGOPV
4065, partial femoral head, prox-imal?MT
II,many
limbbone
fragments;SGOPV
4084, proximal portions ofleft ulnaand
radius,?elbow sesamoid
(Figs. 5, 6).Description
—
Only
a single dentalspecimen
clearly attributable to
Adinotherium
hasbeen
col-lected
from
Chucal:SGOPV
4064,apartial tooth,probablyleft i2 (Fig. 4).
The
tooth preservesonly the base of itscrown and
part ofthe root;none
ofthe occlusal surface is present.
The
rootmea-sures 5.6
X
6.5mm.
Enamel
is restrictedprimar-ily to the front of the tooth but extends slightly
onto the mesial surface
toward
the crown.The
labial
enamel
ismuch
thickerthan themesial.The
labial
enamel forms
an inverted triangle inante-riorview, with a
rounded apex and
abaseformed
by
the broken surface of the tooth. In sizeand
morphology,
thespecimen
closely resembles thebase of left i2 of
FMNH
PI 3097, aspecimen
ofAdinotherium from
Santa Cruz, Argentina; it ismuch
smaller thanFMNH
UC1330,
aspecimen
of
Nesodon from
Santa Cruz.The
tooth isasso-ciated withvarious mandibular fragments,
includ-ing apartial right articularcondylethat
compares
well withAdinotherium.
A
second
craniodentalspecimen,
SGOPV
4011,
may
pertain toAdinotherium. It appearstobe a partial maxilla preserving the bases of
two
teeth, afragment of athird,
and
part ofthealve-olus of a fourth.
Based on
the portions of teeththat are present
and
the size ofthe alveolus, themost
notable aspect ofSGOPV
4011
is thedra-matic mesial-to-distal increase in tooth size; this resembles the condition seen in the premolar se-ries of
Adinotherium and
does not closelyresem-ble the condition present in
any
otherspecimens
from
Chucal.The
fragmentary natureofthespec-imen
precludes a precise identification, however. Despite the paucity ofdental remains, several well-preserved postcranialspecimens
(primarilyforelimb elements) increaseconfidence inthe
rec-ognition of
Adinotherium
at Chucal.Specimen
SGOPV
4084
includes proximal fragments oftheleft ulna
and
radius (Figs. 5, 6).The
radius ismuch
more
robust than thatofthe largermesoth-eriids at
Chucal
(e.g., A. chucalensis,SGOPV
4042) and
differsmost
conspicuouslyin havingavery
pronounced
interosseouscrest (Fig. 6). Sim-ilarly,thefragmentaryulna,while preserving onlythe distal portion of the sigmoid notch, differs
from
the correspondingbone
of mesotheriids inlacking awell-demarcated fossadistal tothe
cor-onoid process (Fig5.).
Except
foritsmuch
Fig. 6. Morphologyoftheproximalradiusin mesotheriinesandAdinotherium. A.
FMNH
PI4482, proximal leftradius of "Typotheriopsis sp." from the late Miocene Araucano Fm. of Catamarca, Argentina. B.
SGOPV
4042,proximalright radius(pictured asleft)ofA.chucalensis(Mesotheriinae,describedin text).C.
SGOPV
4084, proximalleft radiusof Adinotherium. Allspecimensarein medialview. Scalebars
-
2cm.ements
ofNesodon
whilediffering inmorphology
from
those of mesotheriids (and othernotoungu-lates).
Comments
—
As
discussedbelow
(Litoptema)appendicular
bones
ofthemajor
SouthAmerican
ungulate clades are easily distinguished (Cifelli,
1983, 1985, 1993).
Those from Chucal
herere-ferredtothe
Toxodontidae
(viz.,Nesodon
and
Ad-inotherium) are similar in
morphology
but differmarkedly
in size. This difference is wellillustrat-ed by
SGOPV
4044, a partial left proximal ulnaof
Nesodon,
versusSGOPV
4084, a partial leftproximal ulna oi
Adinotherium
(Fig. 5);thedepth ofthe ulnajustdistal tothetrochlearnotchoftheformer is approximately 8
cm,
while thecorre-sponding
measurement
ofthe latteris lessthan 3cm.
The
specimens
attributed toAdinotherium
above
are all fully ossifiedand
thereforedo
notpertain to
immature
individualsofNesodon.
Typotheria
Zittel,1892
Mesotheriidae
Alston,1876
Mesotheriinae Simpson, 1945
Mesotheriids are traditionally divided into
two
subgroups: the Trachytheriinae (comprising
De-seadan
and
earlierforms,most
assignedtoTrach-ytherus)
and
theMesotheriinae(including Friasians.l.
and
later forms) characterizedby
the loss of I2-P2/i3-p3and
the presence ofpersistentlytri-lobed upper molars,
among
other features(Fran-cis, 1965; Villarroel, 1974a; Cerdeiio &.
Montal-vo, 2001;
Reguero
&
Castro, 2002; Croft, Flynn,&
Wyss,
2003;Flynn
et al., in press). Mesothe-riidsareabsentfrom
faunas ofColhuehuapian
ageand
had
notbeen
recorded in faunas ofSantacru-cian agepriortotheirdiscoveryat
Chucal
(Flynn,Croft, et al.,2002).
Mesotheriines are in great
need
of systematicrevision (Pascual
&
Bondesio, 1985; Cerdeiio&
Montalvo, 2001; Flynn,Croft, et al.,2002; Croft,
Flynn,
&
Wyss,
2003; Flynnetal., in press),mak-ing
taxonomic
assignments ofnewly
discoveredforms
challenging.Based on
Francis's (1965)re-vision of Argentine taxa
and
the subsequentde-scription of additional forms
from
Bolivia(Vil-larroel, 1974a,b), Flynn et al. (in press)
recog-nized seven potentially valid mesotheriine "gen-era"
and
described anew
taxonfrom
themiddle
Miocene Huaylas Formation
of northernChile.A
character that has traditionallybeen
impor-tant in mesotheriine
taxonomy
isimbrication: thedegree to
which
the anteroextemalcomer
of an uppercheek
tooth overlaps the posteroexternalFig. 7. Holotype of Altitypotherium paucidens,
SGOPV
4038,apartialrostrum withleft II. leftP4-M3
andrightP4-M
1.A.Leftlateral(above, pictured asright)andocclusal(below)views.B.Line drawings ofocclusalmorphology(toothrows notinnatural position). Scale bars
=
I cm.Fig. 8.
Lower
dentitions referred to Altitypotherium paucidens. A.SGOPV
4024, partial left mandible withfragmentary il-2 andcomplete
p4-m3
inocclusalview.B.SGOPV
4101,partialrightmandibleandsymphysis withfulldentition plusleft il-2in lateral(above) andocclusal(below) views. Scale bars
=
1 cm.northern Chile, late early
Miocene
age, Santacru-cianSALMA.
Etymology
—
Aid, in reference to theAltipla-no, the highplateau of northern Chile
and
neigh-boring Bolivia
and
Peru,where
the referredspec-imens
were
collected,and
typotherium, inrefer-ence to the familiar root
commonly
used inme-sotheriine taxon
names;
pauci, Latin for "few,"and
dens, Latin for "tooth," in reference to thelackofP3, a characteristic featureofthis species.
Diagnosis
—
A
mesotheriine that differsfrom
all other mesotheriines in the absence ofP3.
Differs
from
Microtypotherium in presence ofdeep,
narrow
postpalatal notchthatextendstothelevel of
M3
(does not reachM3
inMicrotypo-therium); presence of subtriangular II that is
pointed distally, with
two
lingual sulci (a singlemesial sulcus is present in Microtypotherium); presence of enlarged
M3
middle
lobe (notsur-rounded by
othertwo
lobes); presence ofone
la-bial sulcus
on
premolar ectolophs (two sulcipre-sent in
Microtypothehum); and
absence ofshort-ened
m2
(length/widthbetween
1.60and
2.30 inAltitypotherium,
<1.6
inMicrotypothehum).
Differs
from Eutypotherium
in the root ofzy-gomatic arch being directed perpendicularto
Ml
(posteriorly directed
from
the level ofM
1 orM2
inEutypotherium); presence of deep,
narrow
post-palatalnotchthatextendstothelevelof
M3
(wideand
shallow in Eutypotherium); presence ofsub-triangular II that ispointeddistally, with
two
lin-gual sulci (wide
and rounded
with lingual sulcus in Eutypotherium); presence ofrounded
il withlittle or
no
lingual sulcus (subtriangular withsmooth
sulcus inEutypotherium); presence ofone
labial sulcuson
premolar ectolophs (two sulcipresent in Eutypotherium); absence of extensive
lingual exposure of
Ml
middle lobe;and
smallersize(based
on
dentalmeasurements,
approximate-ly20%
smaller thanEutypotherium
tehmannnit-schei).Differs
from
Plesiotypotherium in posteriorlydiverging upper
and
lower diastemata (parallel in Plesiotypotherium); absence of well-developedsuborbital fossa; presence of deep,
narrow
post-palatalnotchthatextendstothelevelof
M3
(wideand
shallow in Plesiotypotherium); subtriangular II that is pointed distally, withtwo
lingual sulci (wideand rounded
with lingual sulcus inPlesi-otypotherium); presence of
rounded
i1 with littleor
no
lingual sulcus (subtriangular withsmooth
sulcus in Plesiotypotherium); presence of
one
la-bial sulcus
on
premolar ectolophs (twosulcipres-entinPlesiotypotherium);presence of
Ml
middlelobe with lingually convergent anterior
and
pos-teriorsides (subparallelinPlesiotypotherium);
ab-sence of extensive lingualexposure of
M
1middle
lobe;
and
smaller size (basedon
dentalmeasure-ments, approximately
30%
smaller thanPlesioty-potherium
achirense).Differs
from Caragua
New
Taxon
(Flynn etal.,in press) in presence ofposteriorly divergent
up-per
and
lower diastemata (parallel inCaragua
New
Taxon); lesser degree ofmolar
imbrication(<1.25
m
Altitypotherium,between
1.25and
1.50in
Caragua
New
Taxon); presence ofsubtriangular II that is pointed distally, withtwo
lingual sulci (wideand rounded
withlingual sulcus inCaragua
New
Taxon); presence ofshort, subtriangularP4
withoutcentral fossette(P4 bilobed withshort
and
poorly defined lingual plication in
Caragua
New
Taxon); presence of enlargedM3
middlelobe (notsurrounded
by
othertwo
lobes); relativelysmaller il (il/i2<1.50
in Altitypotherium,between
1.50and
2.00 inCaragua
New
Taxon); presence ofrounded
il with little orno
lingual sulcus(sub-triangular with
smooth
sulcus inCaragua
New
Taxon); presence of
one
labialsulcuson
premolarectolophs (twosulci presentin
Caragua
New
Tax-on); presence of
Ml
middle lobe with linguallyconvergent anterior
and
posterior sides(subpar-allel in
Caragua
New
Taxon); absence ofexten-sive lingual exposure of
Ml
middle lobe;and
smaller size (based
on
dental measurements,ap-proximately
20%
smaller thanCaragua
New
Tax-on).
Differs
from
Typotheriopsisinpresence ofpos-terolaterallydivergentupper
and
lower diastemata (parallel in Typotheriopsis); absence ofwell-de-veloped suborbital fossa; presence of deep,
nar-row
postpalatal notch that extendsto the level ofM3
(does not reachM3
in Typotheriopsis); pres-ence of subtriangular II that is pointed distally,with
two
lingual sulci(wideand rounded
withlin-gual sulcus in Typotheriopsis); presence of
en-larged
M3
middle
lobe (not surroundedby
othertwo
lobes); relatively smaller il (il/i2<1.50
inAltitypotherium,
between
1.50and
3.00 in7\'-potheriopsis); presence of
rounded
il with littleor
no
lingual sulcus (subtriangular withsmooth
sulcus in Typotheriopsis); presence of
M
1 middlelobe with lingually convergent anterior
and
pos-terior sides (subparallel in Typotheriopsis);
ab-sence of extensivelingualexposure of
Ml
middlelobe;
and
smaller size (basedon
dentalmeasure-ments, approximately
30%
smaller thanTypo-theriopsis chasicoensis).
Differs
from Pseudotypotherium
in presence ofposterolaterallydivergentupper
and
lowerdiaste-mata
(parallel in Pseudotypotherium); absence of well-developedsuborbital fossa;presence of deep,narrow
postpalatal notch thatextends tothe levelof
M3
(doesnotreachM3
inPseudotypotherium);lesser degree of
molar
imbrication(<
1.25 inAl-titypotherium,
>1.50
inPseudotypotherium);
presence ofshort,subtriangularP4
withoutcentralfossette (P4is bilobedinPseudotypotherium);
rel-ativelysmalleril (il/i2
<1.50
inAltitypotherium,between
2.00and
3.00 in Pseudotypotherium); presence ofrounded
il with little orno
lingualsulcus (trapezoidal with well-demarcated lingual
sulcus inPseudotypotherium); presence of
one
la-bial sulcus
on
premolar ectolophs (two sulcipre-sent in Pseudotypotherium); absence of elongate
P4
(length/width<
1.50inAltitypotherium,>
1.50in Pseudotypotherium); absence of elongate
Ml
(length/width
<1.75
m
Altitypotherium,^1.75
inPseudotypotherium); presence of
Ml
middle lobewith lingually convergent anterior
and
posteriorsides (subparallel in Pseudotypotherium); absence
of extensive lingual exposure of
Ml
middle lobe;absence of elongate
m2
(length/widthbetween
1.60
and
2.30 inAltitypotherium,>2.30
inPseu-dotypotherium);
and
smallersize (basedon
dentalmeasurements, approximatelyis
25%
smaller thanPseudotypotherium
exiguum).Differs
from
Mesotherium
in posterolaterallydivergent upper
and
lower diastemata (parallel tostrongly convergentinMesotherium); presence of
poorly defined suborbital fossa (absent in
Meso-therium); lesser
degree
ofmolar
imbrication(<1.25
in Altitypotherium,>1.50
inMesothe-rium); presence ofsubtriangularII that is pointed
distally, with
two
lingual sulci (wideand rounded
with lingual sulcus or
wide and compressed
la-biolingually with
two
lingual sulci inMesothe-rium);presence ofshort,subtriangular
P4
withoutcentral fossette (P4 is persistently bilobed in
Me-sotherium); relatively smaller il (il/i2
<1.50
inAltitypotherium,
>3.00
inMesotherium); presenceof
rounded
il withlittleorno
lingual sulcus(trap-ezoidal withwell-demarcatedlingual sulcus or
el-liptical with
smooth
sulcusinMesotherium);pres-ence of
one
labial sulcuson
premolar ectolophs(two sulci present in Mesotherium); absence of elongate
P4
(length/width<1.50
inAltitypothe-rium,
>
1.50inMesotherium); absence of elongateMl
(length/width<1.75
in Altitypotherium,>1.75
in Mesotherium); presence ofMl
middle
lobe with lingually convergent anterior
and
pos-terior sides (lingually divergent in Mesotherium); absence of extensive lingualexposure of
Ml
mid-dle lobe; absence of elongate
m2
(length/widthbetween
1.60and
2.30 in Altitypotherium,>2.30
inMesotherium);
and
smaller size(basedon
den-tal
measurements,
approximately20%
smaller thanMesotherium
maendrum
and
half the size ofMesotherium pachygnathum).
Differs
from
A. chucalensis (describedbelow)
in absence of P3; presence of elongate
Ml
(length/width
>1.3
in A. paucidens,<1.3
in A.chucalensis); middle lobe of
M3
unreduced, notsurrounded
by
anteriorand
posterior lobes;pres-ence of narrower lower molars (widths
<6.7
mm
in A. paucidens, >:7.3
mm
in A. chucalensis);presence of elongate
m3
(15-20%
longerthanm2
inA.paucidens, similarin lengthto
m2
inA.chu-calensis);
and
slightly largersize(basedon
dentalmeasurements,
A.paucidens
is approximately10%
larger thanA. chucalensis).Description
—
The
holotype of A. paucidensconsists ofa moderately well-preserved rostrum
(Fig. 7).
The
nasalshave been
crushed,and
much
ofthepremaxilla is missing, but the leftside
pre-serves the
zygomatic
arch, palate,and
all theup-per teeth.
The
inferior surface of thezygomatic
arch isslightly
damaged
but preserves a well-developedsurface for the origin ofthe masseter.
A
shallowsuborbital fossa is present
on
the dorsal surfaceofthe arch. This fossa is similar in its degree of
development
to that of the holotype of Eutypo-therium superans(MACN
11079), though it isoriented differently; in A. paucidens, the primary
axis ofthe fossa is anteroposterior,
whereas
inE.superans it is transverse. In mesotheriines in
which
thesuborbitalfossaisdeveloped toaneven
greater degree, it is also oriented transversely
(e.g., Typotheriopsissilveyrai,
MLP
36-XI-10-2).The
suborbital fossa isdemarcated
posteriorlyby
a thickstrut of
bone
oriented perpendiculartothetoothrow.
A
large, elliptical infraorbitalforamen
is present, its
major
axis oriented dorsoventrally;it
measures
10.5X
5.5mm.
Very
little of right II is preserved inSGOPV
4038, but left II is well preserved except for itsocclusal surface; in cross section, the
major
axisof the tooth is set at an angle of approximately
45° tothe sagittal plane.
Much
ofthe premaxillais missing
from
the left side ofthe specimen,re-vealing nearly the entiredorsoventralextentof11.
It isa strongly
curved
tooth (approximatinga90°arc)
and
lacks any evidence ofaroot.The
entiresurface of the tooth is covered
by
enamel, withtheexception ofthe
damaged
occlusal surface.An
isolated11 referredto this species
(SGOPV
4024)
better demonstrates the occlusal
morphology
ofthe upper incisor; it is roughly subtriangular in
cross section
and
pointed distally, withtwo
smooth
sulci presenton
the lingual face.The
oc-clusal surface is
worn
such that itis stronglycon-cave.
A
large incisiveforamen
is presenton
thean-terior surface of the palate just posterior to the pairofincisors. It
measures
approximately 9.5X
7.3mm
and
is dividedlongitudinallyby
aseptum
that is recessed relative tothe surface ofthe
pal-ate.
Large
(nearly 25mm
long), posteriorly di-vergent diastemata separate the pair of incisorsfrom
thecheek
teeth.The
palate is relatively flatanterior to the