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Field Museum of Natural History
1400 South Lake Shore Drive
Chicago, Illinois 60605-2496
Telephone: (312) 665-7055
Small Archaeohyracids (Typotheria,
Notoungulata) from Chubut Province,
Argentina, and Central Chile:
Implications for Trans-Andean
Temporal Correlation
Marcelo Reguero
Darin A. Croft
John J. Flynn
André R. Wyss
November 26, 2003
Publication 1526
Geology
NEW SERIES, NO. 48
Geology
NEW SERIES, NO. 48
Small Archaeohyracids (Typotheria,
Notoungulata) from Chubut Province,
Argentina, and Central Chile:
Implications for Trans-Andean
Temporal Correlation
Marcelo Reguero
Departamento Cientı´fico de Paleontologı´a
de Vertebratos
Museo de La Plata
Paseo del Bosque s/n
1900 La Plata
Argentina
Darin A. Croft
Department of Organismal Biology
and Anatomy
The University of Chicago
1027 East 57th Street
Chicago, Illinois 60637
U.S.A.
John J. Flynn
Department of Geology
Field Museum of Natural History
1400 South Lake Shore Drive
Chicago, Illinois 60605–2496
U.S.A.
Andre´ R. Wyss
Department of Geological Sciences
University of California, Santa Barbara
Santa Barbara, California 93106
U.S.A.
Accepted May 7, 2003
Published November 26, 2003
Publication 1526
q
2003 Field Museum of Natural History
ISSN 0096-2651
PRINTED IN THE UNITED STATES OF AMERICA
iii
Table of Contents
A
BSTRACT
............................................... 1
I
NTRODUCTION
.......................................... 1
Chilean Fauna ...................................... 1
Argentine Fauna ................................... 2
Abbreviations ....................................... 2
Nomenclatural Note ............................... 2
S
YSTEMATIC
P
ALEONTOLOGY
........................ 3
Protarchaeohyrax gracilis ....................... 3
Protarchaeohyrax minor ......................... 9
Protarchaeohyrax intermedium ............... 11
T
EMPORAL
C
ORRELATION AND
C
ONCLUSIONS
... 15
A
CKNOWLEDGMENTS
.................................. 16
L
ITERATURE
C
ITED
.................................... 16
List of Illustrations
1. Casts of specimens referred to Protar-
chaeohyrax (gen. nov.) .......................... 4
2. Cast of specimen from Tinguiririca Fau-
na of Chile referred to Protarchaeo-
hyrax gracilis (gen. nov.): mandibular
fragment, SGOPV 2954 ........................ 5
3. Cast and drawing of specimen from Tin-
guiririca Fauna of Chile referred to Prot-
archaeohyrax gracilis (gen. nov.): ros-
trum, SGOPV 2982 .............................. 6
4. Cast of right maxillary fragment collect-
ed by Santiago Roth from Can˜ado´n
Blanco and referred to Protarchaeo-
hyrax minor (gen. et sp. nov.), MLP 52-
XI-4-168a .......................................... 11
5. Cast and drawing of specimen from Tin-
guiririca Fauna of Chile referred to Prot-
archaeohyrax intermedium (gen. et sp.
nov.): paired dentaries, holotype,
SGOPV 3065 ..................................... 12
6. Cast and drawing of specimen from Tin-
guiririca Fauna of Chile referred to Prot-
archaeohyrax intermedium (gen. et sp.
nov.): paired dentary fragments, SGOPV
5007 ................................................. 13
7. Cast and drawing of specimen from Tin-
guiririca Fauna of Chile referred to Prot-
archaeohyrax intermedium (gen. et sp.
nov.): partial palate, SGOPV 2998 ......... 14
Endpiece: Speculative reconstruction of an
indeterminate archaeohyracid
List of Tables
1. Measurements of teeth of Protarchaeo-
hyrax gracilis, P. intermedium, and P.
minor ................................................ 10
FIELDIANA: GEOLOGY, N.S., NO. 48, NOVEMBER 26, 2003, PP. 1–17 1
Small Archaeohyracids (Typotheria, Notoungulata)
from Chubut Province, Argentina, and Central Chile:
Implications for Trans-Andean Temporal Correlation
Marcelo Reguero Darin A. Croft
John J. Flynn Andre´ R. Wyss
Abstract
We describe small-bodied archaeohyracids of transitional Eocene-Oligocene age from Chu-
but, Argentina, including two from Santiago Roth’s important but poorly known Can˜ado´n Blan-
co locality and two occurring in the Tinguiririca Fauna of the Andean Main Range of central
Chile. Three taxa are recognized. We refer specimens from both Patagonia and the central
Andes to one of these taxa, initially named Arachaeohyrax gracilis by Roth (1903) but receiv-
ing a new generic designation here. A diminutive form from Can˜ado´n Blanco and an inter-
mediate-sized form from Chile are each recognized as new species. These taxa help to clarify
the temporal correlation of lithostratigraphic units currently located on opposite sides of the
Andean divide, and aid in the recognition of a biochronologic interval, the early Oligocene (to
possibly late Eocene)-aged Tinguirirican, interposed between the classical Mustersan and De-
seadan ‘‘ages’’ of the South American land mammal succession.
Introduction
Archaeohyracids are among the most poorly
known of South America’s early Cenozoic mam-
mals. In view of the group’s typical rarity else-
where on the continent (apart from the Deseadan
of Bolivia), the abundance and diversity of ar-
chaeohyracids in the transitional Eocene-Oligo-
cene-aged Tinguiririca Fauna of central Chile
(Wyss et al., 1994) are remarkable. Equally note-
worthy is a previously poorly understood, roughly
contemporaneous faunule from Chubut, Argenti-
na—Roth’s Can˜ado´n Blanco assemblage (Roth,
1901, 1903). Two small archaeohyracid taxa are
known from Can˜ado´n Blanco. One was previous-
ly undescribed, and the other occurs also in the
Tinguiririca Fauna; both are named or renamed
below.
Chilean Fauna
The Tinguiririca Fauna (Wyss et al., 1990,
1994; Wyss, Flynn, et al., 1993) is derived from
the dominantly volcanic and volcaniclastic Aban-
ico (
5
Coya-Machalı´) Formation (see Charrier et
al., 1996). Attaining a stratigraphic thickness of
up to 2000–3000 m, the Abanico Formation rep-
resents the geographically most widespread lith-
ostratigraphic unit on the western (Chilean) slope
of the central Andean Main Range. The Tingui-
ririca Fauna, documenting a pre-Deseadan (South
American Land Mammal ‘‘Age;’’ SALMA), post-
Mustersan (SALMA) biochronologic interval
(Tinguirirican SALMA) recently added to the
South American fossil mammal succession (Wyss
et al., 1994; Flynn & Swisher, 1995; Bond et al.,
1996; Flynn et al., 2003), is the first of a series
of Cenozoic mammal faunas discovered within
this formation during the past decade (Flynn et
al., 1995; Wyss et al., 1996; Charrier et al., 1997;
Wyss et al., 1999). Radioisotopic determinations
place the age of the Tinguiririca Fauna at
;
31.5
Ma (see Flynn et al., 2003), based on direct dating
of several fossiliferous horizons (see Charrier et
al., 1996; Flynn & Wyss, 1999). The Tinguirirican
SALMA is certainly earliest Oligocene in age and
2 FIELDIANA: GEOLOGY
possibly quite short in duration (
;
31–33 Ma), but
may extend into the late Eocene (Flynn et al.,
2003).
Among numerous taxonomic peculiarities, the
Tinguiririca Fauna contains by far the most di-
verse archaeohyracid fauna known to date (Wyss,
Norell, et al., 1993; Wyss et al., 1994; Croft,
1998, 2000; Croft et al., 2003). Indeed, archaeo-
hyracids, represented by at least six taxa, are a
dominant element of the Tinguiririca Fauna both
in numerical abundance and in taxonomic diver-
sity. Uncertainty about the number of taxa stems
from the unknown association of upper and lower
dentitions—a problem compounded by the similar
size of several of the taxa and the time-consuming
preparation of specimens from extraordinarily
hard matrix.
Several archaeohyracids from the Tinguiririca
Fauna are referable to forms known from Argen-
tina (Wyss et al., 1994); many such references
could previously be made only informally, owing
to the tangled nomenclature of many of the forms
from Patagonia. Here we seek to update and sta-
bilize the nomenclature of a small archaeohyracid
common to the Can˜ado´n Blanco and Tinguiririca
faunas, and describe two new, closely related
forms. The other archaeohyracids from the Tin-
guiririca Fauna are described formally elsewhere
(Croft et al., 2003). A minimum of three archaeo-
hyracid skulls are known from the Tinguiririca
Fauna (skulls of this group were previously lim-
ited to a single specimen of Archaeohyrax pata-
gonicus from Argentina and undescribed speci-
mens from Salla, Bolivia). In addition, the Tin-
guiririca Fauna provides associated postcranial
and dental material for the group.
Argentine Fauna
The fossil assemblage from Can˜ado´n Blanco is
among the most enigmatic in the South American
land mammal succession. Collected by Roth,
probably during 1897 and 1898, the locale
(known to occur within Chubut Province) has not
been relocated definitively. (A manuscript in prep-
aration by one of us, M.R., seeks to clarify the
locations of Santiago Roth’s collecting efforts, in-
cluding Can˜ado´n Blanco.) Roth’s specimens from
Can˜ado´n Blanco were long considered to repre-
sent a temporally mixed assemblage, representing
the Casamayoran, Mustersan, and Deseadan SAL-
MAs (Simpson, 1967; Patterson, unpublished
manuscript; Patterson et al., in prep.). Discoveries
in Chile and elsewhere in Argentina have re-
vealed, however, that the bulk of the Can˜ado´n
Blanco assemblage likely pertains to a single fau-
na, approximately contemporaneous with the Tin-
guiririca Fauna and Ameghino’s ‘‘Astraponote´en
plus supe´rieur’’ horizon from the Gran Barranca
south of Lake Colhue´ Huapi (Wyss et al., 1994;
Bond et al., 1996; Reguero, 1998).
Among its archaeohyracids, the Can˜ado´n Blan-
co fauna includes two small forms, of which only
Archaeohyrax gracilis (whose subsequent nomen-
clatural history is discussed below) has previously
been named (Roth, 1903). Herein we provide a
new generic designation for this species; we also
place within this genus two new diminutive spe-
cies, one from Can˜ado´n Blanco and one from the
Tinguiririca Fauna.
Abbreviations
APS, Astraponote´en plus supe´rieur; MLP, Mu-
seo de La Plata; SGOPV, Museo Nacional de His-
toria Natural, Santiago, vertebrate paleontology
collections; MACN, Museo Argentino de Cien-
cias Naturales, ‘‘Bernardino Rivadavia’’; SAL-
MA, South American Land Mammal ‘‘Age.’’
Nomenclatural Note
Because the early phase of study of South
American fossil mammals produced a plethora of
dubiously founded names, ‘‘whoever thinks he
has discovered a new taxon in these faunas is eth-
ically obliged to consider the[ir] possible appli-
cability...,’’even though these names may have
‘‘no real meaning at present’’ (Simpson, 1967:
189). Taxonomists revising these faunas therefore
face a recurring conundrum: Is it preferable to sal-
vage ‘‘classic’’ names based on inadequate holo-
types, effectively ‘‘rehabilitating’’ such names by
referring more clearly diagnosable material to
them, or are we better served in marginalizing
very poorly substantiated names by expressly de-
clining to add to their hypodigms? Even if the
second alternative is followed, as Simpson (1967:
189) lamented, ‘‘it is vexatious that there is no
way to jettison the latter [names that are unlikely
ever to acquire any meaning or value] perma-
nently and thus clear up accumulated clutter in
this science.’’ For reasons outlined below we fa-
vor proposing new names over resurrecting prob-
lematic older ones.
3REGUERO ET AL.: SMALL ARCHAEOHYRACIDS FROM ARGENTINA AND CHILE
Systematic Paleontology
Mammalia Linnaeus, 1758
Notoungulata Roth, 1903
Archaeohyracidae Ameghino, 1897
Protarchaeohyrax, gen. nov.
Archaeohyrax Ameghino, 1897 (partim): 431–
432.
Bryanpattersonia Simpson, 1967 (partim): 113.
?Eohegetotherium Ameghino, 1901: 370; Simp-
son 1967; 115–116, figs. 31a, b.
T
YPE
S
PECIES
—P. gracilis (
5
Archaeohyrax
gracilis).
C
OMMENTS
—Patterson (MS) and Simpson
(1967) recognized Archaeohyrax sulcidens and A.
gracilis as belonging to a genus distinct from but
closely related to Bryanpattersonia (and also dis-
tinct from Archaeohyrax), although neither ever
named it formally. Nonetheless, not having seen
Roth’s material, Simpson (1967) elected to pro-
visionally assign both A. sulcidens and A. gracilis
to a single species of his newly erected genus
Bryanpattersonia (B. sulcidens, which had prior-
ity over gracilis), along with a second, clearly dis-
tinct species, B. nesodontoides (the genotypic spe-
cies). Simpson’s (1967) B. sulcidens thus has yet
to receive distinct generic recognition, an action
taken below. It merits note that M. T. Cabrera’s
sketches of Roth’s ‘‘A.’’ gracilis type material
(appearing as figures 29 and 30 in Simpson, 1967)
are not entirely accurate, thus bearing on assign-
ment of that material.
Even though both Patterson (MS) and Simpson
(1967) argued for the synonymy of Archaeohyrax
sulcidens and A. gracilis, one of us (Reguero,
1998) has recently shown that a name proposed
still earlier, Eohegetotherium priscum, placed by
Ameghino (1901: 24) in the Hegetotheriidae,
might represent the same taxon. Thus, if ‘‘sulci-
dens,’’ ‘‘gracilis,’’ and ‘‘priscum’’ could indeed
be shown to be synonyms, Eohegetotherium
would be the valid generic name. Unfortunately,
the types and hypodigms of ‘‘sulcidens’’ and
‘‘priscum’’ offer such scant basis for comparison
(see below) that assignment to various earlier
named archaeohyracid species (each inarguably
distinct) cannot be excluded. The case for syn-
onymy is thus based less on the unmistakable
morphologic similarity of these forms than on
there being so little to compare that they can’t be
shown to be different. Of these three names,
therefore, only ‘‘gracilis’’ is based on reasonably
diagnosable material. Ongoing work (Reguero &
Cifelli, 1997; Croft et al., 2003; Patterson et al.,
in prep.) has shown that Deseadan SALMA ar-
chaeohyracids form a distinct clade (from which
‘‘gracilis’’ is excluded), members of which pre-
occupy the name Archaeohyrax. For these reasons
we propose a new genus, Protarchaeohyrax, to
receive ‘‘gracilis.’’
D
IAGNOSIS
—‘‘Significantly smaller than [Ar-
chaeohyrax
5
Bryapattersonia]nesodontoides’’
(Simpson, 1967: 114). More brachydont than Ar-
chaeohyrax; labial fossettes of upper molars per-
sist little into wear. Parastyle large, more promi-
nent, and situated further labially relative to para-
cone than in Archaeohyrax. Paracone well devel-
oped. Lingual sulcus on upper molars.
Prolongation of M3 ectoloph forms a posterior
lobe.
D
ISTRIBUTION
—Tinguiririca Fauna, Abanico
(
5
Coya-Machalı´) Formation, Chile, of early Ol-
igocene (to possibly late Eocene) age, Tinguiriri-
can SALMA (Flynn et al., 2003); presumably the
Sarmiento Formation, Chubut, Argentina (Roth,
1903); Fray Bentos Formation, Uruguay (Reguero
et al., 1995). The occurrence of the genus in Uru-
guay represents a new species that will be de-
scribed elsewhere.
Protarchaeohyrax gracilis
(Figures 1–3)
Archaeohyrax gracilis Roth, 1903: 22.
?Archaeohyrax sulcidens Ameghino, 1902: 10.
?Bryanpattersonia sulcidens Ameghino, 1902: 10;
Simpson, 1967: 113.
?Eohegetotherium priscum Ameghino, 1901: 370;
Simpson 1967: 115–116, figs. 31a, b.
H
OLOTYPE OF
A
RCHAEOHYRAX GRACILIS
—MLP
12-1522, fragment of left maxilla bearing P1–M3
(Fig. 1A), and MLP 12-1518 (Roth’s No. 4978),
left mandibular fragment with p1–m2 (both spec-
imens probably of the same individual, but with
MLP 12-1522 becoming lectotype should this as-
sociation prove incorrect; Simpson, 1967) (Fig.
1B).
L
ECTOTYPE OF
A.
SULCIDENS
—Based on Amegh-
ino’s description, Simpson (1967: 113) selected
MACN A-10906a (misprinted as MACN 1096 by
Simpson), a left m1 measuring 6.5 by 3.6 mm, as
lectotype. The lectotype is from a lot of 24 teeth,
14 of them lowers, two of which match Simpson’s
4 FIELDIANA: GEOLOGY
F
IG
. 1. Epoxy casts of specimens collected by Carlos
Ameghino and Santiago Roth referred here to Protar-
chaeohyrax gracilis (gen. nov.). Holotypes of ‘‘A.’’ grac-
ilis, including (A) fragment of left maxilla with P1–M3
(MLP 12-1522) in occlusal (top) and labial (bottom)
views and (B) occlusal view of left mandibular fragment
with p1–m2 (MLP 12-1518). (C) Right maxillary frag-
ment with C, P1–2, P3 (broken), P4–M3 (MLP 12-1478)
(alveoli for I1–3 not visible on cast). Scale bar
5
10 mm.
description. Of these two teeth (m1 or possibly
m2), we designate the one less encrusted in man-
ganese and clearly showing the central fossette
between the trigonid and talonid as the lectotype.
Among the various labels accompanying these
teeth, one, apparently an annotation by B. Patter-
son, reads, ‘‘Archaeohyrax sulcidens Ameghino
. . . (2 niveles).’’ Another reads ‘‘Eohegetotherium
priscum Tipo,’’ and ‘‘Astraponotus.’’
P
ARALECTOTYPES OF
A.
SULCIDENS
—MACN
A-10906b, left m1; MACN A-10906c, left m1 or
m2; MACN A-10906d, right m1 or m2; MACN
A-10906e, right m1 or m2; MACN A-10906f, left
m3; MACN A-10909, left m3.
L
ECTOTYPE OF
E
OHEGETOTHERIUM PRISCUM
—
MACN A-10988a, right M1 or 2.
P
ARALECTOTYPE OF
E
OHEGETOTHERIUM PRIS-
CUM
—MACN A-10988b, left M1 or 2, MACN
A-10988c, right M1 or 2.
H
YPODIGM
—The holotype of Archaeohyrax
gracilis and the following specimens: MLP 12-
1478, cranial fragment with alveoli for right I1–
3, right C, P1–2, P3 (broken), and P4–M3 (Fig.
1C); MLP 12-1513a, left mandibular fragment
with p4–m3; MLP 12-1513b (Roth’s No. 4893),
right mandibular fragment with p2–m3; MLP 12-
1539, left mandibular fragment with m1–3; MLP
52-XI-4-168 (Roth’s No. 4894), left maxillary
fragment with dP2–4, M1–2 (consisting of two
pieces with a very good contact); SGOPV 2954,
right mandibular fragment with p1–m3 and por-
tion of left mandibular ramus bearing lingual sliv-
ers of posterior teeth (Fig. 2); and SGOPV 2982,
rostrum with left and right dC, P1, dP2–4, M1–
2; the left successional canine can be seen emerg-
ing above its deciduous precursor, while on the
right side of the specimen P2–4 are visible in their
crypts, nestled above their precursors (Fig. 3).
(The first postcanine teeth in notoungulates are
generally unreplaced, leading to ambiguity over
their proper designation. Are these retained decid-
uous teeth [dP1/dp1] or successional teeth that
erupt unusually early [P1/p1]? Inasmuch as com-
plete ontogenetic series are needed to decide this
question in modern forms, it will likely never be
conclusively resolved for notoungulates. Consis-
tent with the traditional designation, we identify
these teeth as P1/p1.)
L
OCALITIES
—The provenience of the lectotype
of B. sulcidens is uncertain, Simpson (1967: 114)
simply indicating it to be from the Mustersan
(SALMA) of Patagonia (see above, and Temporal
Correlation section below). Similarly, the locality
from which the lectotype of E. priscum (MACN
A-10988) derives is not known but is thought to
be in central Chubut Province. (MACN A-10988
was found among the syntypes of A. sulcidens; it
was separated from this lot of specimens and giv-
en its present number during intervening work on
the collections.)
Specimens bearing Museo de La Plata numbers
are part of Roth’s collection from Can˜ado´n Blan-
co, the precise location of which is now lost (see
above). Roth labeled these specimens ‘‘T.i.C.B.’’
5REGUERO ET AL.: SMALL ARCHAEOHYRACIDS FROM ARGENTINA AND CHILE
F
IG
. 2. Epoxy cast of specimen from the Tinguiririca Fauna of Chile referred to Protarchaeohyrax gracilis (gen.
nov.). Mandibular fragment (SGOPV 2954) with right p1–m3 and slivers of left posterior teeth. Occlusal (line drawing
and top photograph) and right lateral (bottom photograph) views. Only the right side of the specimen is shown, and
p1–2 are not visible in the occlusal photograph. Scale bar
5
10 mm.
([Formacio´n] Terciario inferior de Can˜ado´n Blan-
co [Territorio del Chubut]).
The Chilean specimens SGOPV 2954 and 2982
were recovered near Termas del Flaco. Specimen
SGOPV 2954 is from locality C-89-39 (see Flynn
& Wyss, 1999; Locality Set 3 of Flynn et al.,
2003), 34
8
59
9
S, 70
8
26
9
W, approximately 2 km
northwest of town (i.e., north of the Rı´o Tingui-
ririca; see map in Wyss et al., 1994). It was col-
lected (like the majority of fossils from this site)
in situ on a veneer of volcaniclastic sediment ad-
hering to a high-angle face created by a resistant
dike. SGOPV 2982 derives from the primary set
of localities producing the Tinguiririca Fauna (Lo-
cality Set 1 [‘‘East Ridge’’] of Flynn et al., 2003),
those straddling the Portezuelo El Fierro (identi-
fied by its elevation, 2738 m, on the current to-
pographic map; Anonymous, 1985) approximate-
ly 3 km due south of Termas del Flaco and the
Rı´o Tinguiririca.
A
GE
—Early Oligocene (to possibly late Eo-
cene), Tinguirirican SALMA. Radioisotopic age
estimates are available only for specimens from
Chile. Due to alteration, only the fossil-bearing
horizons and conformably underlying strata south
of the Rı´o Tinguiririca (including the locality for
SGOPV 2982) have been dated directly at
;
31.5
Ma. This species represents a key biostratigraphic
tie between the laterally discontinuous sections of
the Abanico Formation exposed north and south
of the Rı´o Tinguiririca.
D
IAGNOSIS
—As for genus. The species is sub-
stantially larger than P. minor (named below), and
the mandibular corpus is deeper than in P. inter-
medium (also named below).
C
OMMENTS
—Material previously referred (not
6 FIELDIANA: GEOLOGY
F
IG
. 3. Epoxy cast and line drawing of specimen from the Tinguiririca Fauna of Chile referred to Protarchaeo-
hyrax gracilis (gen. nov.). Rostrum (SGOPV 2982) with left and right dC, P1, dP2–4, M1–2 shown in occlusal view
(line drawing—left dentition only, and upper photograph). The slightly oblique right lateral view (lower photograph)
shows P2–4 exposed within their crypts. Anterior is to the left in all views. Scale bar
5
10 mm.
all of it correctly) to E. priscum included three
mandibular fragments and 21 isolated cheek teeth;
this was accompanied by a small note in Amegh-
ino’s handwriting identifying it as the type of this
species (Simpson, 1967). Out of this lot, Simpson
selected as lectotype (and provided a rough illus-
tration, his figure 31) an upper molar (presumed
to be M1) most closely matching Ameghino’s de-
scription. Simpson considered the taxon a ques-
tionable member of the Hegetotheria.
Archaeohyrax gracilis was described as follows
(translated from Roth, 1903: 22): ‘‘The form of
the teeth is similar to Archaeohyrax patagonicus.
The labial face is slightly convex, with poorly
marked crests. The second molar has a sulcus on
its lingual face. On the lower molars the internal
7REGUERO ET AL.: SMALL ARCHAEOHYRACIDS FROM ARGENTINA AND CHILE
sulci are not deep; on the first molar a sulcus can
barely be distinguished on the internal part of the
anterior lobe. This species is smaller than Ar-
chaeohyrax sulcidens.’’ Later he added: ‘‘inter-
mediate between the families Notopithecidae and
Hegetotheriidae.’’ Roth did not figure the type
material.
In sum, the lectotypes of ‘‘B.’’ sulcidens and
‘‘E.’’ priscum each consist of a single isolated up-
per cheek tooth of uncertain tooth position, the
geographic/stratigraphic sources of which are un-
certain (although both are from Gran Barranca,
see below). Needless to say, securely associated
faunal elements are lacking. By contrast, the type
of ‘‘A.’’ gracilis is more than adequate for diag-
nosis; although its locality cannot now be found,
its biostratigraphic context is currently under-
stood. Because of their high degree of hypsodon-
ty, most post-Mustersan SALMA archaeohyracid
cheek teeth vary significantly in size and shape
during wear, hampering identification of isolated
teeth. Although the lectotypes of ‘‘B.’’ sulcidens
and ‘‘E.’’ priscum and the holotype of ‘‘A.’’ grac-
ilis could all pertain to the same species, the first
two names are based on such meager material that
referral to other archaeohyracid species cannot be
ruled out. Thus we regard the synonymy of ‘‘B.’’
sulcidens, ‘‘E.’’ priscum, and ‘‘A.’’ gracilis as
likely but indemonstrable (identifying it above
with a query). We therefore feel justified in by-
passing ‘‘sulcidens’’ and ‘‘priscum’’ as possible
senior synonyms, basing the new genus recog-
nized here on the more definitively diagnosable
type material ‘‘gracilis.’’ We favor a situation
wherein well-preserved and diagnostic material is
given a new name (and earlier, poorly founded
names are essentially ignored) over one in which
the valid name of otherwise easily identified spec-
imens must always remain in doubt. It creates less
confusion to admit that ‘‘E.’’ priscum is conceiv-
ably the senior synonym of Protarchaeohyrax
gracilis than to have to always qualify, with a
query, referrals of much better material to the ear-
lier proposed name. Thus, excellent material cur-
rently allows recognition of three small species of
archaeohyracids from a restricted temporal inter-
val. Insofar as we cannot establish to which of
these three species, if any, the poor types of pris-
cum and sulcidens properly refer, proposing new
names for some of these three seems justified.
Among other benefits, a desirable side effect of
designating ‘‘gracilis’’ as the type of a new genus
is that this name now becomes biostratigraphical-
ly useful—‘‘gracilis’’ not being known from well-
sampled (but as yet incompletely described) Mus-
tersan SALMA faunas from Patagonia or from the
Deseadan SALMA.
D
ESCRIPTION
—Of the skull, little more than a
poorly preserved anterior fragment of MLP 12-
1478 is currently available for study (although
SGOPV 2982 consists of a well-preserved ros-
trum—and possibly more of the skull—only the
dentition, anterior root of the zygomatic arch, and
portions of the palate have been prepared, the re-
mainder of the specimen being encased in ex-
tremely hard volcaniclastic matrix). The rostrum
is apparently long and dorsoventrally compressed;
the premaxilla is small and triangular in lateral
view. The anterior root of the zygoma lies oppo-
site M2–3 (M1–2 in SGOPV 2982, a juvenile)
and otherwise is of primitive notoungulate form,
not being marked by a descending process or zy-
gomatic plate. This feature may have changed on-
togenetically (as in mesotheres and certain other
notoungulates), but evidence for this is lacking in
the available material.
Upper Dentition—Aside from the alveoli for
I1–3 on MLP 12-1478, little is known of the an-
terior dentition. The alveolus for I1 suggests that
this tooth was substantially larger than the other
incisors. The lot of teeth containing the lectotype
of Eohegetotherium priscum includes an isolated
right upper incisor (I1, MACN A-10988d). This
large tooth is smooth both labially and lingually.
The enamel, which is restricted to the crown, is
thin labially. A shallow groove runs along the in-
ternal face of the long, curved root. The long axis
of the alveolus for I2 is oriented anteroposteriorly,
suggesting that this tooth was little specialized.
The I3 alveolus is very small; it preserves part of
the root, which is circular in cross-section.
A short diastema separates the canine from I3.
The canine is simple in form and not markedly
reduced. The tooth is distinctly caniniform and
apparently bore two roots. The premolariform
teeth preserved in this position on SGOPV 2982
are clearly deciduous; the left permanent canine
is seen in the process of replacement.
The first premolar (which evidently is not re-
placed and begins to wear before dP2–4 are shed)
is longer and wider than the canine; it bears a
weak parastyle and is double-rooted.
The second premolar is much larger than P1; a
well-developed parastyle projects anteriorly. A
faint sulcus marks the lingual surface of the tooth
anteriorly.
The third and fourth premolars are closely sim-
ilar, except for the larger size of P4. Parastyles are
8 FIELDIANA: GEOLOGY
well developed and the vertical grooves separat-
ing them from the paracone column of the exter-
nal face are more clearly marked than on the pre-
ceding teeth. Both teeth possess small central fos-
settes and a single elevated cusp on the ectoloph
(paracone). There are no traces of lingual sulci.
Although P3 and P4 are submolariform, both are
distinctly more triangular in occlusal outline than
are the molars.
The first two molars are trapezoidal in outline
and very similar in form. The parastyle is weakly
developed, a shallow vertical groove demarcating
it posteriorly. The ectoloph is distinctly sinuous,
owing to strong expression of the paracone and
metacone columns on the external face, the for-
mer of which is more prominent. The internal fos-
sette is oriented obliquely, paralleling the anterior
edges of these teeth. The lingual sulcus persists
as a faint vertical depression, even through mod-
erate wear. During early wear stages (as shown by
SGOPV 2982) this sulcus forms an open cleft that
is continuous with the central fossa. Other aspects
of the buccal morphology of M1 are also well
displayed in SGOPV 2982. The crochet is well
developed and extends nearly to the ectoloph, ac-
counting for the small size of the central fossa. A
single, small, median external fossette is present
between the crochet and the ectoloph, but this
would likely have vanished with little additional
wear. An unworn posterior cingulum is present at
a height just dorsal to the slightly worn metaloph.
A small depression occurs between these two
structures, but it is unclear whether this would
have formed a fossette during wear or whether the
cingulum and metaloph would simply have coa-
lesced. A moderately worn M1 and a very lightly
worn M2 are preserved on MLP 52-XI-4-168. On
both, the paracone is more prominent than the
metacone. On M1 (as in SGOPV 2982), an inter-
nal bifid sulcus persists through early wear. The
M2 is longer than wide. The lingual vertical sul-
cus is wide and deep, delimiting a median lobe.
The posterior cingulum forms a distinct shelf, less
elevated than the metaloph, and merging with the
remainder of the crown early in wear. This shelf
is separated from the hypocone lingually by a
very shallow groove. The hypocone is distinct and
high. The left M1–2 of MLP 12-1517 bear three
short roots, the two labial ones being smaller than
the lingual.
The occlusal surface of the mildly worn M3 of
MLP 12-1478 is slightly more triangular than
those of the preceding molars, the lingual margin
of the tooth being broadly rounded. A moderately
worn, isolated, right M3 (MACN A-10988e) lacks
roots, the base of the tooth being completely open.
As in other archaeohyracids, a posterior prolon-
gation of the ectoloph is not developed during ear-
ly wear stages. The lingual sulcus is weak, be-
coming barely discernible in late wear.
The deciduous premolars are well preserved on
SGOPV 2982 (Fig. 3). The anterior replacing
cheek tooth, dP2, is longer than wide and bears a
prominent parastyle. Although molariform, dP3 is
more triangular than the permanent molars. A
short sulcus occurs between the parastyle and
paracone. A slight paracone ridge is developed.
An obliquely oriented fossette occurs centrally to-
ward the labial side of the tooth. The internal face
is flat and rounded. Although low-crowned, dP4
is otherwise quite molariform, bearing a paracone
ridge that is even more prominent than those on
the permanent molars. A short, shallow groove
occurs on the tooth’s lingual face. As shown by
MLP 52-XI-168 and SGOPV 2982, dP4 bears
three roots.
Lower Dentition—The mandibular corpus is
deep and robust. The symphysis is not expanded
posteriorly, extending only to approximately the
middle of p2. The dentition anterior to p1 is un-
known.
Little can be said about the first lower premolar,
as no undamaged examples are known; the tooth
is simple in form (apparently unicuspate) and lat-
erally compressed.
The second lower premolar is considerably
larger than p1 and is apparently double-rooted.
The tooth is dominated by a large, crescentic tri-
gonid, as in certain interatheres (e.g., Notopithe-
cus and Cochilius). The talonid is about one-half
the length of the trigonid and is roughly circular
in cross-section. A vertical groove marks the tri-
gonid-talonid junction throughout the height of
the crown labially; lingually only a short, shallow
groove (obliterated by slight wear) occurs.
The trigonids of p3–4 are less anteroposteriorly
expanded than on p2, with the steeply sloping ba-
sins between the paraconids and metaconids clos-
ing lingually after moderate wear. In SGOPV
2954 the roots of the premolars are visible just
above the edges of the alveoli, while in the Ar-
gentine specimens (e.g., MLP 12-1518) none of
the roots are visible, a difference probably attrib-
utable to heavier wear on the Chilean specimen.
The early wear stage morphology of m1–3 is
well displayed by MLP 12-1513b and MLP 12-
1539. The m1 and m2 are approximately equidi-
9REGUERO ET AL.: SMALL ARCHAEOHYRACIDS FROM ARGENTINA AND CHILE
mensional and are otherwise very similar in mor-
phology.
The trigonid of m3 is square, with a small post-
metastylid projecting posteriorly. The m3 talonid
differs from those of m1–2 in its more posteriorly
projecting hypoconulid, which forms a continuous
bladelike lophid. A broad posterolingual groove
separates the entoconid and hypoconulid. On
SGOPV 2954 the m3 is moderately worn; here
the postmetastylid connects with the anterior face
of the entoconid, producing a narrow isthmus lin-
gually that persists through the remainder of wear.
In this specimen a projection of the central fos-
settid into the talonid is present, the fossettid not
having yet become completely isolated; in addi-
tion, the lingual groove separating the entoconid
and hypoconulid is quite shallow.
Despite the seemingly more advanced state of
wear in of SGOPV 2954, a projection of the cen-
tral fossettid into the talonid persists, while in the
less worn MLP 12-1518 this extension forms a
small, faint, but completely isolated fossettid.
This, along with other features, including metric
differences in the dentition and mandible (Table
1), hints that SGOPV 2954 (and possibly SGOPV
2982) may warrant recognition of a separate spe-
cies (Croft, 2000). Given, however, the smallsam-
ple size currently available—including the lack of
an adult upper dentition from Chile—we take the
conservative approach, tentatively referring these
specimens to P. gracilis. This new taxon is listed
as ‘‘Archaeohyracidae, New taxon A1’’ in Flynn
et al. (2003, tables 1 and 2).
Protarchaeohyrax minor sp. nov.
(Figure 4)
H
OLOTYPE
—MLP 52-XI-4-168a, maxillary
fragment with right P4–M2 (possibly P3–M1).
H
YPODIGM
—The type only.
L
OCALITY
—Santiago Roth collected the type
and only known specimen from Can˜ado´n Blanco,
Chubut, Argentina (see above).
A
GE
—Early Oligocene (to possibly late Eo-
cene; as for P. gracilis), based on correlation of
its associated fauna with elements of the radioiso-
topically dated Tinguiririca Fauna.
D
IAGNOSIS
—Protarchaeohyrax minor, the
smallest archaeohyracid known, is clearly smaller
than P. gracilis and all other described archaeo-
hyracids, including another new taxon (see be-
low). In addition, the posterior cheek teeth do not
display the graded increase in size from P2
through M2 typical of other archaeohyracids.
E
TYMOLOGY
—In reference to its small size.
D
ESCRIPTION
—Only a small right maxillary
fragment bearing three teeth is currently known.
There is some question about the tooth positions
represented by the teeth, P4–M2 (or possibly P3–
M1). We initially regarded MLP 52-XI-4-168a as
perhaps referable to the small taxon named below
(P. intermedium), an assignment plausible—on
the basis of size—only if a P3–M1 identification
is accepted. For reasons discussed below, how-
ever, MLP 52-XI-4-168a most likely includes two
molars and thus represents a distinct, very small
taxon. This species is listed as ‘‘Archaeohyraci-
dae, New taxon A3’’ in Flynn et al. (2003, table
2).Upper Dentition—Although MLP 52-XI-4-
168a compares fairly closely with a small palate
from the Tinguiririca Fauna (SGOPV 2998, as-
signed to another new taxon below), this maxilla
is unusual in that the three teeth do not grade
evenly from one to another in size. Instead, the
two posterior teeth are about equal in size—the
middle one perhaps being slightly larger—and the
anterior one is only slightly smaller than the oth-
ers. This contrasts with the condition in P. gracilis
and the taxon named below, wherein successive
teeth increase in size from P2 through at least M2.
The size and general shape of the three teeth in
MLP 52-XI-4-168a agree fairly closely with the
P3–M1 of the new taxon represented by SGOPV
2998. However, a pronounced groove separating
the paracone and parastyle on the anterior tooth
of MLP 52-XI-4-168a suggests, in combination
with the feeble expression of this structure on the
two succeeding teeth, that the anterior tooth rep-
resents P4 (and hence the others represent M1–2).
Therefore, since P4–M2 are the most plausible
tooth loci represented in MLP 52-XI-4-168a, it
follows that this specimen pertains to a taxon con-
siderably smaller than that represented by SGOPV
2998 (M2 in the latter specimen measures 5.4 mm
long by 4.2 mm wide, versus 4.2
3
3.2 mm in
MLP 52-XI-4-168a).
P4 is triangular in occlusal outline. A central
basin and its single median fossette are rimmed
labially by an elevated paracone and parastylar
spur. The molars are more anteroposteriorly elon-
gate than is the premolar, being more trapezoidal
in outline. In addition, as mentioned above, the
buccal surfaces of the molars are topographically
simpler than that of the premolar; the paracone
and metacone folds, as well as the parastylar
10 FIELDIANA: GEOLOGY
T
ABLE
1. Measurements of teeth of Protarchaeohyrax gracilis, P. intermedium, and P. minor (mm).
Protarchaeohyrax gracilis
Upper dentition
P1
LW
P2
LW
P3
LW
P4
LW
M1
LW
M2
LW
M3
LW
MACN A52-623a
MACN A-10911o
MACN A-10911p
MACN A-10988a
MACN A-10988b
MACN A-10988c
MLP 12-1522 5.2 3.5 4.6 4.5
5.8
4.3
6.9
5.1
7.2
7.1
6.5
6.4
6.4
6.7
5.3
5.8
5.3
5.5
5.5
5.0 7.5 5.0 7.4 4.2
MLP 12-1478
MLP 52-XI-4-168
SGOPV 2982
3.9
4.3 2.3
2.5 4.7
4.8
4.9*
2.9
3.4
3.6* 5.2
4.6* 3.7
4.8* 5.7
5.8* 3.8
4.8* 6.4
6.9 3.4
4.3 — — — —
* These values are for deciduous teeth.
Lower dentition
p1
LW
p2
LW
p3
LW
p4
LW
m1
LW
m2
LW
m3
LW
MACN A52-623b
MACN A-10906a
MACN A-10906b
MACN A-10906c
MACN A-10906d
MACN A-10906e
6.7 3.6
8.0
7.1
3.5
3.4
6.5
7.1
7.5
3.5
3.3
3.5
MACN A-10906f
MACN A-10906g
MACN A-10906h
MACN A-10906i
MACN A-10906j
MLP 12-1518 3.4 2.0 4.6 2.2 4.7 3.0
6.0
5.1
3.4
2.6
6.4
6.7
4.7
3.3
3.6
3.3
6.9
5.2
3.4
3.5
7.5
7.1
3.5
3.1
MLP 12-1513a
MLP 12-1513b
MLP 12-1539
MLP 61-VIII-3-398
5.1
4.7
2.1
2.7
5.5
4.7
2.6
3.3
6.1
5.6
5.1
3.3
2.6
3.8
6.0
6.2
5.1
6.9
3.9
3.4
3.2
3.8
6.7
7.4
5.8
3.8
3.5
3.3
7.0
7.1
6.0
3.1
3.5
2.5
MLP 59-II-26-85
MLP 61-IV-14-3
MLP 52-XI-4-196
SGOPV 2954 3.7 1.9 4.5
3.5 3.3
2.8
6.0
5.0
3.8
3.4
3.4
3.6
6.1
6.1
4.2
3.4
3.5
4.0 5.2 4.3 8.2
7.4 3.3
3.5
Mandible Midline distance between posteriormost extent of
mandibular symphysis and posterior edge of m3 Depth of ramus just
posterior to m3
MLP 12-1518
SGOPV 2954 approx. 32.5 mm
approx. 24 mm 3.6
4.6
Protarchaeohyrax intermedium
Upper dentition
P1
LW
P2
LW
P3
LW
P4
LW
M1
LW
M2
LW
M3
LW
SGOPV 2998 2.9 3.2 3.2 4.1 3.9 4.7 4.0 5.1 5.4 4.6 5.8 3.9
Lower dentition
p1
LW
p2
LW
p3
LW
p4
LW
m1
LW
m2
LW
m3
LW
SGOPV 3065
SGOPV 5007 —
——
—4.6
3.9 1.8
2.3 4.6
4.1 2.0
2.4 4.7
4.4 2.5
2.7 5.7
5.1 2.6
3.0 —
(6.3) —
2.6
11REGUERO ET AL.: SMALL ARCHAEOHYRACIDS FROM ARGENTINA AND CHILE
T
ABLE
1. Continued.
Protarchaeohyrax minor
P3
LW
P4
LW
M1
LW
M2
LW
MLP 52-XI-4-168a 3.7 4.3 5.0 4.0 5.0 3.6
F
IG
. 4. Epoxy cast of right maxillary fragment (MLP
52-XI-4-168a) collected by Santiago Roth from Can˜a-
do´n Blanco and here referred to Protarchaeohyrax mi-
nor (gen. et sp. nov.). Top, occlusal view; bottom, lateral
view (anterior to the left in both). Scale bar
5
10 mm.
groove, form little more than low-amplitude rip-
ples. A vertical groove separates the protocone
and hypocone along the internal face of M1; on
P4 and M2 this structure is far less distinct.
Protarchaeohyrax intermedium sp. nov.
(Figures 5–7)
H
OLOTYPE
—SGOPV 3065 paired dentaries with
left p2 (damaged), p3–m3, and right p3–4, slices
of m1 trigonid and m2 talonid, and m3 (Fig. 5).
H
YPODIGM
—The type, and SGOPV 5007,
paired dentaries bearing right p2 (damaged), p3–
m3, plus fragmentary portions and lingual im-
pressions of several left cheek teeth, including
largely intact m2–3 (Fig. 6); and SGOPV 2998,
partial palate bearing left and right P2–M3 (Fig.
7).L
OCALITY
—From near Termas del Flaco, Chile,
all from localities south of the Rı´o Tinguiririca
(see localities for P. gracilis).
A
GE
—Early Oligocene (to possibly late Eo-
cene; as for P. gracilis).
D
IAGNOSIS
—P. intermedium is intermediate in
size between P. gracilis and P. minor. In addition,
the very shallow ramus displayed in SGOPV 3065
clearly differentiates P. intermedium from at least
P. gracilis (the lower dentition of P. minor being
unknown).
E
TYMOLOGY
—In reference to its size.
D
ESCRIPTION
—Although much of a palate is
preserved (SGOPV 2998), little can be said about
this taxon’s cranial morphology in the specimen’s
current state of preparation. The anterior zygo-
matic root, as shown on the left side of the spec-
imen, lies opposite M3, without obvious evidence
of a ventral expansion.
Much of the mandible, including the anterior
portion of the ascending ramus, is preserved on
the left side of the holotype. The symphysis, if it
was fused, was not expanded posteriorly. The
only remarkable feature of the ramus is its striking
shallowness. The vertical depth of the mandible
below p3 in SGOPV 3065 is 5.7 mm, compared
to
.
8.5 mm in specimens referred to P. gracilis
above. This slender form of the ramus is all the
more remarkable given the strong hypsodonty of
the cheek teeth. Patches where the external sur-
face of the left mandibular ramus of SGOPV 3065
is not preserved provide partial windows onto the
ventral reaches of m1 and m2. Both teeth extend
(clearly visible on m2, obscured on m1) as undi-
vided, enamel-covered (i.e., unrooted) columns
that reach the base of the ramus (m2 is approxi-
mately 19 mm high, of which only about 3.5 mm
protrudes above the alveolus).
Lower Dentition—The morphology of the low-
er dentition is best illustrated by SGOPV 5007
(Fig. 6), a pair of dentaries. The right cheek teeth
are well preserved, excepting a damaged and lat-
erally displaced p2 and a missing posterior sliver
on the talonid of m3. Significant portions of the
left m1–3 are preserved, although there is break-
age labially, particularly on m1. The roots and
lingual impressions of p3–4 occur on the left side
12 FIELDIANA: GEOLOGY
F
IG
. 5. Epoxy cast and line drawing of specimen from the Tinguiririca Fauna of Chile referred to Protarchaeo-
hyrax intermedium (gen. et sp. nov.). Paired dentaries (holotype, SGOPV 3065) with left p2 (damaged), p3–m3, and
right p3–4, slices of m1 trigonid and m2 talonid, and m3, in occlusal (line drawing—left side only, and upper
photograph) and left lateral (lower photograph) views. Anterior is to the left in all views. Scale bar
5
10 mm.
as well. The molars and posterior premolars of P.
intermedium tend to have a narrower entoconid
region, resulting in flatter lingual faces of these
teeth than is the case in P. gracilis. Overall, these
teeth are considerably thinner than in P. gracilis.
A fossettid occurs immediately posterior to the
trigonid on p3–m3. A sharp vertical groove sep-
arates the p2–m3 trigonids and talonids labially
throughout most (if not all) of the considerable
vertical height of these teeth. A deep notch sep-
arates the entoconid and hypoconulid on m3,
lending the posterior talonid region a strongly
hooked appearance.
Upper Dentition—The second premolar
through M2 form a closed and evenly graded se-
ries, increasing in size posteriorly. These teeth are
13REGUERO ET AL.: SMALL ARCHAEOHYRACIDS FROM ARGENTINA AND CHILE
F
IG
. 6. Epoxy cast and line drawing of specimen from the Tinguiririca Fauna of Chile referred to Protarchaeo-
hyrax intermedium (gen. et sp. nov.). Paired dentary fragments (SGOPV 5007) with right p2 (damaged), p3–m3, plus
fragments of left cheek teeth, including largely intact m2–3, occlusal view (line drawing of right side only). Anterior
is to the left. Scale bar
5
10 mm.
all fairly obliquely placed, the internal portions
being shifted posteriorly. The upper molars of
SGOPV 2998 (Fig. 7) are similar in size to P.
gracilis, but the premolars are considerably small-
er, both in length and in width, the combined
length of P2–M3 in SGOPV 2998 approximating
that of P3–M3 in MLP 12-1522. The buccal faces
of these teeth are smoother and flatter than in P.
gracilis, the parastyle and paracone folds being
more subdued. The central fossa in each tooth
does not parallel the front edge of the tooth (as in
MLP 12-1522); rather, it is directed more poste-
riorly, toward the posterolingual corner of the
tooth, mimicking the condition seen in the decid-
uous premolars of SGOPV 2982.
The second premolar is simple and roughly tri-
angular, with a single elevated external cusp and
a very weak parastyle. Its degree of hypsodonty
is only modest, with the beginnings of the divi-
sion into roots being visible at the bases of this
tooth on both sides of the specimen. Considerably
more trapezoidal (and hence molariform) in out-
line than P2, P3 is still a rather small tooth. A
very faint indication of the metacone is present,
and the parastyle is enlarged over the condition
on P2. The fourth upper premolar is basically an
enlarged, transversely expanded version of P3. As
on the preceding premolars, the parastylar fold
and paracone column are not strongly expressed
on the tooth’s buccal face. Tapering at the tooth’s
base indicates a fairly low degree of hypsodonty,
as is also the case on P2–3 and M1. A pronounced
groove separates the protocone and hypocone
along the internal face of M1 and M2; only a faint
indication of this structure occurs on M3. The
third molar is also distinctive in bearing a narrow
parastylar column which projects off its antero-
labial corner.
D
ISCUSSION
—Although SGOPV 3065 has fewer
preserved teeth than SGOPV 2998 and displays
occlusal morphology less clearly than SGOPV
5007, it is selected as the holotype because it ex-
14 FIELDIANA: GEOLOGY
F
IG
. 7. Epoxy cast and line drawing of specimen from the Tinguiririca Fauna of Chile referred to Protarchaeo-
hyrax intermedium (gen. et sp. nov.). Partial palate (SGOPV 2998), with left and right P2–M3, right lateral (upper
photograph) and occlusal (line drawing—right side only, and lower photograph) views. Anterior is to the right in all
views. Scale bar
5
10 mm.
hibits the distinctive mandibular morphology
readily distinguishing this taxon from P. gracilis.
The small size of this taxon relative to P. gracilis
is most immediately apparent from SGOPV 5007:
although its tooth row length is similar to SGOPV
2954 (P. gracilis), its teeth are only about 75% as
wide. Lower cheek tooth width in P. intermedium
approaches that of smaller specimens assigned
15REGUERO ET AL.: SMALL ARCHAEOHYRACIDS FROM ARGENTINA AND CHILE
above to P. gracilis (e.g., MLP 12-1518), but the
tooth row of the former is shorter (combined p3–
m2 length is approximately 17.5 mm in SGOPV
3089h, versus 20.4 mm in MLP 12-1522). This
species is listed as ‘‘Archaeohyracidae, New tax-
on A2’’ in Flynn et al. (2003, tables 1 and 2).
Temporal Correlation and
Conclusions
Dating of mammal-bearing sediments at Salla,
Bolivia (MacFadden et al., 1985) highlighted a
substantial hiatus between the Deseadan and Mus-
tersan SALMAs. In hindsight, we now know that
Roth and the Ameghinos uncovered the earliest
evidence, long overlooked, of a post-Mustersan,
pre-Deseadan faunal interval, but the significance
of these early finds did not come into focus until
discovery of the Tinguiririca Fauna in central
Chile. Thus the Tinguirirican SALMA appears to
be recorded at two other locations in southern
South America, Can˜ado´n Blanco (Chubut, Argen-
tina), and a horizon (‘‘Astraponote´en plus supe´r-
ieure’’) at the Gran Barranca (Chubut, Argentina),
the latter of which merits additional comment
here. Several specimens referred to P. gracilis
above, collected by Carlos Ameghino between
1896 and 1899 and published by his brother
(Ameghino, 1901, 1902), likely pertain to this in-
terval. Although exact horizons cannot be deter-
mined with current data, there are strong indica-
tions that these specimens were collected from
levels distinctly above those containing typical
Casamayoran or Mustersan fossils at Gran Bar-
ranca. First, C. Ameghino’s handwritten labels for
some archaeohyracid specimens described in this
paper variously read ‘‘Colhuapi Astraponotense
ma´s superior’’ [Astraponote´en plus supe´rieur—
APS—in F. Ameghino’s French] or ‘‘Colhuapi
Notostylops (parte sup.).’’ Colhuapi alludes to the
Gran Barranca, and (‘‘ma´s superior/parte sup.’’)
indicates that they were derived from above the
typical Notostylops (Casamayoran) or Astrapono-
tus (Mustersan) beds. Although C. Ameghino did
not provide precise stratigraphic information, it
would appear that he applied different names to
the same horizon to reflect which fossils he col-
lected immediately below the ones in question.
Thus, several fossils labeled by him as ‘‘Noto-
stylops (part. sup.)’’ may actually derive from the
same level as those recorded from the ‘‘Astrapo-
notense ma´s superior.’’ Perhaps the clearest indi-
cation of this is that many of the fossils labeled
in these two different ways are indistinguishable
(including ‘‘Eohegetotherium priscum’’ and ‘‘Ar-
chaeohyrax sulcidens’’). At the same time, these
fossils are unmistakably distinct from those of the
Casamayoran and Mustersan SALMAs. Neverthe-
less, F. Ameghino never fully elaborated or for-
mally recognized this faunal interval.
One of Simpson’s measured stratigraphic sec-
tions at Gran Barranca, his profile M (Cifelli,
1985), may coincide with where Carlos Ameghi-
no recovered the specimens just mentioned. Simp-
son collected three notohippid specimens from
this interval, Eomorphippus obscurus (AMNH
29462, Field No. 146, ‘‘Pink beds just under Up-
per Channel at ‘M’’’) and ?Eomorphippus pas-
cuali (AMNH 29405, Field No. 147, ‘‘Under Up-
per Channel beds at ‘M’,’’ and AMNH 29474,
Field No. 148, ‘‘Upper Channel beds at ‘M’’’),
all of considerable biostratigraphic significance.
Cifelli (1985: 9) noted that the notohippids col-
lected by Simpson at Profile M (Fig. 5, points 16
and 17, Section V, p. 11 of Cifelli, 1985) come
from levels ‘‘nearly 20 m higher than site 4,’’ the
latter of which contains typical Mustersan fossils.
A taxon very similar to E. obscurus occurs in the
Tinguiririca Fauna (Wyss et al., 1994), and E. ob-
scurus itself is apparently restricted to the ‘‘As-
traponote´en plus supe´rieure’’ (Bond et al., 1996;
Reguero, 1998). The E. obscurus holotype,
(MACN A-10917), and MACN A-10914 (also E.
obscurus) are almost certainly from the Gran Bar-
ranca. Kay et al. (1999, fig. 1) correlated Simp-
son’s ‘‘Upper Channel Series’’ with horizons
(MZ-16.1 to MZ-17) of their profile, just above a
basalt
40
K/
40
Ar dated at 28.8
6
0.9 Ma (Marshall
et al., 1986). The APS level seems to occur below
these horizons (the basalt and the Upper Channel
Series) within the Puesto Almendra Member of
the Sarmiento Formation (Spalletti & Mazzoni,
1979: 273, fig. 2 therein). Kay et al. (1999) report
a pre-Deseadan/post-Mustersan fauna from 3 to 5
m below this basalt.
Additional evidence for the existence of a dis-
tinct APS horizon at the Gran Barranca comes
from the Italian geologist Egidio Feruglio. Fer-
uglio (1938) collected a few specimens between
81 and 95 m (his locality F31, ‘‘Hard, concretion-
ary, cornice-forming tuff, so-called ‘tosquillas’’’)
above the ‘‘argiles fissilaires’’ beds or ‘‘Tobas de
Koluel Kaike.’’ One of these, a notohippid, was
referred (Simpson, 1967) to Pseudostylops sub-
quadratus, a junior synonym of Eomorphippus
obscurus (Patterson in Simpson, 1967: 184).
16 FIELDIANA: GEOLOGY
The discovery of fossil mammals in the central
Andean Main Range of Chile has vastly improved
temporal correlations between post-Neocomian
lithostratigraphic units located west of the modern
Andean divide with their back arc equivalents in
Argentina (well east of the current Andean di-
vide). Chronologic information yielded by these
fossils establishes the rough temporal equivalence
between the largely volcanic and volcaniclastic
series of the Abanico (
5
Coya-Machalı´) Forma-
tion with portions of the Sarmiento Formation and
related units of Argentina (rather than with the
Neuque´n Group, as has been assumed tradition-
ally). The archaeohyracids discussed herein con-
stitute an important component of this biochron-
ologically based linkage. Similarly, these archaeo-
hyracid taxa form part of the basis for recognizing
a South American Land Mammal ‘‘Age’’ inter-
posed between the Deseadan and Mustersan; this
biochronologic interval (the Tinguirirican SAL-
MA) has recently been formalized (Flynn et al.,
2003).
Acknowledgments
We thank the Museo Nacional de Historia Nat-
ural (Santiago), particularly Daniel Frassinetti, for
their long-term support of our Andean work.
Reynaldo Charrier generously shared his geolog-
ical expertise of the area. He, along with Gabriel
Carrasco and numerous others, provided invalu-
able assistance in the field. Mariano Bond con-
tributed greatly through his unparalleled knowl-
edge of notoungulate systematics and nomencla-
ture. Barry Albright, Jose´ Bonaparte, Bruce
MacFadden, and Rosendo Pascual allowed access
to specimens under their care. John Weinstein and
Mark Widhalm (FMNH) photographed the spec-
imens, and Karen Nordquist scanned the nega-
tives. Line drawings were executed by Marlene
Donnelly. This work would not have been possi-
ble without the skill and dedication of Andrew
Lehman, Robert Masek, William Simpson, and
the late Steve McCarroll, who prepared the ex-
ceptionally challenging fossil material. We are
grateful to Richard Cifelli for an especially help-
ful review. Richard Madden and Richard Kay pro-
vided valuable discussion, and the former gave a
detailed critique. Support for this project was pro-
vided by NSF grants DEB-9317943 and DEB
9020213 to J.J.F. and A.R.W., as well as the Hinds
Fund and NSF Biodiversity Training Grant (GRT-
9355032) from the University of Chicago, and the
Paleobiological Fund (D.A.C.). A John Simon
Guggenheim Foundation fellowship (J.J.F.) facil-
itated completion of this paper.
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