ARTICLE
MEGAPIRANHA PARANENSIS, A NEW GENUS AND SPECIES OF SERRASALMIDAE
(CHARACIFORMES, TELEOSTEI) FROM THE UPPER MIOCENE OF ARGENTINA
ALBERTO LUIS CIONE,1 WASILA M. DAHDUL,*,2 JOHN G. LUNDBERG,2 and ANTONIO MACHADO-ALLISON3
1Divisio´n Paleontologı´a de Vertebrados, Museo de La Plata, 1900 La Plata, Argentina, acione@museo.fcnym.unlp.edu.ar;
2The Academy of Natural Sciences, Department of Ichthyology, 1900 Benjamin Franklin Parkway, Philadelphia, Pennsylvania
19103, U.S.A., wasila.dahdul@usd.edu, lundberg@acnatsci.org;
3Instituto de Zoologia Tropical, Universidad Central de Venezuela, Apartado de Correos 47058, Caracas, 1041-A, Venezuela,
amachado@strix.ciens.ucv.ve
ABSTRACT—Megapiranha paranensis from the Upper Miocene of Argentina is described based on a large, partially
toothed premaxilla as a new genus and species of serrasalmid fish (pacus and piranhas) and is diagnosed and distinguished
from other serrasalmids based on the following unique combination of characters: seven premaxillary teeth with the first
four arranged in a shallow, zig-zag row, and third tooth shaped similarly to the fourth and fifth teeth; large, triangular,
unicuspid crowns with finely serrated cutting edges. The phylogenetic position of Megapiranha was determined by
parsimony analysis of morphological characters. The resulting analysis recovered Megapiranha as sister to the piranha
clade (Pygopristis, Pygocentrus, Pristobrycon, Serrasalmus) and is supported by two synapomorphies: (1) teeth triangular
in labial view with well-developed cutting edges, and (2) serrations along both sides of tooth cutting edges. The pattern of
tooth placement exhibited by the fossil Megapiranha is intermediate between the double-row condition of pacus and the
single-row condition of piranhas, and suggests how the double row of teeth may have been rearranged into a single row in
the evolution of piranhas.
INTRODUCTION
The Serrasalmidae are a family of South American fresh-
water characiform fishes including the well known flesh-eating
piranhas and herbivorous tambaqui and pacus (Ringuelet et al.,
1967; Machado-Allison, 1983a, b; Je´gu, 2003). Correlated with
their dietary diversity, serrasalmids exhibit a remarkable array
of specialized dentitions and jaws. The herbivorous and omniv-
orous species have broad, heavy jaw bones each with a double
row of seven roughly circular teeth bearing one or two low
cutting edges. The slender jaw bones of piranhas each bear a
single, narrowly compressed row of six interlocking, blade-like
jaw teeth. In 1951, Gosline suggested that the characteristic
single row arrangement of teeth of piranhas was derived from
the primitive double row condition of herbivorous serrasalmids.
Gosline hypothesized that the primitive double row of teeth
were “pressed into a single row,” with one tooth dropping out.
Gosline knew of no examples of an intermediate pattern.
Both piranhas and pacus are widespread today in the tropical
lowlands of eastern South America. The oldest known fossil
serrasalmids are isolated teeth from the Upper Cretaceous of
Bolivia (Gayet and Meunier, 1998; Dahdul, 2007). These and
several other fossil teeth and jaw elements from Cenozoic rocks
pertain to the herbivorous pacus (Lundberg, 1998; Cione et al.,
2000; Dahdul, 2004, 2007). The fossil record of piranhas on the
other hand is presently limited to a few isolated teeth of Neo-
gene age (Lundberg, 1998).
One of us (AC) found a very large and partially toothed
serrasalmid premaxilla in the Roth Collection of the Museo de
La Plata (Argentina). The specimen comes from the well known
late Miocene fossil vertebrate locality along the Rı´o Parana´ near
the city of Parana´, Entre Rı´os, Argentina. Whereas the fossil
premaxilla and teeth are obviously distinct from modern serra-
salmids, its sharp, blade-like and somewhat compressed teeth
bear some similarity to piranhas. Further, the arrangement of
teeth on the fossil is intermediate between the distinct double-
and single-row patterns of modern serrasalmids, suggesting as
did William Gosline how the teeth may have been rearranged
in the origin of piranhas. This fossil is described here as a new
genus and species of Serrasalmidae; its relationships and evolu-
tionary significance are discussed.
Institutional Abbreviations—MLP, Museo de La Plata, La
Plata, Argentina; CICYTTP, Centro de Investigaciones Cientı´-
ficas y Transferencia Tecnologı´a a la Produccio´n, Diamante,
Argentina.
GEOGRAPHIC AND STRATIGRAPHIC PROVENANCE
The Neogene fossiliferous beds in the Parana´ riverside cliffs
near the city of Parana´, Entre Rı´os, Argentina have been scien-
tifically known since 1827 when Alcide D’Orbigny visited the
area (D’Orbigny, 1842; Fig. 1). The complex relationships be-
tween the marine and continental units cropping out of the
cliffs provoked different interpretations. Most authors identi-
fied only one marine unit recognizable at the base of the cliffs
(e.g. Ameghino, 1906; Scartascini, 1954; Acen˜olaza, 1976). This
marine unit is overlain by a thick fluvial and a terrestrial se-
quence. However, other authors proposed two or three marine
transgressions (Frenguelli, 1920; Cordini, 1949). The current
stratigraphic scheme was proposed by Acen˜olaza (1976; 2000;
see also Acen˜olaza and Acen˜olaza, 1999; Fig. 2) who interpreted
the marine rocks as having originated during a single ingression
represented by the Parana´ Formation. Acen˜olaza (1976, 2000)
suggested that the marine beds located at higher levels in the
*Corresponding author. Current address: Department of Biology, Uni-
versity of South Dakota, Vermillion, SD 57069, wasila.dahdul@usd.edu
Journal of Vertebrate Paleontology 29(2):350–358, June 2009
# 2009 by the Society of Vertebrate Paleontology
350

riverside cliffs are relicts of an ancient topography that was
wrongly interpreted as different marine ingressions, especially
by Frenguelli (1920). The Parana´ Formation is mainly composed
of green mudstones and sandstones with oyster banks (Acen˜o-
laza, 1976, 2000; Chebli et al., 1989) and was apparently depos-
ited during the large marine encroachment that covered the
Chacopampean region during the middle Miocene (“Mid Trans-
gressive Onlap Sequence;” see Uliana and Biddle, 1988; del Rı´o,
1991). This trangression probably persisted in the East of Argen-
tina until the Tortonian (see below). The fluvial Ituzaingo´ For-
mation overlies the marine unit. This formation is composed of a
basal conglomerate (“Conglomerado osı´fero”) with abundant
vertebrate remains which is overlain by almost unfossiliferous
whitish to yellow brown sandstones and green mudstones. Ter-
rigenous Pleistocene (Ensenadan to Lujanian in the southern
South American continental scale; see Cione and Tonni, 1995,
1996, 2001; Fig. 2), poorly fossiliferous beds assigned to different
units overlay the Ituzaingo´ Formation (Acen˜olaza, 1976;
Iriondo, 1980; Chebli et al., 1989). The Ituzaingo´ Formation (as
Entre Rı´os Formation) was correlated with the “Formacio´n
Puelche” of the Buenos Aires province subsoil (Reig, 1957; see
below). According to the mammals occurring in the “Conglom-
erado osı´fero” and the stratigraphic relationships, the age of the
base of Ituzaingo´ Formation is almost exclusively Tortonian
(late Miocene) or Huayquerian in the local chronology (Pascual
and Odreman Rivas, 1971; Cione and Tonni, 1995; Fig.2). The
Huayquerian ranges from about 9 Ma to about 6 Ma (Marshall
et al., 1983).
The term “Piso Mesopotamiense” or “Mesopotamiense” was
widely in use in the Argentinian vertebrate paleontology litera-
ture. This term was introduced for the first time by Doering
(1882; see also Ameghino, 1883). Frenguelli (1920) restricted the
“Mesopotamiense” to the “Conglomerado osı´fero.” One of us
discussed extensively the use of state/age concept in South Amer-
ica (Cione and Tonni, 1995, 1996) although we did not address
the “Mesopotamiense” problem. Cozzuol (1993) proposed to
define the “Mesopotamiense” as a formal stage/age unit.
Unfortunately, most of the fossils in collections from the Parana´
area do not include adequate provenance. Labels in collections
usually only state that the material comes from the base of the
cliffs near Parana´. However, recent field work has confirmed that
almost all of the Miocene terrestrial and freshwater aquatic verte-
brates come from the “Conglomerado Osı´fero” at the base of the
Ituzaingo´ Formation. Field work is presently in progress and more
precise information will be obtained. The “Conglomerado osı´fero”
occurs in paleochannels, is laterally interrupted and rarely crops
out because of landslides. There is no basis for recognizing chron-
ostratigraphic, biostratigraphic, geochronologic or even biochro-
nologic units based on the fossil and stratigraphic representation
of the “Conglomerado osı´fero.” Consequently, we consider here
the “Piso Mesopotamiense” sensu Frenguelli (1920) or “Mesopo-
tamiense” as invalid. In this paper, we will refer to the fossil con-
tent of the base (“Conglomerado osı´fero”) of a lithostratigraphic
unit (Ituzaingo´ Formation) as present in several localities near
Parana´ without recognizing a local chronostratigraphic or bio-
stratigraphic unit (Cione et al., 2000).
FIGURE 1. Map of the Entre Rı´os province in Argentina showing the approximate location of the holotype of Megapiranha paranensis between
the cities of Parana´ (ca. 31
43’S 60
31’W) and Villa Urquiza (ca. 31
38’S 60
22’W). City limits indicated by hatchmarks and coordinates estimated
from center of cities as indicated by black dot (modified from Cione et al. 2000).
CIONE ET AL.—NEW FOSSIL SERRASALMIDAE FROM ARGENTINA 351