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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

1Division Paleontologıa 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 or lundberg@acnatsci.org

3Instituto de Zoologia Tropical, Universidad Central de Venezuela, Apartado de Correos 47058, Caracas, 1041-A, Venezuela,

amachado@strix.ciens.ucv.ve

Journal of Vertebrate Paleontology 29(2):350–358, June 2009 @2009 by the Society of Vertebrate Paleontology

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

Frank Magallanes

I remember hearing rumors of a 3 foot long piranha swmming the river of Argentina for a number of years (since 2000) . At the time I thought my fellow hobbyist had a bit of  too much Canadian beer. Such a beast would have been not only impressive but largely sought after by piranha collectors. Of course, only species under 20 inches have been the norm for fisherman, unless of course you catch the vegetarian pacu. A close relative of the piranha. But now science has discovered the fossil of a huge beastly piranha along the Paraná River and named it Megapiranha paranensis. Unfortunately, only the premaxllae and teeth were found and not the rest of the body. The teeth are serrated and short, like those of a pacu, yet placed in a zigzag pattern on the upper  jaw.  (Cione et al., 2009). The fossil record of piranhas is presently limited to a few isolated teeth of Neogene age (Lundberg, 1998). This fossil is described as a new genus and species of Serrasalmidae (Cione et al., 2009).

The species Megapiranha paranensis was compared with the tooth structure and jaws of Colossoma macropomum  and Serrasalmus rhombeus. Scientists were only able to code Megapiranha for a small portion of morphological  characters. Several plesiomorphic  characters are present in Megapiranha. The fossil has seven premaxilary  teeth, similar to all serrasalmid genera except Catoprion mento (5 teeth) and six teeth in piranhas (of which the last is a compound tooth (Machado-Allison, 1982). The species has attachment scars of the distal most teeth and are subcircular similar to most serrasalmids and not labiolingually  compressed as in the derived condition seen in piranhas (Cione et al., 2009).

Megapiranha, because of its similar premaxilary characters support the placement with its sisters of the piranha clade (Pygocentrus, Serrasalmus, Pristobrycon, and Pygopristis).  The difference between Megapiranha and modern piranhas; is today piranhas have a large central cusp flanked by at least one small cusp (except P. denticulata which has penticuspid teeth,  (Machado-Allison, 1982).

From the evidence, it becomes clear that Megapiranha evolved independently  from other Serrasalmids. Megapiranha represents the first record of an extinct Serrasalmid (Cione et al., 2009). The teeth of this fish were probably used to feed on plant matter, much like hte pacus of  today. But experts are divided and remains unknown what the ecology was like during the live period of this creature. Piranhas, which were thought to be strictly carnivorous at one time, are now known to also indulge in plant eating as well. Some piranhas (pirambeba) have specialized teeth for shearing off seed husks (P. denticulata), other piranhas eat scales and fins (Nico 1991). This suggests that the extremely compressed  tooth morphology seen in piranhas did not evolve in correlation with carnivory (Cione et al., 2009) . In light of this plasticity, the compressed crowns and round tooth bases of Megapiranha specimens may have been  suited to a range of feeding behaviors (Cione et al., 2009).

Additionally,  catalog problems continue with proper locality data on fossils. This makes it difficult to ascertain where specifically  the fossils are collected .  Fortunately, the Paraná collection offer a generalized area of collection. This will enable field research workers to apply more specific collection data to future fossils.

For now, readers can access eurekalert.org web site to see actual photos of fossil, by CLICKING HERE.

There is still so much out there that has yet to be discovered on piranhas. This is one giant step to understanding them further.

Frank Magallanes, OPEFE

July 3, 2009

REFERENCES:

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LITERATURE CITED

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UPDATED: 12/26/2011