LiveScience.com – Thu Jun 25,
6:02 pm ET
If you thought piranhas were scary, be glad Megapiranha is no
longer around.
Megapiranha was up to 3 feet long (1 meter) - a fish-beast four
times as big as piranhas living today, studies of its jawbones
indicate. It lived about 8 million to 10 million years ago and
might have been quite comfortable stalking cartoon animals in an
"Ice Age" movie.
Another close relative of the piranha, called pacu (singular and
plural), is not so scary. Pacu have squared-off stumps of teeth
used for munching veggies. (For the record, tales of carnivorous
piranhas eating humans are fictional.)
Now a newly uncovered jawbone of a transition species ties all
these teeth together. Named Megapiranha paranensis, this
previously unknown fossil fish bridges the evolutionary gap between
flesh-eating piranhas and their plant-eating cousins.
Here's what's known:
Present-day piranhas have a single row of triangular teeth, like
the blade on a saw, explained the researchers. Pacu have two rows
of square teeth, presumably for crushing fruits and seeds.
"In modern piranhas the teeth are arranged in a single file,"
said Wasila Dahdul, a visiting scientist at the National
Evolutionary Synthesis Center in North Carolina. "But in the
relatives of piranhas - which tend to be herbivorous fishes - the
teeth are in two rows."
The new fossil shows an intermediate pattern: teeth in a zig-zag
row. This suggests that the two rows in pacu were compressed to
form a single row in piranhas. "It almost looks like the teeth are
migrating from the second row into the first row," said John
Lundberg, curator at the Academy of Natural Sciences in
Philadelphia and a co-author of a study of the jawbone.
If this is so, Megapiranha may be an intermediate step in the
long process that produced the piranha's distinctive bite. To find
out where Megapiranha falls in the evolutionary tree for these
fishes, Dahdul examined hundreds of specimens of modern piranhas
and their relatives.
"What's cool about this group of fish is their teeth have really
distinctive features. A single tooth can tell you a lot about what
species it is and what other fishes they're related to," Dahdul
said. Her phylogenetic analysis confirmed her hunch - Megapiranha
seems to fit between piranhas and pacu in the fish family tree.
The Megapiranha fossil was originally collected in a riverside
cliff in northeastern Argentina in the early 1900s, but remained
unstudied until paleontologist Alberto Cione of Argentina's La
Plata Museum rediscovered the startling specimen - an upper jaw
with three unusually large and pointed teeth - in the 1980s in a
museum drawer.
Although no one is sure what Megapiranha ate, it probably had a
diverse diet, Cione said.
Other riddles remain, however. "Piranhas have six teeth, but
Megapiranha had seven," Dahdul said. "So what happened to the
seventh tooth?"
"One of the teeth may have been lost," Lundberg said. "Or two of
the original seven may have fused together over evolutionary time.
It's an unanswered question. Maybe someday we'll find out."
Piranhas inhabit exclusively the fresh waters of South
America, including the Amazon River. Tales of vicious attacks on
humans are mythical.
"There are no documented human deaths from piranha attacks,"
according to the Encarta encyclopedia and other sources. They're
known to eat worms and small fish. "A common feeding behavior is to
nip off parts of the fins or scales from other types of fish," the
encyclopedia explains. "This cropping tactic allows the victim to
survive and regrow the injured parts, providing a kind of renewable
food resource for piranhas."
