200 Years. 200 Stories. Story 90: “A Bite of Evolution ”

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illustration of Megapiranha by Ray Troll
Reconstruction of the Megapiranha by Ray Troll, a fish enthusiast, fossil fan, band member, and artist. In 2007, Ray Troll received the Academy's Gold Medal for Distinction in Natural History Art.

A Bite of Evolution

Curator of Ichthyology Dr. John Lundberg is quick to defend the piranha and dismiss its Hollywood reputation for attacking humans. He’s been bitten, and sure, it bleeds a little, he says, but it’s not all that bad. In 2009 Lundberg and former University of Pennsylvania graduate student Wasila Dahdul co-authored a paper that suggests the modern piranha is hardly a threat compared to its ancestor, the Megapiranha, a late Miocene fish triple the size with teeth far more menacing. The paper describes the fossil upper jaw of a prehistoric Megapiranha (Megapiranha paranensis), which lived in the waters of South America about 9 million years ago. The specimen, collected in the early 1900s in Argentina, sat in a drawer for half a century before being rediscovered by Alberto Luis Cione, a paleontologist from Argentina’s Museo de La Plata and co-author of the paper.

In the jaw of the modern piranha, there is a single row of six interlocking teeth. Scientists believed that piranhas evolved from an ancestor with two parallel rows of teeth, such as those seen in their closest relatives, the plant-eating pacus. The Megapiranha had two rows of blade-like teeth, arranged in a zigzag pattern. The paper suggests that the zigzag placement of the teeth in the Megapiranha jaw represents an intermediate step in the evolutionary path to the single row.

Find out more about what creatures collected on Academy expeditions teach us about evolution.

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