Animals

Ancient Armor-Plated Fish Was a Bottom-Feeding Giant

Make way for Bothriolepis rex, a bottom-feeding fish from the Devonian that represents the biggest of its kind.

A multi-institution team of researchers has discovered the newest, biggest member of a group of extinct, armor-plated fish called Antiarchi.

The new fish, Bothriolepis rex, dates to the Devonian Period, some 370 million years ago, and swam Earth's oceans long before dinosaurs were on the scene. Bony plates covered its front fins, shoulders and head, and its size – about 5.5 feet long – makes it the new top fish among Antiarchs, surpassing Bothriolepis maxima by about 30% in length.

Researchers from Drexel University, Delaware Valley University, Stanford University and the University of Chicago collaborated on the discovery and have published their findings about the ancient fish in the Journal of Vertebrate Paleontology.

The fossils used to describe the fish were found on Ellesmere Island in Nunavut, Canada and included the bony, thick plates that covered the ancient creature's head. The plates probably gave B. rex a measure of protection from the bites of large predatory fish called sarcopterygians, say the researchers.

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The fish wasn't the violent type. It may have a "rex" in its name, but B. rex was no kind of fierce hunter. Instead, the scientists say, it was, like others in the Bothriolepis genus, a bottom-feeder that cruised the sandy sea floor picking up dead plant and animal matter.

With a flattened underside and a downward-angled mouth, "it was not equipped for active predation," said the study's lead author Jason Downs, of Delaware Valley University, in a statement.

Bones from the skull of Bothriolepis rex and a line drawing of the head viewed from above. The bones create an armor with a single opening for the eyes. The mouth is on the lower surface of the skull, indicating a bottom-feeding life. Photo by Valentina Garcia,drawing by Jason Downs.

"Bothriolepis rex extends the range of known body sizes for the group Antiarchi," said Downs. "The large body size and the thick, dense armor present a unique opportunity to address questions about the lifestyle of this unusual group of armored swimmers."

Armor aside, however, the party would "soon" end for B. rex, whose size might not have helped its cause.

"All Antiarchs are extinct by the end of the Devonian Period," said Downs. "We can't know exactly why B. rex went extinct, but large-bodied species are often found to be at a higher risk of extinction than small-bodied ones."

Top Photo: Shown is a model of the fish Bothriolepis canadensis, a member of the same genus as B. Rex in the Antiarch order of armor-plated fish. Credit: WikiMedia Commons/Citron / CC BY-SA 3.0

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