While some may be indebted to a personal trainer for those hard-to-get "six packs," a new study suggests 380-million-year-old fish may have sported rock-hard abs too.
For the study, researchers in Australia and Sweden reconstructed the musculature of placoderms -- a class of armored fish. They analyzed fossils uncovered in a sedimentary rock structure in northwestern Australia called the Gogo Formation.
Based on the soft tissue fibers within fish fossils and the musculature reconstruction, the researchers confirmed in a statement that the placoderm had both well-developed neck and ab muscles "not unlike the human equivalents."
“We were stunned to find that our ancient fossil fishes had abs,” Dr. Kate Trinajstic, the study's lead author and associate professor at Curtin University, said in a statement released by Australian National University. "Abdominal muscles were thought to be an invention of animals that first walked onto the land but this discovery shows that these muscles appeared much earlier in our evolutionary history."
Ab muscles were previously believed to have developed first in four-limbed vertebrates known as tetrapods. However, the musculature of the placoderm indicates that "abdominal muscles are an innovation of gnathostomes," according to the study authors.
As LiveScience noted, the placoderm is the first-known gnathostome, which means it is the ancestor of all jawed creatures with a backbone.
The study was published in Science online on June 13, 2013.
A mid-Devonian placoderm fossil -- specifically the Pterichthyodes milleri -- is pictured in Scotland.
An illustration based on fossil evidence depicts what the placoderm may have looked like.