Sophisticated muscles evolved earlier than previously believed

Published 2013-06-14

Sophie Sanchez, Uppsala University and ESRF, is shown during the mounting of the fish fossil on the X-ray imaging instrument at the ESRF.

This week in the journal Science early online edition, Swedish and Australian researchers present the miraculously preserved musculature of 380 million year old fossil fishes, revealed by unique fossils from a locality in north-west Australia. The finds will help scientists to understand how neck muscles and abdominal muscles – “abs” – evolved.

The word “fossil” naturally conjures up a vision of rattling skeletons. Bones and teeth fossilize far more easily than soft tissues and are usually the only traces of the animal that remain. This makes the rare fossil localities that preserve soft tissues all the more valuable as windows on the biology of extinct organisms.

The Gogo Formation, a sedimentary rock formation in north-western Australia, has long been famous for yielding exquisitely preserved fossil fishes. Among other things it contains placoderms, an extinct group that includes some of the earliest jawed fishes.

A few years ago, Australian researchers discovered that these fossils also contain soft tissues: now they have collaborated with the research group of Professor Per Ahlberg, Uppsala University, and with the ESRF synchrotron in Grenoble, France, to document and reconstruct the musculature of the placoderms.

They prove to have a well-developed neck musculature as well as powerful abdominal muscles – not unlike the human equivalents displayed on the beaches of the world every summer. Living fishes, by contrast, usually have a rather simple body musculature without such specializations.

“This shows that vertebrates developed a sophisticated musculature much earlier than we had thought” says Per Ahlberg, joint leader of the project with Dr Kate Trinajstic of Curtin University in Perth, Western Australia; “It also cautions against thinking that we can interpret fossil organisms simply by metaphorically draping their skeletons in the soft tissues of living relatives.”

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