380-Million-Year-Old Fossil Of Armored Fish Features Preserved Musculature — Finding Provides Surprises

The preserved musculature of a 380 million year old armored fish was recently discovered in north-west Australia. This unprecedented discovery is now giving researchers their first direct insight into how the musculature of these ancient animals worked — providing a means to improve our understanding of how exactly neck and abdominal muscles developed during the diversification of jawed vertebrates from jawless ones.

Image Credit: ESRF/Sophie Sanchez
Image Credit: ESRF/Sophie Sanchez

Fossils of soft tissue — such as this fish’s musculature — are exceptionally rare, this recent finding is a truly unexpected one, and one that offers a great opportunity or new discoveries. Typically researchers have to “extrapolate skin coverings and musculature from knowledge of modern organisms and from the fossilized skeletons.” But now, thanks to the new discovery, we do have some insight into the musculature of some of the armored fish species which lived 380 million years ago.

The press release provides some background:

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

A few years ago, an Australian research team work led by Professor Kate Trinajstic, of Curtin University, made the remarkable discovery that these fossils also contained soft tissues including nerve and muscle cells. Now they have collaborated with the research group of Professor Per Erik Ahlberg, of Uppsala University, and with the European Synchrotron (ESRF) in Grenoble, France, to document and reconstruct the musculature of the placoderms.

“High contrast X-ray images were produced thanks to a powerful beam and a protocol developed for fossil imaging at the ESRF. This is unique in the world and has enabled us to ‘reconstruct’ some fossilized muscles and document the muscles of neck and abdomen in these early jawed fish, without damaging or affecting the fossilised remains,” says Sophie Sanchez, one of the authors, from the ESRF and Uppsala University.

What these reconstructions have shown is that these early vertebrates had very well-developed neck musculature and also very powerful abdominal muscles — perhaps surprisingly similar to modern vertebrates, such as humans. In contrast, almost all modern fish “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, co-author of the project. “It also cautions against thinking that we can interpret fossil organisms simply by metaphorically draping their skeletons in the soft tissues of living relatives.”

The findings were recently published in the journal Science.

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