Unlike bones and shells, which can last for millions of years, soft tissues are rarely preserved as fossils. But a new finding opens the way to the exploration of soft tissues, such as the brain.
Specifically, it appears that arthropod brains can be preserved in a completely different way thanks to concretions made from an iron carbonate mineral called siderite .
No long-term brain changes
The horseshoe crab specimen, Euproops danae, comes from the Mazon Creek deposit in Illinois in the United States. According to one of the study’s authors, John Paterson :
We have shown, for the first time, that the Mazon Creek animals were not only shaped by the rapid formation of siderite that engulfed their entire bodies, but also that the siderite rapidly covered their internal soft tissues before they could decompose. In our fossil, the Euproops brain is replicated by a white clay mineral called kaolinite. This mineral mold would later have formed within the vacuum left by the brain, long after it had decomposed. Without this striking white mineral, we could never have seen the brain.
Amber, or fossilized tree resin, often contains a variety of trapped organisms like insects, preserving the most intricate details.
Burgess shale-type deposits from the Cambrian Period, usually around 500 to 520 million years old, are much older than amber and also retain spectacular brain structures like carbon films in shales. This is where a 310-million-year-old horseshoe crab with a remarkably intact brain has been found.
These fossils are very important as they represent some of the oldest animals on Earth and can tell us about their origins and the earliest evolutionary history. The team’s new fossil effectively demonstrates that arthropod brains can be preserved in a completely different way .