Researchers have discovered one of the oldest and most preserved brains and all of the fossil record. The fossil is a 310 million-year-old horseshoe crab found with its entire brain intact. Researchers note that most of the knowledge of ancient creatures comes from bones because soft tissue doesn’t fossilize as well.
One of the best ways for researchers to get details about soft tissues of ancient creatures is to find them encased in amber, but amber fossil records only go back about 230 million years. By comparison, Burgess Shale-type deposits extend as far as 520 million years back. They are mudstone deposits that can preserve soft tissues as carbon films, typically of the gut. However, on occasion, the soft tissues can include imprints of the nervous system, but those are rare.
The newly discovered fossil is a horseshoe crab called Euproops danae. It was encased in siderite as usual, but a second mineral came into play in the fossil that caused the brain to show up as a stripe of white that contrasts against the brown rock of its body. The brain was replicated by a white-colored clay mineral called kaolinite.
Researchers say the mineral cast formed later in the void left by the brain long after the brain had decayed. They say without the white mineral, they may have never spotted the creature’s brain. Scientists did compare the brain in the ancient fossil to the structure of its living relatives and discovered very little has changed since this creature died.
The fossilized central nervous system is closely comparable to living horseshoe crabs and matches up in an arrangement of nerves to the eyes and appendages. Scientists were surprised at that discovery because there has been substantial morphological and ecological diversification for the group over the last 310 million years.
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