Charles Darwin publicly discussed the “shortcomings” of the geological record in his book On the origin of species. He pointed out that even those with bones and shells could not be preserved as fossils unless the conditions were right.
“No living thing can be totally protected,” he said.
However, after more than a century of fossil hunting since the publication of his book, we know that conservation of soft organisms can actually be done – including even the most fragile animals such as jellyfish.
But what about the delicate anatomy, such as the internal organs of animals? Can they also be fossilized?
Our study was published this week Geology, Shows how even the complex brains of ancient aquatic arthropods (invertebrates with arthropods) can be remarkably protected.
The discovery of the 310-million-year-old equestrian crab brain in the United States has recently been added to a series of fossil finds, including the discovery of some of the oldest arthropods with a preserved central nervous system.
The equestrian crab fossil documented in our study sheds new light on how these fragile limbs – which are usually very rapidly decaying – can be protected with such confidence.
Top: (a) Fossil Equestrian Crabs in Mason Creek, Illinois, USA (B) Closing the brain as shown in box (A) in Figure (A). (C) Modification of the Europus Dane, including the location and anatomy of the brain.
Brain freezing: How arthropods fossilize the brain
Much of our knowledge of the prehistoric arthropod brain comes from two types of fossil deposits: amber and burgundy shell.
Amber is a fossilized resin that escapes through tree bark and traps various organisms. The individuals included are generally represented by insect-like arthropods Jurassic Park Movie.
These fossils preserve incredible physiological information as well as behavior. There is very little decay, mainly after the organism is trapped in the gum.
Top: A centimeter of Mexican amber, roughly 23 million years old, and neighboring ants suspended.
Using the latest imaging technology in these amber fossils, paleontologists can study the tiny arthropod brain on a three-dimensional scale. However, the oldest arthropods in Amber date back to the Triassic period (about 230 million years ago).
Burgess shale deposits increase with age (typically 500 to 520 million years). Specially preserved marine arthropods are abundant.
This fossil is so important that it accurately depicts some of the oldest animals that can tell us about their origins and the earliest evolutionary history. Their ruins are preserved primarily as muddy carbon films.
The fossilization process begins with mudslides caused by storms. It wipes out delicate animals and bury them on the seabed under low oxygen conditions. In time, it turns into mud and compresses, and the animals are wiped off the rocks.
Many burgundy shell arthropod specimens protect the internal organs, especially the intestines. But parts of the central nervous system, such as the optic nerve, the spinal cord, or the brain, show less.
Above: Cambrian Arthropod Chenjiangokaris Kunmingansis from China. See the focal point of the bead-like vertebral nerve cord and remodeling (B) preserved in the fossil (a).
Conservation that confuses the mind
Our new fossil shows that arthropods can protect the brain in a completely different way. Example of equestrian crab, Europus Dane, From the world-famous Mason Creek deposit in Illinois, USA. The fossilized ciderite from this deposit is preserved in concrete made of iron carbonate mineral.
Some Masonic Creek animals, such as the weird “Tully Monster”, have a completely soft body. This implies that there must be special conditions to protect them.
For the first time, we have shown that Masonic crickets not only rapidly form the ciderite that enters their entire body, but also quickly cover their internal soft tissues before the ciderite decomposes.
In particular, the brain Europus reformed by a white clay mineral called kaolinite. These minerals were likely to decompose and form in the empty space left by the brain long after. Without this remarkable white mineral, we would never have seen the brain.
A brain without a fossil
One of the challenges in interpreting ancient arthropod anatomy is the lack of close modern relatives for comparison. But fortunately for us, Europus Live horse cart crabs can be compared to four species.
Even to the untrained eye, the fossil nervous system is no different from that of the modern horse-drawn crab (310 million years apart), but there is no doubt that the same structures are found in both species.
Above: (a) Fossils of the Euphrodis Dane brain and (B and C) interpretation diagrams and ()) Limulus polyphaemus, the brain of a modern young horse-drawn carriage crab.
The fossil and biological nervous system adapt to the processing of nerves to the eyes and appendages, showing a single focal opening for passage through the esophagus.
The discovery of these unique specimens gives paleontologists a rare view of the deep past and enhances our understanding of the biology and evolution of long-extinct animals. Charles Darwin does not seem to be so pessimistic about the fossil record.
John Patterson, Professor of Earth Sciences, University of New England; Greg Edgecombe, Skills Researcher, Museum of Natural History; Assistant Professor Javier Ortega-Hernandez at Harvard Kennedy School; Robert Gaines, Professor of Geology, Vice President of Academic Affairs and Dean of Pomona College, and Russell Dean Christopher Bicknell, Postdoctoral Researcher in Paleo Biology, University of New England.
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