Chuck Bednar for redOrbit.com – @BednarChuck
A brain that is more than 500 million years old suggests that the organs serving as the center of nervous systems in all vertebrates and many invertebrates emerged before actual, defined heads, according to new research published in the latest edition of the journal Current Biology.
In the study, Dr. Javier Ortega-Hernández of the University of Cambridge and his colleagues reported that the ancient organ belonged to a type of crustacean known as the Odaraia alata. This particular crustacean had a pair of large eyes on stalks, and the study authors found that the eyes were connected to a thin, flat and hard body part known as the anterior sclerite.
According to Discovery News, the connection between the eyes and the anterior sclerite was due to nerve endings originating from the front part of the creature’s brain (one of the oldest such organs ever discovered). Over time, most modern arthropods lost the anterior sclerite, which the scientists believe fused with other parts of the head during the group’s evolution.
“What we’re seeing in these fossils, is one of the major transitional steps between soft-bodied worm-like creatures and arthropods with hard exoskeletons and jointed limbs – this is a period of crucial transformation,” Dr. Ortega-Hernández, a postdoctoral researcher in the university’s Department of Earth Sciences, explained in a statement.
“Heading” to modern-day arthropods
The Cambridge-led team looked at two types of arthropod ancestors: A soft-bodied trilobite, a marine creature abundant during the Paleozoic Era, and the submarine-like Odaraia alata. They found that the anterior sclerite and the eye-like features of both ancient arthropods corresponded with how vision in controlled in their modern-day counterparts.
In addition, the results of their work allowed these creatures to be compared to a group of large, swimming predators from the same era known as anomalocaridids. Those comparisons revealed similarities between the anterior sclerite and a plate found on the top of the anomalocaridid head, indicating that both features had a common origin.
While most experts agree that anomalocaridids are early arthropod ancestors, their bodies are vastly different that the insects, spiders and crustaceans commonly found today. Thanks to the well-preserved brains found in the fossils they studied, Dr. Ortega-Hernández and his team can now conclude that the anterior sclerite is a bridge of sorts from the head of the anomalocaridids to that of more familiar jointed arthropods – making it a “missing link” of sorts.
“Heads have become more complex over time, but what we’re seeing here is an answer to the question of how arthropods changed their bodies from soft to hard,” he explained. “It gives us an improved understanding of the origins and complex evolutionary history of this highly successful group.”
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