One of the oldest brains ever discovered is providing clues on how the world's first heads evolved.
The over 500-million-year-old brain, described in the latest issue of the journal Current Biology, suggests that rudimentary brains emerged before defined heads.
Defined heads likely emerged later to protect brains.
The ancient brain belonged to a crustacean called Odaria alata, which had a pair of large eyes on stalks. Scientists also often say that Odaria alata looked like a submarine. You can see the resemblance more in this video.
Javier Ortega-Hernández, who authored the study, determined that the eye-like features were connected to a hard, thin and flat body part called the "anterior sclerite." The connection was made possible via nerve endings originating from the front part of the brain.
"The anterior sclerite has been lost in modern arthropods (insects, spiders and crustaceans), as it most likely fused with other parts of the head during the evolutionary history of the group," says Ortega-Hernández, a postdoctoral researcher at the University of Cambridge.
For the study, he compared the remains of Odaria alata with another very ancient creature: a soft-bodied trilobite. Trilobites were marine creatures that were abundant during the Palaeozoic Era, 542-251 million years ago.
Ortega-Hernández next compared the creatures with anomalocaridids, a group of large swimming predators that lived at around the same time as the other studied species.
These larger organisms, like Odaria alata, were found to have a natural plate in the brain region.
"What we're seeing in these fossils," he says, "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."
The transformation occurred during what's known as the Cambrian Explosion, which was a period of rapid evolutionary innovation about 500 million years ago when most major animal groups emerge in the fossil record.
Prior to this period, the majority of animal life on Earth consisted of soft-bodied species that resembled algae and jellyfish. The Cambrian Explosion then led to creatures with hard external coverings (exoskeletons), defined heads and jointed limbs.
"Heads have become more complex over time," Ortega-Hernández says.
"But what we're seeing here is an answer to the question of how arthropods changed their bodies from soft to hard. It gives us an improved understanding of the origins and complex evolutionary history of this highly successful group." http://www.abc.net.au/science/articles/2015/05/08/4232198.htm
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