There has been no lack of theories to explain the phenomenon of the Cambrian explosion. Some propose that the Cambrian explosion was propelled by a surge in oxygen levels, while others argue for a decline in carbon dioxide.
However, an innovative hypothesis put forth by an Australian biologist suggests a new perspective: the advent of eyes ignited the Cambrian explosion. Learn how the development of vision and the ability to perceive and respond to color may have played a pivotal role in the rapid diversification of life during the Cambrian Period.
What Was the Cambrian Explosion?
The Cambrian explosion is commonly referred to as evolution's Big Bang. The Cambrian Period began some 543 million years ago. Astonishing fossil records reveal the first appearance of various marine organisms, such as trilobites, brachiopods, mollusks, arthropods, and primitive chordates.
These organisms exhibited an impressive range of body forms, including the first evidence of hard skeletons and shells. Within a mere 5 million years the ancestors of almost all animals now living – from mollusks to humans – suddenly appeared on Earth.
Evolution Under a Microscope
Species adaptations contributed to the burst of diversity that initially shaped life. Andrew Parker of the Australian Museum in Sydney reached a stunning conclusion after studying three fossil species unearthed from the Burgess Shale, 515-million-year-old sediments in British Columbia.
Two of the species, Wiwaxia corrugata and Canadia spinosa, were bristle-covered marine worms. The third, Marrella splendens, was an arthropod.
Using an electron microscope, Parker found that closely spaced parallel ridges covered the outer scales and spines of these animals. These ridges, which he has also found on living crustaceans and worms, act like a diffraction grating and split white light into its component colors, imparting an iridescent glow to the animal.
Read More: How Do Animals Evolve to Be So Colorful?
What Happened During the Cambrian Explosion?
The ridges and colors hold remarkable significance in evolution. This discovery, says Parker, marks the first appearance in the fossil record of animals with color. At different times of day and different viewing angles, the marine creatures would have glowed blue, red, yellow, or green.
Since the evolution of these worms coincides with the first appearance in the fossil record of animals with eyes, such as trilobites, the twinkling colors may have warned predators to avoid these armored, and perhaps unpalatable, animals.
Read More: 5 Unique Ways Animals Avoid Getting Eaten
A Blueprint for Evolution
Coloration wasn't the only attribute to evolve in response to eye-endowed predators, according to Parker.
"Before the Cambrian, there were just simple animals – worms and jellyfish. Then all in one go the blueprints for all the animals around today evolved. Now, this worm, if an animal with eyes came along that wanted to eat it, wouldn't survive very long. So, there were massive selection pressures for this worm to change its form into animals that could either swim, burrow, hide, or have armored parts or reflect warning colors. To do those things you have to have a completely different body plan. And by changing its body plan to move into all these different areas, it created all the different phyla we have today," says Parker.
Studying and understanding these ancient adaptations provides valuable insights and reminds us of the astounding complexity that can emerge from the natural world.
Read More: 6 Animals With Unusual Evolutionary Traits