A couple of days ago, I wrote about the mass extinctions that have occurred on planet Earth. In the article, I stressed out that paleontology relies on fossils being unearthed and every once in a while, a new discovery pushes back the boundaries of geologic time. This leads to theories being revised in order to accommodate the new findings.
A team of researchers from the University of Cambridge made such a discovery in a fossil bed in Newfoundland, Canada. The team led by Alexander Liu have identified the oldest known organism to possess muscle tissue.
The organism is called Haootia quadriformis and is an extinct member of the phylum Cnidaria which encompasses hydras, coral, anemones and jellyfish. When the researchers found the fossil in 2008, they observed impressions of fiber bundles on its surface and this led them to suspect Haootia possessed muscle tissue. Since its discovery, they have been working to prove their hypothesis and have recently published a study detailing their findings.
Scientists view the Cambrian Explosion (541 million years ago) as the point of origin for modern animals. It saw a rapid diversification of features and the organisms rapidly filled the available niches. During the Cambrian, animals evolved hard shells and skeletons and began to exhibit body symmetry. In the previous geologic age, the Ediacaran, animals were largely sessile( they were unable to move about).
Haootia lived 560 million years ago and its discovery pushes this date of diversification by some 20 million years. “The problem is that although animals are now widely expected to have been present before the Cambrian Explosion, very few of the fossils found in older rocks possess features that can be used to convincingly identify them as animals,” said Liu. He also pointed out that in order to understand their position in the tree of life, they study aspects of the organisms’ ecology, feeding habits and reproductive cycles.
Another aspect that sets Haootia apart from other Ediacaran organisms is that it possesses a four-fold body symmetry, a feature shared by both fossil and modern cnidarians.
The development of muscle tissue signals the transition from a sedentary life style to a mobile one. This in turn led to the development of new feeding strategies and the colonization of new environments. Animals began to fill ecological niches , became specialized and started their dominion over global ecosystems.