A fossil discovered in Canada is that of the oldest creature known to possess muscles, an important evolutionary adaptation, scientists say.
The fossil found in Newfoundland of a creature possible related to jellyfish and sea anemones shows traces of fibrous bundles suggestive of muscle tissue, they say.
"It's confirmation that muscular organisms were present roughly 560 million years ago," says study co-author Alex Liu at the University of Cambridge in England.
The creature, Haootia quadriformis, had bundles of the muscle fibers in a four-sided symmetrical arrangement similar to that found in corals, jellyfish and sea anemones today, a group known to science as cnidarians.
The evolutionary breakthrough represented by muscles is important, they say, because it eventually allowed animals that had developed underwater to venture onto land.
"The evolution of muscular animals, in possession of muscle tissues that enabled them to precisely control their movements, paved the way for the exploration of a vast range of feeding strategies, environments, and ecological niches, allowing animals to become the dominant force in global ecosystems," paleontologist Liu says.
Liu and research colleagues from Britain's University of Oxford and Canada's Memorial University of Newfoundland compared the fossil with modern underwater species and concluded it was an early cnidarian, and that it represents possibly the earliest fossils ever found anywhere in the world showing evidence of muscles.
The findings suggest that the evolution of such creatures began earlier than scientists thought, Liu says.
The origin, spread and evolution of the world's animals was always thought to have started in the Cambrian Explosion, an era of rapid evolutionary advance beginning around 540 million years ago that saw the first appearance within the fossil record of most major animal groups.
"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," Liu says.
The Haootia quadriformis fossil has been dated to the Ediacaran Period, he notes, which was from 635 million years ago to the start of the Cambrian.
That makes it a rare specimen of an Ediacaran animal in addition to the bearer of perhaps the earliest confirmed muscle tissue, those bundles of cells that make movement in animals possible, the researchers say.
H. quadriformis and other creatures like it, in making the evolutionary step to muscles and movement, may have made a crucial contribution to the explosion of animals lifeforms in the subsequent Cambrian Explosion, they say.
