Using muscle tissue for movement is ubiquitous for animals on the planet, though some, like sponges, branched off before muscles evolved and use alternative methods for movement. While it’s hard to know exactly when this tissue first emerged, a team of researchers led by Alexander Liu from the University of Cambridge have identified the oldest known organism to possess muscle tissue. The paper was published in the journal Proceedings of the Royal Society B.
Haootia quadriformis is an ancient member of the phylum Cnidaria, which contains extant jellyfish, coral, hydra, and anemones. The researchers first suspected that the organism had muscle tissue based on fiber bundles they noticed when the fossil was discovered in Newfoundland, Canada back in 2008. They have been working to verify that hypothesis ever since.
This organism lived during the Ediacaran period approximately 560 million years ago, prior to the Cambrian Explosion roughly 541 million years ago. The Cambrian Explosion marks a time when animals begin diversifying rapidly and is usually regarded as the point of origin for animals and features that we are most familiar with. These findings would push back that diversification by at least 20 million years.
“In recent decades, discoveries of preserved trackways and chemical evidence in older rocks, as well as molecular comparisons, have indirectly suggested that animals may have a much earlier origin than previously thought,” Liu said in a press release.
“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. Instead, we study aspects of their ecology, feeding or reproduction, in order to understand what they might have been,” he continued.
H. quadriformis appears to be fairly unique among other classified fossils from the Ediacaran. Most of the other animals from that time were sessile and shaped like simple tubes or frongs. H. quadriformis exhibited four-fold symmetry indicative of cnidarians and it also had fiber bundles that very strongly indicate muscle tissue that would have allowed it to move.
“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,” Liu concluded.
Due to the fact that all animals from this time period were soft-bodied and therefore harder to fossilize, the gaps in the fossil record make it hard to get an accurate picture of how novel H. quadriformis truly was. More fossils from this period are needed to learn more about the body plans and feeding mechanisms of these Pre-Cambrian animals.