Dickinsonia is an extinct creature usually found fossilized in South Australia. It's often described as resembling a jellyfish. Now, scientists have provided strong evidence that it was an animal, adding to the evidence that animals evolved long before the Cambrian Explosion.
A new study, conducted by the universities of Cambridge, Oxford, Bristol and the British Geological Survey, provides good evidence that the soft-bodied fossil imprint, Dickinsonia, was indeed an animal that developed over millions of years.
"Dickinsonia belongs to the Ediacaran biota – a collection of mostly soft-bodied organisms that lived in the global oceans between roughly 580 and 540 million years ago," explained lead author Dr Renee Hoekzema in a statement. "They are mysterious because despite there being around 200 different species, very few of them resemble any living or extinct organism, and therefore what they were, and how they relate to modern organisms, has been a long-standing palaeontological mystery."
In the past, scientists have tried to categorize Dickensonia into all sorts of groups, from jellyfish and worms to fungi and lichen.
“Discriminating between these different hypotheses has been difficult, as there are so few morphological features in Dickinsonia to compare to modern organisms," said Dr Alex Liu, a co-author of the research. "In this study, we took the approach of looking at populations of this organism, including assumed juvenile and adult individuals, to assess how it grew and to try to work out how to classify it from a developmental perspective.”
The team used computer modeling to determine how Dickinsonia once grew and developed. They found for the first time that Dickinsonia grew from both ends rather than just one. Their analysis also allowed them to conclude that Dickinsonia was indeed an animal.
"When we combined this growth data with previously obtained information on how Dickinsonia moved, as well as some of its morphological features, we were able to reject all non-animal possibilities for its original biological affinity and show that it was an early animal, belonging to either the Placozoa or the Eumetazoa," said Hoekzema.
“This is one of the first times that a member of the Ediacaran biota has been identified as an animal on the basis of positive evidence,” added Liu.