Mystery shrouding oldest animal fossils solved
Scientists from The Australian National University (ANU) have discovered that 558 million-year-old Dickinsonia fossils do not reveal all of the features of the earliest known animals, which potentially had mouths and guts.
ANU PhD scholar Ilya Bobrovskiy, lead author of the study, said the study shows that simple physical properties of sediments can explain Dickinsonia’s preservation, and implies that what can be seen today may not be what these creatures actually looked like.
“These soft-bodied creatures that lived 558 million years ago on the seafloor could, in principle, have had mouths and guts — organs that many palaeontologists argue emerged during the Cambrian period tens of millions of years later,” said Mr Bobrovskiy from the ANU Research School of Earth Sciences.
“Our discovery about Dickinsonia — and many other Ediacaran fossils — opens up new possibilities as to what they actually looked like.”
Ediacara biota were strange creatures that lived on the seafloor 571 to 541 million years ago. They grew up to two metres long and include the earliest known animals as well as colonies of bacteria.
The fact that Dickinsonia and other Ediacara biota fossils were preserved at all in the geological record has been a big mystery — until now.
The team, which includes scientists from Russian institutions, discovered how Ediacara biota fossils were preserved, despite the macroorganisms not having skeletons or shells.
“As the organisms decayed, softer sediment from below gradually flowed into the forming void, creating a cast,” Mr Bobrovskiy said.
“Now we know that what we are looking at is an impression of a soft organic skeleton that may have been anywhere within Dickinsonia’s body. What we’re seeing could be a part of Dickinsonia’s bottom, the inside of its body or part of its back.”
Mr Bobrovskiy said Dickinsonia had different types of tissues and must have been a true animal, a Eumetazoa, the lineages eventually leading to humans.
Co-researcher and RSES colleague Associate Professor Jochen Brocks said the team used a melting cast of a Death Star made of ice to show the physical properties of sediments that enabled the soft-bodied Ediacara biota to be preserved.
“This process of fossilisation could tell us more about what Ediacara biota were and how they lived,” he said.
“These fossils comprise our best window into earliest animal evolution and are the key to understanding our own deep origins.”
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Materials provided by Australian National University. Note: Content may be edited for style and length.
Journal Reference:
- Ilya Bobrovskiy, Anna Krasnova, Andrey Ivantsov, Ekaterina Luzhnaya, Jochen J. Brocks. Simple sediment rheology explains the Ediacara biota preservation. Nature Ecology & Evolution, 2019; DOI: 10.1038/s41559-019-0820-7
Strange Spaghetti-Shaped Creature Is Missing Link: Discovery Pushes Fossil Record Back 200 Million Years
Mar. 13, 2013 — Canada’s 505 million year-old Burgess Shale fossil beds, located in Yoho National Park, have yielded yet another major scientific discovery — this time with the unearthing of a strange spaghetti-shaped creature.
It’s a discovery that pushes back the fossil record of a group of creatures known as enteropneusts by 200 million years — and provides the crucial “missing link” in an important evolutionary transformation.
“Unlike animals with teeth and bones, these spaghetti-shaped creatures were soft-bodied, so the fossil record for them is extremely scarce,” said Jean-Bernard Caron, associate professor of Earth Sciences and Ecology & Evolutionary Biology at the University of Toronto and curator of invertebrate palaeontology at the Royal Ontario Museum.
“Our analysis of Spartobranchus tenuis, a creature previously unknown to science, pushes the fossil record of the enteropneusts back by 200 million years and illuminates our understanding of the early evolution of this group of organisms,” Caron said.
Caron is the lead author of the study published online in the journal Nature March 13 2013 which found Spartobranchus tenuis is a member of the acorn worms group. Acorn worms are marine animals that belong to the phylum hemichordates, a group which is closely related to todays sea stars and sea urchins. While Spartobranchus tenuis is long extinct, other species of acorn worms thrive in the fine sands and mud of deep and shallow waters in present-day ecosystems.
Since the discovery of hemichordates in the 19th century, some of the biggest questions in hemichordate evolution have focused on the group’s origins and the relationship between its two main branches: the enteropneusts and pterobranchs. Enteropneusts and pterobranchs look very different, yet share many genetic and developmental characteristics that reveal an otherwise unexpected close relationship.
“Spartobranchus tenuis represents a crucial missing link that serves not only to connect the two main hemichordate groups but helps to explain how an important evolutionary transformation was achieved,” said Caron. “Our study suggests that primitive enteropneusts developed a tubular structure — the smoking gun — which has been retained over time in modern pterobranchs.”
Hemichordates also share many of the same characteristics as chordates — a group of animals that includes humans — with the name hemichordate roughly translating to ‘half a chordate.’
Spartobranchus tenuis probably fed on small particles of matter at the bottom of the oceans.
“There are literally thousands of specimens at the Walcott Quarry in Yoho National Park, so it’s possible Spartobranchus tenuis may have played an important role in recycling organic matter in the early Burgess Shale environment, similar to the ecological service provided by earth worms today on land,” said Caron.
Detailed analysis suggests Spartobranchus tenuis (illustration at right by Marianne Collins) had a flexible body consisting of a short proboscis, collar and narrow elongate trunk terminating in a bulbous structure, which may have served as an anchor.
The largest complete specimens examined were 10 centimetres long with the proboscis accounting for about half a centimetre. A large proportion of these worms was preserved in tubes, of which some were branched, suggesting the tubes were used as a dwelling structure.
Other members of the Spartobranchus tenuis research team are Simon Conway Morris of the University of Cambridge and Christopher B. Cameron of the Université de Montréal. Last year Conway Morris and Caron published a well-publicized study on Pikaia, believed to be one of the planet’s first human relatives.
The Burgess Shale is found in Yoho National Park, part of the Canadian Rocky Mountain Parks World Heritage Site, and is one of the most important fossil deposits for understanding the origin and early evolution of animals that took place during the Cambrian Explosion starting about 542 million years ago.