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REF NO.: 24
SUBJECT: Solving the mystery of 570-million-year-old Mistaken Point fossils
DATE: Oct. 13
Scientists at Memorial University of Newfoundland may have solved a mystery at the province’s newest UNESCO World Heritage Site, Mistaken Point.
Namely, what were the giant Ediacaran fossils found on the southern tip of Newfoundland’s Avalon Peninsula, and why are they so large?
For many years, the 570-million-year-old fossils at Mistaken Point, named Fractofusus misrai after the Memorial University graduate student who first discovered them, have been at the center of debates regarding the earliest macroscopic fossils of the Ediacaran biota.
The fractal-like fossils of Mistaken Point have been interpreted as many things: giant single-celled organisms, fungi, relatives of the jellyfish, and even a completely extinct experiment at life that was neither plant nor animal.
Dating of the fossil layers shows that they are among the oldest fossils anywhere in the world. But what is even more remarkable is that these first fossils are enormous, up to one metre in length, and dating nearly 30 million years prior to the first evolutionary evidence of comparatively tiny worms and trilobites.
In a new paper, Dr. Suzanne Dufour, Department of Biology, and Prof. Duncan McIlroy, Department of Earth Sciences, have taken a novel approach to interpreting the Mistaken Point fossils.
Ediacaran Pre-Placozoan Diploblasts in the Avalonian Biota: The Role of Chemosynthesis in the Evolution of Early Animal Life, was published by The Geological Society of the U.K. online on Sept. 15. Instead of comparing the fossils to modern organisms, the researchers considered the likely mode of life and biological challenges likely to have been experienced by these earliest animals.
Many Ediacaran fossil organisms had extensive surface areas, lived in close association with the seafloor, and could not move. However, Prof. McIlroy recognized that anything on the seafloor cuts off oxygen supply to the underlying sediment, meaning that bacteria underneath it would use sulfate for respiration, producing toxic hydrogen sulfide as a byproduct. So, how could the Ediacaran animals have survived?
The authors propose that Fractofusus may have functioned like modern animals that have sulfide-fuelled bacterial symbionts in their oxygen-rich tissues, such as gills. In this symbiosis, the bacteria use both oxygen and the toxic hydrogen sulfide as an energy source, thereby detoxifying the waters around the host animal and also providing the host with nutrients. Dr. Dufour is a specialist in such symbioses, particularly in modern clams with sulfur-oxidizing symbionts.
Drs. Dufour and McIlroy think that Fractofusus transported oxygen below its body to the symbionts either by moving water using whip-like appendages called cilia on their outermost cells, or by diffusion through a layer of inert material called mesoglea. A modern example of this is the jelly portion of jellyfish. Fractofusus might therefore consist of a thin layer of cells surrounding the mesoglea, which would also explain how Fractofusus could grow as large as some jellyfish, which can reach two metres in diameter, because it would then have relatively few cells.
So where does Fractofusus and its relatives belong in the tree of life? The researchers consider that Fractofusus were simpler than any modern animals we yet know of.
The Geological Society of London, founded 1807, is a learned and professional body of over 12,000 earth scientists with a remit to investigate, interpret, discuss, inform and advise on the nature and processes of the Earth, their practical importance to humanity, and, in the interests of the public, to promote professional excellence. The society offers advice to Parliament and government, at individual and corporate levels.
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