Los Angeles | Vampires are real – at least the amoebae variety is – say scientists who found fossils of 742-million-year-old single-celled creatures that drilled the walls of their prey to consume cell contents.
Using a scanning electron microscope to examine minute fossils, researchers found perfectly circular drill holes that may have been formed by an ancient relation of Vampyrellidae amoebae.
To my knowledge these holes are the earliest direct evidence of predation on eukaryotes, said Susannah Porter, from the University of California, Santa Barbara. Eukaryotes are organisms whose cells contain a nucleus and other organelles such as mitochondria. We have a great record of predation on animals going back 550 million years, starting with the very first mineralised shells, which show evidence of drillholes, said Porter. We had nothing like that for early life – for the time before animals appear.
These holes potentially provide a way of looking at predator-prey interactions in very deep time in ancient microbial ecosystems, she said. Porter examined fossils from the Chuar Group in the Grand Canyon – once an ancient seabed – that are between 782 and 742 million years old.
The holes are about one micrometre in diameter and occur in seven of the species she identified. The holes are not common in any single one species; in fact, they appear in not more than 10 per cent of the specimens. I also found evidence of specificity in hole sizes, so different species show different characteristic hole sizes, which is consistent with what we know about modern vampire amoebae and their food preferences, Porter said.
Different species of amoebae make differently sized holes. The Vampyrellid amoebae make a great modern analogue, but because vampirelike feeding behaviour is known in a number of different unrelated amoebae, it makes it difficult to pin down exactly who the predator was, she said.
According to Porter, this evidence may help to address the question of whether predation was one of the driving factors in the diversification of eukaryotes that took place about 800 million years ago. If that is true, then if we look at older fossil assemblages – say one to 1.6 billion years old – the fossilised eukaryote will show no evidence of predation, Porter said.
Porter noted that the microfossils those organisms attacked were probably phytoplankton living in oxygenated surface waters, but like vampyrellid amoebae today, the predators may have lived in the sediments.
She suggests that those phytoplankton made tough-walled cysts – resting structures now preserved as fossils – that sank to the bottom where they were attacked by the amoebae.
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