Tiny 'vampires': Paleobiologist finds evidence of predation in ancient microbial ecosystems
Vampires are real, and they've been around for millions of years. At least, the amoebae variety has. So suggests new research from UC Santa Barbara paleobiologist Susannah Porter.
Proceedings of the Royal Society B.
"To my knowledge these holes are the earliest direct evidence of predation on eukaryotes," said Porter, an associate professor in UCSB's Department of Earth Science. 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," she continued, "starting with the very first mineralized shells, which show evidence of drillholes. 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."
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 micrometer (one thousandth of a millimeter) 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 percent of the specimens.
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 1 to 1.6 billion years old -- the fossilized eukaryote will show no evidence of predation," Porter said. "I'm interested in finding out when drilling first appears in the fossil record and whether its intensity changes through time."
Porter also is interested in seeing whether oxygen played a role in predation levels through time. She 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.
|The Chuar Group in the Grand Canyon was once an ancient seabed |
[Credit: Carol Dehler]
"I'm interested to know whether the predators only were present and making these drill holes when the bottom waters contained oxygen," Porter added. "That might tie the diversification of eukaryotes and the appearance of predators to evidence for increasing oxygen levels around 800 million years ago.
"We know from the modern vampire amoebae that at least some of them make resting cysts themselves," Porter said. "A former student of mine joked we should call these coffins. So one of our motivations is to see if we can find these coffins in the fossil assemblage as well. That's the next project."
Author: Julie Cohen | Source: University of California - Santa Barbara [May 26, 2016]