New York, May 26 (IANS): Vampires are real -- at least the amoebae variety -- and they have been around for millions of years, say researchers who found evidence of predation in ancient microbial ecosystems dating back more than 740 million years.

Using a scanning electron microscope to examine minute fossils, the researchers found perfectly circular drill holes that may have been formed by an ancient relation of Vampyrellidae amoebae.

These single-celled creatures perforate the walls of their prey and reach inside to consume its cell contents.

"To my knowledge these holes are the earliest direct evidence of predation on eukaryotes," said Susannah Porter, associate professor at University of California, Santa Barbara in the US.

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 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," she said.

The findings appeared in the journal Proceedings of the Royal Society B.

For the study, 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 (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, the findings showed.

"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.