One important group are the ciliates. While they are not the most diverse, with only about 7000 species, they are some of the most common marine micro-organisms. This immediately creates a problem, as when they die, they simply dissolve into their environment, leaving no fossil traces, making them a very rare fossil group and incredibly hard to assign a date of origin to. However ciliate fossils have been discovered, and are among the most ancient on Earth, which push back the date for the origins of truly complex life itself.
|The remarkable, 635 to 715 million year old, goblet |
shaped, tintinnid ciliate protozoan fossils
They were taken back to the lap, broken down with acid, and the residue examined under a microscope for micro fossils. They found the presence of ciliate micro-fossils with a temporal range of 635 to 715 million years old. Hundreds were uncovered, each with a beautiful, goblet-like shape created by constricted necks and flaring collars covered in a bulbous structure. Tanja Bosak from the Cecil and Ida Green Career Developmental Assistant Professor at MIT's Department of Earth, Atmospheric and Planetary scientists, found that they were almost exactly the same as a modern day group of ciliates called the tintinnids.
Tintinnids are a fascinating group of protozoans because of their tough, bubble-like shell, which is flexible yet resilient. This means they fossilize more readily than many other micro-organisms. These new fossils as well as representing the oldest known protozoans on Earth are also the oldest tintinnids. Nicholas Butterfield, a lecturer of palaeobiology at the University of Cambridge, suggests that protozoans may be even older.
The resistant shell means that tintinnids play a vital role in the oceans' carbon chemistry. 'You have this resistant material that sinks to anaerobic oceans, where it takes longer to degrade,' Bosak says. 'As a result, you could sequester more carbon … that in turn releases more oxygen. More oxygen in the atmosphere would foster complex, oxygen-breathing life. According to Bosak, the geologic timing is consistent with this theory.
The ciliate fossils date to the period between the two ice ages. Soon after the second ice age, fossils of the first animal embryos were identified. 'It’s conceivable that they only evolved, or became ecologically important, at this time,' says Butterfield. 'Ciliates probably do play an important role in how the oceans work, but there’s no reason to believe that that role wasn't defined much earlier.' The team stated that they planned to conduct a closer analysis of the fossils to try and extract as much data as possible.