Two palaeontologists at the University of California, Riverside (UCR) say that they have discovered that Earth's ecosystem has been complex at least since around 565 million years ago, a period which in history is known as the Neoproterozoic era.
Based on a study of ancient fossils excavated in the South Australian outback, the new suggestion is quite contrary to the prevalent belief that the earliest multicellular animals were simple, and that strategies organisms use today to survive, reproduce and grow in numbers have arisen over time due to several factors.
Palaeontologists have so far enumerated evolutionary and ecological pressures imposed on the ecosystem by predators, competition for food, and other resources among such factors.
However, in describing the ecology and reproductive strategies of Funisia dorothea, a tubular organism preserved as a fossil, the researchers found that the organism had multiple means of growing and propagating, similar to strategies for propagation that most of the present-day invertebrate organisms use.
"How Funisia appears in the fossils clearly shows that ecosystems were complex very early in the history of animals on Earth - that is, before organisms developed skeletons and before the advent of widespread predation," said Mary Droser, a professor of Earth sciences at UC Riverside, who was joined in the research by James G. Gehling of the South Australia Museum.
During the study, the researchers observed that Funisia appeared as 30 cm-long tubes in the fossils. They also observed that the tubes commonly occurred in closely-packed groups of five to fifteen individuals, displaying a pattern of propagation that often accompanies animal sexual reproduction.
"In general, individuals of an organism grow close to each other, in part, to ensure reproductive success. In Funisia, we are very likely seeing sexual reproduction in Earth's early ecosystem - possibly the very first instance of sexual reproduction in animals on our planet," said Droser, the first author of the research paper and the chair of the Department of Earth Sciences.
The researcher duo says that the clusters of similarly sized individuals of Funisia are strongly suggestive of "spats", huge numbers of offspring an organism gives birth to at once.
Besides producing spats, say the researchers, the individual tubular organisms reproduced by budding, and grew by adding bits to their tips.
"Among living organisms, spat production results almost always from sexual reproduction and only very rarely from asexual reproduction," Droser said.
Rachel Wood, a paleontologist at the University of Edinburgh, United Kingdom, who was not involved in the research, said that the findings of the study were an indication that fundamental ecological strategies were already established in the earliest known animal communities, some 570 million years ago.
"The fact that Funisia shows close-packed growth on the sea floor allows us to infer that this organism also reproduced sexually, producing a limited number of larval spatfalls. This is how many primitive animals, such as sponges and corals, reproduce and grow today. So although we do not know the affinities of many of these oldest animals, we do know that their communities were structured in very similar ways to those that exist today," she said
Scientists are of the opinion that a clear picture of the early ecosystem on Earth can help discern how early life evolved, what it looked like, and how organisms respond to environmental and other changes.
"The nature of the early ecosystem also clues us on what to look for on other planets in our search for extraterrestrial life," Droser said.
The study has been published in the journal Science.