Eoandromeda is a genus of animals from the Ediacaran Period, dated to around 550 million years ago. These animals are interesting because they appear to be the first adult animals in the fossil record, reflecting a major change for life on Earth. In fact, there’s some debate about whether Eoandromeda belongs in the Animal Kingdom at all, with some scientists arguing that the fossilized remains might be remnants of algae. However, evidence seems to strongly support the idea that these remains are those of animals, and if so, it marks a major discovery.
Only one species in this genus has been discovered, Eoandromeda octobrachiata, an eight-armed organism exhibiting radial symmetry. From the fossils which remain, scientists have hypothesized that the organism had a dome-shaped body, and that it was probably very simple, demonstrating a very crude step along the pathway to the development of animals like those which roam the Earth today, although the organism might have been similar to jellyfish.
Given the location of Eoandromeda fossils, it is believed that the animals lived on the ocean floor, perhaps absorbing dissolved nutrients in the water and using them as food. It was probably a soft-bodied organism, given the body structures of modern deep-sea creatures. Little beyond this is known, which is to be expected, given the limited fossil evidence and the limitations of studying animals which only exist in fossilized form.
Another intriguing thing about Eoandromeda is that the animals are preserved in two distinctly different ways, Ediacaran preservation, and Burgess shale preservation. Ediacaran preservation is a type of preservation in which fossils were preserved by microbial mats on the ocean floor, with the microbes developing a thick film which protected the animal as it slowly decayed and then mineralized with the rest of the ocean floor. In Burgess shale preservation, fossilized remains are trapped in remarkably clear detail in shale formations.
The two types of preservation preserve different structures, which made it hard to confirm that scientists were really looking at the same creature. The fact that examples of both types of preservation can be found suggests that Eoandromeda might be a key part of the history of the fossil record, providing clues which could be used to identify and date other fossils.