Based on genetic analysis, some believe that common sponges today closely resemble our original animal ancestors, while others argue that comb jellies fit this description better. A new study conducted by scientists at the Massachusetts Institute of Technology tips the scales in favor of communal sponges, as it gathers chemical evidence suggesting that these animals emerged during the Neoproterozoic era, more than 541 million years ago.
Unfortunately, the fossil record provides only a fragmented picture of the early days of animals. It is very difficult to find evidence of soft-bodied animals, such as comb jellies and sponges, due to their lack of solid materials like bones and cartilage, which aid in fossilization. Scientists had to get creative, searching in the oil and sediments of the Ediacaran period for chemical fingerprints that might support a sponge origin for animal life, without traditional fossils.
MIT geologist Roger Summons states, “We don’t know exactly what these creatures looked like at the time, but they certainly lived in the ocean and had soft bodies, and we assume they did not have a silica skeleton.” Lead researcher Lubna Shawar told Science Alert, “It is very rare to find a sterol containing 30 carbon atoms, which suggests that ancient sponges may have been the first animals on Earth, appearing long before other multicellular organisms.”
Skeptics argued that the sterane fossils in Oman might have alternative, non-biological or algal origins, but Lubna and her team have now ruled this out through a second ‘fossil’ containing C31. At the end of the simulation, two examples matched perfectly with the remains of ancient C31 sterol, reinforcing the hypothesis of a biological origin.
Now, having confirmed these ancient chemical fingerprints for early sponges, the team hopes to sift through other geological samples in search of more of our early ancestors.
