Many other early deuterostomes that scientists have found are from around 510 to 520 million years ago, but Saccorhytus is 20 to 30 million years older than even that. It lived among the sand grains on the seabed in the early Cambrian period. During the Cambrian, a burst of diversification meant the deuterostomes rapidly split into a large number of groups.
“Saccorhytus now gives us remarkable insights into the very first stages of the evolution of a group that led to the fish, and ultimately, to us,” said co-author Degan Shu of Northwest University.
The discovery could shine a light on another enduring mystery: Why is there a gap in the fossil record from when animals are thought to have arrived on the scene based on the "molecular clock"?
“If indeed the first of these animals including Saccorhytus were very, very tiny, they could only preserve in very, very exceptional circumstances – they basically slip through the fossilisation net,” added Morris to The Guardian.
It’s an intriguing possibility, but more work is needed to confirm it. Perhaps there is an even deeper, more enigmatic history waiting to be discovered.
In image (g), you can see a ventral view of the body cones (bc), the mouth (M), and two circular pores (Bc1). Credit: Simon Conway Morris/University of Cambridge