LIFE × EVOLUTION

The First Trails

~560 to 539 million years ago

Proterozoic · Neoproterozoic · Ediacaran

Before there were bodies hard enough to fossilise, there were the marks bodies leave: trails across the mats, burrows barely below the surface, fans of paired scratches where something scraped a patch clean and moved on. All of it is shallow: Ediacaran animals worked at the sediment surface or just under it. Complexity, depth and signs of hunting all rise only at the very end of the period. Kimberella, found at the end of its own scratch marks, is the first animal we can watch behave.

Why it matters

A trail is evidence of things a body fossil cannot give you: muscle to push with, a front end to aim, and a decision about where to go next. Animals with a left and a right side were already making those decisions before the Cambrian, which makes the explosion look less like an invention than like a change of pace.

Dating & uncertainty

Distinguishing a genuine trail from a tube-shaped body fossil is difficult, and several claimed Ediacaran traces have been reinterpreted. The traces described from the Dengying Formation and the paired scratch marks of Kimberella are the least contested.

Sources

1. Mángano & Buatois (2020), Interface Focus · The rise and early evolution of animals: where do we stand from a trace-fossil perspective?
2. Chen et al. (2013), Precambrian Research · Trace fossil evidence for Ediacaran bilaterian animals with complex behaviors
3. Bobrovskiy et al. (2018), Science · Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals

Earth history as one day

21:02:222 h 58 min before midnight

if Earth’s 4.54 billion years were compressed into a single day