A New Story of 'Evolution' Told by Footprints: The Origins of Life Seen from Footprints, Forests, and Golden Canyons
When and how did life on Earth diversify? The 'Cambrian Explosion,' familiar from textbooks, is considered a period of explosive evolution that occurred approximately 530 million years ago, during which the basic body plans of modern animals were established. However, traces from much older eras have recently been discovered one after another, suggesting that the 'story of evolution' is about to be significantly rewritten.
Premature Mobility Indicated by 540-Million-Year-Old Footprints
Researchers in Spain and the UK discovered fossilized footprints left in geological strata dating back an incredible 545 million years. By examining the shape and curvature of the traces in detail, they estimated that the organisms that left these footprints possessed elongated bodies, muscles that moved back and forth, and segmented structures. Moreover, they were not just moving around aimlessly; they were moving with a sense of direction and using sensory organs to search for food.
Until now, such complex body mechanisms were thought to have appeared during the Cambrian Explosion. However, the research team revealed that these functions already existed 545 million years ago.
The environment at that time was covered in microbial mats, and it is believed that the ability to move around and search for food was essential for survival.
The significance of this discovery is immeasurable, as it suggests that the start of the Cambrian Explosion may have occurred millions of years earlier than previously thought. The fact that 'advanced functions' such as muscles, sensory organs, and the ability to move with direction were present much earlier than expected tells us that early animals were by no means simple in form.
Ecosystem Changes Brought About by the Ediacaran Forest
During the same era when the owners of these footprints lived, a mysterious 'forest' was spreading on the seafloor. The 'forest of marine animals' from the Ediacaran period (just before the Cambrian), discovered in Newfoundland, Canada, consisted of a collection of organisms that looked like plants but were, in fact, animals.
These organisms were firmly anchored to the seafloor, and some reached heights of several tens of centimeters.
When the research team digitally reconstructed the biological community of that time in 3D and simulated its impact on seawater flow, they discovered something surprising. These stationary forests disrupted the flow of water, actively promoting mixing in both vertical and horizontal directions.
Even in modern oceans, this vertical mixing determines the distribution of heat, nutrients, and biological larvae. Researchers point out that this mixing may have redistributed oxygen and nutrients, creating an environment that supported more complex life activities. The Ediacaran period was a crucial time when animals first appeared and new lifestyles such as burrowing, crawling, and predation emerged. The quiet forest was also a stage setting for the grand drama of evolution.
The 'Golden Canyon' as a Competitive Arena of Abundance
Clues as to how Cambrian animals diversified were also found in the Grand Canyon in Arizona, USA, far away. In a 2025 survey, a large number of fossils of soft-bodied organisms, including mollusks, crustaceans, and spiny worms, were discovered in this canyon, dating back 507 to 502 million years.
Until now, Cambrian mollusk fossils had only been found in harsh environments with little oxygen or nutrients, but this discovery was different. Researchers have named this region the 'Evolutionary Goldilocks Zone.' This environment, where the water was neither too shallow nor too deep, was rich in oxygen and nutrients, and was moderately protected from the effects of ultraviolet rays and waves, served as an experimental laboratory for biological evolution.
Among the mollusks found here were crustaceans that used hairy arms to transport microscopic food in the water like a conveyor belt to be crushed by teeth, and shellfish that scraped algae off rocks with belt-like teeth. Even more surprisingly, a new species of priapulid (penis worm) was discovered, which uses mouthparts with over 100 branch-like teeth to rake in food.
Researchers state that the rich environment encouraged animals to 'invest' in evolution, giving them the leeway to experiment with complex and costly new body structures and behaviors. It is as if a message from 500 million years ago, echoing an economic lesson—'invest when rich, save when poor'—is being heard from these organisms.
Experimental Evolution Told by 'Spiky' Worms
Cambrian biological diversification was also a surprising experimental ground in terms of form. A fossil reported in 2015 from China preserved a 'super-armored worm' that filtered nutrients from seawater with feather-like forelimbs and was equipped with over 70 sharp spikes on its back.
This organism is a distant ancestor of the modern velvet worm (onychophoran) and is considered one of the earliest animals to have developed armor to protect itself from predators. Researchers point out the striking contrast between the incredible diversity of these distant Cambrian relatives and the fact that modern velvet worms have remained largely the same in their body plan.
The fossil record shows a pattern in other groups as well, where ancestral diversity is extremely high while their living relatives are monotonous. Although many of those 'evolutionary experiments' ended in failure, the fossils reveal that it was this very trial and error that shaped the ancestors of today's animals.
A Perspective Approaching the Origins of Life: The Last Universal Common Ancestor
Going back even further in time, we arrive at the 'LUCA' (Last Universal Common Ancestor), the ancestor common to all living things on Earth. According to the latest research, this ancestor was a microorganism that lived approximately 4.2 billion years ago. It is estimated to have had a large genome encoding about 2,600 types of proteins and to have performed metabolism by obtaining energy from hydrogen gas and carbon dioxide. It has also been pointed out that it may have possessed a primitive CRISPR immune system to protect itself from viruses and ultraviolet rays.
Even more interesting is the 'panspermia hypothesis,' which suggests that the materials for life were brought by meteorites or from outer space, implying that the stage for the birth of life may extend beyond Earth. Furthermore, LUCA may not have been a single organism, but rather a 'gene pool' where the genetic information of multiple microbial groups was mixed, and it is believed that the three domains of Bacteria, Archaea, and Eukaryota diverged from here.
The Story of Evolution Is Still Being Rewritten
Footprints, forests, valleys, and spiky insects—these diverse pieces of evidence show that evolution is not a straight staircase, but has progressed through trial and error amidst the interactions of diverse environments and ecosystems.
Tracing the history of evolution also provides clues to understanding the environment upon which we currently stand. If future scientists find even older traces or new fossils, our understanding will deepen further, and the 'story of evolution' will be rewritten once again. While reflecting on the complexity of the natural world and the accumulation of coincidences, I would like to continue listening for new discoveries.
Reference Articles
〇These 545‑million‑year‑old fossil trails just rewrote the story of evolution (June 27, 2025)
〇Cambrian explosion may have occurred 15 million years earlier than previously thought (June 26, 2025)
〇Earliest animal ecosystems may have played a role in the evolution of complex life (May 17, 2024)
〇Grand Canyon was a 'Goldilocks zone' for the evolution of early animals (July 23, 2025)
〇Spiky monsters: new species of 'super‑armoured' worm discovered (June 29, 2015)
〇The Beginning of Evolution as Told by the Oldest Common Ancestor 'LUCA' (April 22, 2025)
〇Is Life a Gift from Interstellar Space? Deciphering the 'Panspermia Hypothesis' through Latest Observations and Experiments (July 30, 2025)