Many people assume all fossils come from extinct creatures. However, the fossil record is more complex. Not every fossil unearthed represents a species no longer living on Earth. Some fossils come from lineages that continue to thrive today, offering a deeper understanding of life’s journey through geological time.
Understanding Fossils
Fossils are the preserved remains or traces of ancient life, offering a unique window into Earth’s biological past. These records can range from bones, shells, or petrified wood to microscopic bacteria. The process of fossilization is rare, requiring precise conditions for an organism’s remains to be preserved instead of decaying.
For fossilization to occur, an organism needs to be rapidly buried by sediment, such as mud, sand, or volcanic ash, shortly after death. This quick burial protects the remains from scavengers, decomposers, and physical destruction. The presence of hard parts like bones, teeth, or shells increases the chance of preservation, as soft tissues rarely fossilize. Over long periods, minerals can replace the original organic material, turning the remains into stone in a process called permineralization or replacement.
Why Extinct Organisms Dominate the Fossil Record
The perception that most fossils come from extinct organisms is rooted in scientific reality. Life on Earth has existed for billions of years, and throughout this immense span, countless species have emerged and subsequently vanished. Biologists estimate that over 99% of all species that have ever lived on Earth are now extinct. This staggering figure means that for every species alive today, thousands have come and gone.
Only a tiny fraction of all living things ever become fossilized. Given the vast number of species that have existed and the rarity of preservation, the vast majority of fossils discovered represent long-extinct life forms. The fossil record primarily chronicles the history of lineages that did not survive to the present day, reflecting Earth’s continuous biological turnover and change.
Fossils from Living Lineages
Despite the dominance of extinct species in the fossil record, not all fossils belong to vanished forms of life. Some organisms alive today have ancient lineages with fossilized ancestors that appear unchanged over millions of years. These are often referred to as “living fossils.” Such species demonstrate morphological stasis, meaning their body plans have remained highly similar to their ancient relatives found in the fossil record.
An example is the coelacanth, a lobe-finned fish once thought to have gone extinct around 66 million years ago with the dinosaurs. However, a living coelacanth was discovered in 1938, revealing a lineage with a fossil record extending back over 400 million years. Another example is the horseshoe crab, whose fossil record dates back approximately 445 million years, showing little morphological change from its ancient relatives to the four species alive today. The ginkgo tree (Ginkgo biloba) also represents a living lineage with a fossil history reaching back around 270 million years, being the sole survivor of a once-diverse group of plants.
Beyond body fossils, trace fossils provide evidence of ancient life from lineages that persist. Trace fossils are not the remains of the organism itself but evidence of its activities, such as footprints, burrows, or fossilized feces (coprolites). Many modern animals, from insects to marine worms and bivalves, create traces that can become fossilized. For instance, the burrows of marine organisms are common trace fossils, and such burrowing activities are performed by various invertebrates still living in today’s oceans. These types of fossils directly link the behaviors of past organisms to those of their modern descendants, showing that not all fossil evidence comes from entirely extinct creatures.