Examples of Living Fossils
The Theory of Evolution predicts that living things will change over time, and the fossil record clearly shows that life on Earth has undergone a long history of gradual change. However, there have been some plants and animals that were so well-adapted to their environments that they have remained largely unchanged for many millions of years.
These species, which have survived mass extinctions, continental shifts, and changing climates over millions of years, are referred to as living fossils. In common usage, the term living fossil is used to describe any plant, animal, or microbe with a long evolutionary history, but scientists have a much more specific definition. To be a living fossil, a genus or species must have no other close living relatives. An organism that survived a mass extinction period but then radiated into multiple new orders would not be considered a living fossil. Birds, for this reason, are not considered living fossils even though their lineage dates back to the dinosaurs.
This article discusses the nautilus, the ginkgo plant, and the coelacanth - three excellent examples of living fossils still with us today.
Living Fossil Example One: Nautilus
It should come as no surprise that a creature as prehistoric-looking as the modern nautilus is considered a living fossil. Their pinhole eyes, chambered shells, and soft bodies with as many as ninety tentacles certainly look like something that would be more at home in the Cambrian than the oceans of today.
The nautilus evolved during the late Cambrian period, around 500 million years ago, and reigned as the dominant sea predator for the next hundred million years or so. Even after bony fish and sharks came to dominate the world's oceans, the many species of nautilus and ammonites, their distant coiled-shell cousins in the cephalopod lineage, continued to occupy a niche as both scavenger and predator.
The Nautilidae family, which became the modern nautilus we know today, first emerged about 215 million years ago in the Late Triassic. According to the fossil record, the Nautilidae survived through the Jurassic and Cretaceous periods with only minor structural changes. They then began to diversify after the Cretaceous-Tertiary (K-T) mass extinction, an event that saw the extinction of the ammonites. The rapid diversification of nautilus species after the K-T extinction suggests that the nautilus began to thrive in the niches left behind when the ammonites went extinct.
Today, the nautilus may be poised for a new period of diversification and speciation. The existing nautilus populations living around islands of the West Pacific are disperse and isolated from each other - a textbook demonstration of the accepted mechanism for branching of new species.
Living Fossil Example Two: Ginkgo
The ginkgo tree is a true survivor, in every sense of the word. These extremely resilient plants are resistant to pollution, insects, fungi, weather, and even atomic blasts. Some living ginkgo trees have been found to be more than 2,500 years old. The species itself has survived numerous mass extinctions and periods of climate change over its nearly 200 million year history, making it one of the best known examples of a living fossil.
Ginkgo is a rather odd tree specimen, with unusual leaf structure and reproductive strategy. Ginkgo plants are gendered, with male plants producing flagellated sperm and female plants producing dangling ovules. This dioecious type of reproductive system, as it is known in botany, is rare in modern plants but quite common in fossilized plants from the Jurassic period.
The first fossils considered part of the ginkgo genus date back to the Lower Jurassic, about 190 million years ago, fossils of ginkgo ancestors have been found in rocks from the late Permian, 270 million years old. During the middle Jurassic, the plant spread throughout Laurasia - the supercontinent that would eventually become North America, Europe, and Asia - and diversified into five or six ginkgo species.
During the Cretaceous, the fossil record shows a drop in ginkgo diversity and geographic reach as flowering plants began to dominate the plant kingdom. The species ginkgo adiantoides survived the Cretaceous-Tertiary mass extinction event and thrived for a while in the then-tropical climate of the northern hemisphere. As Earth's climate began to cool in the Oligocene and Pliocene, ginkgo slowly disappeared from the fossil record - first in North America, then Europe.
By the time humans evolved, ginkgo biloba was confined to a few mountainous regions of China. The species may have died out altogether had it not been cultivated by Buddhist monks who considered the plant sacred. These monks later brought the plant down from the mountains and helped it spread throughout East Asia. Contact with westerners then spread the plant to Europe and North America.
Major Coelocanth Findings
Living Fossil Example Three: Coelacanth
The coelacanth is not only one of the most classic examples of a living fossil, but it was also one of the first fossils to be discovered during the modern era of paleontology. The first coelacanth fossils were discovered in the early 19th Century, well before the publication of Charles Darwin's On The Origin of Species. The name coelocanthus was coined by Swiss paleontologist Louis Agassiz in his 1836 book Poissons Fossiles, using the Greek terms koilos (hollow) and akantha (spine) to refer to the hollow bones of the fossil's tail fin.
Fossils of the coelacanth order first appear in the fossil record in the Early Devonian period, 407-409 million years ago. Coelacanth fossils can be found from the Triassic, Jurassic, and Cretaceous periods, but disappear abruptly from the fossil record at the K-T boundary 65 million years ago. For more than a century after the coelacanth's discovery, it was believed to have gone extinct during this mass extinction.
This belief was overturned on December 22, 1938, when a living coelacanth was caught by a fisherman off the coast of South Africa and found in his catch by a museum curator named Marjorie Courtenay-Latimer. At the time, Courtenay-Latimer had been encouraging local fishermen to donate unusual specimens to her museum's collection, and quickly realized the importance of this unusual find.
Since 1938, additional specimens have been found in the waters near East Africa and indonesia, and a sizable population has been found living near the Comoros archipelago between the east coast of Africa and Madagascar.
Although the coelacanth has survived numerous mass extinctions, it is threatened today by fishing activity off the coast of Africa. Coelacanth feed in the same waters and at the same time as oilfish, a lucrative catch for fishermen in the region, and are often caught in fishing nets and trawlers. As coelacanth meat is nearly inedible and unfit for human consumption, encouraging locals to preserve this fish is an uphill battle for conservationists looking to save this living fossil.
Do you think living fossils disprove the Theory of Evolution?
Don't Living Fossils Disprove Evolution?
The theory of evolution predicts quite accurately that living things change over time. It does not require that all living things undergo drastic change. When a species is well-adapted to its environment and resilient enough to survive changes to this environment, new traits occurring by random mutation are unlikely to take over a population.
The term living fossil does not mean that these species have undergone no change over millions of years - they have undergone some small changes along the way. Compared to the drastic diversification of other plant and animal species during the same time periods, however, the pace of evolution of these living fossils has been glacial.
Living fossils do not disprove or even cast doubt on the theory of evolution. They instead provide paleontologists and modern biologists a useful glimpse of the distant past.
Sources and Further Information
- A Broad Brush History of the Cephalopoda - The Cephalopod Page
Cephalopods are one of the few animal groups that are both diverse and ecologically important today and yet have an extensive fossil record going back almost to the very beginnings of complex animal life during the Cambrian period around 550 million
- International Organisation of Palaeobotany (IOP) - Gingko biloba - its ancestors and allies
In the modern day flora Ginkgo biloba is the sole representative of a once greatly flourished plant group in geological history – Ginkgoales.
- Introduction to the Ginkgoales
What plant may cure Alzheimer's disease, increase circulation, tastes like almonds and smells like rancid butter? This plant is none other than Ginkgo biloba.
The Coelacanths belong to the oldest lineage of fish currently known to science. The oldest found Coelacanth fossils imply that the Coelacanth fish species developed around 400.000.000 years ago during the Devonian period.
- Oldest coelacanth, from the Early Devonian of Australia
Coelacanths are well-known sarcopterygian (lobe-finned) fishes, which together with lungfishes are the closest extant relatives of land vertebrates (tetrapods).