The concept of extinction, where a species permanently vanishes, has long captivated human imagination. While the loss of biodiversity is a somber reality, a rare phenomenon occasionally occurs: the reappearance of animals thought to be long gone. This sparks fascination, prompting questions about species that might still exist undetected.
The Phenomenon of Lazarus Taxa
Scientists use the term “Lazarus taxon” to describe a species that reappears after a period of presumed extinction. This term refers to the biblical figure Lazarus, brought back from the dead. In paleontology, it describes a taxon that disappears from the fossil record for a period, only to reappear later. In conservation biology, it refers to species or populations mistakenly thought to be extinct that are later rediscovered alive.
Several factors can lead to a Lazarus taxon event. The fossil record is incomplete, meaning a species might exist without leaving fossil evidence. A species might also become locally extinct in one area but survive in another, creating gaps in the perceived record. Sometimes, low individual numbers reduce the chance of fossilization or detection, leading to a mistaken presumption of extinction.
Documented Cases of Rediscovery
One of the most famous examples of a Lazarus taxon is the Coelacanth, a lobe-finned fish believed extinct around 65 to 70 million years ago. Its rediscovery in 1938 off the coast of South Africa caused a global sensation. Marjorie Courtenay-Latimer identified the unusual fish caught by a local trawler, confirming that reports of its extinction were exaggerated. A second species was later discovered in Indonesian waters in 1997, thousands of miles from the initial find.
Another compelling case involves the Lord Howe Island Stick Insect, also known as the “tree lobster,” thought extinct by 1920. This large, flightless insect was believed wiped out by black rats from a shipwreck. However, in 2001, a small population of only 24 individuals was rediscovered on Ball’s Pyramid, a steep volcanic sea stack off Lord Howe Island. These nocturnal insects were found clinging to a single tea tree bush, providing both food and shelter.
The Takahe, a flightless bird native to New Zealand, also offers a notable example of rediscovery. This species was presumed extinct for nearly 50 years after the last confirmed sightings in the late 19th century. However, in November 1948, a party led by Dr. Geoffrey Orbell rediscovered a small wild population in the remote Murchison Mountains of New Zealand’s South Island. This rediscovery launched New Zealand’s longest-running endangered species conservation program, focused on protecting and managing the Takahe population.
Scientific Grounds for Persistent Existence
The continued existence of species thought to be extinct can be attributed to several scientific factors that make detection challenging. Vast, unexplored habitats, such as the deep oceans, remote jungles, and extensive cave systems, can harbor undiscovered or presumed-extinct species. The deep sea, for instance, is the largest habitat on Earth yet remains largely unexplored, with new species frequently being uncovered. Similarly, remote primeval forests and mesophotic coral ecosystems—”twilight zone” reefs between 30 and 150 meters deep—represent significant portions of the planet that are difficult to access and study.
Extreme rarity and small population sizes also contribute to a species remaining hidden. When a population is very small, encounters are infrequent, making it difficult for scientists to confirm its presence. Some species exhibit reclusive behaviors, being nocturnal, burrowing, or living in highly isolated areas, further complicating their detection through conventional surveys. The ability of certain species to blend into their environment or occupy specialized niches can also allow them to evade discovery for extended periods.
These biological and environmental factors highlight that an absence of evidence does not always equate to evidence of absence. The planet’s immense and often inaccessible biodiversity means that some species may persist, silently thriving in corners of the world that human exploration has yet to fully reach.
The Challenges of Confirming Extinction
Defining a species as extinct is complex, largely due to the difficulty of proving a negative. The International Union for Conservation of Nature (IUCN) classifies a taxon as “Extinct” when there is no reasonable doubt that the last individual has died. This determination typically requires exhaustive surveys in known or expected habitats, conducted over a timeframe relevant to the species’ life cycle.
However, applying these criteria can be challenging, particularly for species that are naturally rare, have small populations, or inhabit remote environments. In such cases, a lack of sightings might indicate extreme rarity or reclusive behavior rather than complete disappearance. The “burden of proof” in science often rests on demonstrating existence; proving non-existence requires extensive survey efforts.
Errors in declaring extinction, sometimes called the “Romeo error,” can occur, potentially leading to the withdrawal of conservation efforts for species that still exist. Therefore, scientists consider data availability, time since the last sighting, and observed population declines when inferring extinction. The inherent challenges in definitively proving a species no longer exists contribute to the ongoing fascination with rediscovering animals thought lost.