Living fossil
Living fossil is an informal term for any living species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 which appears similar to a species otherwise only known from fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s and which has no close living relatives, or a group of organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

s which have long fossil records. Such groups have often survived major extinction event
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...

s, and generally retain low taxonomic diversities.

There are several competing and often ambiguous definitions of the term "living fossil". One definition holds that a "living fossil" is any living taxon morphologically
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 and/or physiologically
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 resembling a fossil species through a large portion of geologic time (morphological stasis)

The term was coined by Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...

 in his On the Origin of Species, when discussing Ornithorhynchus (the platypus) and Lepidosiren (the South American lungfish):

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