Pseudoextinction
Encyclopedia
Pseudoextinction of a species
occurs where there are no more living members of that species, but members of a daughter species
or subspecies remain alive. As all species must have an ancestor of a previous species, much of evolution
is believed to occur through pseudoextinction. However, it is difficult to prove that any particular fossil species is pseudoextinct unless genetic information has been preserved. For example, it is sometimes claimed that the extinct Hyracotherium
(an ancient horse-like animal commonly known as an eohippus) is pseudoextinct, rather than extinct, because several species of horse
, including the zebra
and the donkey, are extant today. However, it is not known, and probably cannot be known, whether modern horses actually descend from members of the genus Hyracotherium, or whether they simply share a common ancestor.
Pseudotermination is extreme form of pseudoextinction, when lineage may continue in form of new species of frequently difficult to predict phylogeny.
Extirpation
or regional disappearance is the stage in pseudoextinction, when progressive diachronous range contraction, may lead to, final extinction by the elimination of the last refuge, or population growth from this temporal bottleneck.
Pseudoextinction can sometimes apply to wider taxon
s than the species
level. For instance, the entire Superorder Dinosauria, as traditionally defined, would have to be considered as pseudoextinct, because feathered dinosaurs
are considered by the majority of modern palaeontologists as the ancestors of modern day bird
s. Pseudoextinction for such higher taxa higher appears to be easier to prove. However, pseudoextinct higher taxa are equivalent to paraphyletic
groups, which are rejected as unnatural groupings in modern phylogenetic
classifications
that are based on cladistic
reasoning (either all dinosaurs are stem-group birds, or birds are derived dinosaurs, but there is no valid taxon Dinosauria that excludes the taxon Aves). Consequently, the alleged pseudoextinction of higher taxa rather represents an artifact
of an obsolete non-phylogenetic classification than a genuine evolutionary phenomenon.
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...
occurs where there are no more living members of that species, but members of a daughter species
Chronospecies
A chronospecies describes a group of one or more species derived from a sequential development pattern which involves continual and uniform changes from an extinct ancestral form on an evolutionary scale. This sequence of alterations eventually produces a population which is physically,...
or subspecies remain alive. As all species must have an ancestor of a previous species, much of evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
is believed to occur through pseudoextinction. However, it is difficult to prove that any particular fossil species is pseudoextinct unless genetic information has been preserved. For example, it is sometimes claimed that the extinct Hyracotherium
Hyracotherium
Hyracotherium , also known as Eohippus or the dawn horse, is an extinct genus of very small perissodactyl ungulates that lived in the woodlands of the northern hemisphere, with species ranging throughout Asia, Europe, and North America during the early Tertiary Period and the early to mid Eocene...
(an ancient horse-like animal commonly known as an eohippus) is pseudoextinct, rather than extinct, because several species of horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
, including the zebra
Zebra
Zebras are several species of African equids united by their distinctive black and white stripes. Their stripes come in different patterns unique to each individual. They are generally social animals that live in small harems to large herds...
and the donkey, are extant today. However, it is not known, and probably cannot be known, whether modern horses actually descend from members of the genus Hyracotherium, or whether they simply share a common ancestor.
Pseudotermination is extreme form of pseudoextinction, when lineage may continue in form of new species of frequently difficult to predict phylogeny.
Extirpation
Local extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
or regional disappearance is the stage in pseudoextinction, when progressive diachronous range contraction, may lead to, final extinction by the elimination of the last refuge, or population growth from this temporal bottleneck.
Pseudoextinction can sometimes apply to wider taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
s than the species
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...
level. For instance, the entire Superorder Dinosauria, as traditionally defined, would have to be considered as pseudoextinct, because feathered dinosaurs
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...
are considered by the majority of modern palaeontologists as the ancestors of modern day bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s. Pseudoextinction for such higher taxa higher appears to be easier to prove. However, pseudoextinct higher taxa are equivalent to paraphyletic
Paraphyly
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
groups, which are rejected as unnatural groupings in modern phylogenetic
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
classifications
Biological classification
Biological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy....
that are based on cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
reasoning (either all dinosaurs are stem-group birds, or birds are derived dinosaurs, but there is no valid taxon Dinosauria that excludes the taxon Aves). Consequently, the alleged pseudoextinction of higher taxa rather represents an artifact
Artifact (error)
In natural science and signal processing, an artifact is any error in the perception or representation of any visual or aural information introduced by the involved equipment or technique....
of an obsolete non-phylogenetic classification than a genuine evolutionary phenomenon.
See also
- Main articles: on ExtinctionExtinctionIn biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
, and the Cretaceous-Tertiary extinction eventCretaceous-Tertiary extinction eventThe Cretaceous–Paleogene extinction event, formerly named and still commonly referred to as the Cretaceous-Tertiary extinction event, occurred approximately 65.5 million years ago at the end of the Maastrichtian age of the Cretaceous period. It was a large-scale mass extinction of animal and plant... - Human extinctionHuman extinctionHuman extinction is the end of the human species. Various scenarios have been discussed in science, popular culture, and religion . The scope of this article is existential risks. Humans are very widespread on the Earth, and live in communities which are capable of some kind of basic survival in...