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Taxonomy and Xenotaxonomy

The classification of naturally-evolved and artificial organisms

Double Biosphere on Elessee
Image from Steve Bowers and Microsoft Image Creator
A double biosphere on the newly-discovered garden world Elessee in the Periphery. This world has two separate unrelated biotas living on its surface, originating in different abiogenesis events. Although both utilise protein-like macromolecules and carbohydrates, as well as nucleic acids for genetic information, their genetic codes are entirely unrelated and many of the macromolecules used are enantiomers of those in the other biota. This means that the two biospheres rarely interact, and organisms from one group generally cannot digest, infect or otherwise utilise the other.
The classification of organisms and life-like phenomena encountered and detected in the Terragen Sphere and beyond is a complex subject, and in order to develop a systematic classification system taxonomists use a number of conventions which can be applied across a wide range of circumstances.

Two common parameters used to establish a taxonomy are the origin and evolutionary history of the organisms concerned, and the nature and extent of any shared characteristics. In the case of biological organisms, most phylogenetic trees can be traced back to a single abiogenesis event, apart from a number which have been transferred across planetary or interstellar distances from an unknown provenance. Each abiogenesis event has the potential to be the origin of a separate taxon of organisms, known as a biota, which is the top-level taxon in any phylogenetic tree.

A few planets have more than one unrelated biota extant on their surface. Because they have separate origins, they are biochemically different, and utilise data-rich macromolecules (such as nucleic acids) to permit the transfer of inheritable information. These separate biota can only interact with each other to a very limited extent, since they do not share many biological characteristics; although worlds with multiple biota are relatively commonplace among newly-emerged microbial worlds, in most cases one single biota becomes dominant and outcompetes the rest. Few mature garden worlds have more than one separate phylogenetic tree; the newly discovered world Elessee is the only known example where two separate macrobial biospheres with similar degrees of complexity coexist.

The skolian garden world Si'swikknii has two almost completely separate assemblages of organisms with significant differences, one on each side of the equatorial ice belt; but these two assemblages shared a common genesis several billion years ago.

Below the level of biota, taxonomists have adopted a rank system to classify organisms, which is derived from the taxonomic ranks adopted by biologists on Old Earth to classify terralife. The details of evolution and development on life-bearing worlds outside the Earth are extremely complex and different to the development of life on Earth; nevertheless many of the conventions used in the taxonomy of terralife can be applied to xenotaxonomy. The ranks used on Earth have been adopted as conventional taxon ranks on a large number of worlds, although they may be used in very different ways. Not all ranks are used on every life-bearing world, and on some the details of phylogenetic development are so complex that interstitial ranks must be included.

Ranks in common use

Biota :: Domain :: Kingdom :: Phylum :: Class :: Order :: Family :: Genus :: species
Additional ranks may be added between each level — these include the prefixes hyper-, super-, epi-, sub- and infra-, all of which are utilised in the extremely diverse and complicated taxonomy on the planet Gtoare (also known as The Fieldwork Beckons). Also used on Gtoare are the additional ranks Division and Tribe, which are rarely used elsewhere. Ranks below species are also used on some worlds, such as subspecies, variants and morphs.

Classification systems used for non-standard phylogenies

The evolutionary history of some worlds is unclear, often due to repeated extinction events, horizontal gene transfer or epigenetics or equivalent processes. For this reason a few alternate taxonomic systems have been developed which rely on shared and highly conserved characteristics, rather than directly inherited genetic information.

Even on Old Earth the genetic inheritance of viruses and other self-replicating macrosystems was fragmentary and unclear, so a new taxonomic rank (Realm) was introduced to replace Domain and Kingdom. This rank has been utilised to classify the biotas on Taebedh and Caethun, where molecular evolution has been disrupted on various occasions by high-energy events in the nearby galactic environment, and only remnants of the original biota survived in a highly degraded state. Despite these disruptive events the various taxonomic Realms have recovered and prospered, and retain a variety of distinctive traits which are conserved.

On some worlds evolutionary pathways are complicated by frequent information transfer between different taxa; hybridisation between species can occur naturally even among terralife species and genera, but in some biota hybridisation can occur between higher order taxa. Hybrid taxa of this kind are known as NothoTaxa, and examples of nothospecies, NothoGenera, NothoOrders or even NothoKingdoms can be found. The Plantanimalia of Tannhauser are the result of an ancient hybridisation between a plant-like kingdom and an animal-like kingdom, due to the versatile and compatable nature of the information-carrying units on this world.

Some biota consist largely or wholly of colonial organisms or organisms with large internal complements of endosymbiotes, and the classification systems of biotas on these worlds can be extremely complex and non-tree-like, since traits can sometimes be exchanged wholesale across taxa. For this reason additional taxa can be devised to describe groups of organisms that retain large reserves of information derived from a wide range of sources, even if this information may be only expressed in particular environmental conditions. Non-standard taxa of this kind include Alliance, Union and League, as well as HyperAlliance, SubUnion and InfraLeague (and so on, as appropriate). The naturally-evolved envomes of Kammerer are classified as HyperAlliances, each of which include very large numbers of potential phenotypes that are expressed according to prevailing conditions. On Mahacalli the dominant colonial macrobial organisms are grouped together into Leagues and Unions, each with complex, net-like (reticulated) ancestries.

Xenotaxon nomenclature

Although many xenotaxa include organisms which resemble lifeforms which originated on Earth, they are all derived from separate evolutionary pathways, so must be given unique names. As a general guide, there are no monophyletic Earth taxa which exist anywhere outside the Earth, unless they have been carried to those locations by artificial or natural means. Mammals, birds, insects, even archaea and bacteria (in the strict sense of those terms) are indigenous to the Earth, and they are not found elsewhere (unless they have been relocated at some point). Although organisms resembling mammals, birds, and bacteria may be found on other worlds, they will have many differences in detail from Terralife examples and will have entirely different genetic and biochemical characteristics. Note that polyphyletic names such as 'worm' and 'fish' may be used for alien creatures, since they are more general terms not tied to specific taxa.

Among the first xenotaxa discovered were organisms with superficial similarities to Earth life, and these were given taxonomic labels such as bacterioids and archaeoids, plantoids and animaloids, but these sorts of label were soon exhausted. In many cases xenotaxa have been given nomenclature which includes a reference to the planetary name, such as Macryphyta (plantlike organisms from Macrystis) or Arborikaryota (eukaryotes from the planet Trees).

Artificial taxonomy

The taxonomy of artificially created or modified entities in the Terragen Sphere is described in some detail here and here. As a general guide the highest ranks of artificially created entities are classed as superphyles, phyles, and subphyles, such as biont, vec, virtual, transapient, archailect and so on, with lower ranking entities classed as classes, clades (in the sophontological sense), morphs, variants or (sometimes) as 'skins' or 'sleeves'.

Since the exact form, history and manifestation of artificial entities can vary greatly, and may be derived from a wide range of sources, any attempt to derive a definitive phylogenetic tree for such beings is likely to be unsuccessful.

Feral and abandoned artificial xenoecologies

Many currently existing garden worlds were originally the product of artificial ecopoeisis by long-vanished or inactive xenosophont civilisations. vitriolic and chlorogaian garden worlds remaining in the Terragen Sphere are almost exclusively the product of ancient terraformation attempts. Although most of these worlds have degenerated into post-gaian status, some retain complex biospheres which have underdone further evolution. The original, artificial species on these worlds were often neogens, splices or synanobots, so the top-level taxa that remain on these worlds are difficult to classify due to the significant level of genetic modification involved. By convention a feral biota is divided into Domains, Realms, Nothokingdoms or Phyles, depending on their physical nature and how much evidence remains.

In many cases these biospheres share characteristics and genetic markers with other similar worlds, and these interstellar commonalities are known as EpiBiota or simply Empires (although the evidence of shared ancestry is generally fragmentary and often takes the form of similarities in design philosophy rather than shared genetic data).

A few feral mechosystems created by ancient xenosophonts remain, but these are particularly difficult to classify, especially since they often include deliberately encrypted design data, possibly to deter unauthorised copying.
 
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Appears in Topics
BiologyBotanyEvolutionary Biology
XenobiologyZoology
 
Development Notes
Text by Steve Bowers
Additional material by TSSL and The Astronomer
Initially published on 10 December 2024.

 
 
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