Dr Paul D Taylor (UK)
There’s a small Cambrian trilobite (Fig. 1) that is collected in copious quantities from a site in the Wheeler Amphitheatre of Utah. Sold just as it is or mounted in jewellery, this trilobite lacks a common name and goes by its scientific name. In its fullest form, this is Elrathia kingii (Meek, 1870). But what exactly do the different parts of the name mean? How did Elrathia kingii – and other species of fossils – receive their names in the first place? And what are holotypes, lectotypes, neotypes and topotypes? In answering these and related questions, this article focuses on the procedures used by taxonomists when describing and naming living and fossil organisms.
Along with living organisms, the formal names of fossils employ the binomial system introduced by the Swedish naturalist, Carl Linnaeus in 1735. A genus name is followed by a species name, the latter sometimes referred to as the trivial name. Both are by convention always printed in italics, the genus name with a capital first letter and the species name with a lower case first letter. Unfortunately, newspapers all too often incorrectly print generic names with a lower case first letter.
Names of species (and genera)
The combination of the genus and species name is unique – there is only one biological species called Elrathia kingii, although there are other species of Elrathia (for example, Elrathia antiquata), while kingii has been used in combination with numerous other generic names (for instance, Hippoglossus kingii, a fish).
Some genera contain only one species and are said to be monospecific. Others contain tens or even hundreds of species. Generic names are frequently abbreviated to a single letter, Elrathia kingii becoming E. kingii, but this should only be done when the full name has already been used in the publication in question. Abbreviation is almost ubiquitous for Tyrannosaurus rex which, like Marc Bolan’s 1970s rock band, has transitioned to T. rex in most people’s minds.
For some living species used in laboratory research, generic names are seldom given in full, such as the bacterium E. coli, the fruit fly D. melanogaster and the nematode worm C. elegans. However, for bryozoan enthusiasts like me, C. elegans refers to something entirely different, the cyclostome bryozoan Cinctipora elegans, which lives in the seas around New Zealand today and is an abundant fossil in the Pleistocene there too (Fig. 2). So, abbreviations can potentially lead to confusion.
When cited in its most complete form, the genus and species names are followed by the name of the author (or authors) and the date when the species was first published. Thus, in the case of Elrathia kingii, the author was called Meek – Fielding Bradford Meek – and the paper in which the trilobite was first described appeared in 1870. A comma is, by recommendation, placed between the author’s name and date. In the case of Elrathia kingii, Meek’s name and the date are written in parenthesis, so the full name for this trilobite is Elrathia kingii (Meek, 1870).
Bracketing is not arbitrary: it signifies that when Meek introduced this species he placed it in a different genus (Conocoryphe). Subsequently, it was transferred to Elrathia by Walcott in 1924, when he first coined this genus name. If a species remains in the same genus in which it was originally described, the author and date are not placed in brackets. For example, the Early Jurassic oyster Gryphaea arcuata (Fig. 3) – the Devil’s toenail – was originally described by Lamarck in 1801 under the same binomen as that which we use today. Therefore, its full name is written: Gryphaea arcuata Lamarck, 1801.
All too often, printers and non-specialist editors are oblivious to this useful convention and attempt to ‘standardise’ species names such that all of the authors’ names and dates are written within brackets, or else none of them are bracketed. Occasionally, the trivial name is followed by ‘auct.’ instead of an author’s name.This is an abbreviation of the Latin word auctorum and means that the species name is being applied in a commonly used way but not necessarily how it was originally intended.
Genus and species names are often derived from place names, stratigraphical provenance, people’s names, characteristics of the organism, or figures from mythology. Turning back to our Cambrian trilobite Elrathia kingii, where did its generic and trivial names come from? The generic name Elrathia, coined by Walcott, apparently derived from a tiny community called Elrath in Alabama, which is unusual as this has no obvious connection with the occurrence of this trilobite in Utah.
Meek’s species name kingii is more easily explicable: the specimens used by Meek when describing this trilobite were collected by the United States Geological Survey, under the direction of Clarence King, after whom the species was named. Nowadays, when naming a species after a man called King, we would use only one ‘i’, to make the name kingi, but, in the nineteenth century, it was commonplace to use a double ‘i’, an original spelling that has to be retained. Gender considerations are important when formulating names of species. If this species of Elrathia had been named after a Mrs or Miss King, the ending would have been ‘ae’ to make kingae.
It is worth mentioning the derivations of a few other common fossils names to illustrate their diverse roots. Introduced in 1808 by de Montford, the name of the Early Jurassic ammonite genus Amaltheus comes from Greek mythology in which Amalthea is a foster-mother of Zeus. The snail genus Bellerophon, which is abundant in the Carboniferous Limestone of Britain, was also named by de Montford. In this case, he borrowed the name of the mythological Greek hero Bellerophon, son of Poseidon and Eurynome.
Species based on place names often carry the suffix ‘-ensis’ or ‘-ense’, as in the Silurian brachiopod Protochonetes ludloviensis (for Ludlow in Shropshire) or the Cretaceous sponge Raphidonema farringdonense (Fig.4) for Faringdon (formerly spelt Farringdon) in Oxfordshire.
An example of the use of a stratigraphical division as the basis of a species name is the brachiopod Ornithella bathonica, the species name referring to the Bathonian stage of the Jurassic. Naming species after their supposed geological age is not always wise. The danger of this procedure is illustrated by a bryozoan named Membranipora jurassica by Gregory (1894), who believed it to have been collected in the Middle Jurassic rocks of Calvados in Normandy. However, it is now known to have come from the Upper Cretaceous deposits of Contentin in another part of Normandy. This leaves us with a species called jurassica, which is actually of Cretaceous age.
Morphological attributes forming the basis for fossil names are numerous and include, for instance, the presence of spines, as in the Cretaceous bivalve Spondylus spinosus and the Jurassic brachiopod Acanthothyris spinosa. Indeed, the first part of the name of the brachiopod genus also refers to its spines, being derived from a Greek word for thorns as seen in acanthus plants. A knowledge of classical languages helps in understanding the derivations of many other names, such as parvus or parva (for example, the snail Conomitra parva from the Eocene Barton Beds), which is Latin for small.
The names of new species and genera commonly honour people. Those honoured may be scientists who have made major contributions to the field, collectors who first discovered the species being named, or family members recognised for their support. Celebrities are increasingly being honoured by having species named after them too. Among trilobites, species have been named for Marilyn Monroe (Norasaphus monroeae), Mick Jagger (Aegrotocatellus jaggeri) and Sid Vicious (Arcticalymene viciousi). Funding agencies have also been recognised in this way, as in the Miocene bryozoan Stylopoma leverhulme, acknowledging financial support provided by the Leverhulme Trust for a research project.
While it is frowned upon to coin names that are insulting, new names can be intentionally amusing. One of my former colleagues – Pat Cook – at the Natural History Museum in London retired to live in Australia and was honoured by having a new bryozoan genus and species from the Pliocene Coralline Crag (Fig. 5) named for her: Goodonia cookae, pronounced ‘good on y’Cookie’, preferably in an Australian accent. The Cretaceous brachiopod species Cyclothyris larwoodi, named by E F Owen to honour his friend G P Larwood, is distinguished by its prominent beak recalling the beak-like nose of the honouree. One important stipulation is that authors cannot name new genera or species after themselves.
Generic names of fossils belonging to particular taxonomic groups often incorporate standard suffixes, for instance, ‘-graptus’ for graptolites (for example, Didymograptus), ‘-aster’ for echinoderms (for example, Micraster), and ‘-ceras’ for cephalopods (for example, Kosmoceras).
Establishing new species and genera
How are new species and genera established? Needless to say, a good knowledge of the group concerned is essential before proposing any new taxa. It may be necessary to scour the literature to ensure the species has not been described already, perhaps in some obscure paper published in the early eighteenth century by the geological survey of a small European state that is very difficult to obtain.
Not surprisingly, mistakes can be made and species are sometimes described two or more times. The alternative names for the same species are known as synonyms. The oldest is the senior synonym and normally ‘trumps’ any younger, junior synonyms. The senior synonym therefore takes priority and is the name that should be used for the species in question.
It is also important to give the new species a name that isn’t preoccupied, that is, hasn’t been used before. If the genus is new, then no previously named genera should have that name. Similarly, if the species is new, then no previously named species placed in that genus should have the same name. The Internet has made it far easier to check for the uniqueness of names than was the case in pre-digital times, when a trip to the library to thumb through C D Sherborn’s massive compilation of names, Index Animalium, was usually necessary.
It is not uncommon for a species to be transferred subsequently from its original genus to another genus already containing a species with exactly the same trivial name. This results in homonomy: two different species having exactly the same name. The species named first is the senior homonym and takes priority over the junior synonym, which has to be given a new name. The abbreviation nom. nov. is used to indicate a replacement name for the junior homonym.
A new name may also be required when a genus name that has been used previously is inadvertently reused for a new genus. For instance, Gabb and Horn (1862) introduced the Cenozoic bryozoan genus Heteractis, unaware that Heteractis had already been used seven years earlier by Milne Edwards and Haime for a sea anemone. It took more than 150 years for this duplication to be corrected when Di Martino and others (2018) introduced Discoradius as a nom. nov. for the bryozoan genus previously referred to incorrectly as Heteractis.
The proposal of a new species or a new genus is usually made explicit by the name being followed by the abbreviations sp. nov. or n. sp. for a new species, gen. nov. or n. gen. for a new genus, or gen. et sp. nov. or n. gen. et n. sp. if both the genus and species are new. In subsequent publications these abbreviations are replaced by the name of the author (or authors) of the new taxon.
Nowadays, rules about establishing new species and genera are very strict, governed by legalistic international codes of nomenclature. Animals and plants are covered by separate codes which differ slightly. Here, I will concentrate on animal names as set out in the International Code of Zoological Nomenclature (https://www.iczn.org/the-code/the-international-code-of-zoological-nomenclature/the-code-online/). Because no equivalent rules existed in the nineteenth century, some names introduced at that time fall short of modern requirements, which can cause problems in their interpretation. Whereas some old species were introduced without illustrations, it is now expected that all new species are fully illustrated to facilitate recognition.
The author must make it explicit how the new species differs from existing species that are otherwise similar, and information must be given about geographical and stratigraphical provenance. Crucially, one or more ‘type’ specimens should be lodged in a museum or similar institution where they are available for future study. Type specimens ought not to be conserved in private collections. One of the type specimens must be selected as the holotype, which is the key specimen defining the species. Additional specimens called paratypes may also be chosen to help encompass the variability of the species.
Holotypes and paratypes were usually not specified by nineteenth century authors. In that case, all of the specimens used when the new species was initially described have equal status and are known as syntypes. The equivalent of a holotype, which is called a lectotype, can then be chosen from among these syntypes, with the remaining syntypes becoming paralectotypes. It is customary to choose a specimen that can be matched with an illustration in the original publication as the lectotype (for example, Fig. 6) as this eliminates any doubt about its status as one of the specimens used by the original describer of the species. Perhaps surprisingly for such a common species, there is no unique holotype or lectotype for our tiny trilobite Elrathia kingii: the latest paper on this species refers to the ‘type specimen’ as a syntype (Hopkins, 2020, p. 7).
Occasionally, no syntypes are known to exist: they may, for example, have been destroyed during wartime. If the identity of the species is in doubt because of this loss, it is sometimes necessary to choose a replacement known as a neotype. This should come from the same place – the type locality – as the original type material, and be of the same geological age in the case of fossils. The term topotype can be applied to any specimen from the type locality. Topotypes are of particular value as they are more likely to represent the species in mind than are fossils from other localities, especially fossils from far distant localities or different stratigraphical horizons.
Type specimens are enormously important in fixing the identity of species. For this reason, they tend to be restudied over and over again. One reason for restudy is that, particularly for species introduced a long time ago, the original description of the species may focus on features no longer thought to be important, whereas other features not even mentioned in the original description may now be regarded as critical. In addition, novel methods of non-destructive investigation and imaging (for example, scanning electron microscopy) can be applied to type specimens, leading to improvements in our understanding of the species that are defined by these type specimens.
There are several reasons for going a step further and proposing a new genus. This action is very often taken when a species is so different in morphology that it cannot be comfortably accommodated in any existing genus. Ideally, however, the phylogeny of the group concerned should show that these species belong on a separate branch of the evolutionary tree. For any new genus to be valid, a type species must be stated. Thus, when Walcott named Elrathia as a new genus, he gave Conocoryphe kingii as the type species, or ‘genotype’ as it was usually known in the days before this term was used for the genetic complement of an organism.
Publications from the nineteenth century seldom named type species for the new genera they introduced. If the new genus included only one species, that automatically becomes the type species by monotypy. Otherwise, the type species has to be chosen by subsequent designation. Sometimes, this is the first species to be listed by the author of the genus, but in other cases it is the best known or most typical species in the genus. Type species are crucially important as they define the genus: all other species placed in the genus are done so with a degree of subjectivity. So, if you want to know exactly what the genus Elrathia is, you need to study the type material of the type species E. kingii.
New names for species and genera are not available until they are published. Since 2008, all new animal names must be registered online with ZooBank (http://zoobank.org/). A unique number is generated by the ZooBank website and this number, or a number for the publication introducing the new species or genus, is generally added to the publication as proof of registration. As new taxa are normally published in journals that enforce stringent peer review, they will already have been checked by specialists that they are not synonyms of previously published species. Nevertheless, this does not guarantee their general acceptance by the scientific community: some new species and genera are subsequently ‘sunk’ into synonymy, or just politely neglected.
Finally, it would be remiss not to mention the naming of trace fossils, such as burrows, borings and trackways (see Bertling et al., 2006 for a comprehensive discussion). These are not biological taxa in the strict sense – a single trace fossil species can be produced by many different biological species – but, for historical reasons, they are named using the same binomial method.
Trace fossil genera and species, referred to as ichnogenera and ichnospecies respectively, are often marked using an abbreviated suffix, for example, Chondrites igen. Both ichnogenera and ichnospecies must have type species and holotype specimens, respectively, as in body fossil genera and species. Occasionally, the holotype of an ichnospecies (for example, a long trackway visible in a coastal cliff) has to be left in-situ rather than collected, although casts are often prepared to be deposited in museums.
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