Taxonomy of the Animal Kingdom: The Noteworthy Taxonomic Ranks and Zoological Nomenclature (Part II)

Every single known biological organism in this world has a unique name assigned to it. With that number being seemingly infinite, how do we ensure that the names don't get mixed up?

Welcome Back!

It's been a while eh? Let's get that groove back!

It has been quite some time since we left off at the first article (a month to be exact!), so let's do a quick recap to freshen up our minds. Follow my lead!

Within the classification of biological organisms, we have learned 3 important points that introduced us into how the ranking system works:

A group of one or more populations of an organism is first identified as a unit, known as a taxon.

The taxon is then given a unique name and assigned a taxonomic rank based on a taxonomic hierarchy.

Within a taxonomic hierarchy, 8 principle ranks are typically used. A taxon will be assigned a taxonomic rank based on its shared characteristics.

In these 8 major ranks, we've already discussed the first five. While each of them are as important in ultimately classifying a taxon, the last three are the ones that really count. At this level, the organisms begin to get incredibly specific, and a standardized nomenclature will be needed to sort them out one by one.

Before we get into the nomenclature for each organism, let's continue by starting with where we left off, at the sixth taxonomic rank: Family!

A Continuation of the 8 Principle Taxonomic Ranks...

6. Family

A family is the third-lowest rank in the taxonomic hierarchy. Similar to the taxonomic rank above it, which is 'order', it is used for the sake of simply slicing up a group of organisms from the rank above into smaller, individual categories with their own respective shared features. Taxonomists can establish their own guidelines on what makes what, and whether this can be that, and what falls under what. There really isn't a solid and hard rule for recognizing, identifying and describing a family.

Nomenclature for Families

*Every taxonomic rank after kingdom (Phylum onward) is actually regulated in how a taxon, regardless of rank, must be named. This typically comes in the form of having to use certain suffixes for certain ranks, and also differs depending on what life form it is. For animals, from this rank (Family) onward up to the very last rank, there is a code that regulates and states the nomenclature for each taxonomic rank (Family and below).

[For the purposes of this article, only nomenclature for animals will mainly be discussed on.]

A. Fungal, Algal and Botanical Nomenclature

- This one's pretty clear cut and simple. Nomenclature for the family names of fungi, algae and plants must include the use of the suffix "-aceae", with the exception of a few families.

B. Zoological Nomenclature

- The family names of animals must end with the use of the suffix "-idae".

*Within the taxonomic rank 'family', also exists the possibility of a superfamily, epifamily, subfamily, infrafamily, tribe, subtribe and infratribe. I'll discuss a little on this later, as this is ALOT to take in. Just letting you know beforehand *winks*

If this is the case (Do refer to the link to fully understand what I mean), then the following suffixes have to be applied when assigning a name to a given taxon:

Superfamily: "-oidea"

Epifamily: "-oidae"

Subfamily: "-inae"

Infrafamily: "-odd"

Tribe: "-ini"

Subtribe: "-ina"

Infratribe: "-ad" or "-iti"

7. Genus

A genus is the second-last taxonomic rank in the taxonomic hierarchy. Though its composition is determined by a taxonomist, and can differ solely based on the taxonomist/consensus of an authority, it is still considered as an important rank in the taxonomic hierarchy. Here's why.

*psst* This is when you start paying attention!

Consensus on Criteria for a Genus

I mentioned that what is deemed to be a genus in terms of an organism's descriptions and such, is decided by a taxonomist. It also differs from taxonomist to taxonomist, and there is no hard rule for what makes up a genus. There is however, a general agreement that a newly defined genus should at least fulfill these 3 criteria to be useful as a taxonomic rank:

A. Monophyly

- Monophyly is defined as the condition for a group of organisms/taxon to be monophyletic. Being monophyletic (for a taxon) is sharing a common ancestry.

- Thus, all descendants of an ancestral taxon should be grouped together at the genus-level rank.

B. Compactness

- At this point in the ranks, the description of a group of organisms would start to get very specific. After all, this is the second-to-last rank!

- As such, when going about the classification of a group of organisms from the rank above into the genus-level rank, the description for a genus should be reasonably compact, in the sense that it should not be expanded needlessly.

C. Distinctness

- In the same way a genus should not be expanded needlessly, it should then also be distinct, in regards to its evolutionarily relevant parameters.

- What do I mean by that? It means that the group of organisms that classifies under this genus-level rank should be distinct from another group in another genus, in the fact that its features that are relevant for evolution should be distinct from another group. This is what allows a genus to be set apart from another.

The Role of Genus in Binomial Nomenclature and Type Genus

This section onwards explains how names are assigned to a family, genus and species. Pay attention!

When an organism is identified, it has to be given a scientific name. Modern-style nomenclature, which is also regulated in the Nomenclature Codes, states that when deciding the scientific name for an organism, it is allowed a single unique name that is Latin and binomial in form. This applies to all life forms except for viruses.

So.... binomial in form. What? A binomial name? Binomial nomenclature is defined as a system of naming species, that is composed of two parts: A generic name and a specific name. The generic name is actually the genus name, and the specific name is the species name. Pretty straightforward eh?

Based on the system of binomial nomenclature:

Species name= Generic/Genus name + Specific name

We now know that when naming organisms, it must be binomial in form/having two parts to it. How about deciding the names itself? This is where the type concept comes in.

The type concept acts as a regulatory guideline to ensure that species within a genus, and a genus within a family, have the same root name, with respect to the rank above it. Let's break it down slowly, shall we?

The Type Concept: Type Species: Defining a Genus (Step 1)

First things first. Within a genus, there are many species yes? With so many species of different names, how can we decide the name of the single genus that covers them all? Thus, a 'type species' is decided.

In zoological nomenclature, a 'type species' is defined as the species name with which the name of its genus is permanently taxonomically associated with. This 'type species' is the reference species that acts as the very 'definition' of its genus name when used in nomenclature. Let's take an example:

Example 1: Genus Cygnus

Swans are birds under the genus Cygnus. The 'type species' of Cygnus is 'Cygnus cygnus', a.k.a the common swan. In breaking down the binomial nomenclature of the common swan, we can deduct that: The genus is Cygnus, the species name is also cygnus, but with a lowercase C.

(Cygnus cygnus, the common swan)

Cygnus cygnus: The common swan

You can tell how the common swan is the 'type species' of the genus Cygnus. Its species name is literally cygnus, and by taking that name, it has been decided as the anchor/referring/defining name for its genus, Cygnus. Thus, making it's name Cygnus cygnus!

Cygnus atratus: The Australian black swan

Then, let's take an example of a species under the genus Cygnus, that isn't the type species, so you guys can differentiate. The Australian black swan, in binomial nomenclature, is Cygnus atratus. You can then deduce that the genus is Cygnus (courtesy of the type species), and the species name is atratus.

The Type Concept: Type Genus: Defining a Family (Step 2)

We have learned that:

A type species decides the name of its genus as a whole. This genus name will represent all the species under it.

Okie dokies, now we have a genus name. But as before, there are many genus within a family. How do we define the name of a family that encloses so many different genera(genus)? Again, this is where the type concept comes in: Type genus!

As before, the type genus is the genus which defines the root of the family name. Let's use an example to speed up our understanding. Just use the same concept as applied in type species to genus name, and you'll be all good!

Based on the system of binomial nomenclature:

Species name= Generic/Genus name + Specific name

Example 2: Genus Anas and Genus Cygnus, Family Anatidae

Okayyy. Here we have 2 genera, one being Anas and the other being Cygnus (Remember the swans?). They both have different names of course, but they fall under the same family: Anatidae.

(Anas platyrhynchos)

Type Species: Cygnus cygnus and Anas platyrhynchos

Here, we can also refer to the type species of each genus to understand better. The type species of the genus Cygnus is: Cygnus cygnus.

The type species of the genus Anas is: Anas platyrhynchos.

If you were to guess between the two genera, which one would you think is the type genus for the family Anatidae? Probably genus Anas right? You'd be right at that! In the family name Anatidae, it's clear that the root word is Anas, instead of Cygnus. And why Anatidae? That's because the suffix for families in zoology must be "-idae". (If you want to know why "-idae", I'll explain it in the next article!)

To make things simpler, the type species that defines the type genus, which then defines the family name, is also the type species of the family as a whole. With this in mind, we can conclude for this example that:

Family Anatidae: Type Genus and Type Species

The type genus of the family Anatidae is: Anas

The type species of the family Anatidae is: Anas platyrhynchos

And as a whole...

The type species decides the name of its genus as a whole. The type genus decides the name of its family as a whole.

You can relax now, the worst of it is over! Whew...

8. Species

A species is the basic unit of classification in biological classification. It is also the final major taxonomic rank. By strict definition, a species is defined as "The largest group of organisms in which any two individuals can reproduce and produce offspring." As you would've guessed, at this point in the taxonomic ranks every single organism is given a unique name. It's clear how important nomenclature is in taxonomy, and as such a strict guideline is set on how to name a species.

But of course, you guys already know how to! In the section above, I've basically covered everything there is when it comes to naming a species, a genus, and its family. There is however, one teeny tiny part which I have not covered, and that's the absolute final sub-rank: Subspecies.

Not Specific Enough?!

Well, yeah. In cases where 2 or more populations of a species are living in different subdivisions and differ in morphology, a subspecies is created. This typically occurs when a species can be found in different conditions and geographical locations.

Where a species is named with two parts, a subspecies is named with three parts to it! That's right: A trinomial name.

Trinomial Nomenclature: Generic + Specific + Subspecific

You heard me. A subspecies has a name that is composed of three parts: A generic name, a specific name, and a subspecific name. The subspecific name is decided purely on what makes the subspecies different. It's that simple!

To compare with a species' nomenclature:

Based on the system of binomial nomenclature:

Species name= Generic/Genus name + Specific name

Based on the system of trinomial nomenclature:

Subspecies name: Generic name + Specific name + Subspecific name

Example 3: Terpsiphone paradisi paradisi, leucogaster and ceylonensis

The Indian paradise flycatcher is a passerine bird with the species name Terpsiphone paradisi.

Initially, taxonomists thought that it could only be found in India. However, it was also identified in other locations throughout the world. At these other areas, the feathers of this supposed only-found-in-India passerine bird were different!

Due to the identifiable differences in it's feathers at different areas, several subspecies were created for the sake of differentiating them. 3 subspecies were created:

A. Terpsiphone paradisi paradisi, the Indian paradise flycatcher

B. Terpsiphone paradisi leucogaster, the Himalayan paradise flycatcher

C. Terpsiphone paradisi ceylonensis, the Ceylon paradise flycatcher

Notice how they all begin with the same generic and specific name, but only differ at their subspecific name? That's how a subspecific name works: It is assigned to a subspecies purely based on how/where they differ from the other.

The End!

And there we have it! We've reached the end on (almost) all there is to know about zoological nomenclature. This certainly isn't everything, and there's a whole lot more that isn't covered, but these are just the basics. Give yourself a pat on the back because surely, that was a lot to take in wasn't it?

With this newfound knowledge, prepare yourself! The next article, which is also the last of this three-part series, will talk about the guidelines that govern zoological nomenclature.

All this while, we've learned that there are a lot of rules and guidelines to adhere to when it comes to naming a subspecies, species, genus, family and other ranks. But we've never discussed on what exactly these guidelines are, and the body that governs it. That's for the next article to settle that, so for now, congratulate yourself and take a break! Don't slack off though; there's a little pop quiz waiting for you next time. Study well! :P

(Yes, you heard me right. A pop quiz :D)

References (Zoological Taxonomy)