Taxonomy: This Will Be on the Final

Taxonomy –

Today we have to go deep into the weeds, to understand the first of several scientific concepts that are going to be necessary to understanding the Pleistocene ecosystem.

That scientific concept is taxonomy, a system for sorting and classifying things, such as animals.

The issue, I suppose, is how to we organize our views of nature.  We see that there is physical resemblance between cats and lions, or tigers.  What, if any, is the relationship between them?  Between a horse and a rhinoceros?  A dragonfly and a bee?

Once you starting thinking about evolution, about one species evolving out of another, then you naturally start considering the relationships between the various species, and groups of species.

Taxonomy is one way to approach that organizational impulse, one way to attempt to delineate the relationship between various animals and between various types of animals.

Taxonomy means “the grouping or categorizing of things into an outline or tree structure.”[1]  It’s used for all kinds of biological sciences.  There are several kinds or systems of taxonomy, but the two best known are “scientific classification,” which grew out of, and is derived from Linnaean taxonomy, and “cladistics.”

Today we’re going to take up scientific classification.  We’ll save cladistics for another time.

First an overview, then on to the details.

Overview:

Every animal (we’re not going to consider plants right now) can be identified, or labeled, as it were, within the system of scientific classification.  There are seven levels which range from the most narrow, specific category – species; to the most broad – (animal) kingdom. Every animal is assigned to some label at each of the seven levels.

Starting with the broadest category, and going to the most specific, the categories are: Kingdom

Phylum

Class

Order

Family

Genus

Species

 

It’s a hierarchy.  Species is the most specific category; Kingdom the most general.

This system of taxonomy is a way of evaluating diversity of animals through time.  That is, if you go all the way back to the very beginning, there was the first member of the animal kingdom – probably a blob of protoplasm.  From there, it divided, and evolved and over eons and millions of years, different types of animals arose.  Taxonomy is a system for sorting through those different types of animals, in order to see their relationship with one another.   And the hierarchical system is sort of a time machine.  Species is the last, most recent type of a given animal; genus is the name for a group of closely related animals that evolved from a common ancestor; family is older and earlier still.

Say you’ve got a cat, an ordinary house cat.   That cat would be identified, taxonomically as

Kingdom:       Animalia

Phylum:         Chordata

Class:              Mammalia

Order:             Carnivora

Family:           Felidae

Genus:            Felis

Species:          F. catus

Taxonomy, then, is a way of organizing our thinking about how animals relate to one another.   As we will see, however,  these categories – Family, Class, Phylum, etc. are imprecise, and imperfect.  For example, when we talk about what is a species, down below, you’ll see that while there is a general idea of what a species is, there are also exceptions to the rule, and cases where the label is useful, but not strictly accurate.  Still this taxonomic system has been a useful tool for decades, so it’s worth taking a look at.

So, lets’ start at the bottom, at a level even below species – “Breed.”

What is a breed?  A breed is a type within a species.  Dogs are the easiest to use as examples.  There are lots of breeds of dogs, right?  Pomeranians to Great Danes.  Each breed had been developed to have certain consistent characteristics – shape, type of fur, behavior.  And when mated with another of the same breed, the offspring will have those same characteristics, too.  Animals of the same breed demonstrate homogenous behavior, and have a homogenous appearance – but only within the breed.  That is why all standard poodles look and act so poodle-y, and not at all like bulldogs.

But breeds are (a) only applicable to domesticated animals; and (b) are still the same species of animals.  All dogs, whatever their breed, are still dogs.  That means that they are still the same species; and capable of mating with any other dog, and having viable, fertile offspring.  That is where mutts come from.

So “breed” is a concept of types of domesticated animals within a single species.

Species.

A species is a group of animals which can interbreed with another animal of the same type, and have fertile offspring.  For the most part, an animal of one species cannot, and probably will not, mate with an animals of a different species.  And animals of one species cannot produce fertile offspring with animals of another species. Thus, for example, porcupines mate only with other porcupines, and have baby porcupines, called, by the way, “porcupets.” Really.   And crows mate with crows.

Crows don’t mate with porcupines, or with seagulls, for that matter; and porcupines don’t mate with skunks.  So, in very broad general terms, these concepts underlying the term species, work fairly well.

But there are exceptions to this rule, or, more specifically, cases where the term species doesn’t have the neat classical boundaries associated with the concept of speciation.

First, occasionally animals of different species do breed with one another, even though they “shouldn’t.”  Recently a grizzly bear-polar bear hybrid was shot and killed in northern Canada.  And even though they’re different species, horses can and do mate with asses, and produce offspring.  So, since people knew that (sometimes, some) different species could nonetheless interbreed, the idea of species was modified to incorporate the idea that even if different species interbred – say a horse and an ass – the offspring would be sterile.  So another test of defining a species was whether its offspring were fertile.  As long as the offspring – the jackass – was sterile, the concept of species was okay.

But even that caveat is not watertight.  Although wolves and coyotes are considered to be different species, they do mate and reproduce, and have fertile offspring.  And lions don’t normally breed with tigers.  But they can, and can produce hybrid offspring:  Ligers or tigons.  Now, in fact, this doesn’t happen outside of zoos (partly because outside of one small area in India, the ranges of lions and tigers don’t overlap; and partly because lions and tigers preferentially seek out their own kind to mate with).  But sometimes, rarely, hybrid offspring –ligons, say –are fertile.

These situations – fertile wolf-coyote hybrids; fertile ligers seem to cause the clean definition of species to break down.

Moreover, it is not always easy to know whether a given animal fits within an already defined species, or should be assigned to a new species.  This can be particularly difficult given the normal variation of animals within a given species – regional differences in coloration, for example.  Likewise, the line between two closely related species can sometimes be blurry.

So the notion of a species is neither perfectly clear, nor perfectly simple. Species is a concept that kind of works, but has lots of holes.

And yet – the idea does work, pretty well.  We can tell a robin from a blue jay, a skunk from a badger, an Indian elephant from an African elephant.

So while the idea of species isn’t perfect, it’s what we’ve got.  It means the same kind of animals, breeding only with the same kind of animal, and producing viable, fertile offspring.  Crows mate with crows, and have baby crows.  Same thing with porcupines, or killer whales.

Moving up the hierarchy, we come  to “genus.[2]

Genus comes into play when you see animals that are kind of like one another, but different, too.  Different kinds of giraffes, say, or seagulls.  They all look kind of similar, but there are enough differences so that it’s clear that they’re not the same.

That’s where genus comes in.

A genus is a group of closely related, quite similar species of animals.  So, for example, a house cat, is in the genus felis, together with other, small, closely related species of cats, such as the jungle cat, the black-footed cat, and the sand cat.[3]  There are lots of animals which have a common name, even though they may fall within different species.  So we might say, “oh look, there’s a sparrow,” even though there are a number of different species of sparrow.[4]  We’d say, “watch out – There’s a skunk,” even though there are different species of skunks.  So we use the name “sparrow” or “skunk” generically.  And that, kind of, is the concept of genus.

800px-Striped_Skunk

Oh hey – a skunk!

 

They all look pretty similar, and its not too hard to imagine that they all shared a common ancestor not too long ago.  So they’re different species; live in different habitats; have different habits, maybe; and don’t interbreed with one another.  But they’re close.

An inherent notion here, although it’s oversimplified, is that members of the same genus evolved from a common ancestor, not so long ago.  That is, as we will see below, members of the same family may have evolved from a common ancestor, too, but the various family members diverged from that common ancestor earlier, before the members of a genus diverged from each other to make new species.

But then, what about similar animals, which are nonetheless still a little more different?  A leopard, say, compared to your house cat.  They’re both clearly cats, right?  And yet, different size, different habitats, different behaviors.  Leopards are in a different genus:  panthera, along with the lion, tiger, and jaguar.  And what about the puma, also called the cougar or mountain lion, you might well ask? Nope, neither felis, nor panthera, but its own genus (along with the jaguarundi) – puma.

The Lynx and the Bobcat are in the genus lynx.

This is where the next level of taxonomical sorting comes in – the “Family.”

This is the level for clustering animals that are somewhat similar, but also quite different from one another.  The idea is that they have all descended from some earlier ancestor, and there are still some anatomic similarities in their skeletal structures, but over long periods of time have adapted to very different conditions, have developed different features, and in short, are not as closely related to each other as members of the same genus are.  A family is a cluster of genera.

So even though house cats are in a different genus than leopards, they’re all still in the same family – felidae.

yeah, this shouldn't happen.

 

 

yeah, so this shouldn’t happen.

 

 

And if you think of clumping related groups (genera) together, it makes sense. Of course all cats – from house cats to lions – belong in the cat family.  Dogs, wolves and foxes – sure, lump ‘em all into the dog family.  Bears are bears.  All tapirs are in the tapir family.

The level, moving up, is “Order.”

This is where animals that are still more distantly related to one another are clustered, based on some similarities.

An order is a group or cluster of families.  For example, the order Carnivora, includes the cats (from lions and tigers on down); dogs (and wolves and foxes); bears (all of them); hyenas; minks; raccoons; civets; and pandas; walruses and seals.  The word Carnivore – meat-eater – is the basis for this order.

The idea, apparently, is that these types of animals, while certainly different, nonetheless have some things in common, derived from a common ancestor long, long ago; so that scientists can lump them together.  In the order carnivora, for example, these are all predators, meat-eaters.

But right away, you can see the problem:  Some of the animals on here – pandas, for example – are in this order, but they almost exclusively vegetarian, subsisting mostly on bamboo.  And some mammals which are carnivorous – orcas, for example – are not in this order.  So, what gives?

There are a couple answers to this question:

  1. It’s not a very good system.  And, in fact, there are lots of differing approaches to how best sort and organize animals in relation to one another.
  1. It is based on organizational underpinnings from the past, when it was the only system of organizing.
  1. It depends on what any given taxonomist says, although some conventions are so well –established that they aren’t going to change. (But that’s not always true for newly discovered animals).
  1. There are underlying anatomic similarities between the families of animals which comprise an order, so that it seems reasonable to lump them together.  For example, the horse family, the rhinoceros family and the tapir family are lumped together in the order Perissodactyla, because they have an odd number of toes on each foot (one or three; and remember, horses evolved from earlier species that had more than one toe, per foot).  So, even thought they are otherwise dissimilar, horses, rhinos and tapirs have this foot anatomy in common, and so are lumped together.

And the teeth and skeletal structure of pandas are so like that of bears that they seem to fit in here, even if they have evolved to have a different diet.

And killer whales’ anatomy is so different that even though they have evolved to eat meat, too, they don’t fit here.

There are lots of orders, just within the class of mammals:

•          Order Artiodactyla (even-toed ungulates: antelope, deer, camels, pigs, cows, sheep, hippos, etc.)

•          Order Carnivora (carnivores: cats, bears [like the panda, polar bear, grizzly, etc.], weasels, pinnipeds, etc.)

•          Order Cetacea (whales, dolphins)

•          Order Chiroptera (bats)

•          Order Insectivora (insect-eaters: hedgehogs, moles, shrews)

•          Order Lagomorpha (rabbits, hares, pikas)

•          Order Macroscelidea (elephant shrews)

•          Order Perissodactyla (odd-toed ungulates: horses, rhinos, tapirs)

•          Order Pholidota (the pangolin)

•          Order Primates (apes, monkeys, lemurs, people)

•          Order Proboscidea (elephants, mammoths, mastodonts, etc.)

•          Order Rodentia (rodents: rats, mice, squirrels, gerbils, hamsters, etc.)

•          Order Sirenia (sea cows, manatees)

•          Order Tubulidentata (aardvarks)

•          Order Edentata [also called Xenarthra] (sloths, armadillos)

•          Order Hyracoidea (hyraxes)

And these are just the orders for placental mammals.[5]  There are orders for birds, reptiles, insects, fish and amphibians, too.  Many, many orders.

“Class” is the taxonomic level where big differences, and these vast numbers of species, genera, families and orders are simplified.  What I mean is that there are (or were, under traditional systems of scientific classification) only seven classes, in which to sort any given animal.  They are:

Class Agnatha (jawless fishes)

Class Chondrichthyes (cartilaginous fishes)

Class Osteichthyes (bony fishes)

Class Amphibia (amphibians)

Class Reptilia(reptiles)

Class Aves (birds)

Class Mammalia(mammals)

Now, obviously, before assigning an animal to one of these classes, you’d need to know the definition of each class.  What exactly is an amphibian, or a mammal?  But – once you have those definitions, you can match your animal up to the list, and see which one of these seven classes it belongs to.  Here, we don’t care which species, or genus, or order the animal is – we’re just sorting it into one of these big classes.

We can spend endless amounts of time worrying out the precise, persnickety definitions of each class, but screw it – we’ve got better things to do.  So let’s not waste time.  Here’s the quick and dirty:

If it’s a fish and it has bones – Osteichthyes

If it’s a shark – Chondrichthyes

Frogs, toads, salamanders –  Amphibia

Feathers –  Aves (Birds)

Snakes, lizards, crocs, gators – Reptilia

Fur, milk – mammalia  – Mammals.

If it’s a fish and it has no jaw, it’s gross and disgusting – Throw it back and get out of there.

LAMPREY0624_3GD_6393811-600x363

Omigod! Omigod! That’s a freakin’ jawless fish!  Run!

But again, the beauty of this system is that we are still sorting based on common characteristics.  There are lots of different types of fish, but here, we put them all into the same class, so long as they have bones.  Same thing with mammals or birds.

Okay, onto “Phylum.”

Phylum, the level of classification below Kingdom, is simultaneously easy, and devilishly difficult to pin down.  There is a lot of disagreement about just what, exactly, phylum means, and how many phyla there are.  We, however, are going to take the simple, straightforward route to understanding phylum.  For our purposes, it is a system of classifying animals based on common bodily attributes, and to make it even easier, there are only two phyla we need to be concerned with, here at Pleistoscenery: Insects, and everything else.

Insects are in the phylum arthropoda –they have segmented legs, and exoskeletons.

Everything else, for our purposes, means all the fish, birds, amphibians, reptiles, and mammals.

And what makes all those different kinds of animals –  fish, birds, amphibians, reptiles, and mammals – fit into the same phylum?  Answer:  They all have spinal cords.  And, indeed, the phylum is called chordata – animals with central nervous systems, and spinal cords.

Overall there are something like 35 phyla.  But the reason we’re going to skip them is because they mostly consist of various types of mollusks and worms.  And, really, who cares?

The final level in this hierarchy is “Kingdom.”

“Kingdom,” although it seems easy, isn’t quite as simple as you might think.  Sure, it’s easy enough to place a cat in the animal kingdom, instead of the plant kingdom, but what about bacteria?  Fungi?  Where do they fit?

Answer:  They fit into their own kingdoms, but guess what?  We’re going to ignore them.

All you need to know is that every fish, reptile, amphibian, bird, insect and mammal fits into the animal kingdom: Animalia.

This system is far from perfect.  It’s based, to a large extent on what a given taxonomist thinks is the best place to assign an animal.  Some of these scientists are splitters – they think each animals should be in its own genus, and its own species. [6] Others are lumpers – they tend to lump lots of animals into the same genus, the same family, even the same species.

And this process of deciding where taxonomically, an animals fits is even more difficult when it comes to paleontology, when all you’re working with is a partial animal skeleton, in a poor state of preservation.  Or when you only have one or two skeletons – total – to base the decision on.

But the fundamental idea makes sense – new species arise out of older ones, evolving and adapting to changes in the environment.  New anatomic adaptations, new appearances, new behaviors emerge, but they do not simply spring into being – they grow out their earlier ancestors.  So by studying the anatomy and behavior of animals, scientists are able to make informed judgments about the (a) evolution of different species; and (b) the relationships between various species.

Is this system perfect?  Absolutely not.  But it is a useful tool to understand (or to try to understand) the network of life around us.

Okay – we’ve studied taxonomy.  You tell me what this is:

JackalopeHistory2


[2] The plural of genus is genera.

[3] By the way, do yourself a favor and look up the black-footed cat.  Adorable.

[4] In fact, it gets even more confusing, because there are many different genera of sparrows.  So any given sparrow is a member of a species, is in a genus, and in a family.  Thus, the name “sparrow,” doesn’t identify the bird too strictly – all it says it that this bird in the family of sparrows.  Two little brownish birds, both called sparrows, could be different species, and even different genera.  But they’d still be in the same family.

[5] Don’t even get me started on marsupials, or the duck-billed platypus.

[6] I’m not saying that whoever is in charge of sparrows is a splitter, but go take a look at “American Sparrow” over in Wikipedia, and tell me what you think.

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