Dino 101: Dinosaur Paleobiology is a 12-lesson course teaching a comprehensive overview of non-avian dinosaurs. Topics covered: anatomy, eating, locomotion, growth, environmental and behavioral adaptations, origins and extinction. Lessons are delivered from museums, fossil-preparation labs and dig sites. Estimated workload: 3-5 hrs/week.
Differentiating Species
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En provenance du cours de University of Alberta
Dino 101: Dinosaur Paleobiology
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What is a Species?
This module will teach the different ways of defining what a species is. Students will be able to compare the strengths and weaknesses of different species concepts for different situations.
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Philip John Currie, PhDProfessor and Canada Research Chair, Dinosaur Paleobiology
Department of Biological Sciences
When Hesperonychus was named,
there was a lot of comparative work that had to be done.
We looked at features in Hesperonychus and
other specimens of closely related dinosaurs.
When naming a new species, we have to be careful when evaluating all the possible
differences between a suspected new species, and previously named ones.
Even animals in the same species are not identical carbon copies of each other.
Take for example these mountain blue birds from the zoology museum at
the University of Alberta.
All of these are the same species, but
the color patterns on the feathers can be very different.
There's a large difference in the color between the bright blue of the males and
the more dull colored females.
Even within the males, some are more vivid than others.
We have to consider sources of morphological variation that might
simply be differences within a species, which we call intraspecific variation.
We have some other great examples of intraspecific variations in our
zoology museum.
All of these skulls are from white-tailed deer, but
there are a lot of differences in the size and shape of skulls and antlers.
Some, like the skull here, don't have any antlers at all.
The size of the skull and
the antlers are related to the age of the animal when it died.
Younger animals had smaller skulls and smaller antlers.
But what about the skulls without antlers?
Well, antlers are only found on male deer, so
skulls without antlers are either from females or
sometimes from young individuals that never developed antlers before they died.
There are three kinds of intra-specific variation represented by these skulls.
The first is individual variation, which is the normal variation you see
among individuals of any species, things like the exact shape of the antlers.
The second is ontogenetic variation, or variation because of age and
growth, like the size of the antlers.
The third is sexual variation, or variation between males and females.
In this case, males have antlers and females do not have antlers.
As paleontologists we have to keep all of these kinds of variations in mind
when we're trying to identify a new species like Hesperonychus.
We need to look for differences that have occurred through evolution,
differences that indicate that two animals belong to a different species.
Even though small details in the shape of antlers can vary in white-tailed deer,
we can still identify large differences in antler shape in different species.
Like mule deer, moose, and caribou.
The forked antlers of the mule deer, the broad flat antlers of the moose.
And the curved,
blunt antlers of the caribou are different because these are different species.
Along with the rules on how to name a species,
there are several ways in which we can define a species.
One of the most important definitions for
paleontologists is Morphological Species Concept.
This essentially states that organisms which all look
the same are considered a single species.
There can be some variation between the different individuals, but
if they look more or less the same, then they are considered to be one species.
How many Tyrannosaur species do you see here?
There are actually four separate tyrannosaur species here.
Tyrannosaurs, gorgosaurus, albertosaurus, and daspletosaurus.
Though these theropods look similar, there are a number of distinct features that
we can use to reliably separate these animals from one another.
Spinosaurus, though a carnivorous theropod, is not a Tyrannosaur.
It has too many distinct features from the others to be
considered part of the same dinosaur genus.
Although the morphological species concept is useful, it's not fool-proof.
We can tell the difference between a Triceratops and
a Tyrannosaurus Rex just by looking at them.
But what about a Daspletosaurus and an Albertosaurus?
These two large tyrannosaur cousins are found in the same rocks, and
are closely related.
However, we have multiple skulls of both these animals.
And when looking at them,
we can find consistent differences between the two species.
Most dinosaurs, though, are only known from a single specimen.
And, often, an incomplete one at that,
making this kind of detailed comparative work difficult.
With some groups of dinosaurs we need specific parts of
their bodies to be able to really tell when we have a new species.
A good example of this is the Ceratopsians.
Overall, the body and limbs of Ceratopsians are highly conserved,
meaning that they are quite similar to one another.
Many species look virtually identical from the neck down.
However, the skulls of these animals have horns over their nose and eyes.
Plus a distinctive frill.
These features are used to differentiate between ceratopsian species.
So if all we find of a ceratopsian skeleton is the rear portion of it,
we would not be able to confidentially say if it could be the holotype for
a new species.
How many species of dog do you see here?
There is only one species here.
Canis lupus familiarise, namely dogs.
The variation we can see within the species is enormous, but
let's be clear: all dogs belong to the same species.
One of the main problems with the morphological species concept
is that members of one species may be split up because they look different.
Take a look at these dogs.
All of them belong to the same species, but
they look very different from one another.
Both in size as well as the relative proportions of their eyes,
noses, bodies and legs.
Never mind color, fur length and all the rest.
We keep all dogs in the same species, Canis Lupus familiaris,
because we know that they can breed with one another and make more puppies.
This brings us to another way of defining a species; namely,
the biological species concept.
The biological species concept defines a species as the group of
organisms which can interbreed.
This definition can address some of the issues associated with
the morphological species concept.
The biological species concept makes sure that cryptic species,
those that look similar but do not interbreed, are separated.
Alternately, species with a lot of individual variation are still
classified correctly, as in the case of dogs.
However, although biological species definition is relatively simple, in
practice, it can be incredibly difficult to apply, particularly to extinct species.
For any species, which of the following are necessary for
individuals to reproduce with one another?
Check all the answers you think are correct.
Do they need to look the same?
Do they need to be in the same place?
Or do they need to live at the same time?
For any two individuals of a species to reproduce,
they need to be living in the same place at the same time.
They do not need to look the same.
There are lots of examples of males and
females looking very different from one another, yet still mating.
Think of peacocks and peahens.
So answers B and C are correct.
Think about what the biological species definition implies.
In order for a scientist to confirm whether animals are from
a single species or multiple species, he must observe the animals interbreeding.
In practice, this can be difficult to deduce even for
animals that are relatively easy to observe.
It can be virtually impossible for animals which are much more secretive.
And it is just about impossible for animals that are extinct.
However, we know that for
animals to interbreed, they need to be in the same place at the same time.
Although we can't observe extinct dinosaurs breeding with one another,
we can observe if they lived in the same area and at the same geologic time.
If we find two similar dinosaurs that lived millions of years apart
or on opposite sides of the planet,
they were likely different species.
There are exceptions to these guidelines, but
it is a good principle to follow when naming a dinosaur.
In ecological science, a population is defined as a group of
animals in the same geographic area that can potentially mate.
Which of the following statements is true?
A, one or more species make up a population.
Or B, one or more populations make up a species.
One or more populations make up a species.
Just because some individuals of a species might not live in the same place.
That doesn't mean that they don't still belong to the same species.
This is another thing to consider when trying to define what is and
what isn't a new species.
Because we cannot directly observe a living specimen of an extinct species,
we have to use our best judgement when we are naming a new species.
Sometimes, this turns out to be easy.
If a dinosaur fossil is found in rocks from an age where no dinosaurs had
previously been found, or
if it has very obvious features that are not present in another dinosaur,
we can be relatively confident that the fossil is a new species.
And we can be confident even if we don't find the whole skeleton.
How to define the species and when to call a fossil a new species or
not is something that paleontologists deal with all the time.
But it's not something that everyone always agrees on.
Sometimes when we're dealing with only fragmentary remains.
It may come down to a judgement call on the part of
the scientists as to whether or not something is really a separate species.
So as long as there's a general agreement amongst the people in
the field a new species name usually will stand.
The naming of a species or taxonomy.
Is an exact science that we try to apply as best we
can to the inexact world of extinct animals.
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