There are over 100 million horses, donkeys and mules in the world today and owners of these animals can be found on almost every continent and in almost every society. The Horse Course will cover many unique aspects of equine ownership and touch upon the science behind many of today’s management practices.
Evolution of Horses and Donkeys
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The Horse Course: Introduction to Basic Care and Management
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Introduction to The Horse Course
Welcome to Week 1 of The Horse Course! To start off the course, we will begin discussing what exactly an “equid” is. We will cover the many equine species inhabiting our globe. Next, we’ll jump into the history of horses and donkeys, touching upon how they have made such an impact on our own societal development. The second half of week 1 will cover the many breeds of horses and donkeys. We will finish up with a lecture on the equine hybrids.
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Chris J. Mortensen, Ph.D.Professor
Animal Sciences
All right, welcome back.
In this next talk, we're going to talk about the
evolution of horses, and donkeys, and zebras, and the other equids.
So, if we look at evolution, you know, here's the definition, you know,
you're looking at the change in genetics over, over long periods of time.
This is, this is something that happens, you know, naturally, relatively
slowly and as we'll see in, in this lecture over 55
million years is how we can trace, how we can go
back and trace back to the earliest relatives of the horse.
Now we could speed this up a little bit with,
you know, natural, or, excuse me, artificial selection with breeding.
So we do that with modern day breeding.
We can actually speed evolution up.
You know, we can breed for, for better genetics and do this quicker.
Now obviously, you know, the theory of
evolution or natural selection dates back to Darwin.
And the reason I bring this up is because the
horse or the equid is really the model species for evolution.
This is a species that we have more bones that show changes over
time than almost any other species that we've found on Earth to date.
So this is why you now, we always go to the
horse as the model, as we'll see in, in this lecture.
And you know, again we can trace this back, these
changes over time, over 55 million years where Eohippus the very
first horse, you know, looks like a small dog to
where we get actually our tall, even our giraffe breeds today.
Our really tall horses.
And, the two, the two parts of the skeleton
that really we can, we can point to this, is
the dramatic changes in toes, and the lower leg,
changes in the lower leg, and then also their teeth.
You know, as their diets changed over time, their teeth changed with it.
Now here's one of the earlier papers.
There's a whole host of papers that were, you know, the early twentieth
century when you know, Darwin in the
nineteenth century proposed his Theory of Evolution.
Scientists were rushing to find support of evidence.
And this is where they, they really started pointing to the
horse, you know, and can see these, these changes in the bones.
So here is a paper, here is a nice
picture taken by this paper published in 1926 by Mathew.
And you can see that, that the Eocene, you know, as it goes up
to today's modern horse, and it's showing you the skull and the lower legs.
And really, the thing that we're going to notice as this
horse goes from four toes to one toe, to the hoof today.
So looking at that, you know, the eohippus, or Hyracotherium, right
there as you can see, you know, was a four-toed animal.
And then over time, it went to three toes, and then
those toes started to migrate up the leg to one toe.
And you can see that in the bottom picture, so the top
picture is actually a modern horse, or equid, you know, zebra, donkey.
That's what their lower legs look like.
And you'll see the, the splint bones remnant
of the toes that their earlier relatives had.
So we can, you know, see the evidence, direct evidence, in our modern day horses.
Now here's a good graph.
You know?
Obviously, if you go online and Google a lot of this, or search
for a lot of this, you can find different images of horse evolution.
But I always like this one, because it shows the lower leg, and kind of what
the animal would look like over time, or
an artist's guess over time in the phylogenetic tree.
You know, the changes going from, you know, earlier to today.
So we're just going to kind of take some snapshots in here.
You know, we don't have time to go through obviously every, every layer of this.
So we'll start at the beginning and we've already talked about Eohippus
and the other name that it's known as is the Dawn Horse.
And, again, here's what it may look like with
the striped patterns, they're trying to take a guess.
You know, this was more of a browser type animal,
probably ate lots of leaves and small plants and shrubs.
So, they were made for that.
They were made for little forest regions, and, and that's
why their toes and they could climb and do other things.
So, they were relatively short, you know, 20 inches at the shoulder or 50
centimeters and they had four toes on the front, three toes on the back.
And they only had three grinding molars, n'kay.
So like they weren't heavy grazers like our horses today.
So again that's where they think they were
browsers and ate more leaves and small plants.
Now, if we jump, you know, 15 to 20
million years, we can jump and see the mesohippus.
And so, this was roughly, you know, they evolved about 40 million years ago.
And what's unique about this jump is they went from four to three toes.
So, this is where we start seeing evidence of
that, that fourth digit disappearing and going up the leg
on those earlier equids are, well they're really not equids
at this point, the earlier species from eohippus to mesohippus.
And you can see there are not that
much taller, so they're getting a little bit taller,
but what's also interesting about this is they
went from three grinding teeth to six grinding teeth.
So, obviously some, there are some dietary changes driving this evolution, where,
you know, they kind evolve more of a, as they, they evolved
a more grass based diet, their teeth changed with them so they
can handle that eating constant grass, grinding it down and eating it.
So, so from that browse diet to more of a grazing diet.
Now we're going to jump ahead, you know, pretty far again and
this is where we get to dinohippus, which is where we
start seeing evidence of a single-toed horse, you know, they go
on from those three toes to that one toe or one hoof.
So that's where we start to see first evidence.
And this is about 12 million years ago.
So they kind of look like equus which is
the forerunner of today's modern equids and you can
see from this, this image here you can look at the the, the lower leg on this.
And you can still see, you know, just that hoof.
And then those two two toes are just, kind of, remnants.
So maybe a little supportive.
Maybe not.
But really they're, they're getting used to, one toe.
And then, gain, those teeth.
You know?
Here you can see those teeth are starting
to be grinders where they're going to start grinding.
And, you know?
Again as, as their diets changed.
You know?
They, their, their lower legs start to evolve so
that they could get faster and could outrun predators.
And that's what driving this development in this species.
Now we're going to jump ahead to Equus.
So, Equus is actually the, the forerunner for today's donkeys, zebras, and horses.
So, they all trace back to Equus, and so that's where we
get that, that family name and they evolved for about 5 million
years ago and they died out about a million years ago and
these were animals that were found all over the world except Australia.
Okay so the, what's really surprise about this
slide is horses or equus evolved in North America.
So that's where we find a lot, all the bones, all the, all the records are
actually in, in North America and mostly in
the United States, some in Canada, some in Mexico.
So you can see about 55, 58 million years ago that's where Eohippus was evolving and
then 20 million years ago as, as they evolved they spread out North America.
And then roughly they've, they think about 10 million years ago, and
onward, Equus started to migrate, you know, throughout the rest of the world.
So it went over this, this land bridge that's been recognized
between, you know, Siberia and United States of Alaska that's, you
know, not only did early man come over a similar land
bridge but horses actually migrated out, or equus migrated out from there.
And then they spread out throughout Asia
and Europe and then evolved, obviously equus
[UNKNOWN] and equus [UNKNOWN] and then the
zebras also evolved from those early horses.
What is also interesting, about 10,000 years ago, the horses completely
disappeared from North America and, and South America and, and Central America.
You couldn't, you couldn't find them anymore.
And this kind of, you know, coincides with,
with dying out of some other mega [UNKNOWN]
such as, you know, the mammoth and the woolly rhino and some of those others.
So it could have been a change in climate,
you know, with some over hunting, their food could of
been dwindling so there, scientists aren't quite clear on,
on what drove them to extinction, out of the Americas.
But they didn't come back until the fifteenth or
sixteenth century, the 1500s when the Spanish came, and
the conquistadors were you know, venturing through Central, South
and North America, and some horses got away from them.
And that's where they establish the wild populations that we see today.
Now the final slide of this presentation is
that the, the two relatives from horses and this
surprises a lot of people it's, it's pretty
neat and that is the rhinoceros and the tapir.
Those are the horses two closest relatives that we can actually trace
them back to that early ancestor there you can see on the slide.
So, so there are all pretty similar er, with a rhino and a tapir and a horse.
It's, it's, it's pretty, pretty funny and pretty neat.
So one thing you can do, you know, in the United States, there's still some
debate about evolution when, you know, there's a
lot of evidence pointing to evolution being fact.
So if, you know, if you want, you can go in the discussion
board and talk about this further and how horses support the idea of evolution.
I mean, the evidence is there in the soil.
We can see the changes in the bones.
You know I think it would be an interesting
discussion to read and then in the next lecture
we're going to talk about, you know, how horses have
played a role in, in our own evolution and development.
[INAUDIBLE]
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