Paleontology: Theropod Dinosaurs and the Origin of Birds is a five-lesson course teaching a comprehensive overview of the origins of birds. This course examines the anatomy, diversity, and evolution of theropod dinosaurs in relation to the origin of birds. Students explore various hypotheses for the origin of flight. Watch a preview of the course here: https://uofa.ualberta.ca/courses/paleontology-theropod-dinosaurs
3.1 Early Coelurosaurs - Part 3
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来自 University of Alberta 的课程
Paleontology: Theropod Dinosaurs and the Origin of Birds
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从本节课中
Coelurosaurs I
In the previous lesson, we explored how the various theropod lineages adapted to their role as apex predators. In this lesson, we will explore a new group of theropods, as much characterized by their speed and agility as their predatory prowess. The coelurosaurs were the most successful and diverse of all the theropods, and included herbivores, the smallest of all dinosaurs, and, of course, the mighty tyrannosaurs.
与讲师见面
Philip John Currie, Ph.DProfessor and Canada Research Chair, Dinosaur Paleobiology
Department of Biological Sciences
Ornithomimids belong to a large group known as the Ornithominosauria.
The most primitive Ornithomimosaurs that we know of appear in the early Cretaceous,
and still had some teeth.
Very recently it's become clear that there are two major groups
of advanced Ornithomimosaurs.
Ornithomimids like dramiciomimus and the deinocheiridae.
Compared to the other ornithomimids deinocheirids were generally larger and
had proportionately shorter legs.
The most famous of the deinocheirids is the group's name sake Deinocheirus.
Since Deinocheirus was first scientifically described in 1969,
it's been clear that it was among the largest of all theropods.
But for more than 40 years, this colossal dinosaur remained shrouded in mystery.
>> People are fascinated with dinosaurs because many dinosaurs in fact are very
bizarre next to the animals that we see today.
I'd like to talk about one of the most strange dinosaurs, an animal called
deinocheirus because it's one that I've been fascinated with in my own history.
Deinocheirus was an animal that was originally discovered in Mongolia in 1965.
And Deinocheirus was based on long arms, and hands with
very large claws, and they give the animal its name, which means terrible hand.
Deinocheirus though is only represented by arms and hands and that's because the rest
of the skeleton had been eroded away before the specimen was found.
Now we've always been very curious as to who exactly Deinocheirus is.
You can make extrapolations from the arms and
you can estimate the size of the animal for example.
But it depends on who it's related to, as to what that size ends up being.
So for example, if you compare to a tyrannosaurus rex the arms of
a deinocheirus which are two meters long are much bigger then the arms of
Tyrannosaurus Rex and if you extrapolate the size of Tyrannosaurus Rex based
on arms of that size and you end up with an incredible figure of more then 30 or
40 meters long which is awfully big for a carnivorous dinosaur.
However if you make the comparison with animals like ostrich mimic dinosaurs,
which have relatively long arms.
The Deinocheirus becomes an animal about the size of a Tyrannosaurus Rex.
Because we didn't have enough information in the hands,
in the arms, to be sure what kind of Theropod Dinosaur this was.
And when we started our project in Mongolia to hunt for
new dinosaurs, Deinocheirus was at the top of the list.
I really wanted to find the original quarry where Deinocheirus came from,
first of all, to see if any bones has been left behind that
might give us a clue as to its relationships.
But of course, the big dream is to find new specimens,
ones that are more complete, that might include parts we've never seen before.
Now Deinocheirus is a very strange dinosaur based on just the arms because
they're so big, but we had no idea how bizarre this dinosaur would turn out to be
when we rediscovered the quarry in 2008.
We had at that point though collected part of another skeleton,
and this skeleton did not include the arms.
And we realized it was a very bizarre animal.
We were trying to figure out exactly who it was when we found the second specimen.
This second specimen really blew us away because that specimen included an arm.
And there is no question that that arm was the same as the arm of Deinocheirus.
Now, we have to paint a picture of this dinosaur, because,
it's not what we expected to find.
We saw enough information on the skeleton to show that
one of the early suppositions was in fact correct.
This is a dinosaur closely related to the ostrich mimic dinosaurs,
most of which are about my height.
But it's an animal that had become very, very large, and in becoming so
large of course it had the long arms and the very huge terrible hands,
but other parts of the skeleton had also become very disproportionate.
So the skull for example turned out to be not a little skull with a sharp beak,
looking a little bit like an ostrich skull.
It turned out the be a skull that was more than a meter long.
And that skull ended in a broad duck like bill at the front.
So if you looked at it superficially we weren't
looking at a theropod dinosaur at all, it looked like a duck-billed dinosaur.
We saw the same kind of thing in the feet because this animal was as
big as a Tyrannosaurus rex.
It was bearing a lot of weight.
It probably lived in a fairly wet area.
And the claws on the end of the feet weren't sharp anymore
like they are in Ornithomimids.
They in fact had become very broad and
again looked like the hoof like claws of the duck bill dinosaurs.
A really strange feature was that although the main body of the vertebra
looked very much like a vertebra of an an ostrich mimic dinosaur.
The spines had become incredibly tall, and in fact this is an animal that had
a sail like back because of the fact that the spines were more than a meter long.
All in all, this very, very strange dinosaur
is definitely related to the ostrich mimic dinosaurs.
But it had gone through a lot of changes,
probably because it was living in a different kind of environment, and
by its large size it maybe escaped predation from the Tyrannosaurs.
What did it eat?
Exactly what it did?
Well, there's still mysteries surrounding there but we have some clues.
So for example, from the second specimen we found also the stomach contents and
the stomach concluded stones.
Like many modern birds that swallow stones to help them grind up plant material,
it appears that this dinosaur was a plant eater at least part of the time.
But mixed in with those stones were also fish vertebrae and scales.
And that suggests that this dinosaur may have been living in a very wet environment
by the shore and eating both plants and fish.
There are a lot of mysteries still surrounding this dinosaur, but
it is certainly one of the most strange dinosaurs we've discovered to date.
>> Here's a selection of Silourisaurs,
place them in their proper spot on their family tree.
Working our way up the Silourisaur family tree, we've now reached a critical point.
From here on all the theropods we'll meet belong to a sub group
known as the Maniraptora.
Among other anatomical traits that all maniraptora share
is a specialized form of wrist bone called a semi-lunate carpal.
A semi-lunate carpal is a wrist bone that has a crescent moon shape.
A semi-lunate carpal granted maniraptorans greater wrist flexibility
In certain directions with them.
Maniraptoran hands could twist strongly towards what on us is the pinky side.
And this is a key trait to take note of,
because that wrist flexibility is important to the wing control of birds.
It also allows birds to fold their wings tightly against their bodies,
When resting.
What advantage did the extra wrist flexibility of the semi-lunate carpal
give maniraptorans?
More than one answer might be correct, so
select all the answers that you think apply.
Is it A, better grip when climbing trees.
B, greater strength when digging.
C improved pray capture.
And or D increased maximum weight support.
The correct answers are A and C.
Semi-lunate carpals gave maniraporans an advantage in capturing prey and
climbing trees.
Among the Maniraptora is a bizarre group theropods called the Therizinosauria.
It has been said that Therizinosaurs looked like dinosaurs built
by an indecisive committee.
Late advanced forms include giants that must have weighed over five tons.
Yet, their heads were small.
Their mouths contained both a beak in the front and teeth in the back.
These relatively small teeth had the leaf shaped form of a herbivore.
But Therizinosaurus had long arms that each ended in
three enormous and terrifying site like claws.
Their necks were long and their tails were short.
Their bodies were rotund with a pelvis adjusted to support large guts.
Their legs were short by Silourisaurs standards and all four of their toes
contacted the ground, this included the normally raised hallux.
Although the sum of a Therizinosaur's parts is a strange sight,
these adaptations were far from mismatched.
Therizinosaurs were probably herbivorous browsers that
used their elongated necks to feed high on growing vegetation.
The small heads were easier to support on such long necks and
the beak at the front of the mouth was used to crop off the vegetation
while the teeth in the rear diced it up for swallowing.
Because plant material is far more difficult to digest,
than meat Therizinosaurs needed longer and larger digestive tracts.
And that was why they had the modified pelvis and the rotund body.
Such a proportionately heavy body was easier to support and
balance on short legs.
Especially with the aid of the extra weight-bearing toe.
And the huge claws, well heavy and short-legged,
Therizinosaurus would have been easy meals for many predatory dinosaurs.
Including their contemporary fellow Coelurosaurs the Tyrannosaurus and
their claws were probably vital weapons used in self-defense.
Let's take a moment to recap.
Which of the following bird traits have we encountered in theropods up to this point?
More than one answer might be correct.
So select all the answers that you think apply.
Is it, A, complex feathers.
B, feet with three forward pointing toes.
C, keeled sternum.
And or D, semi lunate carpals.
A, B, and D are correct.
We have yet to meet a theropod with a keeled sternum in this course.
However, that's about to change.
We are now very close to the branch from non avian theropods to birds.
The next theropod groups are all so birdlike
that paleontologists have struggled to distinguish them from true birds.
The Alvarezsauridae is a prime example.
Alvarezsauridaes are small theropods covered in simple feathers and
have a number of anatomical traits that seemed at first
to suggest that they were an extinct group of flightless birds.
Their skulls have narrow snouts and their jaws have only miniscule teeth.
Those features appear to indicate
that they were well on their way to evolving beaks.
Even more bird-like are their chests.
Their sternums are keeled and enlarged.
In birds, such adaptations are for
the attachment of large breast muscles that are critical for flight.
Their shoulders and arms were also heavily muscled.
Again, consistent with the demands of flapping flight.
But it turns out that Alvarezsaurids had evolved these traits for
an entirely different reason.
Which of the following animals has a narrow snout,
reduced teeth, and strong chest and arm muscles?
More than one answer could be correct, so
check all the answers that you think apply.
Is it A, a nine banded armadillo.
B, a Grey Kangaroo.
C, a bottle nosed dolphin.
And or D, a Three toed Sloth.
The correct answer is A, a nine-banded armadillo.
Grey kangaroos are grazers, and have robust teeth, for
chewing tough vegetation.
The bottle-nosed dolphin is a swimmer, and a fish-eater.
Grabbing fish like a dolphin requires a mouthful of tall, spearing teeth.
The three toed sloth has extremely strong arms for climbing, but
it is a browser, and has a short snout, and large teeth.
Armadillos are insectivores,
that feed primarily on beetles, ants, and earthworms.
To reach these invertebrates, they need strong chest and arm muscles for digging.
They also have tubular snouts for proving into holes and because
such tiny invertebrates don't require much chewing, they've got reduced teeth.
It is thought that Alvarezsauridaes were also digging insectivores and
they have traits that are more in lying with this hypothesis.
Then with the possibility that they were flightless birds.
Like armadillos, the bones in their forelimbs are short and
stocky, and their claws are broad and shovel shaped.
However, while armadillos have multiple large hand claws, and
Alvarezsaurids all their fingers and claws were reduced, except for the thumb.
However this one digit and its claw were extra large and powerful.
Unlike armadillos, Alvarezsauridaes lacked armored shells, but
since their front limbs were modified for
digging they still have the characteristically long hind legs, so
running was their best defense.
