0:36
And these dinosaurs, in fact, come from 228 million year old rocks.
Those rocks are predated, of course, by earlier times when
there must have been dinosaurs, the ones who gave rise to these ones.
But we've never yet found earlier dinosaurs.
They're there, we just have to find them.
0:57
The two dinosaurs that I'm looking at basically are carnivorous dinosaurs.
You can look at the teeth for example and
see that the teeth are flattened from side to side on the front and the back.
These are the same kind of teeth that we see in more progressive animals like
Tyrannosaurus Rex, for example.
However, the relationships of these dinosaurs have been debated.
And that's because they represent the time when
all dinosaurs were diversifying into the groups that they eventually became.
Where they are very obviously different from each other.
But back in the Triassic.
It's not that obvious.
And we can look at Eoraptor, for example, and
although it looks like a good carnivorous dinosaur, in fact,
there are characters in the teeth at the front of the jaws that suggest this
animal may in fact be much more closely related to the earliest.
And consequently have nothing to do with the more progressive
Theropod dinosaurs like Herresaurus.
Neither of these dinosaurs is very large, and
there were no large dinosaurs at that time, but there are characters
in the skull of Herresaurus in particular that it is a theropod dinosaur.
So, for example, we can look at the region between the eye.
And the nasal area, and we can see that there is this large sinus.
Well, in fact, there are several sinuses like this in the face,
which are air-filled and help define all theropod dinosaurs.
We can also look at the lower jaw, and
we can see that there's a very large opening in the middle of the lower jaw.
Which has a joint above it and below it.
And this joint, called the intramandibular joint, is found in basically
all theropods that evolved after Herrerasaurus.
That joint probably represents a safety valve.
So that when the animal was feeding if its teeth got stuck in its prey
those teeth wouldn't break off because there were some flexibility in the jaw.
However, that joint would also allow these animals to have a slightly larger gape and
to allow them to perhaps eat and swallow slightly larger prey.
When we look at the hands of Herrerasaurus,
we can see how primitive this dinosaur is though.
This dinosaur has not two fingers that we find in Tyrannosaurus rex,
it's got remnants of all five fingers,
which is the primitive number of fingers in theropod dinosaurs.
The thing about Herrerasaurus though,
it's lost all of the phalanges on the fifth finger.
All that remains is the metacarpal bone which is in the flat of the hand.
3:50
The fourth finger is represented by the metacarpal bone, of course, but
it also has one single phalanx left.
So it's in the process of losing those two fingers, but
it still has those fingers represented.
It still has three functional fingers and,
as you would expect in a carnivorous dinosaur.
Those fingers end in sharp claws and the hand is capable of grasping its prey.
4:43
When we think of carnivorous dinosaurs, we naturally tend to envision large predators
ruling over the prehistoric world, and that part of the story is coming.
But at their beginning,
carnivorous dinosaurs were more modest components of the ecosystems.
The early theropod dinosaurs like Eoraptor and Herrerasaurus and
their herbivorous cousins are estimated to have accounted for only
about 10% of a large bodied terrestrial species that were alive at the time.
And, of course, these dinosaurs weren't really all that large.
5:50
Alongside such crocodile line competitors, the neotheropda evolved.
Neotheropods have skulls with enlarged lacrimals.
Lacrimals are bones positioned just in front of the eyes that extended
onto the upper skull surface.
Such lacrimals may have strengthen the skull, but
the more dorsal position is also important.
In many later therapods,
the lacrimals would evolve into a range of pressed and small horns.
Neotherapods also have intramandibular joint in each side of the lower jaw.
And the intramandibular joint created a flexible region in the lower jaw.
6:35
What do you think could have been one possible advantage of a flexible joint
on the sides of neotheropod jaws?
Is it, A, greater maximum bite force.
B, the ability to take expanded bites.
C, improved jaw rigidity, or D, a faster bite.
B is the correct answer.
The intramandibular joint allowed neotheropods to expand their jaws and
take bigger bites.
However, it was an adaptation with a number of other potential benefits.
7:16
The intramandibular joint allowed Neotheropods to bite off and
swallow larger chunks of meat.
It also gave a little flex to their bites and this allowed them to grip and hold
onto struggling prey without their lower jaws being easily torqued, or broken.
And finally, it may have provided them with the ability
to wiggle their lower jaws in feeding and attacking.
This would've allowed their lower jaws with their rows of sharp serrated teeth
to function like electric carving knives.
This increase their injuring and butchering ability.
9:57
At the end of the Triassic period, there was a mass extinction event.
Currently, we don't know what caused it.
Many of the other large carnivores and herbivores died off, but
all the major lineages of dinosaurs survived this extinction event.
Of course, mass extinctions are disastrous for many species.
But for others, there can be a time of opportunity.
Philip John Currie, Ph.DProfessor and Canada Research Chair, Dinosaur Paleobiology
