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.
The Age of Dinosaurs
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From the course by University of Alberta
Dino 101: Dinosaur Paleobiology
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From the lesson
Stratigraphy and Geologic Time
This method provides basic stratigraphic concepts and the scale of earth history. Students will understand the evolution of dinosaurs through time, including which groups evolved when and where.
Meet the Instructors
Philip John Currie, PhDProfessor and Canada Research Chair, Dinosaur Paleobiology
Department of Biological Sciences
The Mesozoic Era began with the Triassic Period over 250 million years ago.
There weren't many dinosaurs around at all during the early part of the Triassic.
However by the late Triassic many small bipedal dinosaurs were spreading out
all over the planet.
These species represented the earliest members of the Sertian Theropods and
sauropods as well as primitive Ornithischian dinosaurs.
Early dinosaurs are often poorly preserved in the fossil record.
Like at the Danek Bonebed they are typically preserved in a mud stone,
which tends to squish and distort the skeletons.
Very similar to this Herrerasaurus skull I have here.
Now just to orient you I'm going to point out a couple features.
Here's the nose, the orbit,
the upper jaw and the lower jaw, but I have a better reconstruction to show you.
Here's the reconstructed skull of Herrerasaurus, and
you can see that it is a diapsid based on the skull openings.
Now the relationship of early dinosaurs is often confusing because we don't know
which dinosaur groups they're more closely related to.
The current theory is that Herrerasaurus is an early theropod.
Another skull I have here of Plateosaurus is something called a Prosauropod,
or just a very early long necked dinosaur, and finally the relationship
of another early dinosaurs called eoraptor is currently unresolved.
During the Triassic as dinosaurs were evolving to fill large bodied ecological
niches on land the other amniote groups were evolving to fill the sea and the air.
Here's a skeleton of an animal called an Ichthyosaur.
The name Ichthyosaur literally means fish lizard, but Ichthyosaurs are not lizards,
and they certainly aren't fish, and they aren't dinosaurs either.
Even so the name Ichthyosaur still seems fitting, because they are a group of
reptiles that took on a fish like life style and evolved a very fishy body form.
The ancestors of Ichthyosaurs were fully terrestrial reptiles, but
just like the ancestors of modern whales, dolphins, seals, and
sea turtles, the group found success by making an evolutionary return to water.
To adapt to an aquatic lifestyle,
Ichthyosaurs evolved paddle like front and hind limbs as well as a fin tail.
They also had a sharp leg dorsal fin.
The long snouts of most Ichthyosaurs resemble those of dolphins and
they are filled with conical teeth.
Good equipment for pi severus diet.
Despite their many fish like adaptations Ichthyosaurs never evolved
gills and needed to come to the surface in order to fill their lungs with air.
Late in the Triassic period Ichthyosaurs were joined in the seas
by another group of reptiles that also evolved an aquatic lifestyle.
The Plesiosaurs.
This one you can see here.
You're looking at its underbelly.
Now most Plesiosaurs had large chests and
torsos, broad paddle shaped limbs, and relatively short tails.
In front of their shoulders Plesiosaurs varied tremendously.
Some had short necks and huge jaws, and others like the famous
Elasmosaurus had elongated serpentine necks with small heads.
Like the seaways of the dinosaurs age the sky was a busy place.
Insects had evolved flight at least as far back as the Carboniferous Period.
During the Triassic Period a group of animals branched off
from the archosaur family tree at roughly the same time that dinosaurs did.
We call this group the Pterosaurs.
The Pterosaurs were the first vertebrates able to fly.
Unlike birds, which have wings made of feathers, and
bats that have wings made from skin stretch between fingers Pterosaurs
have membranous wings that are supported by a single extremely elongate finger.
Early Pterosaurs belonged to a group called Rhamphorhynchoids,
which were common in the late Triassic and throughout the upcoming Jurassic period.
Rhamphorhynchoids are small Pterosaurs with the largest forms
approaching the size of a modern raven or hawk.
Long tails characterized the Rhamphorhynchoids, and
some Rhamphorhynchoid tails terminated in flaps of skin called tail veins.
The function of these tail veins is unclear, but
it is hypothesized that they acted as in flight rudders or
stabilizers, and might have been used in courtship displays.
The Jurassic Period began about 200 million years ago.
Giant Sauropods were the dominant herbivores on the planet, and they were
represented by several diverse lineages including the long Diplodocids and
the tall Brachiosaurs.
Stegosaurus like this specimen here and small anthropoids were also present.
Characteristic theropod dinosaurs of this time include predators like Allosaurus,
and the nose horn Ceratosaurus.
The first bird Archaeopteryx evolved in the late Jurassic period.
So what was happening in the sky during the Jurassic period?
First of all this was when the bird line of Theropods evolved.
It was also at this time that the Rhamphorhynchoid Pterosaurs
from the late Triassic gave rise to a new Pterosaur group.
The Pterodactyloids.
Pterodactyloids differed from Rhamphorhynchoids
in the morphology of their tails, which were short.
Also, the carpals in their wrists were elongate and
made a greater contribution to the length of the wing.
There were many species of small pterodactyloids.
Some smaller that a robin, but some species had wingspans of over ten
meters making them the largest animals ever to fly.
This is the skull and partial skeleton of the Pterodactyloid Pterosaur, Pteranodon.
It shows off the most striking difference between Rhamphorhynchoids and
many Pterodactyloids.
Bony head crests.
Although several species of Rhamphorhynchoids did have small crests
made of soft tissues, large bony head crests were common among Pterodactyloids.
After the Jurassic period came the last period of the Mesozoic Era.
The Cretaceous, which began about 145 million years ago.
In the early Cretaceous Stegosaurs became more rare
as their ecological niche was replaced by the armored Ankylosaurs.
The giant Sauropods began their decline and
were not seen across the same ranges that they had in Jurassic times.
The thumb spiked Iguanadons were more common.
Spinosaur Theropods became more abundant as did the giant
Carcharodontosaurus Theropods that rivaled the later Tyrannosaurs in size.
Primitive birds with better flying abilities than Archaeopteryx became more
abundant.
These included species like Confuciusornis and Sapeornis.
By the late Cretaceous, the Iguanodons had been
replaced by the duck billed Hadrosaurids like this Prosaurolophus here.
Ceratopsians and Pachycephalosaurus appear for the first time, and
some Ankylosaurus have evolved tail clubs.
The Sahelanthorus Theropods, including the Ovoraptors, Ornitomimids, Therizinosaur,
Allosaurids, and Tyranosaurids became more abundant in the Northern Hemisphere.
While in the Southern Hemisphere the Abelisaurus Theropods were
the dominant predators.
The dominant herbivores in the Southern Hemisphere are a single lineage
of the once diverse Sauropods.
The round bodied Titanosaurs.
Birds continued to evolve into a variety of lineages that are now extinct,
including the Enantiornithes, or opposite birds, and
Hesperornis, which were loon like diving birds with teeth.
Some species of birds such as shore birds that are still alive today
also evolved during the late Cretaceous.
It was during the Cretaceous period that a third major reptilian group began
patrolling Mesozoic waters joining the Ichthyosaurs and Plesiosaurs.
Mosasaurs like this Clidastes
were reptilian relatives of modern monitor lizards and snakes.
Like Ichthyosaurus and Plesiosaurus, Mosasaurus had tail fins and limbs
modified into paddles, but the bodies and tails of Mosasaurus were more elongate.
Most Ichthyosaurus, Plesiosaurus, and
Mosasaurus are the right size to have preyed on small and
medium size fish, but some like the giant Pliosaur Plesiosaurs
were true sea monsters with huge jaws and bodies over 18 meters long.
These aquatic giants seem adapted for deep sea, big game hunting,
and they likely ate large fish and other marine reptiles.
Let's take a minute to review a few things we know about the distant aquatic and
avian cousins of the dinosaurs.
Pterosaurs and
the various groups of Mesozoic marine reptiles are often mistaken for dinosaurs.
Ichthyosaurs, Plesiosaurs, and
Mosasaurs are all more closely related to modern reptiles like lizards and snakes.
Terrasaurus were close relatives of dinosaurs, but fall outside the group.
Here is one characteristic that distinguishes them.
Looking at this lower jaw of a Tyrannosaurus
you can see a large opening called the mandibular fenestra.
Now, look at the jar of the Pterosaur Anhanguera, and
you can see that as in all Pterosaurs the mandibular fenestra has been lost.
Here are a number of dinosaurs.
Select the dinosaur that would have been alive at the end of the Cretaceous Period.
Multiple answers may be correct, so check all that apply.
A, Stegosaurus.
B, Tyrannosaurus.
C, Triceratops.
D, Pachycephalosuarus, or E, Giraffatitan.
Stegosaurus, Giraffatitan, and
their relatives were long gone by the end of Cretaceous.
Tyrannosaurus, Triceratops, and Pachycephalosaurus,
however were all alive at the end of the Mesozoic Era, so
answers B, C, and, D are correct.
As we end this module on geologic time
here's another chance to interact with the geologic time scale.
We hope that it's given you an opportunity to appreciate not only the age of
the Earth, but also the place of dinosaurs within that long history.
From when they first appeared until the time they went extinct non-avian
dinosaurs were around for almost 180 million years.
Any one particular species of dinosaur only lasted a few million years
before it disappears from the fossil record.
Each of these species would have either gone extinct or
evolved into other species.
Determining of two species of dinosaurs lived at the exact same time
is tricky business, but as new fossils are discovered
our understanding of dinosaurs species, and their place within the great
expanse of time know as the Mesozoic Era becomes more complete.
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