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
5.2 Survival of the Neornithes - Part 2
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From the course by University of Alberta
Paleontology: Theropod Dinosaurs and the Origin of Birds
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From the lesson
The Avian World
66 million years ago, an asteroid the larger than Mt. Everest collided with the earth and brought about the extinction of the dinosaurs…except birds! Now that you’re familiar with some of their larger Mesozoic ancestors and their bird-like features, it’s time to meet the avian lineage proper. With the evolution of flight, birds could exploit habitats and resources that were literally unreachable by other animals. The evolution of birds has been one of diversification. Flightlessness has evolved numerous times, as have specializations for insectivory, swimming, and predation. Although theropods may no longer dominate the land, they still rule the skies.
Meet the Instructors
Philip John Currie, Ph.DProfessor and Canada Research Chair, Dinosaur Paleobiology
Department of Biological Sciences
Sandpipers are shore birds that feed on invertebrates
by probing through beach sand with hyper-elongated beaks.
Despite this seemingly specialized niche, sandpipers
are highly diverse with over 350 species worldwide.
In contrast, gulls are an extremely successful group of generalists,
evolved to feed primarily on fish and beach carrion.
Gulls developed a strong stomach that can handle food items
that other birds would consider past their prime, or downright grotesque.
In the current age of mounting human garbage,
gulls have prospered with their iron stomachs, and
can frequently be found thriving far from their original coastal habitats.
Puffins are one of my favorite bird groups because of their all-terrain versatility.
They're good flyers and adept swimmers.
They can also walk and jump across steep, rocky terrain and
can even burrow to create deep, underground nests, puffins feed on fish.
While many other seabirds are limited to snatching,
spearing or diving for fish that are at or near the water's surface,
puffins are able to spend extended periods of time under water.
Puffins swim using their wings in a motion similar to flight.
Helping them in their underwater pursuits,
puffins have evolved a form of camouflage known as 'counter-shading'.
Most sea birds like the typical gull, are white, and
this light colouration helps to reflect sunlight and keeps tropical birds cool.
But it also helps to conceal the birds from fish in all climates.
Living in deep water, fish are accustomed to seeing darkness below and light above.
A dark coloured bird soaring overhead,
would be a dead giveaway for a fish to dive for safety.
But a light coloured bird is harder to detect when seen from below.
And the same is true for predators that swim within the water.
If they're dark-coloured,
they will be easily spotted by fish swimming below them.
However, an all light-coloured predator swimming through the sea
will be easily spotted by its prey swimming above it.
For this reason, many aquatic creatures, like orca whales and great white sharks,
have light colored under bellies and dark coloured backs.
From either above or below, prey does not easily see them.
Puffins have evolved this counter-shading and
have stark white bellies and black backs.
Although puffins both fly and
swim, the demands of these two activities can be conflicting.
Which of the following flight adaptations do you think
is a detriment to a puffin's ability to swim through the water?
Is it A, the keeled sternum, B,
the pygostyle, C, the sleek contour feathers,
or D, the lightweight skeleton?
Puffins swim using powerful strokes of their wings.
So the keeled sternum and
its associated musculature are still useful while swimming.
Similarly, while swimming the pygostyle, and its supported fan of feathers
serves, along with a puffin's large webbed feet, as a rear rudder and stabilizer.
A Puffin's contour feathers serve to reduce wind resistance when flying and
also to reduce water resistance when swimming.
So all these flight adaptations are also assets while swimming.
The lightweight skeleton is a detriment.
So, D is the correct answer.
The lightweight skeletons of puffins and
other birds do present a significant problem to an aquatic life.
Being so light, the skeleton makes it easy for
the birds to float on top of the water,
but it forces them to fight their own buoyancy
when they try to dive below the surface and swim underwater.
One group of birds solved this problem by evolving
decreased skeletal pneumaticity and more thickly walled bones.
In so doing, they abandoned flight altogether.
They were also among the oldest living lineage of birds: the penguins.
Penguins are thought to have originated in the Late Cretaceous.
Although, the oldest good fossil skeletons, from quarries in New Zealand,
date from just after the mass extinction.
Early penguins still had the ability to fly, but shortly lost it in the Paleogene.
During much of the early part of the Cenozoic, penguins took advantage
of their recent disregard for aeronautic weight restrictions and
some grew to great size, reaching over a meter and 1/2 in height,
in the largest species. These giant penguins became extinct
shortly after the evolution of the toothed whales, one of their primary predators.
Modern penguins are the most adept swimmers of all birds.
And they've evolved a number of aquatic adaptations
besides increased bone density.
Penguins have lost their primary, and secondary feathers.
The alula is lost, and the wing bones are flattened
forming an overall wing shape as more like a fleshy flipper.
All the joints in the arm are rigid and
it's only mobility comes from the shoulder.
Shoulder strength is still vital, so
the sternum has remained well developed and with a deep keel.
Their legs are reduced in length and to let their feet serve well as rudders
and not disrupt their torpedo shape, are angled further back on their bodies.
This is the cause for their upright stance.
Penguins belong to a larger group of water birds called the Aquaornithes.
This clade also includes loons, storks, and pelicans.
Pelicans are famous for their gular pouches,
which are the sacks of skin on the underside of their lower jaws.
Do you know what the function of these pouches is?
Is it for A, storing food, B, scooping fish
underwater C, holding shark-repellant,
or D, transporting their young.
Although it's commonly said that pelicans store food in their pouches,
the pouches actually function to help capture fish.
The correct answer is B.
Pelicans are large soaring birds with distinctive bills
equipped with a hook tip for snagging large fish.
And an expandable throat pouch on the underside of the lower jaw,
that's used like a net when plunge feeding for smaller fish.
Pelicans are good swimmers and have an unusual webbing pattern in their feet.
As in many swimming birds, webbing connects the second, third, and
fourth digits.
But in pelicans, the hallux is rotated to the side.
The webbing also extends between it and digit two.
This foot form is termed totipalmate.
Modern loons are long bodied divers that spend the majority of
their lives in the water coming ashore only to breathe.
A loon's beak is long and spear shaped and
its tongue has spines used to hold onto struggling fish.
Unlike their penguin relatives, loons are strictly foot
propelled swimmers and keep their wings tucked next to their bodies when diving.
Have a close look at a loons foot, what is this foot type?
A, palmate.
B, totipalmate.
C, lobate.
Or D, raptorial.
The correct answer is A, palmate.
Loons have web feet with the webbing extending between only digits two,
three and four.
Totipalmate is the foot type we just observed in pelicans
in which all four digits are webbed.
Lobate, you will recall, is the foot type that we saw in the grebe
with each toe bearing separate, large, flat lobes.
Raptorial is a foot type that we've not yet encountered,
but that brings us to our next group.
The Accipitriformes includes modern hawks, eagles, and some forms of vultures.
These birds are characterized by strongly hooked beaks, used to tear flesh,
and by raptorial feet which have large, curved talons.
Most hawks and eagles kill using their talons after a rapid dive from the air.
They employ their beaks in the butchering of carcasses.
To locate scavengable food, vultures rely on their excellent vision.
They also rely on the power of another sense.
What other sense do you think vultures use to help find carrion?
Is it A, hearing.
B, smell.
C, echolocation.
Or D, balance.
If you're looking for dead meat, smell is a good guide.
The answer is B.
Vultures have one of the most acute senses of smell in the entire animal kingdom.
As we discussed earlier, most birds rely heavily on their sense of sight.
So nocturnal species are extremely rare.
Owls which comprise the clade Strigiformes break this general rule.
Owls are master night-assassins.
They have extraordinary hearing and with one ear positioned
lower than the other, they can hear with depth perception and
can pinpoint the three dimensional position of prey from just a rustle.
However, they're still largely vision based hunters and navigators.
This is the skull of an owl, you can see that the orbits dominate the skull.
Owls need such huge eyes in order to take in enough light to see at night.
Like the Accipitriformes, Strigiformes have hooked beaks and raptorial feet.
But owls have made a special foot modification.
Most of the other birds we have met, have anisodactyl feet.
That is their hallux points backward,
while digits two, three, and four point forwards.
Owls have zygodactyl feet, which means that digits two and
three point forwards, but both digits one and four point backwards,
and this foot arrangement makes owls more awkward on the ground but
gives their feet greater gripping strength.
For owls, this makes their talon-feet truly dangerous,
almost inescapable weapons.
However, it also translates to greater strength when it comes to perching.
Which is why the zygodactyl feet also show up
in the next group we're going to discuss.
Woodpeckers use their chisel-like beaks to tap into hollow chambers in tree trunks.
Do you know what woodpeckers are typically looking to find?
Is it A, boring insects.
B, water reserves.
C, budding fruit.
Or D, edible sawdust.
Woodpeckers are typically on the hunt for grubs and
other boring insects, so A is correct.
Many woodpeckers also chisel into trees to expose tasty sap.
The Piciformes is a group of birds that includes modern woodpeckers and
a few oddballs like toucans and puff-birds.
Woodpeckers and other Piciformes use their zygodactyl feet
to cling to trees in positions that would challenge other birds.
For woodpeckers, this means being able to cling vertically to the trunks of
large trees while using their chisel- like beaks to excavate boring insects.
Many Piciformes also have another adaptation to help with this perching.
Their tail feathers are extremely stiff and
bristly allowing them to be used as a brace against tree trunks.
All the remaining birds that we will discuss belong to a single clade.
The Australaves.
And this clade has only been recognized recently,
because the various bird subgroups that comprise it, including falcons,
parrots, and songbirds, do not appear to have much in common.
But genetic studies have confirmed that these birds
do share an exclusive common ancestor with each other, and
are therefore united in a shared evolutionary history.
The first of the Australaves subgroups is the Cariamiformes.
And they are of special interest to us because they have come close to
doing what Science Fiction writers have only imagined:
Resurrecting the theropod super-predators.
Today, the only living Cariamiformes are the seriemas of South America.
Seriemas are pheasant-sized ground birds with limited flight abilities,
long legs and reduced wings.
They're fast runners, and
when threatened, prefer to flee on foot rather than take wing.
They're primarily carnivorous, and frequently kill small lizards and mammals.
We've actually discussed seriemas previously in this course.
Because they have a special adaptation that is similar to
that of one non-avian dinosaur lineage.
Do you remember what that was?
Was it A, an enlarged foot claw like deinonychosaurs.
B, an arctometatarsus like tyrannosaurs.
C, a boney head crest like oviraptorosaurs.
Or D, an elongated finger like scansoriopterygians.
The correct answer is A.
The Seriema have an enlarged claw on the second toe
similar to that of deinonychosaurs.
Although their claw is not carried in a strongly-raised position, and
is generally used to disembowel prey that has already been killed with their beak.
When I said the cariamiformes had come close to resurrecting the theropods'
super predators, I wasn't referring to the seriemas and
their deinonychosaur-esque claws.
The cariamiformes also includes an extinct group of large, flightless birds
called the phorusrhacidae, commonly known as the t'error birds'.
Phorusrhacidaes first evolved in South America,
roughly 62 million years ago, not longer after the End-Cretaceous mass extinction.
And they only became extinct, roughly two million years ago.
This is the skull of one of the later and larger forms, Phorusrhacus.
The skull of phorusrhacids have the characteristic
hooked beaks of predatory birds.
And look closely at the sides of the beak and you can see that the upper and
lower jaws slide past each other like a pair of scissors.
This gives the a beak a slicing bite.
From the head down, phorusrhacids were typical, of flightless birds.
Most had much longer and more slender legs than moas or
elephant birds, indicating that they were fleet-footed.
Phorusrhacus is a large terror bird, standing two and
a half metres tall but it is far from the largest.
Brontornis stood nearly three metres tall and was far more massively built.
It had a skull twice as long as this one and
an estimated weight of nearly 400 kilograms.
In South America, Phorusrhacus dominated the niche
of large carnivores throughout most of the Cenozoic.
They hunted large herbivorous mammals and
co-existed with several leopard sized marsupial predators.
During this time, South America was an isolated continent and
being flightless, the terror birds could not spread elsewhere.
When the Isthmus of Panama formed roughly three million years ago,
animals from North and South America began to intermix.
The net result was the large scale extinction
of many native South American species.
And their replacement by invasive North American species.
Phorusrhacus were one of the few members of the South American fauna
to cross Panama, and invade Southern North America.
However, perhaps due to competition with saber-tooth cats or
other advanced mammalian carnivores, or possibly because their custom prey species
were dying out, they too became extinct.
Our next avian group is another line of predators and it may surprise you.
The Falconidae consists of the falcons.
With their hooked beaks and raptorial claws,
falcons have long been assumed to be close relatives of hawks and
eagles which belong to the Accipitriformes, but
genetic studies have proven that this is not the case.
There are few morphological traits that can be used to tell falconids apart.
For one,
their feathered coats have a characteristic black streak just below each eye.
This is often called a 'falcon tear'.
And the dark colors are thought to function like the eye black,
worn by athletes to reduce reflected glare.
Additionally, the beaks of many falcons have a process called a 'falcon tooth', and
this allows the falcon to sever the neck of prey that is held captive but
not yet killed by the gripping talons.
Though not closely related to the Accipitriformes, falconids
are close kin to another group of hook beaked birds.
The Psittaciformes or parrots.
Psittaciformes are rarely carnivorous, and
use their hook beaks to rip the flesh of fruits and the hard shells of nuts.
To help them climb trees and pick fruits, Psittaciformes have a zygodactyl foot.
Many Psittaciformes are highly social and intelligent.
Parrots are famous for their ability to mimic sounds in human speech.
In some parrot species, this ability goes so
far as actual word object association, simple sentence construction,
and even the creation of new words to identifying novel objects.
These fundamental language skills are impressive.
So, too, are the mathematical abilities of parrots.
Some are capable of basic addition and subtraction.
Relative to their body size,
the brains of parrots are as large as some higher primates.
Finally, we have come to our last avian group,
the Passeriformes, better known as the song birds.
And this is the largest of all living bird groups.
The living species of passerines out number the living
species of all other bird groups combined.
And that does not mean that the passerines have an exceptionally diverse appearance.
In fact, many species look fairly similar to one another in overall form.
The passerines originated, and began to diversify in the Southern Hemisphere.
The earliest fossils of passerines are from Australia, and
date to roughly 55 million years ago.
Passerines are generally small, and feed on insects and
seeds, which are rich and abundant food resources.
There is one continent where the dominant large land animals are still dinosaurs.
Which one is it?
A, Australia.
B, Africa.
C, South America.
Or D, Antarctica.
The answer is D.
Antarctica is the kingdom of penguins.
And that makes it a land still ruled by theropod dinosaurs.
>> We are in fact, still living in the age of dinosaurs and
that's because dinosaurs gave rise to birds.
Birds are technically living dinosaurs and
they're classified as part of the Dinosauria.
There are over 10,000 living species of dinosaurs and they outnumber living
species of mammals, and they outnumber living species of reptiles and amphibians.
Places like Antarctica, which are ruled by penguins, are technically,
still continents ruled by dinosaurs.
Unfortunately, dinosaurs are facing another mass extinction right now.
And that's a mass extinction that's induced by our own species.
>> Looking back from the branch of modern birds, our trek through the theropod
family tree has been far from a straight and simple path.
We've seen the rise and fall of apex predators like Saurophaganax and
Tyrannosaurus.
We've seen the evolution of fish eaters, insect diggers, and
swift running vegetarians.
We've seen how feathers develop,
and beaks have replaced toothy jaws.
Not all at once, but gradually,
and in stages.
That penguins, ducks, and canaries are all descended from the same
lineage as the mightiest beast in our planet's history,
is a strange fact, but
you have now seen enough of the evidence to understand that it is true.
For over 160 million years theropods ruled the planet.
Today, their ecological roles have changed but they're still going strong.
The scientific fact is, if you want to see a dinosaur,
you don't need to look any further than your backyard bird feeder.
On behalf of the University of Alberta and
the entire Palaeo team, thanks for joining us.
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