Lecture 14 Diversity of Dinosaurs, Birds, and Flying Reptiles
Focus Question:
What evidence links birds to dinosaurs?
1.
Dinosaurs
as a group of specialized descendents of Archosaurs (which are descendents of
the Diapsids), arose in Triassic
time, and radiated into almost all the
niches now inhabited by today’s Mammals.
They ranged in size from very small to the largest animals that ever
lived on the continents, and there is still a lot of research going on to
understand their biology, ecology, and behavior (these are the fields of
vertebrate paleontology, paleoecology and genetics).
They were clearly very successful, because their fossil record extends
from Triassic to Cretaceous time, all together about 160 million years’ worth of
success! Today we will look
at some features of this diversity.
a.
Remember,
the Archosaurs include the Dinosaurs, Pterosaurs, and Birds, as well as
Crocodiles.
b.
We also want to remember that the Dinosaurs are
classified into two general groups-
1.
“Bird-hipped”
Ornithischian dinosaurs-all herbivores-(Stegosaurs, Triceratops)
2.
“Lizard-hipped” Saurischian dinosaurs-some were
herbivores, some were carnivores
3.
This classification is based on shape differences
in the pelvis bones.
2.
The
Saurischian dinosaurs are most commonly known in popular literature.
They include
a.
Carnivores,
such as Allosaurus, Tyrannosaurus, and Deinonychus (all THEROPODS)
1.
Top
predators with skeletal features including bipedalism (ran on two legs), hollow
bones,
recurved teeth, powerful jaws. Many
had long, grasping forelimbs with three digits on each, and strong claws.
b.
Herbivores,
such as Apatosaurus, Brachiosaurus, Seismosaurus (all SAUROPODS)
2.
Enormous
herbivores with unusual growth rates that showed niche partitioning by
specializing in plants at different heights and of different varieties.
Most of these walked on all four legs.
4.RoadTrip!
To see Jurassic Dinosaur saurischian bones in abundance, we can go to
Dinosaur National Monument in Dinosaur, Colorado ( a mere 25 hours in the car,
just get on I-80 and make a left when you get to Wyoming…)
a. Exposures of Brachiosaur
bones in outcrop, along with Allosaur bones
b. the outcrop is Morrison
Formation-middle Jurassic in age.
Morrison is FAMOUS for dinosaur bones.
c. The Morrison is visible
in a north-south exposure from Alberta/Saskatchewan all the way to Arizona and
New Mexico. It is composed of
sandstones and shales, stream and lake deposits, with volcanic ash deposits too.
It formed as mountain uplift to the west shed sediment in immense amounts
eastward, in a north-south line.
5.Growth of these large
SAUROPODs requires a metabolism different from that of modern mammals.
We can see this when we realize that on hatching, these enormous
sauropods are only about 15 cm long.
The growth lines visible in the bones of these fossil sauropods have led
to two working hypotheses about this:
a. They
grow rapidly ‘til they reach sexual
maturity, but this may take 70 to 100 years
b. They grow extremely rapidly ‘til they reach sexual maturity, and do
this in about 20 years.
a. retain some early dinosaur features such as bipedalism
b. larger brains, stereoscopic vision, modified foot bones for speed/turning/.
c. forelimbs generally shorter than hindlimbs, in Tyrannosaurs, become very short and reduced in digits
d. jaws are primary capture/kill weapon, teeth strongly rooted
e. range from small (1 to 1.5 m) to very large (T. rex)
f. protofeathers (fluffy down) on adolescents
7. Eumaniraptors, which include Deinonychus and Velociraptor (think Jurassic Park movies) are another successful group of predatory theropods, appear in Jurassic, flourish in Cretaceous.
a. retain some early dinosaur features, such as bipedalism, and small size-these always stay small (with maybe one or two exceptions).
b. forelimbs generally as long or longer than hindlimbs, hands become long with grasping, clawed digits
c. brachial motion of forelimbs (can reach out and grab)
d. hindlimbs long, with rectractable claw on hind feet for climbing and slashing
e. true feathers on legs
8. Birds-who are they? Archaeopteryx, the "first bird" is a famous fossil from the Solnhofen Limestone of Bavaria, Germany-late Jurassic age.
a. looking at it compared iwth the Eumaniraptors, it became apparent that it IS a Eumaniraptor. Note
a. long forelimbs with claws, hindlimbs with the rectractable claw on the hind feet
b. long tail, feathered
c. long limbs, feathered
d. theropod head and teeth
9. Study of the Eumaniraptors has shown that the birds are a group of Eumaniraptors, and that the feathers were "co-opted" from previous tasks within the Eumaniraptors, probably to do with regulating body heat. The connection between Eumaniraptors and Birds-the motion and development of flight:
a. therapod-like-that is,
they look like little therapod dinosaurs, have hollow bones, similar skulls and
teeth, similar bipedal body plan, similar limbs and tails.
b. feathers are present, but
not necessarily used for flight.
Feathers are found as imprints and as molecular traces in theropod dinosaurs,
indicating that feathers were a temperature regulating feature (kept the animal
warm) first, and only later, in the line of birds, CO-OPTED for flight.
c. Flight involves the same
arm motions as some therapod carnivores had in capturing prey with their
forelimbs, so again, this ability was CO-OPTED for flight.
d. The hypothesis currently
supported is that these early birds were gliders at first, later flyers.
This is a “ground-upward” view, that they lived as theropods on the
ground early on.
e. in behavior, birds have
many similar features to herding dinosaurs (eggs, nesting in colonies, nest
brooding, migrating in groups).
f. in biology, birds have
similar bone features, are endotherms (warm blooded), and most recently, have
been linked to theropods by similar hormones, as molecular traces of these have
been recovered in Tyrannosaur bones.
10.
Another successful group of Archosaurs are the flying reptiles, the
Pterosaurs. These appear as fossils
in the Triassic as small animals with long tails, but by Cretaceous time we find
some enormous soaring specimens with wingspans of 20 to 40 feet, depending on
species, with great bony crests on the skull, and reduced tails.
a. The wing is composed of a
flap of skin, supported by the forelimb and the fourth digit (the little
finger), and a special bone called the pteroid bone.
No feathers here, although some evidence indicates hair of some kind was
present.
b. The bony crest in the
skull is hollow, as are the bones themselves, which reduces the weight of the
body.
c. Most appear to have had a niche similar to that of marine fishing birds, such as pelicans, that fly low over the water and scoop up fish.
11. So, the Mesozoic world was an
exciting time for vertebrates.
Besides the rise of the dinosaurs, two groups developed flight independently:
the pterosaurs and the birds. So
now we have three separate groups that have developed flight:
the Arthropods in the Paleozoic (remember those dragonflies in the
Carboniferous?) and the Pterosaurs (late Triassic) and the Birds (Jurassic).
Also, from the previous lecture, we saw two groups that returned to the
sea and developed life cycles entirely linked to the open ocean: the
Ichthyosaurs and the Plesiosaurs.
To sum up the focus question
for today, the links that we have showing Birds are descendents of Dinosaurs by
way of the Saurischian theropod Eumaniraptor line include the
skeletal structure (hollow bones, similar appearance), metabolism (warm blooded,
growth, similar hormones), the feathers (co-opted from use as insulators) and
the behavior (nest brooding, eggs, migration, herding).
Interestingly, we can now see
that the egg does come before the chicken, and the feather does come before
flight!
Next Lecture:
Mesozoic Mountain Building and the North American West