Briefly compare the positions of the continents at the beginning and end of the Mesozoic.
The continents gradually shifted from a state of connectedness into their present configuration
(the rifting provided for speciation and other important evolutionary developments).
tectonic deformation was comparatively mild following the vigorous convergent plate mountain-
building of the late Paleozoic.
Nevertheless, the era featured the dramatic rifting of the
Pangea gradually split into a northern continent, Laurasia, and a
southern continent, Gondwana.
This created the passive continental margin that characterizes
most of the Atlantic coastline (such as along the U.S. East Coast) today.
By the end of the era,
the continents had rifted into nearly their present form.
Laurasia became North America and
Eurasia, while Gondwana split into South America, Africa, Australia, Antarctica and the Indian
subcontinent, which collided with the Asian plate during the Cenozoic, the impact giving rise to
Identify the two modern groups of animals that are most closely related to dinosaurs.
There is an almost universal consensus among paleontologists that birds are the descendants of
theropod (bipedal) dinosaurs.
Using the strict cladistical definition that all descendants of a
single common ancestor are related, modern birds are dinosaurs and dinosaurs are, therefore,
Modern birds are classified by most paleontologists as saurischians (lizard-hipped).
They are also closely related with modern reptiles, especially the crocodile.
What might have been the advantage of bipedality in early dinosaurs?
Bipedalism and associated traits can offer a species several advantages:
Some evolutionary biologists have suggested that a crucial stage
in the evolution of some or all bipeds was the ability to stand, which generally improves
the ability to see (and perhaps otherwise detect) distant dangers or resources.
In vertebrate species, for whom evolution of additional limbs would be
an enormous genetic change, it can serve to free the front limbs for such other functions
as manipulation (in primates), flight (in birds), digging (giant pangolin), or combat
Raccoons and some primates may adopt a bipedal position in water, allowing
them to stand or walk in deeper water while still breathing air.
In animals without a flexible backbone, such as lizards or
cockroaches, bipedalism may increase running speed.
However the maximum bipedal
speed appears less fast than the maximum speed of quadrapedal movement with a
flexible backbone - compare the fastest bipeds the ostrich (65 km/h) or the red kangaroo
(70 km/h) with the fastest quadruped, the cheetah ( 103 km/h).