CHAPTER 5 - Birth, Growth, and Reproduction Flashcards
a major milestone in tetrapod evolution was reached
An amniotic egg
Animals that lay amniotic eggs are called
amniotes
Being able to hold in their own water, amniotic eggs can be laid in
dry habitats
Mammals, birds, dinosaurs, and reptiles are all
amniotes
Although amniotic eggs are watertight, they are
not
airtight
why would there be no possibility of an extremely large egg, more than half a meter long?
Giant eggs would have a low ratio
of surface area to volume (not enough oxygen) and would die
During seasonal periods, when resources needed for growth are scarce, such as during winter or the
dry season, growth may slow down creating ring bones that are called
lines of
arrested growth, or LAGs for short
The bones of younger dinosaurs are
characterized by having high vascularity which means
many
blood vessels
remodeling
More mature dinosaur bone underwent a
process called remodeling, where the old bone cells were replaced by newer bone cells.
Haversian
secondary
bone
Finally, as growth slows and then finally stops, a closely spaced series of LAGs is formed, which is called the
external fundamental system (EFS)
Changes in the form of an organism
that occur as it matures are called
ontogenetic changes ex. hadrosaurs crests, or ankylosaur clubs
non-isometric ontogenetic changes
Changes in the relative proportions of an animal
as it grows, that are not simply changes
resulting from a general increase in size. ex. beak size in baby Chasmosaurus is so much smaller than the adult version
With Tyrannosaurus, the tibia
was much longer than the femur in juveniles,
while in adults the tibia and femur were close to
the same length. This is an example of
Isometric ontogenetic changes
which are changes in absolute size but not
proportions
sexual dimorphism
Males and females of the same species are
different. debated topic amongst palaeontologists. ex. Theropod bones without medullary bone (male or female that isnt pregnant) therefore could be from a male, or from a female that was not getting ready to lay eggs.
