What are the characteristics of amniotic eggs
- they have encapsulating membranes that are watertight
- > note animals that lay amniotic eggs are called amniote
- being able to hold in their own water
- > amniotic eggs can be held in dry environments
- > note shells improved amniotic eggs to hold in more water and made the eggs more durable and less vulnerable to small predators
Are mammals, birds, dinosaurs and reptiles all amniotes?
-yes they are all amniotes
Are amniotic eggs airtight
- no they are just water tight
- >other wise the eggs would suffocate
Were large dinosaur eggs possible
- no
- > because the amount of oxygen that a dinosaur developing inside an egg requires is a function of its volume
- > while the rate at which oxygen can be exchanged is a function of the eggshell’s surface area
-giant eggs would have a low ratio of surface area to volume and would die
What are lines of arrested growth
- the rate at which osteons are added to bones is not the same
- > during times when resources are scarce, growth may slow down
- > this creates rings inside the bones
-these rings are referred to as lines of arrested growth
How do lines of arrested growth help paleontologists
- they can be studied in old and young dinosaurs
- >and used to determine how long it took a dinosaur to grow to a particular size and at what speed the dinosaur grew
What are the bones of younger dinosaurs characterized by
- they are characterized by high vascularity and a texture called lamellar bone
- > note for younger dinosaurs, lines of arrested growth grow later as they grow
What do more mature dinosaurs go through in terms of their bone processes
- they go through a process called remodeling
- > essentially where the old bone cells were replaced by newer bone cells
- > these newer bone cells are called Haversian or secondary bone cells
- as growth slows and then stops
- > a closely spaced series of lines of arrested growths form
- > these are referred to as the external fundamental system(EFS for short)
What does the EFS indicate
-that the dinosaur is skeletally mature and has stopped growing
What are ontogenic changes
- changes in the form of an organism that occur as it matures are called ontogenic changes
- > some ontogenic changes involve the growth of entirely new structures
- note big heads and big eyes are common traits of young animals
- > baby dinosaurs also had relatively large heads and eyes
What are non-isometric ontogenic changes
- not simply changes resulting from a general increase in size
- > certain features appear at different rates in an organisms life or do not grow proprotionally with the rest of the body
What are isometric ontogenetic changes
- changes in absolute size but not proportions
- > for example, the length of the tibiaa relative to the length of the femur of a baby ceratopsian was nearly the same as the length of the tibia relative to the length of the femur of a full-grown adult
What is sexual dimorphism
- the males and females of the same species are different
- > they are usually subtle but can be extreme
-it is common for sexually dimorphic features to be ontogenic changes as you are not just born with them
What is a medullary bone
- laying eggs with hard shells require a female to donate a large quantity of calcium
- > in preparation for this, the female grows a medullary bone
-medullary bone contains concentrations of calcium that are stored prior to eggshell development
- this bone can be used to identify certain dinosaur genders of a specific species
- > however, females without medullary bones could mean that they were not getting ready to lay eggs
What is predator satiation
- to produce a new generation, only a tiny fraction of eggs that were laid needed ot hatch and grow into adults
- > rather than investing time into guarding and rearing young, some dinosaurs like the sauropods did this
