Learning Objective 5.1
What is a major milestone in tetrapod evolution?
amniotic egg
- prior, all tetropods laid eggs that were similar to those of modern frogs and salamnders and could not reatin water
Learning Objective 5.1
What are animals that lay amniotic eggs called?
amniotes
- mammals, birds, dinos and reptiles are all amniotes
Learning Objective 5.1
why can’t eggs be large (as depicited in media)
- recalling the cube-square law
- the amount of oxygen in the egg is a function of it’s volumbe, the rate at which oxygen is exchanged is the funciton of the eggshell’s surface area
- giant eggs would have a low ratio of surface area to volume and would die
Learning Objective 5.2
Describe lines of arrested growth (LAGS)
- rings inside bones
- as animals grow their bones, osteons are added to the bone’s outer walls
- varies with changes in growth rates; different in seasonal periods where food might be limited = growth may slow down
Learning Objective 5.2
describe the two characteristics of bones in younger dinosaurs
- high vascularity
- texture called lamellar bone
- LAGS formed later as dinosaurs grew
Learning Objective 5.2
describe the process of bone remodeling
what is the new bone called? what are the LAGS called when growth stops?
- old bones cells were replaced by neweer bone cells
- bone is called Haversian/ secondary bone
- when growth slows and finally stops, external fundamental system (EFS) is formed (a closely spaced series of LAGs)
Learning Objective 5.3
define non-isometric onotgentic changes
changes in the relative proportions of an animal as it grows, that are not simply changes resulting from a general incerase in size
- eg. changes in the relative lengths of the horns and frills of ceratopsians
Learning Objective 5.3
define isometric ontogenetic changes
changes in absolute size but not proportions
- eg. length of the tibia relative to the length of the femur of a baby certopsians was nearly the same as the elngth of the tibia relative to the length of the femur of a full-grown adult
Learning Objective 5.4
define sexual dimorphism
males and females of the same species are different
- ex. massive antles of a bull moose, entirely absent on females
Learning Objective 5.4
describe the medullary bone and how that can be used to identify whether or not a dinosaur is a male or female
how is the application of this technique limited?
- bone contains concentration of calcium that are stored prior to eggshell development
- laying eggs with hard shells requires a female to donate a large quantity of calcium
- medullary bone is only grown in females prior to egg produciton and is not present at other times
Learning Objective 5.5
define predator satiation
what dinosaur used this strategy?
- producing many offspring at one time that predators would not have been able to eat them all before they mature
- sauropods used this strategy; laying their eggs at the same time, many eggs and making a mass nesting ground
- they did not invest time into gaurding and rearing their young
