Week 5 - birth, growth and reproduction Flashcards
(26 cards)
What was the major milestone in tetrapod evolution?
the amniotic egg
What is an amniotic egg?
have encapsulating membranes that are water tight –> hard shells or leather
What is the advantage of having eggs with shells?
makes the eggs more durable and less vulnerable to small predators
What is the advantage of amniotic eggs?
eggs could be laid in dry habitats –> allowed amniotes to colonize new terrestrial environments
What are some important characterisitcs of amniotic eggs?
- not airtight
- have pores to allow for gas exchange - cube square law
- limits egg size
Describe how animal growth affects their bones?
as an animal grows their bones, they add osteons to their bones’ outer walls
What are LAGs? How do they form?
LAGs = lines of arrested growth
winter or dry season –> resources are scarce –> growth may slow down –> creates rings inside the bones
What information can we learn from studying LAGs?
how long it took a dino to grow to a particular size and what speed a dino grew
What is a difference between bones of young dinos and old dinos?
young dino bones are highly vascularized and have lamellar bone texture
What is bone remodelling and what does it produce?
- mature dino bones went under remodeling
- old bone cells were replaced by newer bone cells
- remodelled bone = Haversian/secondary bone
What are EFS? How are they produced? What does their presence suggest?
EFS = external fundamental system = closely spaced series of LAGs
when growth slows and stops –> EFS
presence of EFS = dino is skeletally mature and has stopped growing
What are 5 features of newborn dinos?
- less prominent facial extrucsions
- larger eyes
- smaller size
- shorter relative limb lengths
- big head
what are ontogenetic changes?
changes that occur to an organism as it matures
Give an example of how ontogenetic changes can be dramatic?
crests of hadrosaurs were not present in very young indiviudals, but grew gradually as the dinos reacher maturity
Give an example of how ontogenetic changes can involve the growth of entirely new structures
baby ankylosaurs hatched with little to no armour and with no tail clubs
what are non-isometric ontogenetic changes vs isometric ontogenetic changes?
non-isometric = changes in the relative proportions of an animal as it grows
isometric = changes in absolute size
Give two examples of non-isometric ontogenetic changes
- baby the chasmosaurus (ceratopsian)
- frill on juveniles < frill on adult
- baby lacks a nasal horn - legs of tyrannosaurs
- tibia > femur in juveniles (longer)
- tibia = femur in adults
What is sexual dimorphism?
when males and females of the same species are different
T/F: is it common for sexual dimorphic features to be ontogenetic changes?
True
Why is evidence of dino skeletons with eggs in its body not proof that the dino was female?
eggs could hav ebeen eaten or washed in
Why is evidence of dino fossils found brooding over nests of eggs not proof that the dino was female?
male birds (dino descendents) spend time looking after eggs too
What is a piece of evidence that can identify a dino as female? What is a limitation of this?
medullary bone = bone that contain concentrations of calcium that are stored prior to eggshell development
- found only in females because they have to donate a large quantity of calcium
- medullary bone is only grown by females prior to egg production and is not present at other times
what are marrow cavaities?
hollow spaces inside bones
What insights do birds and crocs provide about parental care?
birds = tend to eggs, feed and protect their young
crocs = mamma crocs guard their nests and protect their young for an extended period of time
