Week 5 - birth, growth and reproduction

Question 1

What was the major milestone in tetrapod evolution?

Answer 1

the amniotic egg

Question 2

What is an amniotic egg?

Answer 2

have encapsulating membranes that are water tight –> hard shells or leather

Question 3

What is the advantage of having eggs with shells?

Answer 3

makes the eggs more durable and less vulnerable to small predators

Question 4

What is the advantage of amniotic eggs?

Answer 4

eggs could be laid in dry habitats –> allowed amniotes to colonize new terrestrial environments

Question 5

What are some important characterisitcs of amniotic eggs?

Answer 5

1. not airtight
   - have pores to allow for gas exchange
2. cube square law
   - limits egg size

Question 6

Describe how animal growth affects their bones?

Answer 6

as an animal grows their bones, they add osteons to their bones’ outer walls

Question 7

What are LAGs? How do they form?

Answer 7

LAGs = lines of arrested growth

winter or dry season –> resources are scarce –> growth may slow down –> creates rings inside the bones

Question 8

What information can we learn from studying LAGs?

Answer 8

how long it took a dino to grow to a particular size and what speed a dino grew

Question 9

What is a difference between bones of young dinos and old dinos?

Answer 9

young dino bones are highly vascularized and have lamellar bone texture

Question 10

What is bone remodelling and what does it produce?

Answer 10

• mature dino bones went under remodeling
• old bone cells were replaced by newer bone cells
• remodelled bone = Haversian/secondary bone

Question 11

What are EFS? How are they produced? What does their presence suggest?

Answer 11

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

Question 12

What are 5 features of newborn dinos?

Answer 12

1. less prominent facial extrucsions
2. larger eyes
3. smaller size
4. shorter relative limb lengths
5. big head

Question 13

what are ontogenetic changes?

Answer 13

changes that occur to an organism as it matures

Question 14

Give an example of how ontogenetic changes can be dramatic?

Answer 14

crests of hadrosaurs were not present in very young indiviudals, but grew gradually as the dinos reacher maturity

Question 15

Give an example of how ontogenetic changes can involve the growth of entirely new structures

Answer 15

baby ankylosaurs hatched with little to no armour and with no tail clubs

Question 16

what are non-isometric ontogenetic changes vs isometric ontogenetic changes?

Answer 16

non-isometric = changes in the relative proportions of an animal as it grows

isometric = changes in absolute size

Question 17

Give two examples of non-isometric ontogenetic changes

Answer 17

1. baby the chasmosaurus (ceratopsian)
   - frill on juveniles < frill on adult
   - baby lacks a nasal horn
2. legs of tyrannosaurs
   - tibia > femur in juveniles (longer)
   - tibia = femur in adults

Question 18

What is sexual dimorphism?

Answer 18

when males and females of the same species are different

Question 19

T/F: is it common for sexual dimorphic features to be ontogenetic changes?

Answer 19

True

Question 20

Why is evidence of dino skeletons with eggs in its body not proof that the dino was female?

Answer 20

eggs could hav ebeen eaten or washed in

Question 21

Why is evidence of dino fossils found brooding over nests of eggs not proof that the dino was female?

Answer 21

male birds (dino descendents) spend time looking after eggs too

Question 22

What is a piece of evidence that can identify a dino as female? What is a limitation of this?

Answer 22

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

Question 23

what are marrow cavaities?

Answer 23

hollow spaces inside bones

Question 24

What insights do birds and crocs provide about parental care?

Answer 24

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

Question 25

What are some pieces of evidence that some dino watched over their young?

Answer 25

• skeletons of oviraptosaurs position over top of their egg filled nests –> incubating eggs and guarding their nest
• often skeletons of young dinos are found alonside the skeletons of adult dinos

Question 26

Why did sauropods avoid parental care? How did their young survive?

Answer 26

fossil nests of sauropods show that herds of sauropods laid their eggs at the same time and place –> mass nesting grounds are too close together for a mother to have attended her eggs

survival strategy = predator satiation