Lecture 16: Dinosaurs: tiddlers and titans

Question 1

Dinosaur eggs

Answer 1

very distinctive microstructure
largest sauropod ~40 m long & 100 tonnes
largest egg: ~ 5.5 litres (‘football’)
amniotic egg

Question 2

why so “small” eggs?

Answer 2

Shell thickness- bigger egg is, the thicker the shell- embryo would need to be able to get through
Gas diffusion- too thick a shell would mean inability

Question 3

How did they lay their eggs?

Answer 3

Squatting down?
ovipositor?
no real evidence…

Question 4

Baby factories?

Answer 4

12-100 eggs per year
 40-year old dinosaur ~450-4,000 eggs/lifetime
generally ‘r-strategists’
lots of young, little care
high mortality?
large mammals, e.g., elephant
~12 young/lifetime
‘K-strategists’
few young, lots of care
low mortality

Question 5

Implications for dinosaurs?

Answer 5

rapid reproduction
rapid growth
many juveniles, few adults
expand population rapidly
cope with environmental change

Question 6

Orodromeus eggs

Answer 6

eggs in spirals
large, irregular eggshell fragments
babies’ joints well formed (could fend and walk themselves immediately)
“precocial” offspring

Question 7

Hadrosaur Maiasaura eggs

Answer 7

Bowl-shaped nests
Eggshell fragments small
Juveniles 8-9 months old
Worn teeth
"altrichial” offspring- not ready to fend for themselves.

Question 8

What suggested the dinosaurs were coming back to same places to lay eggs?

Answer 8

several nests on one horizon
evenly spaced
nested in large groups/herds
successive layers of nests in sequence
annual breeding
complex social behaviour

Question 9

Cold or warm blooded?

Answer 9

Reptiles are ectothermic

Use sun

Question 10

You are what you eat..?

Answer 10

endotherms consume more food
endotherms require >10x more food as ectotherms of same body mass
look at population structure

Question 11

Predator : prey ratios

Answer 11

10-60% in modern and ancient reptiles
1-4% in modern and ancient mammals
dinosaurs: 0.5-3.5%

Question 12

Large sauropods dimensions (Sa:vol)

Answer 12

volume increases more than surface area
slow heat loss
“mass homeothermy”

Question 13

Dinosaurs with feathers…?

Answer 13

...but symmetrical feathers
therefore not for flight…
insulation?
foraging?
display?

Question 14

Did flight evolve “ground up”?

Answer 14

ground-dwelling ancestor
feathers for insulation?
feathers used for trapping prey
leaping 
flying

Question 15

Or did flight evolve “trees down”?

Answer 15

arboreal ancestor
feathers for insulation?
glided from tree to tree
feathers became asymmetrical
flying

Question 16

Votes for “ground up”?

Answer 16

dinosaurs with “non-feather” filaments
insulation
dinosaurs with symmetrical (i.e., non-flight) feathers
flight evolved later…

Question 17

Votes for “trees down”?

Answer 17

Microraptor
smallest non-bird theropod dinosaur known
would fit in palm of hand
small enough to have lived in trees
symmetrical feathers
glider?