EPS SCI 17 Lecture Notes - Lecture 12: Adaptationism, Sauropoda, Brontosaurus
26 May 2018
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Lec 12: The Jurassic - The Rise of Giants
May 15
SAUROPODS (“the giant dinosaurs”, large herbivores of the Jurassic)
●includes a number of dinosaurs that are pretty well-known
●Brontosaurus excelsus
(1879) - 70 feet long, 15 tons
○turned out that both Marsh & Cope both discovered and named the same kind of
dinosaur
■Othniel Marsh = Apatosaurus
■Edward Cope = Brontosaurus
○some conflicting evidence & beliefs among the paleontological community
●Brachiosaurus
- 85 feet long, 30 feet tall, 35-55 tons
○in opening of Jurassic Park
film
●Argentinosaurus
- 130 feet long, 24 feet tall, 80-100 tons
BIG QUESTION: Why and how did sauropods get so big?
●Caveat: Avoiding Adaptationist “Just So” Stories
○it’s pretty much impossible to test why any particular adaptation occurred in any
specific species
○instead, we can test trends across groups of organisms
○if it isn’t falsifiable, it isn’t science!
●exaptations
: a trait might evolve for one purpose, but ends up being advantageous in a
different situation
POSSIBLE REASONS
●niche partitioning
: over time, different species partition the environment & ecological
niches → kept from directly competing with one another and can coexist
● predation
:
○ Shnosaurus
- had club tail that can be used to smack predators away
○ Amargasaurus
- smaller sauropod that had spikes along its head, neck, and back
○ in general, most sauropods did not seem to have much defense mechanisms →
got larger to avoid being eaten (more dangerous to go after)
●Jarman-Bell Principle
:
○smaller animals have higher metabolic energy requirements (lose much heat,
need lots of food)
■limited to digestible plant material like roots, fruit, and nuts (have most
nutrition packed in them)
○ larger animals have lower energy requirements, relative to their body size
■ can subsist on less digestible plant material like leaves
METABOLISM
●Endotherms vs. Ectotherms
○ endotherms (warm-blooded)
: generate heat internally
○ ectotherms (cold-blooded)
: need external sources of heat, like the sun
●Homeotherms vs. Poikilotherms
○ homeotherms
: maintain constant internal body temperature
○ polikilotherms
: body temperature varies over time
● most mammals and birds = endothermic homeotherms
● most modern “reptiles” = ectothermic poikilotherms
● Exceptions to this Rule:
○ bats and some birds (also hibernating mammals) = endothermic poikilotherms
○ some fish & insects = endothermic homeotherms
■ ex. tuna get a lot of oxygen → get a lot of food & are very active →
manage to maintain a constant body temperature
○ some large reptiles = ectothermic homeotherms
● Neither way is necessarily better than the other
○predator-prey ratios
- how many predators vs. how many prey (tell you about
metabolism)
■predator has very low metabolism (cold-blooded) → more predators can
feed off the same lower population of prey
●high predator-to-prey ratio = can sustain more predators with the
same amount of prey
■predator has very high metabolism (warm-blooded) → less predators require
more prey to sustain the population
●low predator-to-prey ratio = can sustain less predators with the
same amount of prey
Endothermy
Ectothermy
Benefits
● sustained activity
● active at night
● adaptation to cold environments
● adaptation to hot environments
● need little food
Costs
● requires lots of food (10-30x
similarly sized ectotherms)
● not efficient at small body sizes
● capable of only short bursts of
activity
● limited ability to be active at night
● Surface Area / Volume
:
○ if small → much of body is exposed to environment (high surface area / volume
ratio)
■ lose a lot more heat for body size
■ to maintain body temperature, need to constantly eat (need a lot of food)
■ small endotherms have a problem with retaining heat (because they have
a low SA/V)
○ if large → less amount of body is exposed to environment (less surface area /
volume ratio)
■ lose less heat over time
■ large endotherms have a problem with dumping excess heat, particularly
in hot environments (because they have a low SA/V)
Document Summary
Lec 12: the jurassic - the rise of giants. Sauropods ((cid:343) he gian dinosa rs(cid:344), large herbivores of he j rassic) Incl des a n mber of dinosa rs ha are pre y well-known. Brontosaurus excelsus (1879) - 70 fee long, 15 ons. Rned o ha bo h marsh & cope bo h discovered and named he same kind of dinosa r. Some conflic ing evidence & beliefs among he paleon ological comm ni y. Brachiosaurus - 85 fee long, 30 fee all, 35-55 ons. Argentinosaurus - 130 fee long, 24 fee all, 80-100 ons. I "s pre y m ch impossible o es why any par ic lar adap a ion occ rred in any specific species. Ins ead, we can es rends across gro ps of organisms. If i isn" falsifiable, i isn" science! Exaptations : a trait might evolve for one purpose, but ends up being advantageous in a different situation.
