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What does it mean when we say trophic pyramids are inefficient? What are some implications of this fact?
- <10% of energy is transferred from one trophic level to the next
- Most of the energy is lost b/c it is released as heat
- Implications: carnivores need to eat much more than herbivores to get their energy
What characteristics of mammals allow for chewing in mammals, and how do they do so? How do dinosaurs that chew do so differently from mammals?
- Mammals are heterodont, which allows for them to have precise occlusion (bringing of opposing surfaces of the teeth of the two jaws into contact); OR mammals with hypsodonty (tall teeth), so it takes longer to grind down all of the teeth)
- Dinosaurs are mostly homodont. In order to grind tough plant matter, herbivores have flat teeth with a lot of ridges. Also, they developed dental batteries (line of teeth that grow from the bottom up; conveyor belt of teeth) and cranial kinesis (lower teeth push upper teeth out).
What are the various adaptations in dinosaurs for eating plants? Why do they need special adaptations for eating plant material?
- Sauropods have gastroliths (swallowed stones) to grind the plant material in their stomach
- Thyreophorans and Cerotopsians developed gut fermentation (letting the plant material rot in their stomach)
- They need special adaptations because plant matter is tough and cuticles on leaves are hard to break down
What are the benefits and costs of ectothermy & endothermy?
Ectothermy (receives heat from external source) benefits
- Adaptation to hot environments
- Need little food
Ectothermy costs
- Capable of only short bursts of energy
- Limited activity to be active at night
Endothermy (generates heat) benefits
- Sustained activity
- Active at night
- Adaptation to cold environments
Endothermy costs
- Requires lots of food
- Not efficient at small body sizes
How does the surface area/volume ratio of animals relate to the way they retain heat?
- Surface area is where the animal exchanges heat with the environment
- Smaller animals have a higher surface area, lower volume; larger animals have lower surface area and higher volume
- Small endotherms have a problem with retaining heat, while large endotherms have a problem with dumping excess heat
What are the various lines of evidence that can be used to infer the physiology of dinosaurs, and what does each of those lines of evidence tell us?
Cardiopulmonary evidence: heart & lungs
- Dinosaurs have a four-chambered heart
- Dinosaurs have air sacs that allow for efficient breathing
- The heart and lungs are unclear in showing whether dinosaurs were endotherms or ectotherms
Insulation
- Only modern endotherms have insulation (feather, fur)
- Some dinosaurs may have had feathers
Bone growth
- Mammals and birds had determinate growth, while reptiles that indeterminate growth
- Mammals have vascular bone structures
- Lines of arrested growth (LAGs) are more common in ectotherms than endotherms; however, some mammals had LAGs too
Growth rates
- Mammals and birds tend to have a 3 part growth curve (slow growth as infants and toddlers, fast growth as juveniles and adolescents, slow growth as adults)
- Ectotherms tend to have a relatively constant growth rate
- Dinosaurs had a 3 part growth curve, especially the biggest ones; they grew faster than mammals and birds
- Dinosaur growth rates were similar to endotherms
Neurophysiology (relative brain size)
- Encephalization Quotient
-- Ratio of brain size to body size
-- Endotherms had a high EQ because brains are expensive
-- Dinosaurs show a range, with some similar to modern birds
Isotopic evidence
- Different isotopes are different in weight
- Lighter isotopes are preferred in most chemical reactions - it's easier to move around
- At higher temperatures, differences decrease
- Extremities on the body will be colder in ectotherms
- Dinosaurs show temperature differences comparable to mammals
Skull features
- Mammals and birds have unique structures called turbinates that make their breathing more efficient
- Inhalation: relatively cool, dry air passes over moist, warm turbinates and is heated & saturated with water
- Exhalation: warm, moist air passes over cooler, drier turbinates and transfers heat and moisture to their surface
- Function of turbinates:
-- Condition incoming air
-- Conserve heat
-- Conserve water
- A recent study showed that dinosaurs did have turbinates
Postural evidence
- Like mammals, dinosaurs had feet directly under their body
Biogeographic Evidence
- Dinosaurs lived near the poles, while modern ectotherms did not
-However, the Mesozoic was much warmer at the time
-This shows that dinosaurs could not handle the cold (endotherm)
Why does the "Goldilocks Hypothesis" describe the physiology of dinosaurs as mesotherms?
- Animals can invest their energy in two things
-- Maintenance
- - - Renewing cells
- - - Generating heat
- - - Food
-- Production
- - - Growth
- - - Reproduction
- - - Fat storage
- Endotherm - 97% maintenance + 3% production (Being an endotherm is costly)
- Ectotherm - 60% maintenance + 40% production
- Dinosaurs are MESOTHERMS
-- They had intermediate metabolic rates, but burned energy like ectotherms (i.e., relatively more into production)
-- Used more energy for growth
-- Remember, dinosaurs got bigger over time (Cope's Rule) and probably were gigantothermic
-- Evolutionary arms race (Red Queen)
-- Have a large energy pool, can be used for production (growth)
What are some unique characters of the skull in theropods? What about the limbs?
Pneumatized brains
- Lots of space in the head
- Trend toward larger brains
- Enhanced hearing and smell
- Stereoscopic vision
Bipedal
- Obligate bipedality
- Much longer hind limbs than forelimbs
- Digitigrade
- Reduction in digits I & V
- Stiffened tails
- 5 sacral vertebrae
Forelimb characters
- Loss/reduction of digits IV & V
Some opposability of digit I
Short limbs were still strong
What are the relationships of the various groups of theropods? What are some characters that define some of those groups?
Herrarasaurids
- South American
- Mid-Late Triassic (230 Ma)
- Possibly basal theropods
- Possibly basal dinosaurs
- Defined by lack of characters
Coelophysids
- Mainly small, North American & African forms
- Triassic and Jurassic
- ex) Coelophysis: most numerous dinosaur fossil
Abelisaurs
- Primarily Gondwanan
- Mostly Cretaceous
- Some have "headgear"
- ex) Masiakasaurus knopfleri
Ceratosaurs
- Horned dinosaurs
- Mainly Gondwanan
- Mainly Cretaceous
ex) Dilophosaurus
Tetanurae
- "Stiff-tail"
- Further reduced digits (III, IV & V lost/reduced)
- More pneumatized heads
- Pubic foot: muscle attachment
- Includes Allosaurids, Tyrannosaurs, Ornithomimosaurs, Therizinosaurs, Oviraptors, Deinonychisaurs
Spinosaurs
- Large, but lightly built
- Long snouts that look like alligators
- Some have sail-backs (for fat or support)
- Some piscivorous & semiaquatic
- ex) Megalosaurus
Allosaurids
- Middle Jurassic to late Cretaceous
- Laurasian
- Some attain large sizes, but most are medium-sized
Coelosaurs
- Many convergent on earlier Allosaurs and Ceratosaurs
- Characterized by: Arctometatarsals & Semilunate carpal
- ex) Compsognathus: Late Jurassic of Europe, "turkey-sized," probably feathered
- Includes Ornithomimosaurs, Therizinosaurs, Oviraptors, and Deinonychisaurs
Tyrannosaurs
- Late Crataceous of Asia and North America, possibly also Australia
- Further digit loss (arm use?)
- Robust skulls
- ex) Dilong: feathered Tyrannosaur
Ornithomimosaurs
- Cretaceous of Laurasia (possibly also Gondwana)
- Many become omnivorous & herbivorous
- Some have bizarre osteological adaptations (e.g., duck-like beaks)
- ex) Deinocheirus: largest ornithomimosaur, known originally only from arms
Alvarezsaurids
- Cretaceous of South and North America and Asia
- Short, stout forelimbs, with reduced digits
Maniraptors
- Breast bones present in some
- In some the pubis faces backwards like birds
- Possibly primitively omnivorous
- Evolve flight
Therizinosaurs
- Hyper-specialized forelimbs
- Possibly analogous to giant ground sloths
- Cretaceous Laurasian in distribution
- ex) Falcarius
Oviraptors
- Late Cretaceous of Asia & North America
- Misidentification of eggs gave them their name
- Similar to ornithomimosaurs
- Toothless jaws may have been used for crushing hard objects (e.g., clams)
Deinonychisaurs
- "Terrible claw"
- Late Jurassic to Cretaceous
- Some possibly arboreal
- Some possibly omnivorous
- Group that birds are derived from
How did the feeding style of small and large theropods differ?
- Small theropods like the Allosaurus may have killed by repeatedly applying relatively weak slashing bites and backing off
- Large theropods like Tyrannosaurids used more forceful crushing bites
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