lec 14 Flashcards
Dinosaur Physiology:
Warm-blooded – mammals & birds
Cold-blooded – everything else!
Dinosaurs were initially assumed to be just large cold-blooded reptiles, but Sir Richard Owen noted traits (posture, etc.) that suggested warm-bloodedness.
Research in the last 40 years (i.e., posture, locomotion, feeding adaptations, growth rates, bone histology, inferred respiration, and predator-prey ratios) point to elevated metabolisms relative to today’s non-avian dinosaurs
Archaeopteryx was discovered in 1860 – a year after Charles Darwin wrote his book in 1859
Warm-blooded: internal temp independent of external temp
Cold-blooded: internal temp dependent on external temp
Endothermic - regulating temperature/metabolic rate using internal source of energy (food energy)
Ectothermic - Regulating temperature/metabolic rate using external source of energy (heat from the sun)
Tachymetabolic - ‘Warm-blooded’ (“fast metabolism”) Rate of fuel usage is high.
Bradymetabolic –‘Cold-blooded’ (“slow metabolism”) Rate of fuel usage is low
Homeothermy: (‘same heat’) thermoregulation that maintains a stable internal body temperature regardless of external influence. This internal body temperature is often higher than the immediate environment. ‘Warm-blooded’
Poikilothermy: (‘fluctuating heat’) internal temperature varies considerably (usually with temperature). ‘Cold-blooded’
A typical cold-blooded animal is an ectothermic bradymetabolic poikilotherm:
- Energy comes from the sun & fluctuates with external environment; needs very little food. Cold blooded animals become torpid at night and in colder weather
A typical warm-blooded animal is an endothermic tachymetabolic homeotherm:
- Body temperature is stable and activity levels can remain high for long periods of time, at night, and in colder weather; however, needs a LOT of food or will die
What’s the Cost of being Warm or Cold Blooded?
Resting metabolic rate (RMR) vs. active metabolic rate (AMR): “warm-blooded animals tend to have RMRs 4-10x that of similar sized “cold-bloods”, but AMR is similar in both
“warm-blooded” animals tend to have longer durations of sustained activity
Recovery time between periods of activity is often much shorter for “warm-blooded” animals
Why evolve such an expensive trait as endothermy?
Increased aerobic capacity, allowing for greater total activity levels and greater ability to recover from sustained activity
Greater environmental tolerance: endotherms can live in wider range of latitudes and altitudes
Increased metabolic efficiency due to homeothermy: can “fine-tune” physiological systems to a narrow range of temperatures
Increased ability for parental care: both brooding/gestating at constant temperature; increased ability to watch over young
Large tuna and lamniform sharks (e.g., great whites) are effectively ‘warm-blooded’ due to muscle-generated heat
WHY DO WE THINK DINOSAURS ARE ‘WARM-BLOODED’?
In 1973 John Ostrom determined that the hand, feet, and other significant features of Archaeopteryx were almost identical to the maniraptoran theropod Deinonychus.
He reasserted the hypothesis that birds evolved from small coelosaurian dinosaurs
He predicted that if Archaeopteryx was ever found without feathers it would be identified as a dinosaur
In 1970, a specimen of Compsognathus collected in 1951 was recognized as the sixth specimen of Archaeopteryx
EVIDENCE SUPPORTING WARM BLOODED DINOSAURS
- BONE HISTOLOGY (microscopic analysis of tissue and cellular structure)
- SKELETOCHRONOLOGY (Calculating Growth Rate)
- DATA FROM TRACKWAYS
- DENSITY OF NUTRIENT FORAMINA (holes for blood vessels in bones)
- ISOTOPIC DATA
- PREDATOR-PREY RATIOS
P/P ratios of 0.5-4 %
- Basal synapsid-dominated faunas of the Early Permian: 25-30%, much higher than modern populations. Most paleontologists have accepted this as a cold-blooded community
- Therapsid-dominated faunas of the Middle and Late Permian and earliest Triassic: 10-20%, seemingly between endo- and ectothermic populations
- Pseudosuchian-dominated faunas of the Middle and Late Triassic: 10-20%, as in therapsid communities
- Mammal-dominated faunas of the Cenozoic: 0.5-4.5%, known endotherms
- Dinosaur-dominated faunas of the Jurassic and Cretaceous: 0.5-3.5%, same as in modern endotherms, suggests that dinos were endotherms
- POLAR DINOSAURS
- Modern large ectothermic verts are ~limited to below 45O N & S latitudes
- Dinosaurs, including juveniles, are known from above the palaeo Arctic Circle, up to 80O N & S latitudes, includes Alaska and Antarctica
- EFFICIENT DINOSAUR RESPIRATION
- Required to power muscles and fuel growing tissues
- Most tetrapods breath by gulping air & rib bellows; mammals use diaphragm breathing
- Birds use air sacs in the torso, vertebrae, and limbs keep the air flowing in one direction (unidirectional)
- Crocodilians have unidirectional flow, aided by ‘liver’ pumping
- Saurischians (theropods & sauropods) have bird-like air sacs; ornithischians may have had air sacs
- EFFICIENT HEARTS:
- Birds and mammals have four chambered hearts:
- A “double pump” system, so the heart acts as a control between lungs and body
- Shunts blood to lungs before going out to body, so all the blood getting to the tissues are fully oxygenated
- Crocodilians actually have specialized four-chambered hearts: operate as four-chambered heart on land, shifts to two chambered heart underwater since doesn’t need to get blood to lungs
- Since both birds and crocodilians have four-chambered hearts, assumption is that all extinct archosaurs, including non-avian dinosaurs, did too
- THERMOREGULATION
- PROBLEM: small animals have higher surface area/volume ratio than large ones so they lose heat quickly.
- SOLUTION: Cover the body with feathers for insulation
- Feathers (of some sort) are deep in Theropoda phylogeny (e.g., Yutyrannus, Early Cretaceous, China)
- Some basal ornithischians have fuzzy bodies (e.g.,, Late Jurassic Kulindadromeus (Siberia) & Tianyulong (China)
- Later co-opted for display and flight
- Large Size (‘gigantothermy’): Large bodies retain heat & don’t require insulation (no feathers or fuzz known from sauropods)
Skeletal features to Dump Heat
- Sails, plates frills – unlikely but may have played a small role
- Enlarged nares in ornithischians
- Large fenestra in front of eyes in theropods (e.g., antorbital fenestra)
- Nasal turbinates & large nasal passages (lambeosaurines)
- ENCEPHALIZATION QUOTIENTS (use with caution)
- Vertebrate brains scale allometrically, thus brain size vs. body wgt can be calculated for extant & extinct forms
- Compared to the reptilian norm (crocodile) many dinosaurs, esp. maniraptorans plot in the range of modern endotherms
From Middle Jurassic though the end of the Cretaceous atmospheric O2 >20% (2021 = ~20%) allowing for a high metabolism
Mesozoic plants are estimated to 2 to 3 more productive than present day making move food (energy) available to the food chain
ARE VARANIDS (MONITOR LIZARDS) PROTO-ENDOTHERMS?
Longer periods of sustained activity than other reptiles.
Ziphodont dentition (like Megalosaurus) allowing for efficient slicing of meat.
Proto-four chambered heart, so that the lung and body blood pressures are different,
MESOTHERMY
A 2014 study (DOI: 10.1126/science.1253143) found dinosaurs intermediate between modern endotherms and modern ectotherms based in part on growth rate.
Inferred that non-avian dinosaurs could generate internal heat, but they did not greatly regulate their body temperature
LECTURE 15 ORNITHISCHIA
Opisthopubic pelvis
Predentary bone
Palpebral bone
Jaw joint set below level of the upper tooth row
Ossified tendons above the sacral region
Pubis has a splint of bone projecting backward under the ischium
