October 10-22, 2002 Dinosaurs
Vertebrate cladogram
Other Mesozoic vertebrates
A dinosaur cladogram
Discovering dinosaurs in southern Arizona – Guest lecture by Richard Thompson, Oct 15
Dinosaur paleobiology – Video, October 17
DinoStories
- Endothermy Assigned reading (via e-reserves): Dinosaur endothermy: Some like it hot. Chapter 14 (pp.325-356) in Fastovsky, D.E. and Weishampel, D.B., 1996. The Evolution and Extinction of Dinosaurs. Cambridge University Press.
- social behavior
- sauropod ecology
- relative intelligence
- T. rex bites
Sue’s tale
Other Mesozoic vertebrates
Mammals — First known from late Triassic; small (shrew-sized), insectivores; single bone in lower jaw (other mammalian characters not well-preserved - hair, live birth, mammary glands)
Major diversification not until the early Cenozoic — post-Dinosaurs
Birds — Upper Jurassic, hollow limb bones, feathers
Marine reptiles
Ichthyosaurs Triassic-K
Plesiosaurs - long necks;
Pterosaurs
flying reptiles; Pteranodon
Size in the Texas pterosaur
· how big was Quetzalcoatlus?
The pterosaur from ptexas; Cretaceous of west Texas
Known bones: neck, hind legs, mandibles, parts of four wings (e.g., no
whole preserved specimen)
Estimated size based on known relationship of humerus length to wingspan in six, better-preserved species of pterosaurs = 15 meters.
Applications of allometric relationships
A dinosaur cladogram The major groups:
Dinosaurs sort out into two groups, based on their hip structures:
A cladogram of the major groups of dinosaurs
1. Saurischia - forward directed pubis
Sauropoda – “brontosaurs” and similar types
Theropoda – mostly bipedal and predatory, includes Tyrannosaurus
2. Ornithischia - rearward directed pubis
-in addition ornithischians have a toothless predentary bone in their mandible, and ossified (bone-like) tendons in their vertebrae
Ankylosauria – quadrapedal, armored dinosaurs
Stegosauria – quadrapedal, plates along back
Ceratopsia – quadrapedal, neck shield, often with horns - Triceratops
Pachycephalosauria – mostly bipedal, thickened skull with fringe
Ornithopoda – mostly bipedal, hadrosaurs, “duck-billed”dinos
:
message: dinos include both carnivores and herbivores; both quadrupedal and bipedal
Dinosaur
Paleobiology - dinostories
Popular, fun topics, and the subjects of some recent, interesting books on the subject (Wilford, Bakker, Horner). But I want to talk about them no just because they are neat dino-stories, but because they illustrate the approaches paleontologists take to interpreting the biology of extinct organisms, whether or not they are dinosaurs.
Some evidence is from the fossils themselves, some is by analogy with living organisms.. Some reasoning is soft, other is hard. Whatever, dinosaurs studies are now a lively field.
Sources of evidence:
from fossils themselves,
from the rocks,
from analogy with living organisms
from mathematical analyses
Four examples of interpretations of dinosaur
paleobiology:
1) the argument concerning endothermy, or warm-bloodedness;
2) various lines of evidence for social behavior,
3) evidence concerning the ecology of brontosaurs.
4) relative intelligence in dinosaurs
5) was T. rex a predator or a scavenger?
1. Endothermy-Ectothermy argument "hot-bloooded" dinosaurs. The lines of evidence:
what does "warm-blooded" mean and who is warm-blooded
ectothermic (cold-blooded) body heat from external source (sun). Body temperature varies with external conditions "heterotherms". “reptiles”, amphibians, most fish, invertebrates
endothermic (warm, or "hot" blooded) body heat generated internally. Body temperature nearly constant "homeotherms". Mammals, birds
As endotherms, we tend to thinks it's the way to be. A superior metabolism and all that. Not necessarily so. Just because there's lots of mammals and no dinosaurs doesn't mean that endothermy is automatically so great. After all, mammals were around during the entire duration of dinosaurs. If endothermy is so great, what took it so long? Furthermore, endothermy comes at a price. You've got to eat all the time. In low nutrient settings, being an ectotherm is clearly superior.
The evidence and reasoning for dinosaur endothermy
a.posture
living ecotherms have sprawling postures and gaits
living endotherms have upright postures and gaits (exception of aquatic mammals)
dinosaurs were (mostly) upright ---> endothermic
plus: really good correlation (activity levels)
minus: correlation ok, but no cause and effect relationship is clear
b. speed, activity and agility
High speed, active, agile ----> endotherms today
Low speed, sluggish, clumsy -----> ectotherms today
dinosaurs: 1. some clearly built for speed (light bones, balance in Velociraptors), 2. some trackways indicate fast speeds for some
3. fast and agile? larger brains: relative brain size large in some dinosaurs
good evidence for carnosaurs and some ornithopods as highly active,
not so good for others
c. bone microstructure - vascular bone
high metabolic rate (endotherms) - many blood vessels in bone
low metabolic rate (ectotherms) - few blood vessels in bone
dinosaur bone - many blood vessels in bone ---> endothermic?
minuses: turtles and crocs have many blood vessels in their bones
some mammals and birds have only few blood vessels in bone
...imperfect correlation
d. Bone structure - growth rings
warm blooded vertebrates in seasonal habitats don't have growth rings in the bones.
cold-blooded vertebrates in seasonal habitats have pronounced growth rings in the bones.
dinosaurs from what were presumed to have been seasonal habitats (high Mesozoic latitudes) don't have growth rings.
e. geographic distribution
ecotherms today distribution limited to warmer climates
endotherms today occur in all climates
dinosaurs known from all latitudes and climates. Even if not as cold as today, there were long polar nights. Little food and cold weather.
but what if they migrated? could still be ectotherms (tho such large-scale migrations of ectothermic vertebrates not known today)
Alaska hadrosaurs: Alaska to Alberta is 3,000 km. 60 days: 50 km/day. Could you be an ectotherm and maintain such a pace?
f. predator-prey ratios
Remember, being an ectotherm exerts a cost: constant eating to maintain that
body temperature.
This is reflected in the amount of food that is consumed by an endotherm versus and ectotherm.
endotherm: 150 kg lion must eat approximately 50 times its body weight each year, or 7,500 kg. With the average tourist weighing about 80 kg, that's about 94 tourists per year.
Ectotherm: 150 kg Nile crocodile, on the other hand, eats about five times its own weight each year, or 750 kg, that's about 9.4 tourists per year
endotherm predator weight/prey weight = 0.02 2%
ectotherm predator weight/prey weight = 0.20 20%
where studied, predatory dinosaurs make up only about 2% of the whole fauna by weight. This is an argument that at least predatory dinosaurs were endothermic
f. body size and gigantothermy.
an alternative metabolism?
leatherback turtles: 1,000 kg, low metabolism, but nearly constant body temperature. How do they do it? Heat retention or gigantothermy
surface area to volume:
-small animals have a greater surface area relative to their volume than larger animals.
- small animals lose heat faster than large ones. Mouse will freeze to death sooner than, say a human.
- large animals sometimes need to cool themselves: elephants and ears; behavior too.
- many dinosaurs may have had heat-reducing adaptations; plates on stegosaurs, neck frills on triceratops. Maybe they were
- “gigantotherms” Endothermy as a consequence of large size rather than physiology
Summing up:
1. all ectotherms
2. all endotherms
3. some ectotherms, some endotherms
4. large ones gigantotherms as adults, smaller, juveniles were endotherms. Metabolism changed during life?
5. some combination of 3 and 4.
2. Social behavior (3 examples from three different dinosaurs - social behavior probably varied among dinosaurs, just as it varies among mammals today. Don't generalize).
a. Parental care. Jack Horner, a paleontologist at Montana State found a cluster of small (juvenile) skeletons and eggshells in K rocks in Montana. Fossils clustered within a "nest" measuring 2 m in diameter. Juvenile teeth were slightly worn. "Dinosaur love nest discovered in Montana"
-young still in nest
-worn teeth suggesting that they were feeding (or were fed)
Evidence suggests extended parental care. More nests have been found since. Recall Penguin nesting grounds.
Dinosaur genus named Maiasaura - the good mother reptile.
b. Gregarious herding.
Evidence here is not from the fossils themselves, but from trace fossils - the footprints - indeed trackways. Eubrontes
Dinosaur trackways in Triassic/Jurassic rocks in the Conn. River valley of Mass and Conn.
Ostrom plotted the orientations of the trackways and found that 70% were all going in the same direction. A herd?
Note assumption that all were made at the same time.
c. Vocalization.
The hadrosaurs are a group of bipedal, herbivorous dinosaurs often called duck-billed dinosaurs. One subfamily is characterized by elaborate crests and crowns in the skulls. (see handout)
These are hollow and are connected to the nasal passages. Possible functions that have been proposed include under-water feeding (not likely), sexual display and identification, and/or vocalization.
Consider that adults, being large, would resonate with a low frequency, and juveniles would resonate with a high frequency (Tuba vs flute).
3. Sauropod ecology.
The traditional interpretation, from the Peabody Museum mural semi-aquatic,
swamp dwellers, munching contentedly on soft vegetation. So interpreted because of their bulk and a presumed sprawling posture, high external nares, long neck
How does this stack up to the evidence?
-high nasal openings
snorkel in semi-aquatic, humidifiers in terrestrial organisms
-tail
broad and flat paddle as in crocs in semi-aquatic
round or reduced in terrestrial
round in hippos
-teeth
little-wear and molar like in aquatic hippos
peg-like and worn in terrestrial
peg-like and severe wear in sauropods
-thorax
broad and flat in semi-aquatics like hippos
deep and narrow in terr. like elephants
deep and narrow in elephants
-posture
sprawling where weight is supported in water as in hippos and crocs.
upright, underneath body in elephants and giraffes.
upright, underneath body in brontos (tracks)
-necks
typically short, as in hippos and crocs in semi-aquatic
long necks in terr associated with feeding from trees, as in giraffes, or with elephants -the equivalent of a long neck.
sauropods had long necks.
4. Relative intelligence
Can’t give ‘em an AIMS test or run them through a maze to check their intelligence. But we do have some direct evidence available: the size of the brain case
large brain case à large brain à intelligent?
BUT: need to correct for body size. A large animal will have a larger brain than a small animal, even if the small animal is smarter by some standard. So, we need to calculate
Relative brain size: brain size volume/body size volume
Set a standard: living lizard = 1.00
larger number means bigger brain for its body than a lizard
smaller number means smaller brain for its body than a lizard
Dumb and dumber?
Smarter than lizard or dumber than lizard?
predictions? Sauropods
Stegosaurs
Carnosaurs
5. Was T. rex a carnivore or a scavanger? T. rex bites
Erickson, G.M., Van Kirk, S.D., Su, J., Levenston, M.E., Caler, W.E. and Carter, D.R., 1996. Bite-force estimation for Tyrannosaurus rex from tooth-marked bones. Nature 382: 706-708.
Was T. rex an active carnivore or a lowly scavenger?
Jack Horner resurrects idea of T. rex as a scavenger
--teeny little, useless(?) from limbs/arms
--large olfactory lobe
--small (for its size) eyes
others: weak teeth and jaws
What abut the strength of the teeth and jaws?
Evidence from T. rex tooth marks on pelvis of a Triceratops from Hell creek Formation
(K) of Montana.
Punctured bone to a max depth of 11.5 mm.
Casts of punctures indicate large, caniform tooth: T. rex.
What sort of force would be needed to puncture bone like that to that depth?
Erickson et al, 1996. Nature 382: 706-708 do an experiment:
Made replica of T. rex tooth out of aluminum-bronze
Used cow pelvis and then measured the force needed to penetrate bone to depth of 11.5
mm.
Triceratops bone: dense cortical bone on surface to depth of 2.5 mm over weaker,
cancellous bone.
Cow bone: used portion of hip bone with a similar-depth surface layer of cortical bone.
Attached tooth replica to hydraulic press that measures the force being applied, press into cow hip bone.
Penetration to 11.5 mm required 6,140 Newtons (N) of force. Estimate is for nn anterior tooth; posterior max estimate would be 13,400 N
Estimates of maximum bite forces for extant vertebrates at posterior tooth positions:
Labrador dogs 550 N
Humans 749 N
Wolves 1,412 N
Dusky sharks 1,446 N
Lions 4,168 N
American alligator 13,300
Tooth shapes similar in alligators and T. rex. In alligators teeth used in predation and in conspecific confrontations (fights between individuals).
Proof that it was a predator?
n no, but indicates that T. rex was not limited by its dentition to being a scavenger. Consistent with a predatory mode of life. This experiment could have supported a scavenging interpretation. It didn’t.
Erickson, G.M. and Olson, K.H. 1996. J. Vertebrate Paleontology 16: 175-178.
Currie, P.J. and jacobson, A.R., 1995. Canadian Journal of Earth Sciences 32: 922-925.
Sue’s Tale
Express yourself: the fossil debate.
What
do you think about these issues and why?
Should fossil collecting and selling
be regulated? If so, how?
--will explain the basic controversies; illustrating them with a famous case that came to some sort of a strange resolution recently
Two issues:
1. Selling fossils
pro: Fossils are no different than any other natural resource that is bought and sold.
con: Sale of fossils to private collectors prevents their scientific study; commercial collectors damage scientifically valuable fossils while excavating commercially valuable ones.
2. Collecting on public lands
pro: Businesses and individuals have the right to use public lands (often for a fee) for grazing, mining, timber, recreation, why should fossil prospecting be any different?
con: Fossils on
public lands are a unique resource that belong to the American people. Only professional paleontologists should be
allowed to excavate for fossils so that the fossils can be protected and
displayed for the public.
Sue, the T. rex, a brief history
~ 70 million years
ago, in what is now central North Dakota
death of a Tyrannosaurus rex
Spring, 1990.
Peter Larson, Black Hills Institute, pays rancher Maurice Williams $5,000 for right to excavate for dinosaurs on his land
August 12, 1990
Susan Hendrickson, working for the Black Hills Institute, finds part of T. rex skeleton sticking out of the ground. Dinosaur nicknamed after its discoverer.
1990-1992
Black Hills Institute excavates rest of Sue. Prepares skull and part of post-cranium. One of only 22 specimens of the species, Sue is the most complete specimen of T. rex ever discovered.
---Healed leg bone, scar on skull, robust form (prob a female)
1992
FBI and National Guard confiscate Sue. Larson and Black Hills Institute charged with stealing fossils from Government-owned land. Williams’ ranch part of Sioux Reservation held in trust by Federal Government for a tax obligation.
--partially prepared Sue stored in bank vault in Rapid City SD while legal issues are ironed out
1995-1996
Peter Larson, his brother Neal Larson, and others of the Black Hills Institute tried on about 75 different charges. Acquitted on 72, Neal Larson convicted for stealing government property (fine and probation); brother Peter convicted for money smuggling (serves 18 months). Court awards ownership of Sue to Williams.
October 4, 1997
Sue (all 130 crates of her) is auctioned at Sotheby’s in New York. Field Museum of Chicago, with backing from Disney and McDonald’s, pays $8.4 million dollars for Sue.
Sale proceeds held in trust for Williams.
Field Museum has three interest-free years to pay; two years of preparation work still required; replicas to be provided to Disney and McDonalds.
Effect of sale:
1. Sue available for study and for public to enjoy, thanks to philanthropy of major corporations (a long and excellent American tradition).
2. Fossil prospecting by commercial operations (for dinosaurs at least) will be encouraged. But prospecting for fossils isn’t easy; a lot of damage can be done by people who don’t know how to do it.
3. Fossil prospecting by academic and museum paleontologists will be discouraged. Private landowners aren’t likely to donate or cheaply sell their “fossil rights”. This is likely to keep academic and museum paleontologists from prospecting for fossils.
What should have been done?
Has the Field Museum hurt all museums in the long run?
Should fossil collecting and selling be regulated? If so, how?