Dinosaurs October 7, 12 and 14, 2004
A dinosaur cladogram
How to interpret fossils (including dinosaurs!)
DinoStories
Endothermy or not: or something else
Social behavior
Relative intelligence
How much did dinosaurs weigh?
T. rex bites
Pterosaur (OK, it’s not a dinosaur) wingspans
T. rex growth rates
Sue’s tale
Assigned readings (via e-reserves):
1. 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.
2. 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.
Vertebrate phylogeny again
Jawless
fish
Jawed
fish
Amphibians
Anapsids
Lizards
Dinosaurs
Birds
diapsid
skull
synapsid skull
amniote egg
tetrapods
jaws
vertebrae
Synapsid
“reptiles”
Mammals
A dinosaur cladogram:
Theropoda
Sauropoda
Ankylosauria
Stegosauria
Ceratopsia
P achycephalosauria
O rnithopoda
Saurischia
O rnithischia
Dinosaurs
The major groups of dinosaurs:
Dinosaurs sort out into two groups, based on their hip structures:
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
:
Note that dinos include both carnivores and herbivores; both quadrupedal and bipedal
forms.
Interpreting fossils (including dinosaurs!)
The major sources of information:
1.
2.
3.
4.
The fossils themselves (analyses of bones and their geometry, for example)
The rocks (footprints, geographic distribution, environments, for example)
Analogy with living organisms (large mammals, bird descendants, for example)
Mathematical analyses or physical models (estimating size, weight, sound production)
Consider these different lines of evidence and reasoning in the examples below. What
sort of information does each line of evidence produce? Are some sources of
information better than others? How can these different lines of evidence be used
together? Does this sound like an exam question?
Dinosaur Paleobiology - dinostories
Popular, fun topics, and the subjects of many 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.
Note that some reasoning is soft, other is hard. Be sure to be able to strong evidence
from weak evidence, to distinguish the evidence from the interpretation, and to consider
the weight of the evidence.
Five examples of interpretations of dinosaur paleobiology:
1. Endothermy or not: or something else. Were dinosaurs “warm-blooded?
2. Social behavior. Were some dinosaurs social animals? What about parental care?
3. Relative intelligence. Which were the smartest dinosaurs? Compared to what?
4. How much did dinosaurs weigh?
5. T. rex bites. Was T. rex a scavenger or a predator with a good bite?
6. Pterosaur (OK, It’s not a dinosaur) wingspans. The pterosaur from Ptexas
7. T. rex growth rates. Estimating growth rates.
1. Endothermy-Ectothermy argument "hot-bloooded" dinosaurs.
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.
1. 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 cause and effect relationship is not clear
b. speed, activity and agility
High speed, active, agile ----> endotherms today
Low speed, sluggish, clumsy -----> ectotherms today
What about 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?
But: turtles and crocs have many blood vessels in their bones while some
mammals and birds have only few blood vessels in bone: an imperfect correlation
Lucas, 1997
d. Bone structure - growth rings
Warm blooded vertebrates in seasonal habitats don't have growth rings in their
bones.
Cold-blooded vertebrates in seasonal habitats have pronounced growth rings in
the bones.
Some dinosaurs from what were presumed to have been seasonal habitats (high
Mesozoic latitudes) don't have growth rings. But others do.
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.
Migrating dinosaurs and metabolic rates: What if these high latitude dinosaurs
migrated? Maybe they could still be ectotherms (though such large-scale migrations of
ectothermic vertebrates not known today).
Consider Alaskan hadrosaurs migrating from Alaska to Alberta, a distance of
3,000 km. Suppose the trip required 60 days: 50 km/day. Could you be an ectotherm
and maintain such a pace? Not likely.
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
ectotherm predator weight/prey weight = 0.20
2%
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
g. 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” because of small
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 – even mammals: elephants
and ears; behavior too.
Many dinosaurs may have had heat-reducing adaptations; plates on stegosaurs,
neck frills on triceratops. Maybe they were “gigantotherms” Endothermic as a
consequence of large size rather than physiology.
Summing up the possibilities:
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, a paleontologist at Yale, 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.
Lucas, 1997
c. Vocalization.
The hadrosaurs are a group of bipedal, herbivorous dinosaurs often called duckbilled 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. 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 Æ large brain Æ 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
Smarter than lizard or dumber than lizard?
Lucas, 1997
4. How much did dinosaurs weigh?
Fossils probably have soft parts similar to their living representatives. If same
species, then soft parts probably the same. But this approach may not work as well with
very distant relatives. But given that cautionary note, consider how we might estimate
the weight of a dinosaur:
No matter where you go or read about dinosaurs, people want to know how big
they were. Not only height, which you can, after all, estimate after you re-assemble the
bones, but weight.
How can you estimate weight when the soft, fleshy parts of the dinosaur aren't
preserved?
Many estimates of dinosaur weight are based on scale models and analogy with
living organisms. Here’s an example:
Scale model ankylosaur is 1/40th the length of a life-sized ankylosaur. The life-size
length can be estimated by putting the bones back in place in an articulated mount.
We now need to figure out the volume of the model. We can do this by seeing how much
water the model displaces when submerged.
Volume without ankylosaur: 850 milliliter
Volume with ankylosaur: 895 milliliter
The difference is the volume of the ankylosaur = 45 ml
Volume is the cube of a linear dimension, so a 1/40 length (or width or height, i.e. any
linear dimension) model is a 1/40 x40x40, or 1/64,000 volume model,
So, the volume of a full-size ankylosaur is 45 x 64,000 = 2,880,000 ml
Dividing by 1,000 to get liters = 2,880 liters = volume of the ankylosaur
Here, finally, is the analogy with a living organism:
Living crocodiles have a density of 0.9 kg/liter, assuming the same density for the
ankylosaur, a full sized ankylosaur weighed 0.9 kg/l x 2,880 l = 2592 kg
= this is 2.592 metric tons, or 5,702 pounds, or 2.85 US tons (Chevy Suburban)
Assumptions: Might these be sources of error? If so, how much error?
1. model is correct (not too skinny and not too fat)
2. measurements are correct
3. density estimate is correct (armor higher density?), croc not a good analogy?
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. His evidence:
--teeny little, useless(?) front limbs/arms
--large olfactory lobe
--small (for its size) eyes
other evidence that has been cited: supposedly 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) 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 N
Tooth shapes similar in alligators and T. rex. In alligators teeth are used in predation and
in conspecific confrontations (fights between individuals).
Proof that it was a predator?
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. How?
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.
6. Estimating wingspan in a pterosaur. A mathematical approach
Pterosaurs “wing lizards”:
Flying reptiles; Pteranodon
Benton and Harper,
1997
Quetzalcoatlus northropi The pterosaur from Ptexas
Discovery from Cretaceous rocks in Big Bend National park area. Known bones: neck,
hind legs, mandibles, parts of four wings. Note all specimens are disarticulated (e.g., no
whole preserved specimen).
How big was Quetzalcoatlus? Application of relative size relationships.
Estimated size of Quetzalcoatlus based on known relationship of humerus length other
species of pterosaurs.
Wingspan estimates:
1.Intraspecific relative growth in Pterodactylus, growth series of same species;
wingspan estimate = 11 m.
2. Intraspecific relative growth in Pteranodon, growth series of same species;
wingspan estimate = 15.5m
3. Interspecific relative growth: Different sized species within related group;
wingspan = 21 m
Extrapolation beyond the data. Yes, but a range of estimates is reasonable
Lawson, D.A., 1975. Pterosaur from the latest Cretaceous of west Texas: Discovery of
the largest flying creature. Science 187: 947-948.
Kellner, A.W., and Langston, W., Jr. 1996. Cranial remains of Quetzalcoatlus
(Pterosauria, Azhdarchidae) from Late Cretaceous sediments of Big Bend National Park,
Texas. Journal of Vertebrate Paleontology 16: 222-231.
7. T. rex growth rates
How fast did dinosaurs grow and how long did they live? An example from
tyrannosaurid dinosaurs. DinoStory based on 2004 article in Nature.
Erickson, G.M., Makovicky, P.J., Currie, P.J., Norell, M.A., Yerby, S.A. and Brochu,
C.A., 2004. Gigantism and comparative life-history parameters of tyrannosaurid
dinosaurs. Nature 430: 772-775.
Used growth lines in rib bones of specimens of Tyrranosaurus rex and relatives in many
museums.
Figure 1 Growth-line counts in
tyrannosaurids and reptiles of known
ages. a, Thin-sectioned Gorgosaurus
fibula (FMNH PR 2211). The growth
record in this element is complete and
shows five growth lines (arrows),
indicating that it died early in its sixth
year of life. b, Haematoxylin-stained
fibula from an 8-year-old alligator
(Alligator mississippiensis) showing
the expected seven growth lines. Inset,
gastralia (unstained) from 9-year-old A.
mississippiensis showing the expected
eight growth lines and the chemical
label used to verify the periodicity of
ring formation. c, Tyrannosaurus rib
(FMNH PR 2081) showing the 15th to
19th growth lines. Inset, external
fundamental system16 with nine tightly
spaced growth lines, indicating lateadulthood senescence and growth-rate
attenuation.
Erikson et al., 2004.
What then is the relationship between age and size (absolute growth)?
Figure 2 Logistic growth curves for Tyrannosaurus and three related tyrannosaurids. Note
that the exponential stages (the regions of maximal slope) are similar in duration but differ
in slope (that is, growth rates). Regression equations (mass in kg, age in years) are as
follows: T. rex, mass = {5,551/[1 + e-0.57(age-16.1)]} + 5, r2 = 0.953; D. torosus, mass =
{1,728/[1 + e-0.44(age-12.1)]} + 5, r2 = 0.992; G. libratus, mass = {1,234/[1 + e-0.38(age-12.4)]} + 5,
r2 = 0.950; A. sarcophagus, mass = {1,218/[1 + e-0.43(age-14.1)]} + 5; r2 = 0.985.
Erickson et al., 2004
Some results:
More rapid rate of growth in T. rex than in its relatives.
Growth appears to be determinate (though leveling off is based on one specimen).
Very slow rate of growth in first 5- 10 years. Was there parental care during those years?
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?
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 postcranium. 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?