Download Dinosaurs and Their Relatives

Dinosaurs and Their Relatives
Lecture 1: 02/02/06
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Science B—complex systems (historical)
o Idiographic—description of unique events
o Nomothetic—rules, laws
The first text was the Bible
Francis Bacon (1561-1626) argued that there are two great books authored by
God, the Bible and the Natural World; but if ever there were a conflict between
the two, the Natural World would take precedence in our understanding
Bishop James Ussher (1701) proposed that the Earth was formed in 4004 BC on
October 23 at 9am
James Hutton (1788) believed the Earth was much older and is known as the
founder of modern geology
o Hadrian’s Wall was erected 2,000 years ago by the Romans to keep the
Scots out of England (the wall is between England and Scotland)
o Noticed that the there was a very thin layer of soil at the bottom of the
rock wall that was the same color as the rock; deduced that soil is decayed
rock
o The accumulation of thick soils meant that the Earth was very old
o Principle of uniformitarianism—“the present is the key to the past”—
processes that operate today have also operated in much the same way in
the past; the rate of soil formation is roughly the same in all places and
throughout time; foundation of modern geology
Charles Lyell (1830-1833)—made Hutton’s work known and established geology
as the premier science
o Realized that there must be a rock cycle in which soil and rock are
recreated by each other since soil is necessary for growing food and
sustaining life; influenced by the deistic belief that God must have
designed this
Fossilization
o Key aspect is burial in sediment
o Sediment—rock fragment
o Fragments can be clays, muds, silts, sands, cobbles (goes from small to
large in terms of grain size)
o Burial needed to prevent decay/rotting and bacterial action
o Other ways to prevent these things include oxygen or water deprivation
(drying out)
Burial in sediments
o Occurs in river deltas, flood plains, lakes, and sometimes deserts (even
though there is no water, sand moves things around)
o Unlikely places are on most surfaces of land, including forests, mountains,
and Harvard Yard
Means two things: the fossil record is incomplete, as most remains rot or are
scavenged; the fossil record is biased, as some environments are more conducive
to burial than others (mountainous species will likely never be seen)
Dinosaurs and Their Relatives
Lecture 2: 02/07/06
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Fossilization—burial (any way of stopping decay, bacteria, or scavenging)
o Lacustrine/lake is good for burial, acolian/desert is okay (even though
there is no water, sand moves things around), glacial is terrible, and
fluvial/river is particularly good (floodplains, deltas)
o Marine (sea) is not ideal for finding dinosaur fossils; can find fossils in
oceans though due to bloat and float
o Terrestrial settings are best for finding fossils
The fossil record is: incomplete—most remains rot or are scavenged; biased—
some environments are more conducive to burial and fossilization than others
100-year floods cause sediments to become compacted/cemented to layers of
sedimentary rock
Geologic time is very long; suppose 1 foot of sediment compacts to 1 inch of
sediment in 100 years, then you will have 1 foot of rock in 1,000 years, 1,000 feet
of rock in 1,000,000 years, and 100,000 feet of rock in 100,000,000 years
Sediments are usually deposited horizontally
o Exceptions include when air and water disperse them across sand dunes
and they become deposited at an angle; form cross-beds
Stratum—a layer of sedimentary rock (plural is strata)
Stratigraphy—the study of sedimentary layers
Law of Superposition—younger layers are always on top of older layers
o One exception is faults (usually up and down but sometimes horizontal)
and folds; when land drifts and collides it gets scrunched up, and it
becomes difficult to see which layer is on top
o Another exception relates to geographic distance since it is difficult to
compare layers from different regions
Correlation—the process of identifying rocks of the same or similar age
o Difficult when there is a complex geology or wide geographic distances
o Evolutionary processes are slow on human time-scales but fast on
geologic time-scales
o Evolution charts out a unique history, meaning that there is a unique
succession of fossils in the rock record
o Can determine which rocks have the same age by identifying which
contain the same fossils; helps clarify cases with folds
Biostratigraphy—if rocks contain the same fossil specimen, then they are
approximately the same age
o Can correlate with a single species or whole communities since evolution
is fast with respect to geologic time
Can determine absolute ages by radiometric dating, e.g., Carbon 14 (14C) dating
o Lacking since only fossils about 50,000 or 70,000 years and more can be
dated; for the most part, there is no way to date fossils directly
Can date only igneous rocks—rocks that crystallize from a melt like lava or
magma (molten rock); can determine the ages of the igneous rocks and deduce
that certain fossils must be older or younger than them
Dinosaurs and Their Relatives
Lecture 3: 02/09/06
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With a combination of stratigraphy and biostratigraphy (fossils to correlate rocks,
relative ages) and radiometric dating (absolute ages), we have been able to
develop a global geologic time scale
Igneous rocks are dated by radioactive decay (disintegration of atoms)
o Radioactive elements are trapped in crystals as the crystal forms (as
magma cools); of most use are volcanic ash falls
o Half life (T½)—the time for half a set of radiometric atoms to decay
o 14C: T½ = 5,730 years; after about 12 half lives (about 70,000 years), you
have only 1/4,000 original atoms left, a limit of measurement
o Uranium 235 (235U): T½ = 704 million years; the 235U is trapped in
zircon (crystal)
 235U  207Pb (lead, Latin for plumbing); can estimate how many
half lives have passed by comparing the ratio of uranium and lead
 Double check for loss of 235U and 207Pb: use a second uranium
series, 238U  206Pb, which decays with T½ = 4,470 million
years (4.47 Ga), much longer
History of the Earth (think in terms of a football field)
o Origin of the Earth = 0 yard line
o Now = 100 yard line
o First fossils (bacteria) = 24 yard line
o Good fossil record = 87 yard line
o First dinosaurs = 95 yard line
o Last dinosaurs = 98.5 yard line
o First humans (Homo) = 4 inches from the end zone
o Civilization = 1/10,000 of a yard from the end zone
Alfred Wegener (1915)—concluded that continents drift but did not know by
what mechanism; matched fossils and rock types to determine that the continents
were once attached at their coastlines
o After matching fossil and rock types, argued that there was a super
continent called Pangaea 225 million years ago at the beginning of the
Triassic period
o Theory became accepted in the late 1960s
Plate tectonics—explains continental drift and a general theory for Earth’s
geology
o Accepted after the discovery of symmetrical magnetic stripes about the
mid-ocean ridges on the sea floor
o North to south to north flipping of the Earth’s magnetic field, as trapped in
the sea floor
o Earth’s core rotation causes the flipping of the magnetic field
o Hawaii is a string of islands formed as plates shift over a hot spot; the
volcano forms islands that drift away and erode
o Evidence for plate boundaries comes from Earthquake epicenters and
volcanoes
Dinosaurs and Their Relatives
Lecture 4: 02/14/06
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All mountain ranges (volcanoes) occur at the edges of plates or what used to be
the edges of plates
 Major controls on dinosaur global distributions:
o Climate
o Position of continents
o Epi-continental seaways
 Plates move at about the rate of fingernail growth (1-20 cm/year, 10 cm/year on
average; 100 km/million years)
 Deathdecayburialre-mineralization
 Fossils:
o Body fossils (e.g., bones)
o Trace fossils (e.g., footprints—tracks and trails)
o Both body and trace fossils are given formal scientific names; names are
always in two parts (genus and species) and written in italics or underlined
(e.g., Homo sapiens and T. rex)
o We tend to use the Genus (plural genera) name and not the species name
(e.g. Triceratops, not horridus, and Stegasaurus)
 1770—discovery of Mosasaurus (not a dinosaur, closest relative is the lizard) in
Holland
 1795—Cuvier (in Paris) proposes that the species had become extinct
 First dinosaurs were discovered in England
 1815—Dean William Buckland finds Megalosaurus jaw fragment
 1822—Mary Ann Mantell finds Iguanodon teeth and other elements
 1824—Buckland describes Megalosaurus
 1925—Mantell describes Iguanodon
 1833—Buckland describes Hylacosaurus
 1842—Owen coins the term “Dino saur,” which means “terrible lizard”
 1677—Reverend Plot describes Scrotum humanum, probably a thigh bone of
Megalosaurus
 1851—Dino-mania begins in the Crystal Palace (Victorian England)
 Dinosaurs begin to be discovered in the USA
 1858—A few teeth found in the West
 1858—First almost complete dinosaur, the Hadrosaurus (duck bill), found in New
Jersey; suggested that dinosaurs had a bipedal (two-leg) stance
 1877—Cope and Massh make first great dinosaur discoveries in the West
 1878—39 complete skeletons of Iguanodon are found in a fissure (uncommon) in
Belgium (Bernissart)
Dinosaurs and Their Relatives
Lecture 5: 02/16/06
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David Norman’s work with Iguanodons
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o Teeth form grinding surfaces and are packed in large numbers (up to 2,000
in some); teeth wear down and grow continuously
o The tooth row is inset from the cheek in order to make room for chewed
food
o The predentary bone has a rough surface in order to support a keratin
sheath (or beak) that has no teeth
 Keratin is the stuff in hair, fingernails, and claws
o Foramina (small holes) are along tooth rows and behind the predentary
bone; they supply blood (nutrients) to the “beak,” gums, and cheeks
o The jaw articulation lies below the occlusal plane (where the teeth meet),
enabling the teeth to meet altogether as the jaw closes and facilitating
grinding
o Novel method of grinding food; the upper jaw flexes out as the lower jaw
closes; “past is the key to itself”
Results for dinosaurs
o Great diversity of biologies
o Some functions are unique
o Modern analogs for inferring function can be hard to find
o Analysis led to a revolution in dinosaur biology
Species definition—there are many
Population—an interbreeding group of individuals
Biological species concept—a species is a group of interbreeding (or potentially
interbreeding) populations that cannot interbreed successfully with other such
groups
o Complications include how we know individuals can interbreed if they are
not currently interbreeding and ring species (see readings book)
o Not so useful for fossils, so instead we use a morphological species
concept
Morphological species concept—different species will look different from one
another since like begets like
o Can distinguish species based on head width when you have a lot of
fossils but not when you have just two (don’t know how similar they are
since there is no other comparison)
o As you gather more fossils and information, you can determine if the head
widths form one or two clusters; however, even if there are two clusters,
one might be male and the other female
o Sexual dimorphism complicates the application of species concepts
It is hard to distinguish species in the fossil record given few specimens,
incomplete preservation, or species extinction; as a result, we typically work at
the genus level
Classification—in 1735 Carlis Linnaeus (real name Karl Linné) established genus
and species binome
Evolution
o Formal study began in 1859 with Darwin and Wallace; Darwin wrote
“The Origin of Spcies”
o Malthus proposed the idea of the struggle for survival in 1789
o Phenotype—the morphological, biochemical, and/or behavioral
characteristics of an organism
o Genotype—the genetic material, or DNA, that gives rise to the phenotype
o Driving force of evolution is the fecundity of nature (i.e., its propensity to
over-produce)
o Evolution is historically contingent, as windows of opportunity open and
close over and over again
Dinosaurs and Their Relatives
Lecture 6: 02/21/06
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Humans have 23 pairs of chromosomes (DNA)
o There are two pairs of each gene, one coming from the father and one
coming from the mother
Regular hemoglobin gene H, sickle cell hemoglobin gene S
o HH—normal blood
o SS—sickle cell blood
o HS—normal blood
o If each parent is HS, ¼ of their children will be HH, ¼ will be SS, and ½
will be HS
Sickle cell and resistance to malaria
o HH has no special resistance to malaria
o HS has some resistance to malaria
o SS has resistance to malaria but also has the sickle cell disease
o If malaria is present, there is a tradeoff for HS parents between some
resistance and losing offspring; ¼ of their children won’t have resistance
to malaria, ¼ will develop sickle cell disease, and ½ will have just some
resistance
Principle of Frustration—all organisms have multiple needs, and there are often
conflicting solutions to those needs; the overall optimal solution for an organism
is unlikely to be optimal for any single task or need
o Explains why there are so many species; organisms are complexes of
compromises; we maximize, not optimize (keep the tree evolution
computer simulation in mind)
The nature of variation (particularly important during growth) constrains the path
of evolution; in other words, the variation available limits the scope of possible
evolutionary changes (e.g., there are many breeds of dog and pig and fewer breeds
of cat and horse)
o In dogs, nose length is particularly allometric
o In cats, nose length is basically isometric
Evolution is influenced by selection, variation availability, and chance!
o Complications in understanding how selection operates include the
Principle of Frustration (which need accounts for the evolution?) and the
“hitchhiking” correlation of characters
 Evolutionary “hitchhiking” makes it hard to identify the targets of
selection (e.g., balls of different colors and sizes and T. rex)
Speciation—the origin of a new species
o Change within a species over time; in other words, species 1 evolves into
species 2; called anagenesis or phyletic evolution
o Origin of a new lineage; in other words, species 1 branches into species 1
and species 2; called cladogenesis or branching
 Speciation itself refers to the origin of a new lineage, includes many mechanisms,
and involves allopatric speciation
 New species form (allopatrically) when populations diverge over time so that they
can no longer interbreed; a barrier to reproduction occurs and lasts long enough so
that sufficient differences accumulate (by chance, by selection)
 Species are related to one another, and the closer they are, the more similar they
should be (in general)
Dinosaurs and Their Relatives
Lecture 7: 02/23/06
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Amnion—surrounds the embryo and prevents it from drying out
o Enabled tetrapods to reproduce on land, freeing them from living in or
near water
o Amniotes were the first fully terrestrial vertebrates
 Fenestra (means “window)—large openings in the region of skull behind the eye,
called the temporal region
o Most amniotes have fenestra in their temporal region
 Molecular Revolution—cladograms start to be built with synapomorphies found
in DNA
o Can apply this method to all organisms and thereby develop a tree of life
o Use the genetic code (A, T, G, C)
o Each of your cells contains about 6,000,000,000 bases of DNA (6 feet
worth)
 Mitochondria—bacteria derivatives that provide cells with energy
o Mitochondria in humans have just 16,000 base pairs; they are super
stripped-down bacteria since with the a new host, they didn’t need prior
functions and genes; purple bacteria (see back of handout 4)
 Chloroplasts—bacterial derivatives that harvest light
Dinosaurs and Their Relatives
Lecture 8: 02/28/06
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Phytosaurs
o Aquatic
o Carnivores
o Triassic
Aetosaurs
o Terrestrial
o Herbivores
o Triassic
Crocodiles
o Aquatic (mostly)
o Carnivores
o Triassic  Recent
 Biped—walk on two legs (e.g., T. rex, Homo sapiens)
 Quadruped—walk on four legs (e.g., dogs, cats)
 Obligate (can be only bipedal or only quadrupedal) vs. facultative (can be either)
o A chimp can be considered a facultative biped
 As of 1990, there were 285 genera described
o 246 genera were from 1 species
o 2,100 skeletons were found
o 45% of genera were from 1 individual (partial skeleton)
o 75% of genera were from fewer than 5 individuals
o 20% of genera had at least one skull found (about 55 genera)
 On average, a genus lasts 5-10 million years (7-8 million years for mammals)
o Saurischia—contained about 6 types of individuals/genera
o Ornithischia—contained about 9 types of individuals/genera
 Scientists have discovered (approximately) 1/4 - 1/8 of all large dinosaurs and
1/20 - 1/40 of all large dinosaurs by finding at least one skull
Dinosaurs and Their Relatives
Lecture 11: 03/09/06
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Darwin (1859) said almost nothing about the origin of birds but did complain
about the fossil record
1861—skeleton of Archaeopteryx discovered (ancient wing)
Huxley noticed numerous resemblances between dinosaurs and birds
Heilmann (1926) noticed features shared by theropods and birds; but dinosaurs
lacked clavicles (fused collar bones); means that dinosaurs must have lost their
collar bone and then regained it
Dollo’s Law—complex structures, once lost, are not regained; birds must have
been derived from primitive Archaesaurs, not dinosaurs
We now believe that birds evolved from theropods
o Dollo’s Law no longer inviolate, can be outweighed by other evidence
o Clavicles (sometimes even fused) are known in some dinosaurs but are
rare
 Clavicles easily lost during preservation
 Clavicles remained cartilaginous, didn’t ossify
Archaeopteryx and Bird differences: Archaeopteryx lacks:
o Loss of teeth
o Large sternum
o Reduced tail
o Expanded brain
o Fused fingers
o Fused pelvis
Archaeopteryx is a theropod and a bird, but a very primitive bird
Dinosaurs and Their Relatives
Lecture 12: 03/14/06
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Pterosaurs—means “winged lizard”
o First appeared in the Triassic
o Became extinct at the end of the Cretaceous
o 50 genera known (smaller group than dinosaurs)
o Most are small
o Synapomorphies include an elongated fourth digit to support the wing
o Active fliers—large shoulder muscles; brain has a large plocculus for
balance; large sternum for flight musculature
Dinosaurs and Their Relatives
Lecture 13: 03/21/06
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Either the fossil record of theropods and birds is incomplete (more likely) OR
birds branched off earlier than the cladogram suggests
 Feathers predate birds
 Origin of feathers—modified scales; evolved for:
o Flight—rejected because some dinosaurs had feathers
o Display—not good at explaining the origin of feathers but may explain
why feathers became large
o Insulation (temperature control)—fits with the small size of feathered
theropods
o Predation (of insects)—seems farfetched
 Origin of powered flight in birds
o “Ground-up” hypothesis—theropods lived on the ground and
gradually made the transition to flight; but how? hard to see how there
could have been selection for incremental improvement in flight
ability
o “Trees-down” hypothesis—first came gliding and then powered flight;
allowed for incremental improvement
 Ostram (at Yale) argued that the claws of Archaeopteryx looked like the claws
of ground dwelling birds; supports the “ground-up” hypothesis
 A more refined, quantitative analysis suggests that Archaeopteryx could
have/did live in trees (see graph in packet); supports “trees-down” hypothesis
 Mammals and living birds both are warm-blooded; this is perhaps the reason
why they have weaker muscles; if Archaeopteryx was cold-blooded
(reptilian), then maybe it had more powerful muscles
o Can test physiology by looking for growth rings in bones
Dinosaurs and Their Relatives
Lecture 16: 04/06/06
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In Montana, there are bone beds with thousands of bones of Maiasuara; these beds
extend over a couple of square miles
10,000 individuals preserved; implies herding and catastrophic death
o Possible that a volcanic eruption poisoned them (with CO2) and then
buried them in ash
Evolution (Darwinian)
o Variation
o Selection
 Natural selection
 Sexual selection
o Have to reproduce to pass genes onto the next generation
 Sexual selection is very important if species are non-monogamous
(harems); can lead to exaggeration of some characters even if they
do not look advantageous from a natural selection point of view
(e.g., peacock tail feathers, which are actually
Dinosaurs and Their Relatives
Lecture 17: 04/11/06
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It is assumed for birds and reptiles that females are the ones who choose and
males are the ones whom are chosen
It is the sex with the highest parental investment that usually chooses
1. The female makes and lays the eggs and then has the responsibility of
parental care
2. An exception is sea horses: males look after the young in a pouch for
some time after hatching; males choose and females display
We want to test the hypothesis that sexual selection is responsible for crests in
hadrosaurs
1. “Use it or lose it” test: some elements of the crest are not part of the air
passageway; the extra bone is for display
2. One would expect that eyes and ears are well developed; there are
plenty of other reasons for having good eyes and ears
3. Crest shape should be species specific; this seems to be true based on
non-crest demonstrations
4. One would expect to see more elaborate crests when more specifies
are present; this seems to be true
3.  On balance, the hypothesis is plausible and reasonable  one
would expect sexual dimorphism, and that seems to be true
Head (flank) butting in Stegocerus
1. Thick skull
2. Wide hips
3. Extra bone in the back vertebrae that stiffens the back
4. 45-degree angle at which the backbone meets the skull
5. Shelf at the back of the skull for extra muscle support during collision
6. Closure of the upper temporal fenestra as the skull is strengthened
Dinosaurs and Their Relatives
Lecture 18: 04/13/06
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Dinosaur fossils from the late Cretaceous have been found near the poles (e.g., in
northern Alaska); they suggest that the Earth was ice-free (sea-ice) and much
warmer then; the poles had forests, etc.
Today, the temperature gradient between the poles and the equation is about 80
degrees F; in the late Cretaceous, the gradient was about 40 degrees F
The Earth’s tilt is about 23 degrees; this suggests that the poles are dark 6 months
of the year; therefore, dinosaurs must have migrated large distances
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We have covered about 80 percent of the well-preserved dinosaurs
We can expect new types of dinosaurs to be found in coming years; there has
been an exponential increase in the discovery of new species
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Euryapsids
Modified diapsids
All marine (ocean)
All derived from terrestrial ancestors
o Breathed air
o Started with 4 limbs, etc.
Dinosaurs and Their Relatives
Lecture 19: 04/18/06
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In advanced ichthyosaurs
o Ribs are attached to the backbone by two heads
o Tail bends downwards (most Jurassic and all Cretaceous forms); we know
this because:
1. The tail is always bent downwards
2. The body outlines always show the backbone in the lower fluke
3. A wedge-shaped vertebra(e) creates the bend
Most reptiles lay eggs
Some, though, produce eggs, which are incubated and hatched inside the mother
(oviviporous); in these cases you get live births (e.g., snakes, lizards, sharks)
o There is usually no nutrient exchange between the mother and embryos;
however, there is in few reptiles (e.g., lizards)
Ichthyosaurs gave live births (oviviporous)
Dolphins echo-locate; could ichthyosaurs?
o Dolphins have ear (otic) capsules that are isolated from the skull by soft
tissue; they need this for echo-location
o Ichthyosaurs have otic capsules that are fused to the skull; they did not
echo-locate
Dinosaurs and Their Relatives
Lecture 20: 04/20/06
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Snakes and Lizards
o 6,000 living species
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o Small
o Most are tropical
Mammals
o About 4,000 living species
The first snakes and lizards appear in the fossil record in the Jurassic; we suspect
that their origins are in the Triassic, so the record must be poor
Two origins of neck retraction in turtles
Evolution of sea-going turtles
Warm-bloods = endotherms
Cold-blooded = ectotherms
Humans
o Warm-bloods
o Endotherms
o Homeotherms
Lizards
o Cold-bloods
o Ectotherms
o Poikilotherms
Hummingbirds
o Warm-bloods
o Endotherms
o Poikilotherms (their body temperature drops at night)
There is a gradient between being and endothermic and being ectothermic
o Sea turtles (endotherms, poikilotherms) keep their body temperatures at
about 10 degrees F above the ambient
Parts of the body can be endothermic
o Sail fish (marlins) are cold-blooded and ectotherms but have a heater
organ (muscle) that warms the forebrain and the retina to see depths in the
sea
Note: an ectotherm in a constant environment (e.g., a cave) is a homeotherm
Dinosaurs—were they endothermic or ectothermic, and to what degree?
o They are traditionally considered ectotherms because they are reptiles
o 1970-1980s—Deinonychus hunting in packs
Sustained activity
Enthodermy…(?)
o Birds are endotherms, so maybe their theropod ancestors were endotherms
too
o Polar migrations of dinosaurs
 Sustained activity
Endotherms require about 10 times more food (energy) than ectotherms
Dinosaurs and Their Relatives
Lecture 21: 04/25/06
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Taphonomy concerns itself with the study of biases in the fossil record
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Hadrosaurs, ceratopsids, and sauropods traveled in herds; the whole group would
get buried in one preservation event; can get huge numbers of individuals
preserved
Theropods (T.rex) tend to be found as single individuals or very small groups;
likely to get only 1-2 individuals per preservation event
Predator/prey ratios will be biased towards over counting herbivores
“Hand-bag” farms (Alligator farms)
o Constant, warm temperature
o Fast, continuous growth
o Bones look mammalian (even though Alligators are ectotherms)
Bone histology can tell you if something is warm-blooded and whether it is a
homeotherm or poikilotherm
In the Late Cretaceous
o The world was warm
o Most dinosaurs were large
 Large body size means they could retain heat well
o Very large animals were likely to be approximately homeothermic even
if they were ectothermic
Elephants
o Naked
o Losing heat is a problem
 Large ears to drop heat
o Must eat almost all the time to keep endothermic fires burning
It is hard to see how sauropods could have eaten enough to be endotherms
At the other end of the size range, we have small theropods, some with feathers
o Feathersinsulationendothermy; small size if
ectothermicpoikilothermy
o Supports that small theropods were endotherms
Nasal turbinates
o Don’t fossilize
o Inside nasal cavities
o Increase the surface area inside the nose
o Only found in endotherms like birds and mammals
o Large nasal cavities
o Function
 Warm and humidify the air as we breathe in
 Extract heat and moisture from the air as we breathe out
Dinosaurs have small nasal cavities
o Did not have nasal turbinates
o Ectotherms…?
But if the environment was moist, maybe they didn’t need turbinates…?
Summary
o Not decided
o Expect different physiologies in different groups
o Small theropods were likely endotherms
o Large sauropods were likely ectotherms
o Everybody else was likely somewhere in between
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Hard to read extinction patterns in the fossil record
o At the coarse (global) scale, extinctions tend to look sudden
o At the local scale (individual outcrops of rock), extinctions tend to look
more gradual; extinctions also tend to look more intense since it is easy to
mistake a local extinction for a global extinction
Dinosaurs and Their Relatives
Lecture 22: 04/27/06
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There is evidence of a large impact (by a comet/asteroid = bolide) at the K/T
boundary (exactly!)
Evidence:
1. Global Iridium layer
 Gubbio, Italy
 Signature of bolides
2. Chicxulub crater Yucatan Mexico about 110 miles across
3. Glass-bead layers around gulf of Mexico (tektites)
4. Tsunami—deposits all around the Gulf of Mexico
5. Global soot layer
6. Shocked quartz
Meteor—in space
Meteorite—meteor large enough to reach Earth’s surface
Size—about the size of Mt. Everest; about 6 miles across
Mt. St. Helens produced about 0.5 cubic km of debris
Krakatau produced about 12 cubic km of debris
Chicxulub produced about 22,000 cubic km of debris
o Global, short-term climate change
 First heat, then cold as the sun was blocked
Dinosaurs and other amniotes:
o The extinction rate if greater than 25 kg is almost 100%
o The extinction rate if less than 25 kg is variable
Larger body size = more extinction prone
1. Have smaller population sizes
2. Require more food and are more often specialized
At the end of the K, the vast majority of dinosaurs were large; dinosaur extinction
is due to chance
o Mammals not superior to dinosaurs
Signor-Lipps effect—mass (sudden) extinction, given the incompleteness of the
fossil record, will appear gradual!
In the marine fossil record of Antarctica, and in Western Europe, the gradual
extinction of ammonites, appears to be due to the Signor-Lipps effect (most went
extinct of K/T boundary)
The Signor-Lipps effect makes it hard to gauge the impact of the impact
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The difficult sedimentary processes associated with terrestrial settings makes
quantification of the incompleteness of the fossil record of dinosaurs hard
Dinosaurs and Their Relatives
Lecture 23: 05/02/06
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Living mammals synapomorphies
o Mammary glands
o Warm-blooded (endothermic)
o Fur/hair
o Don’t fossilize well
o The first mammal is defined by the first time the dentary bone articulated
with the skull to form the “new jaw joint”
Endothermy (mammals)
o Characters 1-8 give agility and capacity for sustained activity; the price of
endothermy is having to eat frequently
o Characters 11 result in needing to extract energy quickly; efficient predigestion in our mouths (drawing)
DNA data (molecular clocks)
o Rates of DNA change, in some genes, is roughly clock-like; DNA
differences between species can be used to estimate when they diverged
o Molecular clocks suggest that most living mammalian groups diverged in
the Cretaceous; DNA suggests that primates existed about 85 million years
ago; the oldest primate fossil suggests that primates are 55 million years
old
In terms of the fossil record, we need to take into account the geologic ranges of
species not preserved (or found by us) when we are estimating when lineages first
evolved
o This is hard
o But we get similar dates to molecular estimates, at least for primates
Dinosaurs and Their Relatives
Lecture 24: 05/09/06
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The ecological diversity of mammals exceeds that of dinosaurs
The big cladogram indicates that synapsids (mammals) and diapsids should be
compared instead; these groups have similar ecological diversities
Eutherians (placentals) have full development in the womb
Genetic change and morphological innovation
o There may be very few genes involved
o Est 2 gene in mice, mimics Down’s Syndrome
o Different morphologies do not seem to arise from new genes but from
changes in the way existing genes are “wired”
Final Exam on May 18
 NOT cumulative
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o First lecture—pterosaurs
o Second lecture—origin of avian flight
Length is about two times the mid-term length; as a result, questions will be more
detailed
Equal balance across the lectures (6-8 questions)
No blue books
Closed book
Q&A Review Sessions
o Monday May 15, 7-8pm
o Tuesday, May 16, 7-8 pm
o Geological Museum Lecture Hall