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Geologists can compare layers of rock to decide which are older or younger, and which fossils represent animals that lived long ago or more recently. This process is called relative dating.
But relative dating does not give us a NUMBER. If we want to ask, "Yes, but WHEN did this rock layer form?", we need a different tool. When we try to measure the number of years that have passed since a rock formed (or since a piece of pottery was crafted, or since a tree died), we are trying to do absolute dating (the fancy word is time-measure: chronometry).
There are several techniques that can be used to assign a numeric age to a specimen. For our purposes we'll discuss two that are broadly applicable to fossil specimens; radiometric dating and luminescence dating.
The age ranges assigned by these methods are not the last word on how old a rock actually is! That's because different methods, or different laboratories, can give us conflicting dates. Thousands of scientists have spent the past decades improving the chemistry and technology for absolute dating.
Your typical oxygen atom will have a nucleus with 8 protons and 8 neutrons. This isotope of oxygen has 16 items in the nucleus. We call it O16.
Some rare oxygen atoms have an extra neutron! This isotope of oxygen has 17 items in the nucleus. We call it O17.
Very rare oxygen atoms have two extra neutrons. This isotope of oxygen has 18 items in the nucleus. We call it O18.
These atoms will always behave like oxygen. The heavier isotope might make stronger bonds. An oxygen can join an ion and have a negative charge. But it will always be oxygen. All isotopes of oxygen are stable.
Some isotopes have stable AND radioactive isotopes.
Most carbon atoms have 6 protons and 6 neutrons in the nucleus. This isotope of carbon has 12 items in the nucleus. C12.
Some stable carbon atoms have an extra neutron. This isotope of carbon has 13 items in the nucleus. C13.
Some carbon atoms have two extra neutrons. This isotope of carbon has 14 items in the nucleus. C14.
Carbon 14 is radioactive. It is not stable.
Carbon 14 has 6 protons and 8 neutrons. Eventually, one of the neutrons can eject a tiny beta particle and swap to act like a proton. If the atom now has 7 protons and 7 neutrons, it just turned into ... a Nitrogen atom!
If you have a pile of C14 atoms and you check back in 6,000 years, about half of them will have turned into N14.
The time it takes for half of any amount of radioactive material to decay to a daughter element is referred to as a half life. Based on this time and the ratio of parent to daughter element in any given sample allows us to assign how much time has passed for that sample.
Carbon dating is the most well known of radiometric dating methods.
What: items with carbon in them. Sea shells, bones, wood, pottery, etc.
Good to measure: thousands of years
Half-life: 5730 years
This technique measures the ratio of radioactive isotope Carbon-14 to its stable isotope peer Carbon-12. The half-life of this process is 5730 years. We can get very precise and accurate dates on items that are a few thousand years old, and pretty good estimates for items that are up to 50-60 thousand years old. But! Eventually all the C14 in a given item will transform. That item is now "C14 dead". If you can't measure any C14, you can't estimate a date.
ALSO weird! Some systems get goofy carbon concentrations, such as hot springs and tufa deposits. If you don't know how your C12, C13, and C14 SHOULD be mixing, you can't interpret measurements to tell time. There's a funny line in the movie Prometheus where the geologist gives a C14 date for a dead alien (spoiler) and Dr. Ritterbush is in the theater like, "Girl. You don't know the FIRST thing about C14 ratios on this planet. STOP."
What: minerals that form in igneous rocks and include some Argon in their structure
Good to measure: hundreds of millions of years
Half-life: 1.25 billion years
Geoscientists have made this method much more precise and accurate over the past 20 years by working together at labs around the world to get all the machines measuring it equally.
What: minerals that form in igneous rocks and include some Uranium in their structure
Good to measure: hundreds of millions of years
Half-life: 710 million years
Instead of one parent-daughter pair (as in C and N), Uranium-238 to Lead-206 has LOTS of steps. The half-life of this method is 710 million years which makes it a useful middle ground between the above methods. The longer series of decay reactions adds to the precision of this method, because there are more parts to measure.
Here are recent observations using this technique on rocks made from volcanic ash.
The volcanic ash forms layers of rock:
After geologists (a hard-working team of graduate students, probably!) find the target minerals in their rock samples, they can check the minerals in a scanning electron microscope.
Geoscientists can zap the grains with very tiny lasers. This lets us count atoms in super-tiny areas of the mineral grains. This map shows mineral grains that have been sliced into microscope slides and lit up with a cathode ray, to show the layers. That's right, instead of the entire mineral forming instantaneously as a single crystal, these minerals can grow layers like rock candy. This means that each layer of crystal has its OWN formation date. By now, the lasers we use are so tiny, and our machines that tally atoms are so strong, we can get multiple dates from a single grain! This is good, because it gives us more data and allows us to estimate our precision and accuracy better. But it's also SO ANNOYING because OY geology is challenging!!
What: minerals exposed to the sun as part of a sediment
Luminescence dating is a relatively new dating method which is often used as a second check on ages retrieved by other means. As grains within a sample sit after deposition, they slowly lose radiation that was accumulated while they were exposed to direct sunlight. By bringing these grains into a controlled environment (thermally or optically) this radiation can be released in such a way that we can measure how long the object has been buried.
Because of the nature of these methods it is less consistently retrievable in a sample than something like radiometric materials. Additionally the rate of decay in the sample is not as well constrained making it less accurate as a stand-alone method. For this reason it is often used to increase confidence in the numbers retrieved from another method.
In this class, we will NOT memorize the exact dates assigned to geologic time intervals.
Instead of memorizing exact numbers, we want to:
remember the basic estimates:
The Triassic Period began about 250 million years ago.
The Jurassic Period began about 200 million years ago.
The Cretaceous Period began about 150 million years ago.
The Cenozoic Era began about 65 million years ago.
Understand WHY the absolute dates change as science progresses.
If we estimate the age of a rock layer or geologic time interval, that exact number keeps changing as we get better at absolute dating techniques.
In the 1990s, we estimated that the Jurassic Period began 208 million years ago.
Twenty years later, we estimated that the Jurassic Period began 202 million years ago.
In 2008, labs around the world coordinated to estimate that the Jurassic Period began 201 million years ago.
That sounds silly, but remember: we're trying to measure when a piece of ash fell to the ocean floor 201,000,000 years ago.
If we see a date assigned to a rock (or fossil, or human item), what should we look for?
Pay attention to Precision and Accuracy.
At archery lessons, Dr. Ritterbush always hit the same spot on the target. All her arrows hit within five inches of each other! Dr. Ritterbush is a very PRECISE archer!
Sadly, Dr. Ritterbush couldn't get the arrows to hit the bullseye. They would all be clustered tightly together at, like, the third ring and over to the left. Dr. Ritterbush is not yet a very ACCURATE archer!
Geoscientists publish absolute dates with estimates of the ERROR on that date.
The error on the date combines both precision and accuracy.
Chemists can tell you how good their machine is at getting a consistent answer. Maybe they run the same sample ten times, and the answer changes each time. We can measure the precision of the instrument. Low precision = the date is an estimate!
A geo-chemist can also run a bunch of samples from one rock layer. Each sample might give a slightly different isotope measurement. Technically, all of these answers are "right", but if they don't converge on one answer, it decreases the precision of our estimate.
Different methods can give us consistent, but disagreeing, values.
Throughout the 1990s and 2000s, Argon-Argon dating gave values consistently below Uranium-Lead dating.
Each method was increasingly precise, but they could not both be totally accurate!
We now estimate that the Jurassic Period began 201.38 +/- 0.31 million years ago.
That means our BEST GUESS is 201,380,000 years ago.
But it could have been 310,000 years earlier, or later!
Radiometric dating methods are constantly improving, thanks to efforts of scientists on every continent. Ten years from now, the exact dates we guess for geologic time, and the precision and accuracy of those estimates, will be different from today.
We are also always comparing absolute and relative dating. The methods often give different answers, so we have to try again to improve all of our methods.
This page explores two frameworks for derivation in lineages of animals.[edit | edit source]
Generally, a population of animals includes individuals with a wide range of trait expressions.
When we learned in grade school about genes, we often compared eye color to our parents. Two parents with brown eyes can have a kid with blue eyes if each parent is carrying a recessive gene. They have a 1/4 chance of this occurring.
Most traits in animals are not so simple. While our DNA includes the information to build our bodies cell-by-cell, it includes a ton of information that isn't necessarily put to use in our body at any given time.
Gene expression is complex. Many different factors can influence how a body actually produces cells and structures day-to-day.
Thus, the traits that we see expressed in individuals are not a one-to-one match with the information for potential traits that their offspring will inherit.
Once offspring get their suite of DNA instructions, the actual execution of those instructions is subject to many factors influencing gene expression.
If each individual animal lives for many years, populations can include multiple generations of offspring and parents.
Genetic drift refers to shifts in the typical DNA pattern found within a population or group.
If one population splits into two, the typical gene coding and expression can shift in one of the groups.
If the animals rejoin a mingled population, they might re-mix their DNA and the genetic drift wouldn't have much impact.
If the animals do not rejoin into a mingled population, and they do not mix their DNA for some generations, then the typical genetic code in one population may become different enough from others that offspring are not possible, or are rare.
Many factors can lead to distinct populations.
Geographic barriers can arise within a population, or present opportunities for populations to split.
Habitat fragmentation can reduce mixing between individuals, creating sub-groups.
Environmental conditions like seasonality (how early the flowers bloom; how late it stays dark) or climate can alter the challenges animals face. Individuals that handle these challenges differently may find themselves mingling with only a sub-set of their broader population.
Animal behavior can also influence where, when, and how animals meet, court, and reproduce. This is a particularly powerful force in social animals that have complex cognitive behaviors associated with mating.
Traits that confer success can be reinforced in a population.
If a trait helps an individual survive, that animal is kept in the population. The individual's reproductive or behavior actions may affect the population.
If an individual expresses traits that aid reproduction, or that improves offspring survival, then ANY heritable trait the animal possesses may be passed to the next generation.
Behavior traits can be spread without direct sexual reproduction.
Gene expression can influence which traits are produced from a potential list within the DNA, and how traits interact with other physical and behavioral features.
"Survival of the fittest" is a phrase often attributed to Charles Darwin, but not actually from his work. Darwin speculated about "decent with modification" a hundred years before scientists discovered DNA as a mechanism for the process. He was correct about some speculations, and incorrect about others.
"Survival of the fittest" is an inadequate assessment of genetic and behavioral forces in evolution. It's also been used to justify cruel and inhumane slaughter of people and civilizations in recent history.
A phrase we prefer in this class, taken from Dr. Frank Corsetti, is "survival of the minimally fit". This makes it easier to understand the existence of pandas!
When populations separate, new species can arise.
For a new species to arise, a population needs to become distinct enough from its peers that they do not mingle their DNA.
The kind of distinction varies, as explained above. Animals can cease to intermingle their genetics due to behavior, gene expression in anatomy, and environmental influences.
The rate of this process differs with the kind of animal, behavioral complexity, habitat, geography, etc.
Natural Selection describes the processes by which specific traits are changed within populations.
A trait that aids survival or reproduction may increase its expression within individuals.
Hazards in an environment can remove traits from the population if the trait-holders die before reproducing, or cannot yield sufficient offspring.
Parasites, diseases, and microbial growths can remove individuals from populations.
An individual could have really awesome traits that are terrific for one environmental challenge, but could die or be removed from the reproductive cycle due to insufficient response to a different challenge.
We can observe natural selection influencing trait expression at a variety of scales over time and space. Natural selection is not always going to work in the same direction, on the same traits, or produce the same consequences.
Below we will learn about Adaptation and Exaptation.
Basically, if a trait is exaggerated (enlarged, increased frequency, etc.) in the context of a particular function, we call this set of changes adaptation.
A trait can also become exaggerated in the context of a totally new function, different from the context in which it first became valued. Think of this as the natural selective processes taking a sudden left-turn. This is called exaptation.
Some traits allow an animal to succeed in the context of a specific environmental challenge.
Example: seeds are hard to open. A finch with a strong beak can crack strong seeds.
That environmental challenge can become a source of natural selection if it increases, or decreases, associated trait expressions in an animal population.
Example: During a drought, birds that cannot open the tough seeds die. Birds that can open the seeds live. Strong beaks are more common in the hatchlings later that year.
Natural selection does not guarantee long-term change in a population.
Example: The next three years the weather is mild and wet. Birds with keen eyesight that spot small but nutritious seeds do well, and produce a few generations of offspring with generalized beak shape.
IF a trait increases to be present in all of the members of a species, and if that trait increases in expression in the context of a continued environmental challenge for which it presents an advantage, then this is adaptation.
Sometimes a trait increases in the context of a challenge very different from the context in which the trait arose. Example:
Maniraptorans (including Therazinosaurs, Oviraptors, and Utahraptor) have a half-moon shaped wrist bone that allows the hand to swivel differently than in other theropods.
A humming bird has very large hands that flip back and forth to generate lift on the backswing and forward swing. This takes advantage of the flexible wrist. But the wrist bones did not originally appear in the context of flight.
The wrist architecture was "hijacked" or "hacked" for a different function.
Basal vs Derived
The terms "basal" and "derived" are relative. They only make sense if you provide the context - what clade are you talking about?
Basal animals have the traits required to belong in their clade, but otherwise have a lot in common, still, with that last common ancestor that unites the clade.
Derived animals have features really different from the last common ancestor at the base of their clade.
Examples:
Coelophysis is a derived tetrapod, but it's a basal dinosaur.
Archeopteryx is a derived dinosaur, but it's a basal bird.
Come up with your own examples. Within any clade of animals, what is a good example of a basal animal? What is a good example of a derived animal?
Biomechanics
We can study the function of animal anatomy by comparing the mechanical properties, advantages, and challenges presented by their physical structures.
This page will link out to interesting research topics in biomechanics of dinosaurs.
Locomotion: walking, running, muscles, all that![edit | edit source]
Different generations in society grow up with different images of dinosaur life. Spooky creeping swamp monsters, lurking giants, or nimble assassins - the movies and pop culture presentations of dinosaurs influence our ideas about past life. But how do scientists decide what dinosaurs really could have done?
Armored dinosaurs like Ankylosaurs aren't just strange of their osteoderms they also have have very convoluted and intricate nostrils given the nickname "Krazy Straw" nasals.
Parasaurolophus has one of the most iconic skulls of any dinosaur but in reality that crazy crest is part of the nose! This nose is hypothesized to have a number of different functions from amplifying sounds to helping regulate temperature.
Skull modifications are not limited to typical or pre-existing anatomy. But what these modifications are for or how they develop can be difficult to research and can vary substantially.
In ceratopsians skulls these horns change throughout life giving them a very different appearance at various stages in life. Think about how this might affect our interpretations about how these features might be used.
Certaopsians are often thought of as using their horns for defense and combat. Studies in recent decades show that while this may have been true in some (like Triceratops) based on evidence of combat scars, for others (like Centrosaurus) we see so few combat scars that it is unlikely they were primarily used in this way.
Instead, the horns of Centrosaurus were likely to have been used for visual purposes. Sexual selection or perhaps even species identification by other ceratopsians
Pachycephalosaurs are often depicted as combative, head-striking animals like some modern sheep and deer today. Using 3D models and Finite Element Analyses (FEA) we can observe and compare how forces spread through the skull.
Genosaurs
The clade of dinosaurs that had the derived trait of chewing were called Genosaurs.
We propose that the last common ancestor of a cat and a crab had bilateral symmetry. If you draw a line down the middle of a cat, both sides match. Same with a crab.
The clade that includes the last common ancestor, and all of its descendants, we call bilaterians.
bi = two, lateral = along
Do ALL animals in this group still show bilateral symmetry? No.
Feel your heart in your chest. It's not exactly in the middle, is it?
A garden snail has a coiled shell, and some of its organs are a bit twisty. That's ok. It's still a bilaterian.
We propose that the last common ancestor of a cat and of a lizard had the ability to bear young on land, by protecting the egg from drying out.
The clade that includes the last common ancestor of the cat and the lizard, and all of its descendants, we call amniotes.
The amnion is a layer in an egg that protects the developing fetus from drying up.
Frogs and other animals that are not in this clade need to lay eggs near or in water, so they don't dry out.
Sea turtles and lizards and chickens can lay eggs on land. Ever notice the thick stretchy layer inside the crunchy part of a chicken egg? That's the amnion.
Mammals, including dogs and cats and humans, have young that develop internally. The amniotic sac is the stretchy layer protecting the egg as it grows. Ever heard of a pregnant woman having her "water break"? This is when the amniotic sac is ready to, well, hatch!
We propose that the last common ancestor of a cat and a frog had a pelvis.
We will call that last common ancestor, and ALL of its descendants, tetrapods.
Literally translated, tetrapods means "four feet".
But do all animals included in this clade STILL have four FEET? Nope.
What's the deal with tetrapods?
A pelvis forms a bridge between the legs and spine.
Similarly, shoulder blades and collar bones form a bridge between the arms and spine.
Each of these (the pelvis and the shoulder stuff) is easily considered as a package: a girdle.
The pelvic girdle manages the legs.
The pectoral girdle (think about lifting weights to get swole and have huge pecs) manages the arms, or fore-limbs, or front legs, or wings, or whatever you've got up there.
Fish already have a pectoral girdle, which is how their pectoral fins are linked to the spine.
By adding the pelvis, and with it the hind limbs, this new lineage of animals can generally be imagined as animals with FOUR LIMBS.
Tetrapods have been around for a LONG time, based both of fossils and DNA observations.
Because different subclades within tetrapods have been evoloving for such a long time, a lot of them are now very DERIVED.
Fossils of basal tetrapods include Acanthostega, and Ichthyostega.
Many derived lineages of tetrapods do not currently walk on four legs.
Birds
Humans
Whales
Snakes
Next time you see a rattlesnake while hiking, you probably don't want to shout, "Hey! Watch out for that tetrapod!" because this will be confusing to the average person. But you can always give the snake a respectful nod and say, "Nice rattle, there, fellow tetrapod. Look at us, being so derived."
We interpret that the last common ancestor of a cat and a bird had an amnion. We refer to this clade as amniotes.
An amnion allows an animal to reproduce away from water, by protecting the embryo in a special layer within an egg (i.e., lizard, platypus, chicken) or womb (cat, rat, etc.).
"With a window". The traits that help us diagnose membership in this clade are often hidden on derived, living animals, so let's dig into the puzzle.
Today, we can easily observe that lots of mammals have a mouth full of differently-shaped teeth. Consider a human and a wolf.
Humans have teeth that can cut, crush, and grind.
Wolves have teeth that can stab and crush.
Taking advantage of these teeth to do interesting things (bite into food, crack it open, chew it up) requires muscles to move the jaws, and cheeks to keep the food from falling out of the mouth!
The skulls of humans and wolves have a large arch of bone (on each side of the skull) that allows the muscles to pass between the skull and lower jaw.
The arch of bone also provides attachment points for muscular cheeks.
In biology, we call this the "zygomatic arch" which is fun to say!
We can look at this arch and consider it as a window for the passage of chewing muscles.
Now, let us consider the fossil animal Dimetrodon.
Dimetrodon means "two size teeth", named for the differently sizes teeth in it's mouth.
Dimetrodon has a skull with a large round hole placed behind each eye socket.
Paleontologists interpret that this hole allowed for muscle attachments for chewing.
Our current interpretation is that Dimetrodon is a synapsid - "with a window" - and that it is a basal member of our clade.
The clade synapsid contains the last common ancestor of a monkey and a Dimetrodon, and all of its descendants.
Casually, in this class, we will ignore synapsids.
So you'll often see us group Dimetrodon with some familiar mammal, to really drive the point home.
For example, see our Dinosaur Time Tree. We leave synapsids alone in their little lineage, and show a basal Dimetrodon back in the Paleozoic Era, and a fuzzy cat in the Cenozoic era.
Were synapsids around during the Mesozoic? Of course!
"Two windows". Above, we considered synapsids, which have a single archway in the skull to allow chewing muscles.
Diapsids have TWO archways in the skull behind each eye socket.
We interpret that one set of holes aided in muscles to work the jaw.
We interpret that the set of holes on TOP of the skull aided in temperature regulation. Let's explore!
In 2019, a team of scientists published peer-reviewed observations of heat-exchanging organs in the skulls of crocodiles and birds.
Living crocodiles have holes in the top of their skull.
So does the living tetrapod Tuatara.
Derived birds don't show these holes in the top of the skull. But many feathered dinosaurs related to birds DO show the holes.
Dr. Ritterbush agrees with the interpretation that the skull-top-holes were used to house heat-regulating organs. Dr. Ritterbush likes to call these holes the HotPockets.
AND, special bonus, there is another useful trait that we can observe in living tetrapods that we group together as diapsids.
Corneous beta protein is a tough material that builds outer body coatings.
Corneous beta protein is found in living lizards, alligators, turtles, and birds.
Corneous beta protein is composed of tiny protein strings woven together.
Corneous beta protein allows construction of strong, flexible materials, such as feathers.
It is NOT found in mammals or other synapsids. Mammals make keratin, a different set of proteins.
Observations clarifying this situation are fairly new, such that they haven't made it into mainstream teaching practices or textbooks.
Beta proteins were long recognized in microscopes, but were just named beta because they looked different.
Recent observations include the microscopic structure of the protein,
the number of different beta proteins made by different living animal groups,
and the placement of the genes that produce the protein on the DNA patterns of these living animals.
The result is a compelling interpretation that the last common ancestor of birds and lizards had corneous beta proteins.
Diapsids are a case study in the connections between paleontology and biology.
Biologists can observe the detailed chemical structures and DNA patterns of living animals.
Paleontologists can observe the shapes, sizes, structures, and microscopic appearance of extinct animals.
Interpreted relationships between living and dead animals are always changing, because biologists and paleontologists are continually making new observations.
Very important note!
Diapsids and synapsids are SISTER clades, both within the larger clade of amniotes. Diapsids are tetrapod amniotes. Synapsids are tetrapod amniotes. We don't have compelling evidence that either skull configuration is more basal or derived. We typically show them diverging within the amniote clade, and we mark the traits (two windows; one window) on each separate diverging branch.
"Old lizard". The last common ancestor of a bird and an alligator, and all of its descendants, are a clade we call archosaurs.
Archosaurs are diapsids.
Basal archosaurs show a large lump on the rear face of their thigh bone (femur).
The lump allows stronger attachment for a muscle that runs between the tail and the thigh (caudal-femoral muscle).
The fancy name for this is the "fourth trochanter",
but we won't use that term in this class
because it implies we are going to learn all the other trochanters,
which we definitely will not!
The size of this muscle attachment spot varies in different archosaurs.
On fossils, it's easiest to see in crocodiles and dinosaurs.
In live animals, it's easier to see in crocodiles.
In modern birds:
the tail is so reduced and stumpy that,
although the muscle is still there
and still attaches to the femur,
the big lump is not so prominent or easy to see.
Fossils reveal an amazing variety of archosaurs, some of which were enormous and probably terrifying. That's super fun to explore, but we aren't making time in this class.
A clade refers to one bushy branch of an evolutionary tree.
If we consider any two animals, we can guess what features were common to their last common ancestor.
If we consider this last common ancestor, and ALL of its descendants, we are considering one whole clade.
A clade can be small or large.
A biologist studying squid might be interested in one particular clade of squids related to the giant squid.
A paleontologist studying birds might be interested in a clade so broad that it even includes crocodiles!
If we intentionally exclude a sub-branch, we are no longer talking about a whole clade.
For example, the clade dinosaurs includes the last common ancestor of a Triceratops and a pigeon, and alllllllll of its descendants.
If a person says, "Well, birds don't really count, because they are birds!" that's ok. Just know they are no longer talking about the WHOLE clade.
There are LOTS of different terms for the ways folks break up or combine parts of clades, which anyone can learn about in advanced classes, books, online, etc.
In this class, we just want to ask, "Hmmmm, are the animals I'm considering constituting a whole clade? Am I excluding anyone?"
Phylogeny refers to a set of evolutionary relationships between animals.
We can consider this as an absolute concept. For example, "We may never know the entire phylogeny of Cretaceous birds, but we have learned a lot more about it in the past decade."
We can also use the term to refer to a specific interpretation of the evolutionary relationships. For example, "Dr. Smith and Dr. Kunungo present conflicting phylogenies for fossil crabs." We'll need more observations to decide which best resembles their actual history.
Traits that arose as lineages of animals diverged and became more and more different from each other.
Example: Stumpy tailbones arise on branches of birds as they diverge away from flying dinosaurs that still had long tails.
Traits that arose as lineages of animals that were really different acquired similar anatomy to meet an environmental challenge.
Example: Penguins have flippers, and dolphins have flippers, but the last common ancestor of a penguin and a dolphin did NOT have flippers.
This is called convergent evolution and it's so rad.
Clades nest within each other:
Parrots are a clade of birds.
Birds are a clade of dinosaurs.
Dinosaurs are a clade of vertebrates (animals with a spinal chord).
Cladograms do NOT illustrate:
When, why, or how the branches split.
What the common ancestor looked like, exactly.
Which animals are "most evolved"!
Dr. Winkelman studies squid, so she'll make a cladogram all about the nuanced differences between calamari squid and giant squid.
Dr. Melstrom studies crocodiles, so he'll make a cladogram all about the nuanced differences between alligators and crocodiles.
Dr. Yacobucci studies ammonites (extinct shelled squid monsters), so she'll make a cladogram about different ammonites.
Because each person studies different animals, they pay attention to different traits. If the animal they study is extinct, or smart, or fancy, doesn't make it more or less evolved.
Why are cladograms important for this class?[edit | edit source]
Once you get the hang of it, cladograms are easy and fun to read.
It's like a road map for evolution.
Every cladogram shows an interpretation.
Most interpretations can be improved with more observations!
Paleontologists can use cladograms to:
Predict that an animal with a certain set of traits should exist in the fossil record.
Predict that an animal with a certain set of traits should be fossilized in a particular layer or time-period.
When paleontologists find new fossils:
The cladograms can be changed to include these new observations.
The new tree gives folks ideas for new predictions on where or what to look for.
In World of Dinosaurs, we want to observe the anatomy features that were used to support the phylogeny illustrated in a cladogram. This class will provide special access and focus on fossils – in the Natural History Museum of Utah, as digital models, and as 3D prints – and live animals – at the Tracy Aviary and via video – on which we can SEE the traits marked on the branches.
This class uses claodgrams as puzzles.
We will ask students to read, remember, and reconstruct some cladogram features.
This is because the cladogram puzzles are useful tools to visualize and talk about our interpretations.
This class is NOT about memorizing cladograms as unchanging facts!
Depositional Environments
Sedimentary rocks are made of pieces - parts of busted up rocks from some place else, or chemical bits that form minerals and rocks in place.
Conveniently, the basic principals of sedimentology are on display all around us today.
This page will explore how sediments form, move, and make rocks.
Sediments: What are they, and how do they form?[edit | edit source]
Sediments can include dirt, sand, mud, debris, boulders - whatever you've got that's ready to move and then sit around.
Consider a mountain of intrusive igneous granite, which has been sitting around eroding for a very long time.
Weathering breaks the granite down: freezing water breaks it apart; acid rain tears ions off some minerals.
Erosion turns granite chunks into smaller and smaller pieces: floods and snow and glaciers move big chunks of rock; rivers smash the pieces into smaller bits.
Clasts of rock, grains of mineral, and chemical elements of dissolved minerals all travel in water: rivers, springs, ponds, lakes, oceans.
It takes energy to erode and transport sediment.
If a pile of dead Camarasaurus jam up an old river, you might get some dinosaur fossils out of the deal!
Environments where erosion produces lots of sediment include:
river (smashes clasts into smaller and smaller bits)
(Ever come home from a long day and just drop all your stuff at the door and lay in bed? Same thing.)
Why (generally):
Confined flow causes erosion.
Unconfined flow allows deposition.
Examples:
A roaring river smashes rocks along; a quiet delta lets the rocks settle.
A thunderstorm flash flood sweeps rocks down a desert canyon; the water spills across the desert floor and lets the rocks settle.
Sea shells are swept off a high reef running around an island; they tumble down the slope and settle in quieter water.
If you zoom out, many settings have weathering, erosion, transport, and deposition all happening in a jumble.
Consider a river or an ocean beach.
Forming a rock from a sediment deposit requires a lot of things to go just right.
Where (generally):
Erosion happens high and fast.
Deposition happens low and slow.
Depositional Environments: What clues do they leave in rock?[edit | edit source]
Different environments collect different sediments.
A deep ocean will collect layers of quiet mud and dead micro-organisms.
A river bottom will collect alternating layers of sand, cobbles, and mud.
A reef-ringed island will collect layers of coral and sea shells.
Sediment layers can capture snapshots of flow patterns.
Water flowing along a beach can erode the sand and form ripples in the remaining sediment.
If deposition outpaces erosion, many layers of rippled sandstone can form.
Little animals leave burrows and trails in ocean mud.
If deposition outpaces erosion, crystals can form in the mud to record the little trails, and fossilize tiny dead animals.
Huge debris flows during flash flood landslides dump jumbles of huge boulders, big cobbles, and mud onto lower land.
If deposition outpaces erosion, the biggest clasts show how much energy the flow had, and the range of clast sizes and compositions shows the places the material came from.
Geologists use sedimentary structures like these to...
See which way was "up" on a layer or sample of sedimentary rock.
Remember - although we are interested in the way these animals lived and interacted with the changing Earth, we are grouping the animals based on shared derived anatomy, NOT on outward similarities. So will all the four-legged animals group together? No. Will all the plant-eaters group together? No.
The more derived long-neck dinosaurs are proper sauropods.
Surprising things about Sauropods include:
Quadrupedal posture (walking on four legs) is a derived trait in Sauropods.
Basal dinosaurs, including basal sauropodomorphs, walked on two legs.
Derived Sauropods have thick, dense leg bones, like pillars of a huge suspension bridge.
Sauropods did NOT chew their food!
They certainly ate plant material, and a LOT of it!
But they did not grind up the plants in their mouth. We can tell because:
They don't have cheeks to keep the food in their mouth while chewing!
They don't have flat grinding teeth.
When their teeth DO show wear-marks, it's from repeated crashing together of the teeth in the upper-and-lower jaw.
Think of their jaws like hedge-clippers, not like a wood chipper.
Sauropods have five toes on their back feet, with big claws.
Their ankle would be a little off the ground, but not high up like theropods.
There would probably be a pad of fat under the foot, like an elephant.
UNLIKE an elephant, Sauropod feet have big claws. It seems weird for walking but they figured it out.
This is why they're called "lizard foot"; living lizards today have five long toes with claws.
Sauropod vertebrae have big air pockets!
Think of their spine like the archways of a suspension bridge crossing a river or bay.
Complex struts extend between the elements in the archway to keep it from collapsing, folding, or bending at too sharp an angle.
Air pockets probably helped reduce the overall mass in a Sauropod body.
Air pockets in bones are a basal dinosaur trait (and probably basal to ornithodira - including the flying pteranodon), but big air pockets are a derived trait in Sauropods AND Theropods.
Within Sauropods we can consider two sister clades.
Welcome to a very important dinosaur category that has a very silly name!
Ornithischians include:
The last common ancestor of a spiky Stegosaurus and a horned Utahceratops, plus all of its descendants.
Most of the classic, easy to recognize "plant eating" dinosaurs EXCEPT the long-necked Sauropods.
At least two different independent lineages of quadrupedal gait!
What traits distinguish an Ornithischian dinosaur from other dinosaurs?
The pre-dentary bone.
This is a "beak"-like tip on the lower jaw. It is an additional little bone that makes the jaw come to a tip.
Once you know what to look for, it's pretty easy to recognize on the skull of ornithischian dinosaurs.
The predentary bone is present in basal ornithischians,
AND the predentary bone is critical to the fancy feeding structures that appear in derived ornithischians.
File:AnkyloSkullObliqueNHMU.jpgThat funny little tip on the lower jaw is a derived expression of the PREDENTARY bone, an ornithischian trait.A rear-facing projection on the pubis bone.
The dinosaur pelvis is made of three bones: illium, ischium, and pubis.
The illium runs parallel to the spine. This is the part that gets all expanded like a big shield in the derived armored Thyreophoran dinosaurs like ankylosaurids.
The ischium frames the rear-end plumbing of the animal. (Rather than the specialized variety of pelvic anatomy found in most mammals, we can guess dinosaurs had a simple multi-purpose outlet channel, called a cloaca, like frogs and birds have today.)
The pubis bone produces the forward corner of the pelvis socket where the femur fits in.
In ornithischians, some portion of the pubis bone is pointing backward, toward the plumbing side of the animal's pubis.
This can look very obvious in derived animals, where the rear-facing pubis bone is almost parallel to the ischium.
One proposed advantage of the rear-facing pubis bone is that it would leave more space for a big, gassy belly in these plant-eating animals, allowing them more space for digestion aided by bacteria and other microbes. Contrast this to the giant pubis bone that jams into the belly of long-necked Sauropod dinosaurs.
Derived thyreophorans are easily recognized by their gnarly body armor: Stegosaurus, Ankylosaurs, etc.
Dinosaur body armor is made from scutes (pronounced "scooooooooooots", as in "Hey let's get some of those scooters and go to Yoko."), which are bones that grow right out of the skin!
Scutes are what make a crocodile look bumpy!
Scutes are basal in archosaurs, so they pop up in a lot of different groups
Scutes appear on some sauropods and theropods, but not as big or as many as on thyreophorans.
Our favorite basal thyreophoran is Scutellosaurus, aka "scute lizard" aka "skin bone lizard".
Fossils of Scutellosaurus are rare
Reconstructions of the animal's skeleton, posture, and capabilities are constantly revised & debated.
General observations & interpretations include:
The overall body is small; it is small like other basal dinosaurs.
the hindlimbs are longer and stouter than the forelimbs; this was a bipedal, or primarily bipedal, animal
the teeth are simple, spread across the whole jaw, and not very pointy; this animal ate plants or plants + bugs and stuff
the body is lined in little scutes; the skin was protected by this tough exterior
This paper by Benn Breeden has a beautiful reconstruction of a Scutellosaurus.
"wide foot" Honestly I don't understand this name because their feet aren't that wide, but I guess compared to the more basal dinosaurs like Scutellosaurus it fits.
Lots of traits distinguish this clade but the coolest one is their bony eye sockets. Although scutes grow out of skin, on the skulls of these animals that scutes can tend to collide and grow along with the skull bones. Also a lot of the skull bones fuse together and get thick and wide, which is very different from the theropods and sauropods. A consequence of this that's easy to see on a skeleton in a museum is the fused bony socket around the eye - it's serious.
Also - obligate quadrupedalism. Eurypods walk on four legs, unlike basal thyreophorans and other basal dinosaurs.
But then the two main groups of eurypoda go very weird and different directions with the whole scute business.
"roof lizard" Stegosaur dinosaurs have big plate-shaped scutes on their back.
Different species of stegosaurids are distinguished easily by their wacky combinations of plates and spikes. Some have spikes on the tail, some have spikes on the shoulders, and all look like no one was taking their lunch money easily.
General observations and interpretations about stegosaurids:
Long femur and robust lower humerus; Stegosaurids were obligate quadrupeds, always walking on four legs.
Big plate-like scutes on the back and tail; Stegosaurids are really derived and these features might have served many different functions.
Stegosaurs are typically found as individual fossils, rather than big piles of bones from many individuals; Stegosaurids probably lived alone, like Pandas, rather than in a herd, like Reindeer.
Ankylosaurs look a little less flashy than stegosaurs from a distance, but they have lots of wacky derived features with ecological interpretations.
Scutes line their back and sides; they were probably hard to bite.
Their top hip bone flares out to make a big sheild-like flat lower area along their back; they were probably less nimble than other dinosaurs.
Their tail bones can be fused together, making a stiff feature like a baseball bat.
Ankylosaurids include two sub-clades. Regular Ankylosaurs – that includes Ankylosaurus, a classic, and Acainocephalus, a new one from Utah – had clubs on the end of the tail.
Members of their sister clade Nodosaurids ("knot lizard") do NOT have the club on the tail, but they do rock AMAZING big shoulder spikes. Very cool.
Ankylosaurs have fancy nose chambers that might have helped them maintain their body temperature.
Ankylosaurs have decent teeth and cheeks more inset than Stegosaurids; they could probably chew tough plants better than other Thyreophorans.
What's this? An extra clade that is a NODE joining the branches that lead to duckbills and to horn-faces.
Duck-bills and horn faces have these features in common, which they get from a last-common ancestor:
rear-facing pubis extension
pre-dentary bone on lower jaw
cheeks
diastema
The name horn-foot can refer to the hoof-like toes that form in the derived members of this clade.
By now we are starting to notice that a lot of clades are named for DERIVED traits that show up in their famous members, so sometimes the name of the clade doesn't match to the trait that shows up on the branch leading to that node and joining all those animals via mutual inheritance.
Better-known as Duck-Billed Dinosaurs!
Includes the last common ancestor of an Iguanadon and a Parasaurolophus, and ALL of its descendants.
These animals could CHEW, and are members of the genosaurs.
This means they share a closer common ancestor to Stegosaurus than to, say, a Diplodocus.
Duckbills and iguanadontians have feet with THREE TOES. (hence: bird foot, ornithopod)
Duckbills and iguanadons have derived features for eating plant material.
Iguanadon teeth have ridges that would help gnash plant material.
Derived duck-billed dinosaurs, like Parasaurolophus, had packed-together batteries of teeth that could slap together to grind food.
Cheeks set the teeth in closer to the tongue, allowing muscles to hold food in the mouth for extra processing.
Even fancier, these mouths have a diastema!
This is an open space in between a snipping front and crunching back.
It leaves space for the tongue to move food around for more chewing time.
Lots of derived mammals have evolved a diastema, too.
Duckbills and Iguanadons probably mostly walked on two legs, but could also support their weight on their front legs.
Their toes on the hindlimbs developed hoof-like toenails.
Iguanadons also had hoof-like toenails on their forelimbs, PLUS a wacky stabby pointy nail on one digit.
The ecology of derived duck-bill dinosaurs is really well known from some excellent fossil examples of nests, and even from whole-body fossils from settings where the soft-parts preserved a bit, like a mummy.
this is a bone that is added to the front of the face
Together with the pre-dentary, this forms a "beak" on the face
Derived example: Utahceratops, "Utah horn eyes"
A lot like the more-familiar Triceratops, but this is our special Utah version!
Walked on 4 legs, with hoofed toes
Horns
two substantial brow horns and a nose horn
Has a big frill with horns along the edges
and cheek horns!
Elaborate chewing features
cheeks!
packs of tough replacing teeth that form a grinding surface
plus the "beak" in the front
and a diastema in between - a space to move food around with the tongue.
Big belly
the ornithischian trait of a rear-facing pubis bone is really exagerated.
This makes a lot of space in the belly area
One interpretation is this space was used for guts filled with bacterial symbionts that processed tough plant foods.
Derived example: Centrosaurus, "middle lizard"
Centrosaurs are derived ceratopsians with a few key distinctive features:
usually a big nose horn
usually small or absent brow horns
usually a not-huge rostral bone (the upper "beak" bone on the face)
Walked on 4 legs, with hoofed toes
Elaborate chewing features
cheeks!
packs of tough replacing teeth that form a grinding surface
plus the "beak" in the front
and a diastema in between - a space to move food around with the tongue.
Big belly
the ornithischian trait of a rear-facing pubis bone is really exagerated.
This makes a lot of space in the belly area
One interpretation is this space was used for guts filled with bacterial symbionts that processed tough plant foods.
Dinosaurs Through Time
Here we show a rough schematic of the TIMETREE of dinosaurs as they proliferated throughout the Mesozoic.
Fossils from Triassic rocks show few dinosaurs, and these animals are relatively small and basal in their anatomy. Dinosaur fossils are much more common, and show greater animal diversity, in Jurassic rocks. Finally, the most famous and culturally iconic dinosaurs (Tyrannosaurus, Triceratops, etc.) are known from fossils in Cretaceous rocks.
Earth is an imperfect sphere, with a hot weird middle and a crust of rock around the outside.
The crust is a tiny part of our planet – it is just 50-100 km deep, on a planet with a radius of ~6400 km.
The crust is roughly equivalent to an eggshell while the entire earth is the egg.
Earth's rocky crust is constantly changing and adjusting from internal and external forces. We reconstruct past environments and continental configurations using geology.
Rocks on Earth's Continents Reveal Change Over Time[edit | edit source]
Continents contain a mix of metamorphic, igneous, and sedimentary rocks.
If you hike in the Wasatch Mountains, you'll see all three kinds!
Past presence of rivers, lakes, oceans, etc. are easy to spot in sedimentary rocks.
Metamorphic rocks demonstrate wacky changes in physics and chemistry that acted on the rocks over time.
Certain minerals only form at high pressure, or high temperature.
We can experiment with high pressures and temperatures in the laboratory using a diamond anvil cell (one of the specialties of our own Dr. Lowell Miyagi)
A diamond anvil cell places a tiny experimental chamber between the tips of two diamonds.
The diamonds are strong enough to squeeze together and create just a tiny pocket of crazy-high pressure and/or temperature.
People spend their entire careers studying how, where, how, and when metamorphic rocks form.
We won't discuss them much in this class because metamorphic rocks usually ruin fossils. Boooooo!
But their chemistry and physics require explanation! And that underpins many of the finer details of plate tectonic idea
Igneous rocks on continents are MOSTLY the intrusive kind.
Intrusive igneous rocks formed by slow-cooling magma that didn't pour over the Earth's surface.
Generally intrusive rocks form within the crust.
Great examples are the granite and granodiorite found in the Wasatch and Uinta ranges of Utah, and in many historic SLC buildings, including the Temple.
The big rocks of Yosemite National Park (Half Dome, El Capitan, etc.) are made of granodiorite, too
You can easily see cool igneous rocks from lava flows over continental areas:
All around Southern Utah.
In the Craters of the Moon National Monument in Idaho.
All around Northern Arizona and Eastern California.
Along the Columbia River in the Pacific Northwest.
Along the Palisades in New Jersey.
Here is a 3D model of an extrusive igneous rock called lava spatter!
Earthquakes also change continental rocks – even in REAL TIME!
f you've felt an earthquake, you've felt the consequence of rocks moving over time
It takes a long time for rocks to move, and they usually are stuck where the edges rub together.
The tension is occasionally released as an earthquake that lets the rocks slide past each other, but feels very weird for the rest of us.
We can easily observe signs of PAST earthquakes in lots of ways – rock layers cut by a highway that show offsets; trenches in sediments; and big shifts in the rocks displayed in our local mountains.
If you were in Salt Lake City for the Magna earthquake (a 5.7 magnitude earthquake) then you've felt the movement of the crust!
Rocks on Earth's Seafloor Reveal Change Over Time[edit | edit source]
Ocean water sits low.
Think of the Earth as a solid rock, like the moon, and then just POUR water onto its surface.
Continents, made of thick low-density rock slabs, peak above the surface of water.
Thinner slabs of denser crust made of extrusive igneous rock usually stays low, wrapped tightly around the Earth's mantle, so the seawater settles above.
Rocks at the bottom of the sea floor are usually made of extrusive igneous basalt.
We can actually see new basalt forming at the sea floor and coming out as new rock.
We can study the microbial life that flourishes on these fresh minerals.
Sediments can build rock layers that layer on top of the basalt slab.
We can use the texture, quality, and chemistry of the basalt rocks to measure how long they've been exposed to weathering.
We can use the sediment piles or layers of rock to measure changes in environmental conditions during this time.
Some of the basalt that forms under the sea pokes above the ocean's surface.
Basalt can pile into enormous undersea volcanoes.
The islands of Hawai'i are an example: the islands poke above the ocean's surface.
Colonies of coral and other carbonate-mineral-making animals coat the flanks of these islands, and add layers of sedimentary rock.
People living there have to cope with volcanic eruptions.
Basalt can make under-sea mountain ranges where new rock is born every day.
A good example is the Mid Atlantic Ridge.
The Mid Atlantic Ridge is a mountain range running N-S half-way between the Americas and Europe/Africa.
Iceland is built on a part of the ridge that pokes above the surface of the ocean.
People living there have to cope with volcanic eruptions.
Magnetic particles form little compass indicators inside of basalt rocks.
Basalt rocks have lots of iron-based minerals.
These minerals can form little magnets that align to the Earth's magnetic poles as the rock cools and solidifies.
If basalt rocks form layer on top of layer on top of layer, in a big stack...
we can measure the magnetic particles through the stack in order.
Typically, the older rocks are at the bottom of the stack.
If basalt rocks form at the Mid Atlantic Ridge and then get pulled away...
they make room for new basalt rocks to enter the crack and form more fresh rock.
One consequence is that instead of building up in a vertical pile, they form side-by-side stripes.
Oldest rock stripes are farthest from the ridge. Newest rock stripes are closest to the ridge.
Layers of basalt rock can be matched to other layers far away that erupted at the same time, or from the same chemical soup.
The little magnets aligned to poles tell us which way was magnetic north.
In a stack of basalt flows, or in a series of neighboring basalt stripes, our measurement of North SWITCHES DIRECTION over and over!
Lots of physics reasons explain why Earth's magnetic field SHOULD flip periodically, rather than stay exactly the same as today.
We can measure the field in detail today, and it's way more complex than we draw in books!
We can measure and compare the timing of basalt eruptions by comparing the magnetic north orientation.
Earthquakes are also always happening in the thin under sea basalt crust.
Usually they don't impact life on land.
They are always happening near the Mid Atlantic Ridge and other places where lava is forcing its way out.
We can detect these a lot better with modern equipment.
Many of the basic observations of rocks on our planet were not available one hundred years ago.
Many big surprises about rocks under the sea came to scientists' attention during the second world war, when submarine warfare required us to learn about the structure, bathymetry (underwater elevations of stuff) and physical traits of the rocks down there. We used magnets a lot because we were searching for submarines. The size of undersea mountains, and the stripes of rock with opposed magnetic signals baffled geologists at first.
Observations that demonstrate motion and change of Earth's crust can be interpreted in the conceptual framework called Plate Tectonics. We recommend this explainer video with lots of diagrams, here.
Here are the basic ideas in Plate Tectonics:
We represent the crust as a set of crunchy units that shift around on the Earth's surface.
Each plate has a slab of rock that makes most of its material.
Some plates contain thick slabs of low-density intrusive igneous rock (granite, diorite, etc.).
Some plates contain thin slabs of high-density intrusive igneous rock (usually basalt).
Some plates contain both kinds of rocks slabs.
Water sits in low spots.
Oceans nestle between continents.
Basalt rocks, located deep under the sea, form thin crusts of dense rock.
CHEMICAL COMPOSITION of the lava causes the basalt rocks to be dense.
The presence of water above them is NOT the reason the lava forms dense rock.
Thick slabs of low-density intrusive igneous rocks poke above the ocean's surface and are easy to see as continents.
High-density extrusive igneous rocks can also build up enough to poke above the ocean's surface: consider Iceland and Hawai'i.
Sediments settle and form sedimentary rocks on these plates.
Sediments can build rock on land, which adds to the thickness of continental slabs.
Sediments can build rock on the coasts, which makes the slope transition between continent and sea floor a lot more gradual.
Sediments can build rock on the seafloor, too.
Metamorphic rocks form wherever the plates get nasty.
Collision, scraping, or squishing of the Earth's crustal plates changes the physics and chemistry acting on rocks.
This can cause different minerals to fall apart or to form.
If the same elements are there but they now have a new mineral configuration, a different kind of rock will form.
Igneous rocks form continually where...
plates are stretching away from each other, leaving a little crack for lava to push through.
This is always happening under the sea, in places like the Mid Atlantic Ridge.
Or where plates are smashing together, making a thin slab of sea floor basalt slide under another plate.
This is happening in the Pacific Northwest of North America, and along the Andean Mountains of South America.
Or where a pimple seems to let lava leak through.
This is happening all the time in Hawai'i, as lava is trying to make its way up through the pile.
The northwest islands of the archipelago are no longer active, because the crust slab slid away from the pimple.
The fancy name for this concept is Hot Spot.
Volcanoes form where the plates are crashing together.
Earthquakes from where the plates are crashing together, AND where the plates are trying to slide past each other.
Nasty earthquakes from plate collision happen in...
Tibet (continent plate crashing into continent plate)
Indonesia (ocean plate crashing into ocean plate)
the West Coast of South America (ocean plate crashing into continent plate)
the California Coast of North America
Here a plate that is MOSTLY ocean, the Pacific Plate, is dragging a sliver of continent on its edge.
Los Angeles is located on the Pacific Plate.
Los Angeles is moving NORTH with the Pacific Plate.
The North American Plate is carrying most of the North American continent, plus half the crust underneath the North Atlantic ocean.
San Francisco is moving SOUTH with the North American Plate.
If you measure the plate motion from the middle of each plate, say, a GPS unit in Hawai'i vs one in Nevada, the plates are moving apart about a 5 mm per year. That's about as fast as fingernails grow.
If you measure the plate motion right near the San Andreas Fault, you get zero motion. It's stuck. Until it's not stuck, and then we need Dwayne Johnson to save us.
ACTIVE MARGINS are continent edges that sit at plate boundaries that are crashing into or alongside each other, causing volcanoes and earthquakes.
PASSIVE MARGINS are continent edges that sit in the middle of a plate. Volcanoes and earthquakes are rare along passive margins.
We Can Reconstruct Past Geographic Conditions[edit | edit source]
Certain magnetic minerals can tell us the position of Earth's magnetic poles AT THE TIME that mineral formed.
We compare magnetic minerals to relate stripes of seafloor basalt
We can measure the order and spacing of each stripe.
We can use the periodic flip-flop pattern of Earth's magnetic poles to organize basalt stripes into a relative timeline of eruptions.
We compare magnetic minerals to relate layers of lava rock that piled up on continents of Earth's surface.
We can measure the thickness and order of each lava rock layer. Older rocks should be at the bottom, newer rocks on top.
We can use the periodic flip-flop pattern of Earth's magnetic poles to organize lava rock layers into a relative timeline of eruptions.
If part of a continent has ROTATED while its plate moved through time, the magnets can show this, too.
It's taken decades to learn how to observe magnetic minerals correctly, and to interpret what they say about a rock's relative age, original orientation, and relationship to its neighboring rocks. Scientists like Utah's Dr. Pete Lippert still spend their entire careers unraveling the history of ancient rocks, so we can better understand how our planet works as a dynamic system.
Fossil are vital to reconstruct paleogeography in two main ways.
Paleontologists compare fossils from around the world.
Some fossils of plants or land animals are found on far-away continents today, but may have lived in a time when these continents were not so far apart.
Fossils can show what habitats were present:
Echinoderms (sea urchins, sea stars, crinoids, etc.) generally only live in OCEAN water of normal salinity.
Sea snails can tolerate a wild variety of salinities.
Feedback Loops
A feedback loop occurs when two things change together repeatedly.
In casual conversation, people often use the phrase, "vicious cycle" to describe a feedback loop.
From what I can tell, this was popularized by quoting a scene from a movie released in 1999 which... did not age well.
Ironically, the movie scene describes a POSITIVE FEEDBACK LOOP, but it concerns an unhappy topic, so the phenomenon is characterized as a "vicious cycle".
This leads to odd conversations 20 years later, e.g., "It's like a vicious cycle! But, like, not bad, you know?"
Using the term feedback loop is much easier and more practical.
Cause and effect are typically difficult to discern in deep time research (fossils, ancient life, etc.). Realistically, most natural events that we characterize as having a simple cause and effect involve much more complex feedback loops.
This class will focus on the Mesozoic-Cenozoic transition to appreciate a major positive feedback loop in Earth history.
This describes systems that tend to settle into a balance.
Casual example:
1:00 PM: Few shoppers are trying to check out at Smiths, so the manager tells some staffers to go on break.
1:10 PM: More shoppers line up, and now there are two long lines.
1:20 PM: As staffers come off of break, the manager sends them to registers.
1:30 PM: The two long lines of shoppers are spread out across five check-out stations.
1:40 PM: Two of the staffers have no one in their line, so the manager asks one to get carts and another to take lunch.
1:50 PM: It's pretty easy to check out at Smiths. Thanks, dynamic equilibrium!
Dynamic means shifting around and responding to stuff.
Equilibrium means balance.
A system with dynamic equilibrium will get out of balance one way, then another, and kind of settle on a balance
Some systems are always shifting back and forth - the supermarket is quiet, then busy, etc. But on the whole, the system does not get so out of balance in any one direction that it breaks apart.
Many dynamic equilibrium systems have a feature like a buffer to mitigate the responses between the different factors. In the example above, the manager is able to buffer the interaction of shoppers and staffers.
Science example.
Giant kelp is a tall algae that grows into large patches, called forests, along the pacific coast of North America.
Kelp forests are home to spiny purple sea urchins, sea bass fish, and carnivorous mammal sea otters.
Urchins eat the kelp. Otters eat the urchins.
If the kelp forest grows too small, the urchins are easy to spot and get eaten by otters.
If the kelp forest grows large, more urchins can hide there, and they eat the kelp.
The size of any kelp forest is always changing, but if you fly over the coast there would be about the same total amount of kelp growing along the coast.
This interaction between kelp and urchins is mitigated by otters.
This describes a system where at least two features reinforce each other, growing and growing. This system will not automatically find a balance.
The actual system does not need to involve things that have positive emotional connotations - this is not about how the system FEELS.
Science Example:
Humans hunt sea otters (they make great hats!!).
Sea urchins grow unchecked, and gnaw through the narrow anchor points of giant kelps.
The giant kelps float away, leaving behind an "urchin barren": rocks teaming with spiky purple urchins, and no kelp forest.
Urchins graze on short algae that easily grow on the rocks in sunlit water.
Urchins continue to go berserk, and obliterate kelp forests up and down the coast.
This is a postive feedback loop. It might sound sad (poor kelp!) or happy (yummy urchins!), but it is OUT of EQUILIBRIUM because more urchins leads to less kelp leads to more urchins leads to less kelp.
Social Example:
Sub-prime mortgage lending.
Sub-prime mortgages are given to individuals with lower than average credit score.
Due to the lower credit score, lending agencies charge a higher interest.
The higher interest rate makes it harder to pay of the loan.
If payments aren't made the individual's credit score drops.
As the credit score drops companies refuse to grant regular loans.
This describes a system where at least two features reduce each other, shrinking and shrinking in their impact on the system. This system will not automatically find a balance.
The actual system does not need to involve things that have negative emotional connotations - this is not about how the system FEELS.
Science Example:
I am cold.
I shiver.
I am less cold.
I shiver a little less.
I am fine. Thanks, negative feedback loop!
Horns vs Antlers
Horns are bone coated in a protein. They stay on the animal's skull and continue to grow throughout the animal's life.
Examples include:
Bison
Cows
Giraffe
Utahceratops
Pachycephalosaurus
Antlers are bones, and they can come off the animal's skull in many cases. In many cases they regrow yearly.
Examples include:
Moose
Deer
Elk
Geoscience
Geoscience is the study of earth.
Sauropods
These dinosaurs are famously known for their extremely long necks.
Theropods
Theropods are a dinosaur clade with hollow bones and three-toed limbs.
How do scientists determine what's a bone and what's a rock? The answer lies within the tongue. Due to bone's porosity, it will stick to your tongue.
Relative Dating
Geologists can easily compare sedimentary rock layers in one canyon, across a state, or across a continent and decide which layers are older, and which are younger.
It's taken hundreds of years to make enough observations to interpret the relative age of rocks on every continent, and there is still so much work to do!
Geologists make many interpretations by following a few principals for how sedimentary rocks form. Paleontologists refine relative age estimates for rocks by tracking fossils in the rock layers.
Unlike Absolute Dating, where we can simply measure something and assign a number, for relative dating we rely on a series of principles and assumptions that help us place events and samples into sequence.
Uniformitarianism is the principle that the physics, chemistry, and basic rules that play out on earth today had the same behavior in the past. Some geologists say, "The present is the key to the past." If we research ancient limestone rocks, we need to visit modern depositional environments that form calcite and aragonite minerals. If we research ancient sandstone rocks, we need to visit modern rivers and beaches.
Uniformitarianism is not a law. Certain animals, plants, and chemical settings that existed long ago appear to be quite different than what we have today, and can cause odd rocks to appear. But in general, we think the physics and chemistry details remain the same.
Generally, old sedimentary rocks are on the bottom and young sedimentary rocks are on the top.
If you have a huge stack of mail, or notebooks, or books near your desk, you've probably read the one on top more recently.
This happens in normal sediment deposition and layered rock formation.
Consider a stack of rocks that has:
sandstone at the bottom,
a set of layered volcanic ash beds in the middle,
and some coal on top.
We could interpret that this depositional environment changed over time:
from a sandy area,
to an area pestered by frequent volcanic eruptions,
to an area filled with dense forest and plants.
Superposition is not a law, it's just logic. Some sedimentary features build differently. Consider a coral reef, which piles calcite made by animals on top of each other in a big growing pile. This will be more like a pile of laundry in your room: that shirt you wore last month is probably at the bottom. A sock from yesterday might be on the floor. In this case, the superposition refers not just to the HEIGHT of the material, but its position away from a core of deposition.
NOTE: Igneous rocks that flow across a landscape, or layers of ash that gently fall down over a landscape, can form nice layers that DO follow superposition. But not all igneous rocks behave like this!
Original Horizontality & Lateral Continuity[edit | edit source]
Sediments usually spread far and flat before becoming rock.
Consider the mud at the bottom of the Great Salt Lake, or the ancient Lake Bonneville.
One layer of this mud might be only a few mm thick,
but it would spread a long distance,
with very little elevation change.
Consider the sand that spreads out during floods of the Mississippi river, or sand from a river during the Jurassic Period.
One layer of sand from a huge flood might only be a few cm thick,
but it would spread over a huge distance,
with very little elevation change.
The area that we call a "flood plain" around a river is the area that has a better chance of collecting sediment that can become rock, because this is an area of deposition. The river itself is a tiny area, by comparison, and it is frequently eroding material.
We can make two practical interpretations using these two rules.
First, if we see sedimentary rock units that are tipped at a big angle, we can stand back and say, "I bet when these ORIGINALLY formed sediment layers, that each layer was basically flat."
Second, we can see, or we can guess, where a layer of rock should be visible far away, even if it's covered by some plants in between.
What do we mean by a "layer" of sedimentary rock?
It depends on what we're studying!
In the Fredrick Albert Sutton Building on campus, you can see displays of fossil fish and fossil leaves. The displays are framed in slabs of rock that show little mud layers. Each thin mud layer had lateral continuity, and had original horizontality.
We could also be mapping the shores of Lake Bonneville by tracing outcrops of ancient limestone clusters on a map. This might be a layer of rock one meter thick, that extends for dozens of miles in each direction.
Scientists who look for oil and natural resources need the most sophisticated techniques to consider layers of sedimentary rock. Here's a good page explaining sedimentary rock layers that are not exactly flat, but still spread very far.
Again, igneous rocks that flow across a landscape, or layers of ash that gently fall down over a landscape, can form nice layers that DO follow original horizontality and lateral continuity. But igneous rocks are sneaky and have their own rules!
If you're looking at a rock cliff of sedimentary layers:
Fossils in the bottom layers should represent animals that died a long time ago.
Fossils in the top layers should represent animals that lived less long ago!
If an animal lived all around the world, and then it went extinct, we can use its fossils to decide which rocks are RELATIVELY older or younger.
If we use fossils to reconstruct a sequence of animals (A, then B, then C), we can use any of these to compare rocks (maybe you find only animals A and C, but you know their relative age now).
Ancient sedimentary rocks are usually pretty messed up by the time we can see them!
Events, features, or even other rocks can break up, disrupt, or cut across the sedimentary layers. In order for the cutting features to be present, the disrupted layer(s) needed to already be there first! This can help establish sequence, or identify areas of missing time, in some records.
If I find a chunk of rock A inside a layer of sedimentary rock B, then rock A must be older. Rock A must have already existed before Rock B could include a chunk of it!
The principal of inclusion has helped geoscientists advance absolute dating dramatically in the past decade.
The best methods for absolute dating on rocks that are millions of years old requires mineral grains that form in igneous processes.
Those minerals are very durable, though, so a sandstone from a beach setting might have a bunch of those grains.
Zircon is a super-durable mineral that we can measure atoms in really well.
By the principal of inclusion, zircon grains found in a sandstone are OLDER than the day that sand actually stopped moving and started its journey to becoming rock.
If we zap one zircon and get an age of 200 million years, we know the sandstone layer cannot be OLDER than 200 million years. But how much younger is it? Dunno!
If we zap twenty zircon grains and get a range of ages, we can make a better guess of the sedimentary layer's formation time.
Extrusive igneous rocks can don't have to follow the rules for sedimentary rocks, but sometimes they CAN.
Intrusive igneous and metamorphic rocks don't have to follow any rules of sedimentary rocks.
If geologists discover fossils of a new dinosaur, they will need to decide how old the fossils are.
Consider all the observations that are necessary to even make a good guess!
Consider three people exploring some rocks near a river.
On the left bank, who is standing on the oldest rocks? Can we use superposition?
We can apply original horizontality to interpret that these rocks were originally more flat, and have only become tipped at this angle due to Earth motions.
Lateral continuity tells us that the rocks on the right side of the river should connect to the rocks on the left side. BUT! If there is a fault causing offset in these rocks, we might not see it right here because the river might cover it up.
Some fossils are very easy to correlate between layers of rock far away. Criteria include:
The animal (or plant, or spore, etc.) lived in very distant places at the same time.
The animal fossilizes well.
The shape of the fossilized animal makes it easy to distinguish from animals that lived at different times.
Specific varieties of the animal are widespread but go extinct pretty fast, then evolve new, differently-shaped varieties that also spread out and go extinct pretty fast.
Some of the best index fossils are ammonites, extinct squid-like animals that had a coiled shell divvied into air chambers.
Ammonites rapidly evolved distinctly-shaped shells that made abundant, distinct fossils.
Ammonites died really easily, and then added diversity really easily, and lived all around the world.
The drag is that ammonites only lived in the ocean, so they aren't helpful for relative dating of rocks from land habitats.
Here is a 3D model of a fossilized ammonite shell.
Rocks
Kinds of Rocks: Igneous, Sedimentary, and Metamorphic[edit | edit source]
Earth's crust is made of minerals in rocks. We categorize rocks because they form differently: Igneous, Sedimentary, and Metamorphic.
This is a common extrusive rock, which forms from lava.
Lava cools so quickly that it only produces very small crystals, so it is difficult to see individual crystals in basalt.
Where lava flowed under air or water, it retains its flow texture - rough, smooth, bubbly, etc.
Lava can flow through cracks in existing rock, and can produce upright or flat-out expanses.
Idaho's Craters of the Moon is made of basalt.
Basalt that is mostly bubbles and floats is called pumice, and is an important economic resource.
Most of Earth's sea floor is made of basalt that is continually erupting under water.
Here is a 3D model of basalt. The green crystals are peridotite, and the grey rock is the basalt.
Granite
Granite is a common intrusive rock, which forms in magma.
We can easily see the individual crystals in granite. Large crystals form slowly while the magma is trapped underground.
We find granite on continents that are very eroded. Mountains of granite exposed by glacial erosion are easy to see in Yosemite National Park in California.
The durability and beauty of granite make it an important economic resource and common building material.
If you pick up a sedimentary rock from the ground, as you drive by a highway road cut, or as you stroll on the Bonneville Shoreline Trail, try these observations.
Taxonomy is the study of categorizations. There are many ways that paleontologists have grouped and categorized animals in the past ~200 years of formal western-anglo-European-American paleontological practice.
Generally, both in this class and in today's American universities, folks say, "taxonomy" when they refer to hierarchical classifications that are built around animals' (extinct and extant) apparent physical traits and resemblances.
Today's paleontologists, particularly those that work on animals with bones, usually use cladistic analyses and phylogenetic approaches to group animals based on their shared evolutionary histories.
Consider how a person would answer the question below, using each of the three schemes presented.
"Which two things belong in the same category? Snail, Sea Urchin, Eagle."
Snail and Sea Urchin according to early Lineeaus work, and a late-century (1980s) taxonomy, and a phylogeny.
And again.
"Which two things belong in the same category? Lizard, Alligator, Eagle."
Lizard and Alligator according to early Lineeaus work, and a late-century (1980s) taxonomy, and a phylogeny.]
Growing up in the 1990s, Dr. Ritterbush was taught during science class to sort animals into groups, and to memorize the RANKS of these groups:
Kingdom
Phylum
Class
Order
Family
Genus
Species
We don't teach this scheme any more in college. Why? Well, the short answer is that these particular "ranks" are human constructs that look nice on paper, but don't have a strong link to real biological principals or processes. Exceptions include fossil studies that focus on Phyla, Families, and Genera, but these are a little too niche for this class. Please do chat with Ritterbush for more info.
What makes a Bird a Dinosaur
What makes a Bird a Dinosaur? To answer this question let's take a look at a timetree.
Timetrees are a great way to visually understand the evolution of animals and the formation of clades.
Animals to Know
We chose a specific list of animals for focus in this book. We will build a page specific to this book for each animal listed below. While we update our custom pages, links may visit the related wikipedia page.
Rocks from the Jurassic period indicate hotter, wetter conditions than we experience on Earth today.
Rocks do not show signs of ice caps near the poles, of traveling ice-bergs, or other signs of "ice house" conditions.
Allosaurus would have roamed deserts and river systems. The super-continent Pangea was splitting up throughout the Jurassic Period, adding volcanic activity, particularly along the west coast, and warm, seasonally-variable habitats.
Rocks from the Jurassic period indicate hotter, wetter conditions than we experience on Earth today.
Rocks do not show signs of ice caps near the poles, of traveling ice-bergs, or other signs of "ice house" conditions.
Barosaurus lived in a semi-arid, seasonal floodplain. The super-continent Pangea was splitting up throughout the Jurassic Period, adding volcanic activity, particularly along the west coast, and warm, seasonally-variable habitats.
Rocks from the Jurassic period indicate hotter, wetter conditions than we experience on Earth today.
Rocks do not show signs of ice caps near the poles, of traveling ice-bergs, or other signs of "ice house" conditions.
Brachiosaurus lived in a semi-arid, seasonal floodplain. The super-continent Pangea was splitting up throughout the Jurassic Period, adding volcanic activity, particularly along the west coast, and warm, seasonally-variable habitats.
Camarasaurus had a much stronger bite force than earlier saurodomorphs such as Plateosaurus which helps illustrate that Camarasaurus is a derived sauropod.
Rocks from the Jurassic period indicate hotter, wetter conditions than we experience on Earth today.
Rocks do not show signs of ice caps near the poles, of traveling ice-bergs, or other signs of "ice house" conditions.
The super-continent Pangea was splitting up throughout the Jurassic Period, adding volcanic activity, particularly along the west coast, and warm, seasonally-variable habitats.
This fun dino has a fancy little crest. It's an extension of its nasals. This means that an immense amount of air could be circulated through this large void.
Scutelosaurus was about the size of a german shepard dog, with a long narrow tail, a fairly long, narrow torso, and a small head.
Scutelosaurus had long hindlimbs and relatively short forelimbs, and many toes on each.
Scutelosaurus had several rows of skin bones ("scutes") along each side of its back. These are similar in appearance to the skin bones that grow on alligators and crocodiles today.
Scutelosaurus had a special pointy beak bone (a "predentary") at the front of the lower jaw. The lower jaw, aka "mandible" is made of "dentary" bones, which hold teeth. The predentary bone brings the jaw together at a point.
Based on its limb length in comparison to other dinosaurs, we think Scutelosaurus could walk quickly on its hindlegs, or could use all four legs to walk more slowly close to the ground.
Based on similarities to the scutes in modern alligators and crocodiles, we think the skin bones in Scutelosaurus would provide some protection against predators' claws or attacks.
The teeth would be suitable for eating plants or bugs, but didn't do a lot of chewing.
Scutelosaurus fossils are known from the early part of the Dinosaur age, and are extremely rare. Recent research by University of Utah PhD student Benn Breeden shows the most up-to-date work on these animals.
