Combining physics and vertebrate paleontology

Often, students in biology and paleontology wonder why it is that we “force” them to take physics.  I ought to know — I was one of those students!  It wasn’t until later in graduate school that I began to appreciate the application of physics to matters of dinosaur movement.  I believe part of this reticence among many future biologists and paleontologists to embrace and understand physics is that they feel (as I once did) that it was mostly the arena of engineers and cosmologists.

Yet, the questions we are often so interested in about living organisms and those in the fossil record relate to physics.  How did they move?  Were they moving in water?  How could their heart pump blood to their head?  How did a giant sauropod move, let alone stand, without breaking its bones?  So, if you are interested in dinosaurs and other magnificent animals of the past in the context of how they went about their daily lives, then you are interested in physics.

When I first began teaching vertebrate paleontology back in 2003, my goal then as now was to communicate to biology and paleontology students how modern vertebrate skeletons and body form are related to their function.  Too often, in my opinion, we tend to emphasize taxonomy and relationships over how, as scientists, we reconstruct paleobiology.  To be clear, taxonomy and the study of evolutionary relationships (systematics) are hugely important — they provide the context in which we test evolutionary hypotheses.  However, I wanted to strike a balance in my courses of teaching how the vertebrates were related in combination with how they lived their lives and responded to the physical world.

Today in my vertebrate paleontology course at Richard Stockton College, I hope a new group of students has begun to appreciate this intersection among biology, paleontology, and physics.  In the lab, students used a small wind tunnel and “smoke” from a fog machine to test how three different fossil fishes may have moved through the water.  I have found it is one thing to talk about Bernoulli’s Principle or discuss friction and pressure drag.  It is a whole other kettle of fish (pun intended) to see for one’s self how body shape actually changes the fluid around it.

Each group of students was assigned a fossil fish to research and model out of clay in lab.  Then, after hypothesizing how they thought their particular fish would behave relative to the water current (or in this case, the air current with “smoke”), they put their models in the wind tunnel, turned on the smoke, and put their hypotheses to the test.  They will later present their findings to the class.  My hope in all of this is that these students appreciate that our hypotheses about past life rely heavily on our models of the present flesh, bone, and physical laws.

Student group modeling and studying the effect of body shape on fluid movement in the early chondrichthyan, _Cladoselache_.

Student group modeling and studying the effect of body shape on fluid movement in the early chondrichthyan, _Cladoselache_.  Our wind tunnel can be seen in the background, upper left.

The _Cladoselache_ model sculpted by students based on data from fossils.

The _Cladoselache_ model sculpted by students based on data from fossils.

The student group studying the heterostracan (jawless fish) _Drepanaspis_.

The student group studying the heterostracan (jawless fish) _Drepanaspis_.

_Drepanaspis_ model.

_Drepanaspis_ model.

The student group studying the osteostracan (jawless fish), _Hemicyclaspis_.

The student group studying the osteostracan (jawless fish), _Hemicyclaspis_.

The _Hemicyclaspis_ model.

The _Hemicyclaspis_ model.

The _Hemicyclaspis_ model in our wind tunnel, sitting on a box of clay to prop it into the (faintly visible) stream of "smoke."

The _Hemicyclaspis_ model in our wind tunnel, sitting on a box of clay to prop it into the (faintly visible) stream of “smoke.”

I want to dedicate this short post to the following people at Richard Stockton College.  First, having a wind tunnel and smoke machine would not have happened at all were it not for the help of our shop staff in the Natural Sciences — Bill Harron, Mike Farrell, and Mike Santoro.  They worked on this small scale wind tunnel with my input, and helped give our students a wonderful lab experience.

Second, Christine Shairer was invaluable for her help with getting me the materials my students and I needed to do this small-scale experiment.

Finally, third, Dr. Jason Shulman in physics who is a colleague, research collaborator, and one of the few physicists willing to put up with a paleontologist who is constantly asking what I can only assume are ignorant and humorously simple questions.  If only I had had such an enthusiastic professor when I was questioning why I had to learn physics all those years ago!

Apparently I’ve gone viral -or- Stick figures and evolution

I came back from teaching an introductory biology course yesterday (Friday, Sept 13, 2013), to find a whole lot of messages from friends and family waiting for me on Facebook.  It turns out, unbeknownst to me, that my stick figure evolution cartoon was picked up by I F**king Love Science and went viral!

Stick figure evolution, by me — an illustration I use to explain to my students and lay audiences how evolution is not a straight line but a family tree of life. This went viral on IFLS: https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-prn2/1185649_635460856485590_1073680004_n.jpg

First, I am honored — honored that anything I did would even remotely reach this kind of an audience, and honored that IFLS found it worthy.

Second, please keep in mind this is intended to be fun, simple, and, above all, a diagram.  I submitted it for a Stick Figure Science contest back in 2010 for Florida Citizens for Science: http://www.flascience.org/ss2010top10.html   I was pleased at that time that it made the top 10.  So, this cartoon of mine has been out and about for a while.  It was quite surprising to see it “discovered” and shared so rapidly just now.

Third, the comments section under this cartoon has been interesting to read.  I wanted to tackle some of the recurrent themes here and put to rest any misunderstandings.

First, I will tackle the whole relationship aspect of the questions:

  1. There a lot of comments that suggest the human family tree is wrong — that I should have aunts and uncles where I have cousins.  The confusion here seems to be the conflating of “relatives” in a general sense and common ancestry.  Certainly, you share DNA with your aunts and uncles, and no doubt they descended from your grandparents.  But remember – your have aunts and uncles on your mom’s side and on your dad’s side.  Therefore, they are related to your parents and to you, but they are not your direct common ancestors.
  2. Regarding your relationship with your cousins – the only direct common ancestor you have with your cousins are your maternal and paternal grandparents.  Why?  This is because, unless there is a lot of close family intermarriages, your aunts and uncles, from which your cousins are descended, likely married someone not related to them.  So your cousins share some but not all of their DNA with you and your parents.  To find a common ancestor – a group of people whom you and your cousins could all call blood relatives – we have to look to your grandparents.
  3. Regarding second-cousins — as it turns out, there are many colloquial and law-based ways in which this word is used.  When I made the cartoon, I was simply thinking of the children of your great aunts and uncles, to which you would share a last common ancestor with your great grandparents.

Now, I want to clear up biological evolution and comments related to how I drew the “family tree”:

  1. The point I am making with the cartoon is that if you can appreciate that you have descended from common ancestors you call your parents, grandparents, and so on, you can understand biological evolution at it’s most basic level.  Darwin said that biological evolution is a theory that explained the diversity of life because of “Descent with modification” from a single, common ancestor.  All living things on earth, and all those we find as fossils, are/were part of a great family tree of life.  That is the sum total of what biological evolution means to a scientist.
  2. Saying you “evolved” from a cat or chimp or whatever else is as incorrect and ridiculous as saying your morphed from your dad to you.  No serious scientist would accept that.  But saying that we have a closer common ancestor with other mammals, like a cat, than we do with a salamander is what the data support.  As an example, the theory of biological evolution predicts there would be a common ancestral population of mammals from which all of we milk-giving fur balls have descended.  But no monkeys are mutating into humans, I promise.
  3. I stress BIOLOGICAL EVOLUTION – that is because the word “evolution” means a lot of things and is used in various ways to describe change over time, star development, the development of cultural ideas, etc.  BIOLOGICAL EVOLUTION strictly means “Descent with modification from a single, common ancestor.”

Finally, there has been a “fishes” controversy:

  1. Please keep in mind that our common use of words doesn’t always apply in science.  Theory is a great word that outside of science means a guess or hunch, but in science a theory is a powerful tool – an over-arching explanation of laws, hypotheses, and observations that can be tested, falsified, and has predictive power.
  2. Yes, yes, I know — we were all scolded by our English teachers that “fish” is singular and plural.  Except that in biological and paleontological science, “fish” is, well, “fishy.”  Based on common ancestry, for example, we humans are highly derived bony fish!  Why?  Because we share homologies with everything that has an internal bony skeleton that set us apart from non-bony backboned (vertebrate) animals.  Sharks are a type of “fish,” technically called chondrichthyans; the fish we consume tend to be ray-finned bony fishes or actinopterygians, etc.  In science, it is perfectly acceptable to use the term “Fishes” to acknowledge that “Fish” is not a catch-all for everything with fins, scales, and gills.  Don’t believe me?  Fine, see Berkeley’s evolution website right here: http://evolution.berkeley.edu/evolibrary/article/fishtree_01

Still confused?  Please remember that what you were taught in high school for biology is often simply a list of beasties with name tags — the good old Linnean classification system: Kingdom, Phylum, Class, and so on.  The Linnean system is fantastic for being a universal labeling system, but it does not often reflect evolutionary relationships, just as your name and family name don’t always accurately reflect your DNA and actual ancestry.  Why else would National Geographic and other entities be so popular at tracing people’s lineages through DNA?  Modern biology and paleontology use a tool called cladistics which focuses on unraveling relationships through special, shared traits called homologies — however, most of the non-career-science public is not familiar with this science, and that understandably causes confusion.

Finally — yes, technically what I have drawn in the cartoon are over-simplified cladograms.  They still reflect the fundamental principle of BIOLOGICAL EVOLUTION — a family tree of life, descent with modification from a single, common ancestor.  If you can communicate this family tree concept to a lay audience with stick figures even more elegantly in a single panel, I would love to see it and cherish using it in my teaching and outreach.

If you want to learn more, I have a whole audio series and other “resources” on evolution.