Along the Backbone is not forgotten … just dormant and undergoing updating

Posted in Along the Backbone Information with tags , , , , on June 13, 2013 by Dr. Matt Bonnan

Since my last post on Along the Backbone, things have changed.  How so?  Well, read here to find out: http://matthewbonnan.wordpress.com/2012/07/12/dr-bonnan-is-moving-east/

This site is not defunct, but it is undergoing a major overhaul to update it to my new position.  The audio files have to be reconfigured as well in order to update them with my current information.

At some underdetermined but not far-off future point, the podcasts will be re-released and new material will begin to surface.

In the meantime, I hope all visitors to this site will use and enjoy what I have already made available.

Thanks for your patience.

Is there a topic you’d like to see covered on Along the Backbone?

Posted in Along the Backbone Information, Along the Backbone Polls with tags , , , , on February 22, 2012 by Dr. Matt Bonnan

Is there a topic you would like to see covered on Along the Backbone?  Post your comments in this topic thread and let me know.  In the meantime, I will continue to produce new episodes on a variety of evolutionary anatomy topics, from brains to bones, across deep time.

Episode 8: Face the Face

Posted in Individual Podcasts and Transcripts with tags , , , , , , , on February 16, 2012 by Dr. Matt Bonnan

Podcast Teaser: Of all the vertebrate animals, only mammals have muscles of facial expression … why?

Transcript: You are more than just a pretty face.  Your face contains facial muscles that allow you to express and emote to fellow human beings and, some recent data indicates, even to your dog.  But in e-mail, Facebook, and other electronic media that is text-based, we often encounter first-hand how important facial expressions are and how often we are misinterpreted without these visual cues.  To prevent ourselves from being misunderstood, we have given electronic birth to the now ever-present smiley-face emoticons.

But did you ever stop to think about all of the vertebrate animals that lack muscles of facial expression?  Think about it: when is the last time a fish winked at you?  When have you seen an alligator genuinely smile?  What about a frog frowning and expressing deep sorrow?  You haven’t, of course, because most vertebrates except mammals lack facial muscles.

I often ask my students this question: why do mammals have muscles of facial expression?  The usual answers revolve around communication – that mammals are good communicators and need muscles of facial expression to get their various emotional points across.  It’s a nice hypothesis until you consider that a substantial amount of evidence from genetics, brain structure, and the fossil record show quite convincingly that the earliest mammals were nocturnal, and probably spent a good deal of time in hiding from dinosaurs.  As the old Monty Python saying goes, in the darkness nods are as good as winks to blind bats.

But we have another conundrum aside from why facial muscles evolved in mammals, and that is where did these muscles come from in the first place?  Evolution, like a lazy engineer, often doesn’t invent new structures but instead borrows, steals, and augments anatomy from already existing anatomical architecture.  One good thing about muscles and tracing their evolution is that the nerves that supply them with the stimuli to twitch and pull are very conservative.  In other words, no matter how mother nature sculpts the muscles of vertebrates into different forms and functions, the same old chemoelectrical supply lines come along for the ride.  So, we can trace the nerves and their branches to diverse muscles and muscle groups in various vertebrate animals, and using thorough comparative studies we can then determine which muscle groups are related from sharks to shrews.

So, what do comparative studies tell us about facial muscles in mammals?  During embryonic development, the jaws develop from an arch of cartilage that folds forwards.  Behind the jaw arch, a second arch develops called the hyoid arch.  Just as there are muscles that develop with the jaw arch that help close the jaws, so there are muscles that develop with the hyoid arch that accomplish similar ends.  In a shark, the hyoid arch muscles help compress the throat and push struggling prey towards the stomach.  This function of the hyoid arch muscles continues into most other vertebrates, and part of this muscle group is often called the constrictor colli.  These hyoid arch muscles are all innervated by the same nerve, and so we can follow their development very precisely in all vertebrates.

In mammals, the lower hyoid arch muscles do something very fascinating during development: they expand from the hyoid arch onto the face!  It is these muscles that become our facial muscles.  In fact, since these muscles were first identified in human cadavers long ago during the early days of anatomy, the nerve that innervates them is called the facial nerve.  This always throws my students for a loop because it does seem rather odd that the throat-constricting muscles in a shark would be innervated by the facial nerve.

So, we know where the facial muscles are coming from, but we still haven’t tackled why during mammal evolution their lower hyoid muscles would have expanded onto their face.  The answer seems to be rooted in that most fundamental of mammal products: milk.  When most mammals are born, they instinctively search for the mammary glands of their mother, often contained within teats, and begin to suckle.  To suckle effectively, one needs to form the mouth into a gasket around the teat to create the appropriate suction for extracting the life-giving fluid contained within.  To assist baby mammals in obtaining milk from their mothers, there seems to have been strong selective pressure for the expansion of muscles previously associated with swallowing and throat compression.  So far as we can tell, milk production and the evolution of facial muscles go hand-in-hand.

Once a foundation of facial muscles was established in mammals, the way was paved for smiles, winks, frowns, and smirks.  But it is fascinating to consider that what has become an indispensible part of human expression, began with a simple sip of milk.

References / Further Information

Just for fun — dinosaurs are the American Thanksgiving meal …

Posted in Uncategorized with tags , , , , , on November 24, 2011 by Dr. Matt Bonnan

No podcast for this — just a quick bit of fun:

  1. Birds are dinosaur descendants, so today on U.S. Thanksgiving you are consuming a derived dinosaur called a turkey.  So, we know that at least some dinosaurs were delicious.
  2. Because birds inherited a relatively inflexible back from their dinosaurian ancestors, bird back meat is usually not very well-developed, so you baby-back bird ribs tend not to be on the menu.
  3. The most delicious part of your turkey tends to be pectoralis muscles which pull down the wings and the supracoracoideus muscle that pulls up the wing — both on the chest.  When you cut into your Thanksgiving bird, you can see the difference in these muscles: the pectoralis is the big one on the outside, and you can see the supracoracoideus as the triangular wedge separated from the large muscle mass inside.
  4. Happy derived dinosaur eating!

P.S. Can you imagine how delicious a giant sauropod feast would be?

Episode 7: Hands Down, or, Why Velociraptor Could Not Open Doors

Posted in Individual Podcasts and Transcripts with tags , , , , , , , , , , , , on November 5, 2011 by Dr. Matt Bonnan

This podcast was chosen by popular demand by the followers of this blog.  Thanks for your continued interest in Along the Backbone.

The ability to open doors depends on two things: 1) being able to grip the door handle and 2) being able to rotate the hand so that the door handle turns.  Could a hungry Velociraptor turn a door handle to get at you, the delectable human in hiding?

Podcast Teaser:  In the science fiction story Jurassic Park, the predatory dinosaurs known as Velociraptor are able to use their hands and arms to open doors behind which delectable people hide.  My students often ask me if this could actually happen, and more generally, how much I liked Jurassic Park.  My responses are, “no,” and “it was good science fiction!”

References / Further Information

Help select the next story you hear on “Along the Backbone”

Posted in Along the Backbone Polls with tags , , , , , , , on November 1, 2011 by Dr. Matt Bonnan

Time for some feedback: influence which story is produced for “Along the Backbone”:

The polls will close Friday, November 4, at 12:00 midnight!

Episode 6: How the Dentist Came To Be So Important to Mammals

Posted in Individual Podcasts and Transcripts with tags , , , , , , , , , , , , , , , on November 1, 2011 by Dr. Matt Bonnan

Why don’t mammals continuously replace their teeth?  The answer may surprise you.

Podcast Teaser: I hate the dentist.  Well, I like my dentist, but I hate going.  I suspect many of you don’t put a visit to the tooth doctor up on your list of favorite things, either.  You can blame a number of things for the necessity of dentistry: our love of sugar top among them.  But actually the problem is an evolutionary one.  We don’t often stop to think about it, but doesn’t it seem odd that you only get two sets of teeth?  First you have your baby teeth (technically, your milk teeth) and then you get a set of adult teeth.  And you better take care of those adult teeth because when they’re gone they’re gone.  But why is this?  Non-mammals, everything from fish to amphibians to reptiles to birds (well, their ancestors anyways) regularly shed and replace their teeth.  Why should non-mammalian vertebrates have it so good?

References / Further Information

Follow

Get every new post delivered to your Inbox.

Join 242 other followers