Wednesday, March 20, 2013

Living Fossil: A Tortoise That Cares

Lets face it, there is something just likeable about turtles and tortoises. (called testudines)  People who are generally afraid of other reptiles are totally fine with them.  Maybe it's their roles in fairy tales as the underdog or the old, wise ones?  Maybe it's their later portrayal as ninja-trained, pizza-eating superheroes or the popular water-type starter pokemon?  I'm not sure but it seems to me that everyone has a soft spot for turtles.  I'm totally okay with that.  There needs to be a universally likeable reptile ambassador (poor snakes!).  Today's living fossil is a tortoise that I have had the pleasure of working with at my job and thus, have gotten to know pretty well over the years, the Burmese Mountain Tortoise (Manoria emys)!

Manoria emys

First of all I would like to explain the difference between what is considered a tortoise and a turtle because the two are different.  Tortoises, like the Burmese Mountain, do not swim, have stubby feet with tough nails for walking and digging and eat plants.  Turtles generally spend at least some of their time in the water, have webbed feet or flippers and most species will eat other animals in some form.  There are some exceptions- Green Sea Turtles eat plants BUT they also swim, Box Turtles spend most of their time on land BUT they also eat meat so they are both still true turtles.   Got it?  Okay now are you ready to get confused?  If you live in Australia, a continent with no tortoises(land-living, plant-eaters), the term "tortoise" is used to refer to what we call turtles that live in fresh water and the term "turtle" is used to refer to sea turtles in salt water.  I might have to make a chart for that... If you want to get more specific, you can refer to a turtle that only lives in fresh or brackish water as a terrapin.  

Now that I have gotten that out of the way I can get to the part that explains why I consider the Burmese Mountain Tortoise a living fossil.  The first turtles appear on the fossil record during the Triassic Period about 250 Million years ago (roughly the same time as the first dinosaurs).  They were designed to live in the water much like sea turtles and freshwater turtles today.  These guys must have really relied on the water especially for food because somewhere along the line in evolution, they lost the ability to literally eat outside of the water.  Many aquatic turtles rely on creating an underwater vacuum by quickly opening their beaks to capture prey.  Fish eat in the same fashion.  Other aquatic reptiles like crocodilians, however, don't do this and must consume their food with their heads above or out of the water.

So we know the first testudine was a swimmer.  Land tortoises must have evolved from them some time later.  In order for this to happen they needed to re-evolve the ability to eat on land.  Dang, evolution, why you gotta make everything so tedious!  Burmese Mountain Tortoises show evidence by the physiology of their mouths of evolving from underwater ancestors.  As a personal observation, I also notice that Burmese Mountain Tortoises have a relatively lower shell compared to most other land tortoises which have very high shells (there are some exceptions in the case of some specially adapted tortoises, however).  Lower shells is a trait seen in water turtles that helps their bodies cut drag in the water while swimming.  Is the low shell on the Burmese Mountain Tortoise a derived trait from that?  I'm not exactly sure but it is something that my colleagues and I have noticed. 

Spur-Thigh Tortoise (Geochelone sulcata).  Note the much higher shell which typical of most tortoises. 

Burmese Mountain Tortoises also behave differently from all other testudines in that they build an above-ground nest for their eggs which they guard.  Every other known testudine parent just buries its eggs in a hole and then ditches them to fend for themselves.  All sources on Burmese Mountain Tortoises that I have seen only mention the mother building and guarding the nest but I have personally witnessed the father helping as well.  This may not be the case in the wild, however.

Check out this movie of this totally awesome, smart and handsome guy talking about Manoria emys!

Burmese Mountain Tortoises are highly endangered in the wild in the rainforests of Asia due to habitat loss and over-hunting for meat.  Unfortunately this is the case for a LOT of amazing animals out there.


Boulenger, G.A.(1890) Fauna of British India. Reptilia and Batrachia.

Heiss, Egon, Nikolay Natchev, Thomas Schwaha, Dietmar Salaberger, Patrick Lemell, Christian Beisser, and Josef Weisgram. "Oropharyngeal Morphology in the Basal Tortoise Manouria Emys Emys with Comments on Form and Function of the Testudinid Tongue." Journal of Morphology 272.10 (2011): 1217-229. Print.

1 comment:

  1. I noticed that you referred to there being no land tortoises in Australia. I'm fascinated by what Robin and Honey Badger have to say on this:

    "...The real reason for the lack of land tortoises in Australia is a combination of salinity and fire that occurs on no other continent or island. Tortoises survive wildfires mainly by aestivating underground, but aestivation is impracticable in saline environments. This is because aestivation involves desiccation and consequently a risk of excessive sodium in the blood.”