Turtle or Tortoise first?

[crazy_sailor]

I saw the post last night by Shellys1984 with the tortoise that could swim. My first thoughts were "Cool, a swimming tortoise".

Then I thought (in my opinion) that he didnt look overly bothered. He wasnt swimming frantically, his leg movements were certainly slower than when I have seen my tortoise trying to get himself back the right way after falling on his back and to me looking a bit distressed. He moved away from the edge and even climbed over a hose and carried on. If he was distressed then I would have expected him to find refuge on the hose or put his legs down on the turtle he swam over. However I'm no expert on reading tortoise emotions and this isnt the point of this thread.

My next thought was, he must have remebered what to do in water because he used to be a turtle (in evolutionary terms). I then looked at my turtles (Musk) and saw that they had legs which were adapted for the marine environment not fins/flippers that could also be used for the land. They also swam with a 'walking' motion not a combined breast stroke style. This made me think that turtles came from tortoises (I know they are all turtles but bear with me).

After a bit of Googling I found evidence for both theories but as there are massive gaps in the fossil records it's not a cut and dry argument.

General history

http://dinosaurs.about.com/od/otherp...-Evolution.htm

Turtles first

http://www.kgbanswers.co.uk/which-an...turtle/3303733

Tortoise First.

http://creation.com/evidence-for-turtle-evolution

And then I read that some tortoises can hold their breath for long periods for which they have used when walking accross rivers. Which again could have been a throw back to being turtles.

http://uk.answers.yahoo.com/question...2233630AAVGErx

If turtles started life in the sea then why do they come ashore to lay eggs? My mind was going into overdrive.

So I have a few questions for a general discussion -

1. Did they start in the water (like us) and then some came ashore.
2. Did they start on land and some went in the water?
3. Did they start in the water, some come out and then some of those go back in (legged turtles).

But also

4. What strange abilities/traits do tortoises have from turtles that they dont really use and what do turtles have from tortoises that they dont use. A bit like why we have separate little toes that are no longer required to be separate for climbing, why do we still have an appendix?

Every day I find these little fellas more and more interesting!

[egyptiandan64]

Well the oldest fossils are fossils of turtles. Now whether they were water turtles or land turtles it's hard to tell. Tortoises as a group are younger than turtles, so turtles came first. Marine turtles come between the 2.
Turtles/Tortoises as a group lay eggs and reptile eggs won't develop if laid in the water. With a hard shell it would pretty much be impossible to give birth to live young (the pelvic girdle isn't wide enough).

Danny

[crazy_sailor]

That all makes sense.

My turtles definately have legs that have been marinised so I reckon at some point it was land variety that then went back to the water.

I still dont understand why turtles that never left the sea still lay hard eggs that need to hatch on land and dont have eggs more similar to fish. But then again evolution does wierd and wacky things. Just look at the T-Rex or the Duckbill Platypus!

[egyptiandan64]

But Marine turtles have lungs and breath air, so their eggs need to do the same. If they were fish (there were some very armoured fish in the past ) which don't breath air, than they would lay eggs that could develop in water.

Well the platypus is fairly easy to figure out as mammals are descended from reptiles (which lay eggs). So the platypus is a bridge between the 2. They were just isolated on a large island, so survived all the changes mammals under went. As the placental mammals out competed the monotremes in the rest of the world.

Danny

[crazy_sailor]

Ah, I had not considered the breathing thing, every day is a school day! Good point and the ability to breath underwater in some species would have come along later from when the species diversified. Also the current system works so why do they need to evolve and change it.

All the features of the platypus make sense for what it does but it certainly is 'different'.

[meacy]

You have got to love planet earth, it will be hear a lot longer than us, and lets see what evolves then