Why no Australian Land Tortoises?

[ascott]

The soil was not appropriate for torts either...seems that is a huge factor...I mean, the torts can get there but can not sustain itself....when burrowing is required the earth in that part is not appropriate in addition to the other factors...

 

[dmmj]

Sounds to me like you were all fooled by those blood thirsty koalas, pity.

 

[shanu303]

Now tortoises have colonized many islands, eg., the Galapagos, by floating, likely on debris, out to them. I'd guess the ocean currents between Australia and the mainland are not favorable for that sort of animal dispersal and of course why placental mammals only made it there with the help of humans.

i agree..... there is the East Australian Current

 

[FLINTUS]

Now tortoises have colonized many islands, eg., the Galapagos, by floating, likely on debris, out to them. I'd guess the ocean currents between Australia and the mainland are not favorable for that sort of animal dispersal and of course why placental mammals only made it there with the help of humans.

But Australia is much further away from Asia than the distance between the different islands of the Galapagoses-they did not float out to the island group, they were on there when they broke away many years ago, and have just floated between the islands.
Same with mammals, while some have been introduced, it is due to plate tectonics and breaking away from the continent.

 

[Star-of-India]

The Galapagos tortoises did float to the Galapagos. Those are volcanic islands.

It is true that Australia separated from Gondwanaland, or whatever we call the early mega continent at that very early point in geologic history. Certainly before the placental mammals.

I work nights in an ER so my brain is a little fuzzy having just gotten off work. But there are tortoises in Southeast Asia, I can't remember whether there are any in New Guinea, which is getting much closer to Australia and was certainly the embarkation point of the Australian aborigines. They are finding fossils/proto-fossils of tortoise-like, or very primitive tortoises, on many of the South Pacific islands whose doom clearly came at the hands of early human explorers, I believe those are thought to have floated to those islands too. Certainly the volcanic ones.

I have heard of any found in Australia. -Not that by any means signifies that such fossils haven't or won't be found. Australia having been attached to the early mega continent could certainly have gotten tortoises overland if indeed tortoises were anywhere nearby at the time of separation.

But you know, I'm an amateur and hardly expert at any of this.

Doug

 

[Star-of-India]

I'm frightened by blood thirsty koalas btw. So please don't even mention them! ;-)

 

[Yvonne G]

You know, I just had to do it!

 

[shanu303]

Highly Graphic IMAGE! Viewers Discretion is Advised

 

[FLINTUS]

The Galapagos tortoises did float to the Galapagos. Those are volcanic islands.

They are volcanic islands, but I thought they still were part of Pangea of some sort, before the construction of them along the Nazca plate boundary. I may(and I probably am) wrong, but I thought that the land was there before, it was just pushed up by the boundary.

 

[LLLReptile]

They are volcanic islands, but I thought they still were part of Pangea of some sort, before the construction of them along the Nazca plate boundary. I may(and I probably am) wrong, but I thought that the land was there before, it was just pushed up by the boundary.

No, they are relatively young islands, and didn't exist when pangaea was around.
http://www.pbs.org/safarchive/5_cool/galapagos/g22_geo.html

Interesting quote that might be relevant about how tortoises got to the galapagos islands, but not so much Australia -
"Though the islands are now quite isolated, at 600 miles from the nearest mainland, some biologists believe that the Cocos Ridge, which runs under the sea and extends almost the entire distance from Costa Rica to the northern islands, was once a land bridge. These biologists use this theory to explain how some of the life on the Galapagos Islands arrived there, but it has not yet been proven. "

I've heard the drop bears in Australia are quite terrifying....

-Jen

 

[Yvonne G]

I thought the various methods of protecting one's self from the dropbears was insightful:

Various methods suggested to deter drop bear attacks include placing forks in the hair, having Vegemite or toothpaste spread behind the ears or in the armpits, urinating on oneself, and only speaking English in an Australian accent.

 

[LLLReptile]

So a bit of google fu...

Started with this fossil record map of how different continents must have been connected. My thought was that turtles/tortoises must have been on a part of Pangaea separated by geography from the rest of the continent.
http://en.wikipedia.org/wiki/File:Snider-Pellegrini_Wegener_fossil_map.svg

Looking back at when turtles/tortoises evolved, it was back before the Triassic, so right smack in the middle of Pangaea's existence.
http://tolweb.org/Testudines

Side note, looks like to find where turtles were from, you look for people looking for how they evolved their shells. They clearly were on the African continent - http://www.elsevier.com/connect/how-the-turtle-got-its-shell-clues-revealed-by-fossils

If I had to make a guess, Australia just separated before tortoises/turtles could make it to the part of the mega continent that Aus is on.

Anyway, if anyone else finds those links interesting, there you go!

-Jen

 

[Cowboy_Ken]

I thought the various methods of protecting one's self from the dropbears was insightful:

Various methods suggested to deter drop bear attacks include placing forks in the hair, having Vegemite or toothpaste spread behind the ears or in the armpits, urinating on oneself, and only speaking English in an Australian accent.

Be warned though. Urinating on ones self, once started, is a hard habit to break. Particularly in the winter when you are cold…

 

[chosen2030]

Thank you for all of the really well-informed and insightful responses. I am not well versed in Pangaea and what Australia's ecology was like at the time. I've just always wondered since freshwater turtles exist in Australia and because tortoises exist in not-so-distant Burma (with the excellent example given of the Galapagos). I am obviously no ecologist and as a layman didn't see a huge difference between the semi-arid deserts of South Africa and the SW U.S. when compared to those of Australia, but I now have a much better understanding thanks to you learned folks that were willing to share your knowledge with this thread. Much obliged!