Re: Land Bridges

John Harshman wrote:
Edward Hennessey wrote:
I copy this post by J. Taylor from sci.geo.geology.



"They speculate that land bridges must have persisted between southern
South America and the Western Antarctic Archipelago"

Land bridges where have we heard this before??

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http://news.yahoo.com/s/afp/20080610/ts_afp/sciencedinosaurspaleontologygeology;_ylt=AoCiwpShDYFCyxNZzEj1.pMPLBIF

http://tinyurl.com/4mklxh

Tue Jun 10, 7:07 PM ET



PARIS (AFP) - A dinosaur bone discovered in Australia has defied
prevailing wisdom about how the world's continents separated from a
super-continent millions of years ago, a new study published on
Tuesday said.

The 19-centimetre (eight-inch) bone was found in southeastern
Australia but it comes from a very close cousin to Megaraptor, a
flesh-ripping monster that lorded over swathes of South American some
90 million years ago.

The extraordinary similarity between the two giant theropods adds
weight to a dissident view about the breakup of a super-continent,
known as Gondwana, that formed the continents of the southern
hemisphere, the authors say.

Gondwana broke up during the Cretaceous period to form South America,
Africa, Antarctica and Australia.

The standard theory is that the first continents to go were South
America and Africa, which pulled away from Gondwana around 120 million
years ago.

Not to my knowledge. As far as I know, the standard theory is that Africa pulled away from the rest of Gondwana at that time, while South America remained attached to Antarctica. Just when South America separated from Antarctica has been a matter of contention, but it's been suggested before that there was some kind of connection, if only a series of islands, up into the Oligocene. This would help explain the distributions of some marsupials, for example.

Here: "The cordilleras of Andean South America and West Antarctica were continuous into the Paleogene (Dalziel & Elliot 1971), thus providing coninuity of the terrestrial biotas between South America and West and East Antarctica. Some connection may have persisted as late as 30-35 Myr ago when the cordillera was disrupted and formation of the Scotia Sea was initiated (Lawyer et al. 1992)."

This from a review in Cracraft, J. 2001. Avian evolution, Gondwana biogeography and the Cretaceous-Tertiary mass extinction event. Proc. R. Soc. Lond. B 268:459-469.

Connection between Australia and Antarctica was similarly late.

Australia remained attached to Antarctica before the two entities
drifted apart around 80 million years ago, according to this theory.
Australia began an insular existence that incubated flora and fauna
which remain unique to this day.

The forearm bone, found near Cape Otway in the state of Victoria, is
the first link ever found between a non-flying therapod -- or
two-footed dinosaur -- in Australia and another component of Gondwana.

The investigators, led by Nathan Smith of the University of Chicago,
say the two dinosaurs are so similar the two land masses of South
America and Australia could not have been separated for so many
millions of years beforehand.

If that had been the case, evolutionary pressures would have pushed
the dinos in different directions as they adapted to their changing
environments.

The horseshoe crab among others doesn't seem to have done much changing at least in gross anatomy in a lot longer than that. If much of anything changed we can't detect it. In which case would have is reduced to might have.



They speculate that land bridges must have persisted between southern
South America and the Western Antarctic Archipelago "until at least
the Late Eocene," a period that began some 40 million years ago.

This is by no means a new idea.

The study is published in the Proceedings of the Royal Society B, a
journal of Britain's de-facto academy of sciences.

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