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Re: Mesozoic mountains?



On Thursday, March 3, 2005, at 05:24  PM, David Marjanovic wrote:

My take on the theory that spinosaurs are derived coelophysids.

Then you'd first have to explain why they lost all coelophysoid autapomorphies ( = the features found in that clade but not in close relatives), and then how they converged so heavily on Tetanurae.


I imagine that as the continents spread apart, namely NA & what is now Europe, chains of island would have periodically ascended & descended from the tectonic movements.

The North Atlantic is much, much younger. It started around the K-Pg boundary, if not later...


My support for this comes from the fact
that Coelophysids are found in North America[albeit dang-near
everywhere],

Absolutely everywhere so far, except Antarctica and Australia.

[HP] Randall B. Irmis: First report of *Megapnosaurus* (Theropoda: Coelophysoidea) from China, PaleoBios 24(3), 11 -- 18 (December 22, 2004)

Abstract:
"The biota of the Lower Jurassic Lufeng Formation (Yunnan Province, China) is critical to understanding Early Jurassic tetrapod evolution and biogeography. Theropod dinosaur material from the Lufeng Formation remains enigmatic and poorly known. For this reason, any theropod material that can be unequivocally identified as a particular taxon is valuable in understanding the theropod fauna of the Lufeng Formation. Here, two specimens are reported as being the first record of the dinosaur *Megapnosaurus* from the Lufeng Formation, and the whole of Asia. The presence of *Megapnosaurus* is consistent with previous work suggesting an Early Jurassic age for the Lufeng Formation. It also greatly extends the geographic range of the genus, and confirms the pangeographic distribution of Early Jurassic terrestrial tetrapods."


The paper concludes that Pangaea had almost completely the same fauna everywhere.

including here in Nova Scotia, the furthest eastward
extension of North America.

In the Triassic and Early Jurassic, you wouldn't have noticed that.* In fact, it wouldn't have meant anything. North America didn't exist in a meaningful sense. No plate boundary or anything was between the Newfoundland Bank and the Iberian Peninsula.


* Besides, it's not quite true. Even if you don't count Newfoundland because it happens to be an island this interglacial (as in: "this week"), Labrador extends farther to the east. :-)

Also, the gracile build, relatively
similiar body proportions, and kinked snouts - unless the latter trait
evolved again in these theropods, wouldn't be the first time.

Or unless all normal theropods look that way -- "normal" meaning "plesiomorphic", which in turn means they haven't evolved some other shape _from that one_.


If there indeed was a chain of periodic landmasses in the Atlantic Ocean,

The _central_ Atlantic Ocean (between Africa and North America) is no older than the Middle Jurassic. The other parts are younger still.


A beautiful hypothesis, I must say, but it is slain by a conspiracy of several ugly facts!

Pretty good though for talking off the top of my head fresh home from work.