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Re: extinction events



>During the age of Dinosaurs a number of extinction events occurred.
>I am looking for information or the timing for such events and how
>they may have effected the development of certain groups of Dinosaurs.
>
>Example: A sauropod extinction in North America during the early Cretaceous
>         and reintroduction of titanosaur sauropods in the late Cretaceous.
>         Robert Bakker hinted on a possible event at the end of the late
>         Jurassic.

This is one of the most common myths with Bakker has perpetuated.  There is
no major Jurassic-Cretaceous extinction event, as nearly every family found
in the former persists into the latter.  For example, camarasaurids and
brachiosaurids are both found in early Early Cretaceous units of Utah. 
Brachiosaurids do very well, thank you, in North America during the late
Early Cretaceous, producing the Paluxey Trackways and leaving body fossils
in Maryland, Texas, Oklahoma, Montana, Wyoming, and other states. 
Allosaurids (in the form of Acrocanthosaurus) are also present as the
dominant carnivore during this time period.  The apparent extirpation of
sauropods (ONLY in North America) occurs between the early Late and the
late Late Cretaceous.  In the meantime, sauropods continued to flourish on
every other continent.

>
>         Gregory Paul in his book "Preditory Dinosaurs of the World" has a
>         graph showing bolide impacts throughout the Mesozoic.  Is there good
>         documentation for these events?

His chart, copied from a previous article whose biblio info I don't have at
the moment, show how the bolide impacts are utterly UNrelated to the
dinosaurian extinctions.  Of course, some of the dating has changed since
then, and many of the mid-Mesozoic "impacts" are hard to demonstrate at
present.

Hope this helps.
                                     
Thomas R. Holtz, Jr.
Vertebrate Paleontologist in Exile
U.S. Geological Survey
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092

email:  tholtz@geochange.er.usgs.gov 
Phone:  703-648-5280
FAX:            703-648-5420