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Re: Extinction at end of Jurassic



>I am a second grade student studying dinosaurs. I am also writting a story to
>publish in my classroom. I looked in some books but can't find this out. Was
>there an extinction at the end of the jurassic period?         Jordon from N.
>Y.

[I think Jordan has made it clear that this is his last resort, and that
this is for a story (fiction presumably), and not science homework, so here
it goes...]

The ends of all Periods have extinctions - that is how they are recognized.
However, most of these extinctions are of marine animals (shellfish), and
are not the extinctions of major groups of animals, but only particular
species of them.

Dr. Robert T. Bakker does talk about an end-Jurassic extinction.  However,
more recent evidence has shown that there doesn't seem to be a big
extinction of families at the end of the Jurassic, although many species
may have died out.  Almost every important dinosaur family, superfamily, or
other group of the Jurassic is found in the Early Cretaceous:
megalosauroids, allosaurids, coelurosaurs, titanosaurians, brachiosaurids,
camarasaurids, diplodocids, dicraeosaurids, stegosaurids, polacanthids,
nodosaurids, ankylosaurids, hypsilophodontids, iguanodontians, and the
common ancestor of pachycephalosaurs and  ceratopsians.  About the only
groups that are in the Late Jurassic but not in the Early Cretaceous are
sinraptorids and euhelopodids, both primarily (if not exclusively) Chinese.
Since there are no well-dated early Early Cretaceous dinosaur-bearing
formations in China, even these two families may not have gone extinct at
the end of the Jurassic, but instead at some point in time in the Early
Cretaceous.

This is probably a lot more information than you could want, or use, for
your story, but I hope that you can make use of it.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.