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RE: Horseshoe Canyon dinos
firstname.lastname@example.org [mailto:email@example.com]On Behalf Of KELL00BELL@aol.com
> Thanks to
Thomas Holtz for his answers. I'm currently seeking more details and
> Is the
fifth (top) unit of the Horseshoe Canyon formation early Late Maastrichtian in
the Gradstein et al. Time Scale, the Lower Maa/Upper Maa boundary is placed
between the clinolobatus and aff. nicoletti Ammonite biozones
in North America. This would actually be in the middle of the Paleomag 31r
polarity chronozone, which (according to the Eberth et omnia paper cited
previously) is within Unit 4 of the Horseshoe Canyon. Incidentally,
according to that paper the lower limit of the Horseshoe Canyon is within 32r,
and hence deep inside the late Campanian.
Breaking down the
Horseshoe Canyon into its subunits, Unit 1 and Unit 2 are Late Campanian, Unit 3
and the lower part of Unit 4 are Early Maastrichtian, and upper Unit 4 and Unit
5 are early Late Maastrichtian.
lambeosaurs and Saurolophus absent in this top unit? Are any
ornithiscians already absent in the underlying fourth
> (late-early or
shows Edmontosaurus, Arrhinoceratops, Anchiceratops, Pachyrhinosaurus,
and Edmontonia in Units 1 & 2, and Parksosaurus,
Saurolophus, and Hypacrosaurus in Unit 4. The theropods
Eberth mentioned an Albertosaurus bonebed in the upper Horseshoe Canyon.
Are these remains in the top unit or
the fourth one below it?
The Barnum Brown
Albertosaurus bonebed is in the boundary between Units
4 & 5.
> How well are tyrannosaurs represented
in the top unit?
According to Eberth et al., "the vertebrate assemblage
is poorly known" in Unit 5.
Thomas R. Holtz,
Department of Geology
Director, Earth, Life & Time
University of Maryland
College Park, MD
301-405-4084 Email: firstname.lastname@example.org
(Geol): 301-314-9661 Fax (CPS-ELT):