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RE: Horseshoe Canyon

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of KELL00BELL@aol.com
 >     I have a few questions concerning Horseshoe Canyon research: 
 >       --What is the age of Upper horseshoe Canyon strata?  Is the entire unit only basal Maastrichtian in age, or is  
> the upper part mid-Maastrichtian (as it underlies the Late Maastrichtian Scollard?) 
According to the guide to the Alberta dinosaur field trip for this year's SVP, the boundary between the Horseshoe Canyon Fm. and the overlying Whitemud Fm. in the Red Deer River valley region is a significant hiatus of unknown duration.  It would be within the 30n-30r magnetic chron boundary, near the top of the M. gibbus miospore zone, and thus somewhere in the 67-66.5 Ma range.  Dinosaur fossils are represented in the 2nd, 4th, and 5th (top) units within the Horseshoe Canyon.
      --What faunal changes, if any, are evident by late Horseshoe Canyon time, compared to lower in the unit? 
Excellent question.  According to the field guide to the Dinosaur Provincial Park field trip for this year's SVP (which I did not attend, unfortunately: had to get back to the University), Loris Russell had written but never published a manuscript mapping out the position of various fossils within the Horseshoe Canyon.  Based on his work (as conveyed in the field guide), theropods show little change within the Horseshoe Canyon, but ornithischians show "significant declines" within the Horseshoe Canyon (after, of course, a major diversity drop between the Dinosaur Park Fm. and the Horseshoe Canyon).
      --Is it certain the tyrannosaurs are albertosaurs, not subadults of an early species of Tyrannosaurus  
>  eg .  bataar?  
Well, since the Horseshoe Canyon specimens were named first, if they were synonyms then the Mongolian guy would have to be T. sarcophagus...  However, that isn't an issue, as the named and referred material from the Horseshoe Canyon is distinct in details from T. rex, T. bataar, and the like.  Albertosaurus is a valid taxon.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742      
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796