Re: Duration of Dinosaur Reign

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>I have noticed what appears to me a wide disparity in the estimation of
>how long dinosaurs reigned on the earth, generally ranging from 140
>million years (in Sattler's _New Illustrated Dinosaur Dictionary_
>published in 1990) and 180 million years (in Spinar and Currie's _The
>Great Dinosaurs_ published in 1994). Is the disparity due to evidence
>discovered in the last few years that extends the reign, or is the 60
>million year difference a case of "... 160 million years, give or take
>20 million years..?"


I think most of it has to do with differently calibrated time scales.  For
example, by some methods the K-T boundary is at 64.0 Ma, by others at 66.0
Ma.  Most people use the average (65.0 Ma).

By the Harland et al. time scale of 1990, the first dinosaurs appeared in
the Carnian (which began 235.0 Ma) and died out at the end of the
Maastrichtian (65.0 Ma), giving a duration for the nonavian dinosaurs as
170 million years. (Since no dinosaur is yet known from the base of the
Carnian, a mid-Carnian beginning of 230.0 Ma results in a 165 myr
duration).

>Also, authors are fond of pointing out how long the dinosaurs reigned,
>comparing it to how brief the reign of humankind has been. Wouldn't it be
>more accurate to make a comparison based on individual species?
>Is there any evidence to indicate, for example, how many millions of
>years Deinonychus thrived before it became extinct?

You are absolutely right - those are comparisons of apples and gymnosperms.
;-) [That is, one species and one group of many, many species].

Species duration is hard to ascertain for most dinosaurian species (e.g.,
Deinonychus antirrhopus), since most are known only from a single
formation.  Dodson and various others have calculated something like a 5-8
million year duration for an average dinosaur species.

A better example (and the one I use) which illustrates the long reign of
the dinosaurs is:
More time seperated Tyrannosaurus and Stegosaurus than seperates
Tyrannosaurus and us.
Twice as much time seperates Tyrannosaurus and the earliest dinosaurs than
seperates Tyrannosaurus and Stegosaurus.

                                
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.