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RE: Extinct vs Disappeared



> From: Andrew Simpson [mailto:deathspresso@yahoo.com] 
> Sent: Friday, March 05, 2010 12:57 PM
> To: tholtz@umd.edu; tijawi@yahoo.com; dinosaur@usc.edu
> Subject: Extinct vs Disappeared
> 
> With Stegosaurs it is often said that they went extinct 
> midway through the Cretaceous. This always bothers me 
> slightly as I prefer the phrase 'disappeared from the fossil 
> record' over the word extinct do to the fact that disappeared 
> from the fossil record is a factual statement were as went 
> extinct is speculative. I for one tend to assume that 
> Stegosaurs would have likely still existed in small remote 
> niches and on islands where advanced predation and food niche 
> taking new herbivores with better defenses couldn't get to 
> them and thus wouldn't cause their end. 

But you could argue this for ANYTHING. Hence, "disappeared from the fossil
record" is effectively synonymous to "extinct": a hypothesis falsifiable by
discovery of new specimens younger than the previous extinction date.

There are statistical arguments you can make to better estimate the best
extinction date for a given taxon based on its observed distribution and
frequency in the fossil record, but in the end a paleontological estimate
for extinction is: we find fossils of taxon X in the record up to this
point, and then it disappears.

Will we be wrong? Darn tootin', some of the time. That is Science for you.

But it represents the best approximation of the data at this time.
Taphonomically stegosaurs should be no different than other dinosaurs. If we
are finding stegosaurs in environments throughout the Jurassic and earliest
Early Jurassic, then stop finding them but continue to find other dinosaurs
in abundance, the simplest solution is that Stegosauria is extinct in those
regions we are sampling. And barring evidence of them at this interval or
higher in other regions, an hypothesis that they were indeed extinct as a
clade is the simplest solution.

Hope this helps,

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA