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Re: CORRECTION Tiny Jurassic mammal



On Thu, 24 May 2001 16:27:33  
 Daniel Bensen wrote:
>>>>>Its skull measured just 13
>MILLIMETERS (not centimeters), and its weight was estimated at 2
>grams -- smaller than the modern 2.5 gram least shrew.<<
>That
><<
>That's _minuscule_!  How could a mammal so small survive from minute to
>minute?  Wouldn't it have to be eating constantly to fuel such a high
>metabolism?  Was it exothermic, or did it carry an IV bag with a glucose
>drip stuck into a vein?

Well, all I can say is that it obviously did survive, somehow :-)  As Ken 
mentioned, some bats can reach really small sizes, and the same is true for 
some rodents, particularly shrews.  The smallest shrew I know of is _Suncus 
etruscus_, which is something like, oh, 3 inches long.  Shrews in particular 
are very active, and much of this is due to their ultra-fast heart rate, 
sometimes reaching 1,000 beats per minute!  

So, either this little new guy was an ectotherm, or it was an early endotherm 
mammal with a very fast heartrate and very high metabolism.  I wouldn't at all 
be surprised if it turned out to be ectothermic, which may say a lot about the 
origins of endothermy in mammals (which may have re-evolved).  What is 
particularly interesting is if this critter is a direct ancestor of extant 
mammals.  

Zhexi Luo has been uncovering some great small Mesozoic mammals in China during 
the past five years.  He has named something like three or four of them, and 
each one seems to be smaller and older.  He also must have a very good eye (and 
patience), as determing the absence or existance of any skull bones, much less 
small jawbones and inner-ear bones, in this little guy has to be incredibly 
difficult!

Steve

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