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Re: Mononykus, Titanis, and Ground Sloths



From: Adam Black <paleoart@digital.net>
Date: Mon, 12 May 1997 23:15:51 -0500
To: dinosaur@usc.edu
Subject: Re: Mononykus, Titanis, and Ground Sloths

Richard L. Dieterle wrote:
> According to
> Farina, for an animal MegatheriumÕs size to achieve the fastest stabbing 
speed,
> the olecranon process must be 3 to 5 inches long.  MegatheriumÕs is 4..75 
inches.
> He believes that the claws were used particularly for flipping over and 
stabbing
> Glyptodonts, which resemble armadillos.  So we have an animal thought to be a
> bark-stripper that now appears, on the basis of its arms, to be a carnivore.
> 

Adam Black wrote: 

"I haven't read the article yet, and I have not recieved any posts yet in
response to this, so I can not resist. This has got to be one of the
most ludicrous theories that I have heard in a long time! Does this
apply only to Megatherium (and possibly Eremotherium as well) or does
this theory also include the Megalonychid and Mylodont sloths. There is
preserved dung  that verifies the herbivorous tendancies of the giant
sloths. Is Farina taking into account that the dentition and overall
makeup of the Megatherium's toothless premaxillary and symphesial region
of the mandible is not one of the best adaptations for a carnivorous
lifestyle? I can't stop laughing about the thought of a huge
Megatherium, perhaps a group of them, lumbering over to a pathetic
Glyptodont, flipping it over on its back, and rapidly STABBING it to
death with its claws in the soft underbelly!! Then the Megatheres gather
around and attempt, despite their edentulous mandibular symphesis and
premaxillary, to consume the murdered fellow Edentate out of its
carapace and masticate with their blund molars what small pieces of
glypto meat they could manage to bite off. Now I know what my next
painting will be!!

Of course we all know that the giant sloths evolved large claws in order
to tear down the villages of those pesky Homo sapiens that seemed to be
increasing in population at an alarming rate in the sloths' home range."


Actually Farina argues (apparently) that this sloth was omnivorous, and its 
habits something like those of a bear.  He believes that there were a great many
herbivores in an environment in which vegetation was not luxurious.  He 
addressed the matter of dentition, but seemed to think it could serve adequately
for an omnivorous diet.  I shouldn't have (inadvertently) represented him as 
suggesting that speed of stabbing was needed for hunting Glyptodonts, he merely 
mentioned (or rather the news item did) that these animals could have been 
targets.  What his case rests upon is the olecranon process, specifically the 
alleged absolute correlation (for whatever reasons) between its size and 
carnivory.  

However, this whole matter might be resolved by an approach suggested by another
article in this same June Discover Magazine.  This was about cave bears.  There 
the investigator cleverly noted a correlation between the amount of nitrogen 
(isotope?) preserved in the tissue of an animal and the degree of its carnivory.
So the matter can probably be laid to rest for once and all if the right tests 
are made.  

Finally, all this seems to have excited your indignation.  Keep in mind that I 
am a complete tenderfoot in this subject, although I am making at least some 
small effort to build up my sophistication.  I probably should not have tried to
build anything on a news blurb; but you didn't even read the news item.  Your 
"sin" is the greater here.  

Richard Dieterle

"If it weren't for the honor of the thing [hanging], I'd just as soon skip it." 
-- Mark Twain