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Re: JFC-Bloodiest Battle ??
It's highly likely that you are right about there being biological
niches that existed in the past that are not extant (indeed, it would
be shocking if that weren't true). But "keeping a very open mind" has
to be constrained by the data we have. In the case of terrestrial
obligate scavenging there is not a single case amongst the hundreds of
extant species. Since they are otherwise diverse in their adaptations,
it seem that there may be some factor other than chance serving as the
limiting factor here. Considering the strong appeal of scavenging (and
the concurrent lack of it as a full-time profession) it's been
suggested that there may be energetic reasons why carniverous species
cannot rely soley on scavenging, and no one has succesfully
demonstrated to the contrary (I am including Ruxton & Houston 2003 in
that assessment).
Scott
Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333
www.skeletaldrawing.com
-----Original Message-----
From: Dan Chure <danchure@easilink.com>
To: dinoboygraphics@aol.com
Cc: dinosaur@usc.edu
Sent: Mon, 25 Aug 2008 5:57 am
Subject: Re: JFC-Bloodiest Battle ??
I remain agnostic on the myrmecophagus habits of Mononykus. The
forelimbs are very short and I can't see how that would work
functionally with the long neck. As for therezinosaurs, one early
interpretation of their
biology, I believe, was that they were
myrmecophagus. Another was that they were the ecological equivalents of
tree sloths. I don't believe that the modern day world contains all
possible biological niches and there is a danger in always making
dinosaurs fit into existing niches. Doing so is not necessarily a sign
of success and we should keep a very open mind, especially when highly
unusual morphologies are involved.Â
Â
DanÂ
Â
dinoboygraphics@aol.com wrote:Â
Â
What, pray tell, is the modern day niche equivalent of >
therezinosauroids and Mononykus and its relatives? <<<Â
Â
Mononykus has been compellingly linked via osteological correlates to
> myrmecophagous animals, of which there are several extant. >
Therizinosaurs appear to have been high-browsing herbivores, and while
> the giant sloths and chalicotheres that they have been compared to
are > extinct, high browsing itself is hardly a novel ecological niche.Â
Â
Scott HartmanÂ
Science DirectorÂ
Wyoming Dinosaur CenterÂ
110 Carter Ranch Rd.Â
Thermopolis, WY 82443Â
(800) 455-3466 ext. 230Â
Cell: (307) 921-8333Â
Â
www.skeletaldrawing.comÂ
Â
Â
-----Original Message-----Â
From: Dan Chure <danchure@easilink.com>Â
To: dinosaur@usc.eduÂ
Cc: dinosaur@usc.eduÂ
Sent: Sun, 24 Aug 2008 10:56 amÂ
Subject: Re: JFC-Bloodiest Battle ??Â
Â
Scott wote: > > "but inventing a niche that does not currently exist
is an > extraordinary claim, and requires comensurate levels of
evidence." > > What, pray tell, is the modern day niche equivalent of >
therezinosauroids and Mononykus and its relatives? > > Dan > >
dinoboygraphics@aol.com wrote: >>>>> My point is that the default
should not be active predation -- > other > options are viable, even if
it is difficult to distinguish > between > them morphologically. <<< >>
>> Sorry, I have to disagree with Dan. In the absence of any
terrestrial > > carnivores that are not active predators, the burden of
evidence has > > to be on advocates to show that it's even
energetically possible. Of > > course it's entirely possible that
dinosaurs (or other extinct > > organisms) filled niches that are empty
today, but inventing a niche > > that does not currently exist is an
extraordinary claim, and requires > > comensurate levels of evidence.
Furthermore, if support for such a > > niche is possible, then we would
need to evaluate osteological > > correlates on a species by species
basis. >> >> Given the excellent finite-element analysis done on
allosaur skulls, > > whose interpretted slash and rake attack style has
been corroborated > > by recent phylogenetically constrained muscle
restorations, there > > seems little reason to speculate that allosaurs
filled an ecological > > niche that does not
exist in current
ecosystems. >> >> Scott >> >> Scott Hartman >> Science Director >>
Wyoming Dinosaur Center >> 110 Carter Ranch Rd. >> Thermopolis, WY
82443 >> (800) 455-3466 ext. 230 >> Cell: (307) 921-8333 >> >>
www.skeletaldrawing.com >> >> >> -----Original Message----- >> From:
Dan Chure <danchure@easilink.com> >> To: habib@jhmi.edu >> Cc: DML
<dinosaur@usc.edu> >> Sent: Fri, 22 Aug 2008 2:44 pm >> Subject: Re:
JFC-Bloodiest Battle ?? >> >> >> 0AMike; > > I agree. I admit it is arm
waving. My point is that the > default should > nÂ
ot be active predation -- other options are viable, even if it is > >
difficult to distinguish between them morphologically. Varanoids have >
> low wide skulls, crudely like that of crocodilians (for the sake of >
> this argument). Allosaurus and a number of other large headed > >
theropods have extremely narrow preorbital regions, quite in contrast >
> to varanoids. Take a look at the dorsal view of the skull of > >
Monolophosaurus or Sinraptor. While vertical loads might be > >
accommodated, I am less certain about resistance to torque along the >
> long axis of the preorbital region, especially given all the
pneumatic > > penetration of the region. > > Given the lack of
similarity between > theropods and living terrestrial > vertebrates, it
would not surprise > me that they are making livings in > ways unlike
anything around now, > including a life b
ased primarily on >
scavenging. As Peter Dodson once > wrote "let dinosaurs be dinosaurs."
> > Dan > > Mike Habib wrote: >>> > Allosaurus, like Sinraptor and
Monolophosaurus, has an exceedingly > > >> narrow preorbital region.
All three are like a pair of scissors and > > >> quite unlike
Tyrannosaurus with arched and fused nasals. I doubt > >> > Allosaurus
was capable of sustaining great stresses, especially > given > >> the
extensive pneumatic system enclosed in the narrow > skull. Given > >>
the abundance of Morrison sauropo >> ds, Allosaurus might have been >>
primarily a scavenger, rather than > =0Â
Aa > predator, although that is >> pretty much am waving. Jurassic >
> Scavenger Club anyone? >> >> An open skull construction need not mean
> that the maximum loads are > > low - depending on the particular >
strain distribution, a kinetic skull > > can often take fairly >
substantial loads without failure. A more > > heavily built skull may >
indeed be stronger still, but I would be > > hesitant to assume that a
> more open, mobile skull morphology entails > > carrion feeding. >
Varanids, for example, have a very open skull > > construction, with a
> high degree of cranial kinesis, and yet are > > active predators of a
> range of prey items. >> >> Cheers, >> >> --Mike H. >> >> >> Michael >
Habib, M.S. >> PhD. Candidate >> Center for Functional Anatomy and >
0AEvolution >> Johns Hopkins School of Medicine >> 1830 E. Monument >
Street >> Baltimore, MD 21205 >> (443) 280-0181 >> habib@jhmi.edu >> >
>> >> >> No virus found in this incoming message. >> Checked by AVG - >
http://www.avg.comVersion: 8.0.138 / Virus Database: >> 270.6.6/1627 -
> Release Date: 8/22/2008 6:48 AM >> >> >> > > >> >> No virus found in
this incoming message. >> Checked by AVG - http://www.avg.com Version:
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6:32 PM >> >> >> > >Â
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