[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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: 8.0.138 / Virus > Database: > 270.6.7/1628 - Release Date: 8/22/2008 6:32 PM >> >> >> > >Â
Â
No virus found in this incoming message.Â
Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus
Database: > 270.6.7/1631 - Release Date: 8/24/2008 12:15 PMÂ
Â
Â
Â
Â