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RE: Size Isn't Everything (WAS Re: cause of Gigantism in sauropods)
And it's not just size: in dentition, you must (absolutely, MUST) consider
the arrangement of the teeth and the association with the jaw closing mechanism
(joint, jaw levers, muscle actions and placement) when assessing teeth in a
close to a vacuum as some analyses may do. A single blade-shaped tooth can
belong to a small, short-faced taxon (*Atrociraptor*) while it could also
belong to a long-jawed taxon (*Austroraptor*), and both taxa would do different
things with their jaws because of the jaw-tooth complex. In extension to
sauropods, the staggered, "serrated" model is found in *Camarasaurus*, while
diplodocids have a half-moon "cookie-cutter" of chisel-tipped teeth, and would
act like shears rather crimpers. And this can be found in otherwise
Jaime A. Headden
The Bite Stuff (site v2)
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion
> Date: Mon, 7 Feb 2011 19:24:54 -0700
> From: firstname.lastname@example.org
> To: MHabib@Chatham.edu
> CC: email@example.com; firstname.lastname@example.org
> Subject: Size Isn't Everything (WAS Re: cause of Gigantism in sauropods)
> The big, well known Morrison theropods (Allosaurus, Ceratosaurus, and
> Torvosaurus) have strikingly different teeth. Allosaurus has relatively
> small, standard fare theropod teeth. Ceratosaurus has long and very
> blade-like tooth crowns. Torvosaurus has large teeth with crowns that
> remarkably robust. The Torvosaurus teeth from Dry Mesa Quarry described
> by Brooks Britt are way too large to fit in the mandible of the largest
> Allosaurus (the roots would stick out of the ventral surface of the
> dentary). Saurophaganax has one incomplete crown referred to it and that
> seems to resemble Allosaurus as best one can tell. Nothing is known of
> the teeth of Epanterias.
> It has long been recognized that Morrison sauropods have spoon shaped
> teeth running the length of the jaws (Camarasaurids) and pencil like
> teeth restricted to the front part of the jaws (diplodocoids). This has
> generally been regarded as reflecting some partitioning of the food
> sources. Might not the same be true of Morrison theropods and that the
> widely differing tooth structure reflects either different prey or
> hunting strategies? The Morrison fauna is unusual (say compared to many
> Cretaceous faunas) in that there are multiple, co-existing, large
> theropods, with multiple genera co-occurring in the same quarries.
> So guys, don't get hung up on size --- it isn't everything.
> On 2/7/2011 6:11 PM, Habib, Michael wrote:
> > On Feb 7, 2011, at 7:29 PM, wrote:
> >> Yes, elephant-lion is rare.
> >> But Cape buffalo are a *major* part of lion diet, IIRC more than half of
> >> some lion populations' diet (Lake Manyara National Park is one, I
> >> think<60% Cape buffalo) and that's something like 3-4x the lion's mass;
> >> especially since lionesses do most of the hunting, and they're often like
> >> 120kg animals, not 200kg. *Allosaurus amplexus* or *Saurophaganax* were
> >> larger in comparison to *Diplodocus carnegii*.
> > Group attacks by lion on cape buffalo are common in some populations, true,
> > but I am under the impression (admittedly from older literature) that solo
> > attacks on such animals is extremely rare. Taking into account that the
> > average hunting group of lions is at least 3-4 individuals strong, that
> > means that the mass ratio is actually close to 1:1, with the added
> > advantages that a group of attackers naturally has on a single target.
> >> And what were *Allosaurus amplexus* and *Saurophaganax* --doing-- if they
> >> weren't specialist sauropod, possibly big-sauropod, killers? Everything
> >> else *A. fragilis* was quite big enough to deal with.
> > I suggest that perhaps they were killing larger juveniles, primarily. Under
> > that model animals such as A. fragilis would be killing smaller juveniles
> > and the adults of small ornithopods, etc. There's no reason to expect that
> > any animals must have regularly predated the adults of large sauropods. And
> > there is no reason that the prey sizes could not overlap significantly;
> > prey sizes taken by large carnivorans in semi-arid African habitats overlap
> > quite a bit among multiple predators. Far more is made of
> > niche-partitioning that probably aught to be.
> >> But yes, the real titans were probably safe most of the time barring
> >> really hungry / desperate theropods. Still, the idea you sometimes see
> >> that 'adult sauropods were basically immune to predation' needs, at the
> >> least, qualification.
> > True enough. However, the reverse notion, that theropods regularly mauled
> > giant sauropods to death, is seen very regularly, and seems highly
> > implausible. Adult sauropods were probably not immune to predation, but
> > some of them were likely close.
> > Cheers,
> > --Mike
> >> William Miller
> >> ----- Original Message -----
> >> From: "Michael Habib"
> >> To: email@example.com
> >> Cc: "dinosaur"
> >> Sent: Monday, February 7, 2011 12:11:46 PM GMT -06:00 US/Canada Central
> >> Subject: Re: cause of Gigantism in sauropods
> >> On Feb 7, 2011, at 12:45 AM, wrote:
> >>> So in the Morrison, the sauropod-theropod size gap seems smaller than the
> >>> elephant-lion one. I see little reason to believe that Saurophaganax or
> >>> A. maximus could not take down even Giraffatitan or Supersaurus.
> >> Neat comparison with the body mass estimates (thanks for punching the
> >> numbers!) but I'm not sure I quite agree with your conclusion. It seems
> >> reasonable that something like Saurophaganax could take down something
> >> like Giraffatitan under very rare, extreme circumstances, just as living
> >> terrestrial macro-predators (or groups of them) very rarely kill much
> >> larger animals than themselves. However, I see no reason to expect that
> >> such events were common, or even occurred with a high enough frequency for
> >> us to seriously consider them as major factors in our reconstructions of
> >> Mesozoic ecology. Living terrestrial vertebrate predators rarely take prey
> >> even three times their own mass, much less 6-8 times.
> >> The elephant-lion size ratio probably does not represent the ratio at
> >> which predation is regular or ecologically important; at best it is a
> >> ratio at which a very rare predation event is still barely feasible - and
> >> that is for a specific guild of predators and herbivorous mammals. The
> >> more important size ratio is the maximum predator:prey mass ratio among
> >> *regular* predation events. Phrased as a question: Of those large
> >> terrestrial animals that are predated as adults with a high enough
> >> frequency for its impact on total population mortality to be measurable,
> >> how large are their smallest predators (or total mass of packs, if they
> >> are predated by groups)?
> >> I don't know exactly what the answer to that question is, but qualitative
> >> observation suggests that the size gap is pretty small. The vast majority
> >> of predators, even large ones, mostly take prey smaller than themselves.
> >> Even animals like water buffalo, which are a fraction of the size of
> >> elephants, are large enough as adults to be predated upon rarely (albeit
> >> more often than elephants).
> >> Cheers,
> >> --Mike
> >> Michael Habib
> >> Assistant Professor of Biology
> >> Chatham University
> >> Woodland Road, Pittsburgh PA 15232
> >> Buhl Hall, Room 226A
> >> firstname.lastname@example.org
> >> (443) 280-0181
> > Michael Habib
> > Assistant Professor of Biology
> > Chatham University
> > Woodland Road, Pittsburgh PA 15232
> > Buhl Hall, Room 226A
> > email@example.com
> > (443) 280-0181