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Re: attack on dinosaur--horrific video



On 11/25/07, David Marjanovic <david.marjanovic@gmx.at> wrote:
> >> I can't imagine the size difference between *Daspletosaurus* and
> >> *Tyrannosaurus* can be explained by selection for nest defense.
> >
> > Hadrosaurs gang up on D...
>
> ...and not on its nest.
>
> >> 2. We have fairly large eutherians in the Maastrichtian of North America.
> >> Good. But we have just as large metatherians in the Campanian of North
> >> America (and isn't there a "stagodontid" skull from Mongolia as well?).
> >> You don't have any evidence to argue for a relaxation of size
> >> constraints!
> >
> > Close relatives of the clades that adaptively radiated after the boundary
> > increased in size before the boundary--
>
> I really wouldn't say "close relatives". The *Maelestes* paper finds
> Cimolestidae and Placentalia far apart. (Explaining at last why some
> cimolestids, such as *Maelestes*, retain five premolars like *Eomaia*.)
>
> I just had another look at the paper. The cimolestids are farther away from
> the crown-group than the zalambdalestids, which retained the epipubic bones.
> These bones prevent the belly from swelling much. Furthermore, the
> sister-group of Cimolestidae is Asioryctitheria; of these, at least
> *Ukhaatherium* retains the epipubes, too.
>
> Either they had evolved it convergently, or the cimolestids _lacked the
> placental mode of reproduction_. In the absence of direct evidence, the
> latter conclusion is more parsimonious.
>
> > their descendants have an observable major influence on the
> > community structure of oviparous species via predation--
>
> But so do all other egg-eaters.
>
> > Look at the forest for a minute:
>
> Looking at the forest for a minute will not tell you if it's composed of
> seed plants, of lycophytes like *Lepidodendron* and *Sigillaria*, or even of
> leafless protero-ferns (Cladoxylopsida such as *Pietzschia*). Sometimes this
> is an interesting question, and simply assuming the forest consists of seed
> plants will be misleading.
>
> > Continental placental predators and
> > herbivores--and whatever else--are invading/have invaded global
> > terrestrial
> > niches.  Rabbits, cats, rats, mice, dogs, pigs, goats--these animals are
> > the
> > subject of thousands of papers dealing mainly with how to ameliorate their
> > influence.
>
> Yes. One reason is that they come from the same places where invasive humans
> have come from. Another is that there simply are more placentals than
> marsupials.
>
> > Placentals enjoy a great diversity of
> > morphologies--probably a greater diversity than is available to, for
> > example, marsupials.  It is a fact--ref. if needed--that marsupial embryos
> > rush to develop craniofacial muscles and bone in order to be able to feed
> > early...it is a fact that placentals spend this early phase developing
> > neurosensory ability, i.e., laying down neurons.  Thus marsupials start
> > late
> > and are therefore at an ontological disadvantage in this respect.
>
> Are you sure the marsupials don't simply do that in the pouch?
>
> > Also, limb morphology diversity is far less in marsupials because the
> > front
> > legs are already chaneled into being legs, not wings, not fins, not arms.
> > Point is, ontogenic imperatives are a limit on morhological diversity in
> > marsupials.  This is not going to go away for them.
>
> Sure it is.
>
> There's a very interesting SVP meeting abstract on this decades-old
> assumption that was never tested before; I'll retype it tomorrow in the lab.
> In short, the only reason why there aren't marsupial whales or bats seems to
> be that the placentals got there first and immediately spread around the
> world.
>
> >> ...reliance on nest defense does nowhere near guarantee extinction.
> >
> > Why has it not re-evolved in your view?
>
> I bet the phorusrhacids and gastornithids did it, and the sebecids, too --
> remember that *Sebecus* at least lacked those extra sensors for movements in
> water and can therefore be safely assumed to have been fully terrestrial.
>
> Sure, these are just three. But it's obvious why there aren't more
> nest-defenders: because there aren't enough egg-layers left for that. As far
> as I can see, the available niches are all occupied by placentals and
> marsupials. From what should a large egg-layer evolve today?

Varanidae. From a brief web search, there appears to be disagreement
of to what extent komodo dragons actually *do* protect their nests,
but there should be little doubt they *could* - prior to the arrival
of a certain meddling monkey there wasn't anything around to beat up
an adult komodo dragon.

Megalania is another suspect.

-- 
Andreas Johansson

Why can't you be a non-conformist just like everybody else?