Re: Spinosaurs ate pterosaurs

[David Marjanovic <david.marjanovic@gmx.at>]

> <No, no -- the prey must provide more energy than the efforts to get it,
> and I can't imagine this would be the case in an animal that would live
> off climbing up a tree over and over again.>
>
>   Nonetheless, there are animals that do this, contrary to this
> "neccessary" statement of comparitive energetics.

No, there are none that do _this_ -- to jump down from a tree to catch one
insect in mid-air and then climb back up, many times a day. I haven't said
that parachuting wouldn't evolve _at all_! I've just said that no parachuter
is going to live off catching insects in flight.

> The flying squirrel, though not a typical predator species,
> like the aye-aye, does expend much energy foraging, as do bees,
> without much succor in attaining a full belly
> by the time it's back at "home."

Still, they get _quite a bit_ more energy from their food than the
hypothetical example above would.

> For a given mass, indeed, a prey species
> seem to exert MUCH more effort to escape than the predator expends to
> catch it, with some notable exceptions. Including _cheetahs_. When you are
> adapted to catch fast prey, it becomes the _predator_, not the _prey_,
> that is the more costly animal. This has led to various adaptations of the
> feline form in some species to adapt to catching food. All a serval has to
> do is crouch and stalk before the prey species "bursts" from the
> underbrush, expending massive amounts of calories in the effort to not
> being killed, then leap out and snatch it from the air, then back to
> ground. This is, relative to it's massive, very little expenditure than
> the bird's.

Er... all correct, all unrelated to what I wrote.

> <Yep. But they do so in order to get from one entire feeding ground to the
> next. They don't jump down a tree and climb back up to catch one fly.>
>
>   I mentioned that flying squirrels really did do this in the attempts to
> catch food if it was prey, but then again, flying squirrels are not a
> predator species, being herbivores for the most part and grub-eaters at
> least. But a leaping predator does exists in the same general ecology,
> including flying snakes, who do this to gain vantage point and access to
> prey, colugos who get to feeding sites, etc.

I'm talking about parachuters (almost only downwards), you about gliders and
leapers (mostly forwards). But even then, none of these gliders (AFAIK)
catches insects in mid-air at all, let alone for a living!

> Cats will also climb after food, including nests of birds,

...while the speculative lifestyle of *Epidendrosaurus* would involve
climbing high trees for very little food _many times a day_.

> <Because they can afford it. They are efficient enough hunters.>
>
>   This is also contradicting a statement, and the reason I brought them
> up. They will expend an _unneccessary_ amount of energy for the sake of
> something unrelated to catching food.

They have enough energy at their disposal that they can afford to play.
(Besides... the comments on wake-riding are AFAIK correct.) Under the
proposed lifestyle, *E.* would not -- to the contrary, it would have too
little energy to live.

> Why should a flying squirrel NOT have the same consideration?

Did I say it shouldn't? :-)

> <I'm still not convinced that the short skull isn't merely a juvenile
> feature of this very young specimen.>
>
>   Would you mind demonstrating the U-shaped jaws in a juvenile of a
> non-insectivore that did not, as a juvenile, eat insects?

I suppose I don't count, having an apomorphically short skull even as an
adult? :-)

> Though others
> have also brought the large head/large eye "evidence" up for juvenile
> *Epidendrosaurus,* the nearly identically-sized *Scansoriopteryx* shows
> similar proportions with slight differences, a huge head and orbit, and
> fused neurocentral sutures with developed epipophyses of limb bones,
> indications of maturity. This would suggest that *Epidendrosaurus* could
> very well be subadult at the most, rather than a super-young juvenile.

*Scansoriopteryx* seemingly lacks ossified carpals and tarsals almost
completely. The tail vertebrae do seem to have fused neurocentral sutures,
but neither the photos nor the drawings allow one to judge the other few
preserved vertebrae. Why are you so certain about the epiphyses of the limb
bones? I probably can't tell from the photos how well ossified they are.

Impressive postzygapophyses on the tail behind the transition point. But the
prezygapophyses and chevrons are normal. Are Scansoriopterygidae and
Dromaeosauridae sistergroups...???

> <Yep. It starves.>
>
>   Cats and otters and seals and polar bears repeat their process as
> neccessary ... they will lose 5 times out of 6 for most species. This does
> not make them starve.

Because a seal is to a polar bear, or a fish to an otter, as perhaps 100
insects are to an *Epidendrosaurus*!

> <Totally incomparable. Firstly, seal is much, much bigger compared to a
> polar bear than most insects to the type specimen of *Epidendrosaurus*.
> Secondly, plunging into water costs _nothing_ compared to the costs for a
> rather tiny animal to climb up tens of meters tens of times per day.>
>
>   The cost of plunging into water includes the swimming underwater, the
> struggle to subdue prey under water, the struggle to get BACK to the
> surface and pull the prey up with you, and possibility to defend your
> kill, and the neccessity of drying one's fur off. The same effort is
> performed in anhingas for similarly-sized prey to themselves. They will do
> this 3-5 or so times a day, and exert a great deal of energy for a single
> moment, and then spend more time and energy _fixing_ themselves. This will

Yes?

Still, my argument is the size difference, see above. An *Epidendrosaurus*
would starve if it could only eat 3 -- 5 insects per day, I bet.

> <They aren't dependent on this. They're just capable of taking advantage
> of the rather rare situation that a bird flies by closely enough and
> slowly enough.>
>
>   Quite on the contrary: servals have physical adaptations for the purpose
> of hunting through tall grass and high-speed running, catching extremely
> fast and tiny animals, and leaping, including the observed bird-snatching.

Does not contradict what I wrote above.

> They often catch food on
> the wing thet they themselves have flushed, so the idea that they just
> spot a low-flying bird is ridiculous: the birds of the area have an easy
> choice here -- don't fly low.

Does still not contradict what I write above. I didn't equate "low enough"
with "50 cm", as you seem to think.

> <The suggestion was that *Epidendrosaurus* jumped down
> from trees _for a living_.>
>
>   As noted before, the elongated arm and finger seem similar to
> pterosaurs, and could relate to a parachuting structure.

Phylogenetic bracketing (birds, *Microraptor*, *Caudipteryx*) suggests,
however, that the wing feathers attached only to the 2nd finger, not to the
3rd.

> *Scansoriopteryx*
> has integument arrayed along the arm that has been described as sifaka
> like, and *Epidendosaurus* has been inferred as having similar integument.

To me it looks birdlike, not sifaka-like. I have no trouble imagining that
adult scansoriopterygids were capable of powered flight as much as
*Archaeopteryx*.

> If the animal were arboreal, then perhaps like sifaka they would have lept
> to and fro.

Their leg proportions don't contradict this, but don't give additional
support either.

> If so, then unlike such "leapin' monkeys," their large heads
> would serve a dietary function. The only arboreal animals with similar
> heads are flying insectivores, yet clearly these animals were not volant.

"Clearly"?

> the aye-aye does not have a huge skull
> with tiny teeth at the subadult level with a U-shaped jaw, nor does it
> require this to eat grubs, so the use of the finger and the skull appear
> mechanically unsuitable if they were for aye-aye--like predation together
> (otherwise, why have such a huge subadult cranium with insectivore
> features?).

I suggest that these "insectivore features" are merely ontogenetic. The
aye-aye has its distinctive skull because of its rodentlike incisors that
allow it to bite through wood, so it can reach the grubs easier. Seemingly
scansoriopterygids didn't have this extra feature and had to find natural
holes through which to stick their 3rd fingers in...

The stiff, scale-covered tail should have served a function similar to that
of the tail feathers of a woodpecker (I've also seen blackbirds do this).