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Re: attack on dinosaur--horrific video
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
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
niches. Rabbits, cats, rats, mice, dogs, pigs, goats--these animals are
subject of thousands of papers dealing mainly with how to ameliorate their
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
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
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
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
...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?
They (crocs) are the exception...because they are exceptional:
gives home-field advantage; they see at night (are practically
Are you sure seeing at night isn't normal?
It's dark outside...at night.
From what you told, ostriches are outright night-blind. I have walked home
from a dig in the French countryside at 4 at night; the moon was not
visible, I had only starlight, and I found the way even though I had never
walked it before (only sat in the rear of cars).
many would-be predators don't like getting wet
The eggs are not laid in water.
They are laid in swamps--many nests are accessible only by getting one's
Not those I've seen on TV. Sure, these may be a small minority, but still
crocs do it and get away with it.
Predators are not required to have their own nests very close.
Yes...in fact, predators have to enter the crocs homefield...the one place
where they are the only game in town.
That would be the water.
predatory threat can only come
from 180 degrees not 360;
No, croc nests are not directly next to the water.
But a croc only has to scan 180 degrees--predators are not going to be
accessing the nest from the water.
Again: croc nests are not directly next to the water.
each of many hatchlings represent less reproductive effort than
dinosaur hatchlings (and are therefore more expendable).
You are making this up. I submit that each croc hatchling represents
_more_ of an effort than just about any sauropod hatchling.
Croc eggs are smaller relative to parent than dinosaurs of the same size,
That's probably the case for small theropods -- though even there, the eggs
are half the size of a bird egg. It's cringingly obviously not the case for
sauropods. Maybe that's because the maximum thickness of an eggshell is
limited by the requirements of diffusion; still, no known sauropod egg is as
big as an *Aepyornis* egg.
Yes, and this does not only apply to crocodiles. All known Mesozoic
dinosaur nests are very large.
Remembering that parental investment includes: yolk mass, incubation time,
quality of incubation--e.g., brooding, post-hatchling care, and not just
Sauropods: no incubation.
has fueled, I think, some interesting hypotheses: e.g.,
dinosaurs were big because they had to defend nests.
Except those that weren't big, and those that were already way bigger than
necessary to defend a nest...
Second, I think extinctions are always very complex events.
Sure, but very complex events can have very simple causes.
Third--the only thing that is _falsifiable_ about your explanation, is the
event itself. The event happened. But any specific cause of death for
clade, population, or individual is unfalsifiable.
That's not true.
Why did the ammonites die out but the nautiloids didn't? Because the
ammonites had planktonic larvae -- known in the fossil record -- while at
the very least the modern *Nautilus* broods its few large eggs hundreds of
meters below the surface. The only way I can imagine to make the ammonites
extinct is to sterilize the upper layer of the ocean; anything less than
that won't do (and indeed the ammonites rebounded very fast after losing
most of their diversity at the Devonian-Carboniferous, Permian-Triassic, and
Triassic-Jurassic boundary mass extinctions). This sort of thing (a
"Strangelove ocean") is exactly what we expect to happen after a big impact.
In other words, the impact hypothesis predicts that the ammonites died out,
and die out they did. In addition to never being part of the plankton,
*Nautilus* has a low metabolism and yolk-rich eggs. That's bad for taking
over the world, but great for surviving in a food-poor ocean. In other
words, the impact hypothesis predicts that the nautiloids survived, and
survive they did.
Now lather, rinse, and repeat this for planktonic vs benthic foraminifera,
and for the coccolithophores. And then up the food chain to plesio- and
mosasaurs, and the ammonite-eating protostegids -- but not the other sea
turtles, which eat jellyfish and other survivor types.
And then factor in that we have firsthand evidence of the Strangelove ocean,
e.g. in Denmark (the "fish clay") and New Jersey.
That's the marine side. On the continental side, the impact hypothesis
predicts the death of most green plant parts, in other words, widespread
extinction among animals other than insectivores, granivores, and freshwater
animals. What do we observe in the continental fossil record (which is
famously worse than the marine one)? More or less just that. In the
freshwater, what died out are *Brachychampsa* (a crocodile apparently
specialized on turtles) and specialist predators like the gars over most of
the world. Judging from their pitiful fossil record, most amphibians
survived, as did plenty of insectivorous eu- and metatherians and
Also, complex synergy remains equally parsimonious.
Equally parsimonious as the scenario outlined above, which explains so much
data from biology and geology _at once_? Please explain.