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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 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

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?

They (crocs) are the exception...because they are exceptional: semi-aquatic niche
gives home-field advantage; they see at night (are practically nocturnal!!);

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 self wet.

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, right?

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 clutch-size.

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 any
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 granivorous multituberculates.

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.