[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Vegavis gen. nov. - new anseriform in today's Nature



All very good points, Graydon.

I'd like to comment on the "dumb luck" matters idea. If nothing else (besides the absolute horror and terrible loss of humanity), the recent tsunami should show the presence of dumb luck in a disaster. You had people, side-by-side, similar ages and physical conditions - one dies and the other lives. Just dumb (bad!) luck. You had people swept out to sea who survived for days hanging onto uprooting, floating palm trees; and others who were killed when the room they were in was squashed by the mud and water, several miles inland.

IMHO, the variations in which terrestrial animals survived and which animals didn't - which correspond with the extinction of sea creatures - large and small (note that some obvious exceptions exist in this realm as well [sharks, etc.]) - point to some sort of global scale disaster. Dumb luck matters.

If we were discussing whether or not terrestrial (n-a) dinosaurs met with a mass extinction - AND NO OTHER GENERA WERE AFFECTED, then John Bois' arguments for the gradual elimination of dinosaurs by niche usurpation and competition/predation by birds - would hold a great deal of merit. As these events do NOT stand alone, the discussion is interesting, but lacking full conviction. (To an informed observer - or to me, at the least).

Please note that while I think that there was a global catastrophe - and believe that it was most likely triggered by a large bolide striking the earth, this does not mean that I think the the catastrophe was (or would need to be) totally, directly responsible for all the deaths. Although some of the effects created by the large bolide (or major, major volcanic eruptions) are quite alarming (!!!), they do not necessarily affect every organism, everywhere on earth, equally - or with total deadly force.

Primary causation is often difficult to ascribe to one thing or another - especially in regards to cause of death. (Or in this case, cause of extinction). A person could die in the hospital, and his cause of death might be listed as Heart Attack, with a secondary cause of Pneumonia, and a tertiary cause of Sepsis. However, the reason that patient was in the hospital was because he was shot, and developed the infections and died from the effects of those after his surgery. And the primary reason that he had any bullet wounds at all, was because he walked into the wrong 24-hour convenience store at the wrong time. What would you say his cause of death was? Heart attack, infections, gun shots, or just being in the wrong place at the wrong time? [Personally, I'd put it to the gun shots as the root cause].

For me, the root cause of the real, catastropic extinction of the dinosaurs was a large bolide. After the hellstorm that followed (various effects to various degrees), those n-a terrestrial dinosaurs that survived that WERE probably out-competed by their 'cousins' - the avian dinosaurs.

Allan Edels

From: Graydon Reply-To: oak@uniserve.com To: dinosaur@usc.edu Subject: Re: Vegavis gen. nov. - new anseriform in today's Nature Date: Fri, 21 Jan 2005 12:22:48 -0500

On Fri, Jan 21, 2005 at 11:34:25AM -0500, John Bois scripsit: > On Thu, 20 Jan 2005, Graydon wrote: > > > On Thu, Jan 20, 2005 at 02:13:07PM -0500, John Bois scripsit: [snip] > > > Birds should have been affected as badly as non-avian dinosaurs. > > > The more species we find that are ancestral to extant species, > > > > There's a slippery bit of logic in there -- recent findings are not > > of ancestry; they're of common clade membership. 'Something like > > this lived in enough numbers to continue to breed'. > > Right, but it does show that the ancestors of ducks were present, that > the genes in them survived into modern ducks.

Doesn't show that at all; it shows that the point of common ancestry between modern ducks and their next closest non-duck relative is back in the K somewhere.

It doesn't tell us what proportion of the descent of that ur-duck made it over the boundary, nor do we have any way to put the known fossils into the pathway between the hypothesized ur-duck and a modern duck.

> If substantiated, it also means that the chicken/duck split was > pre-K/T--mass survival.

Sure.

But you're looking at this as though there was no loss of diversity, and we can be sure there was a substantial one, both through finding Cretaceous birds that don't have post-K/T descendants, on the one hand, and through noting that the extant neornithine bird clades represent a small fraction -- and not the most populous fraction in the Cretaceous -- of the Cretaceous bird diversity.

Rather like the extant mammal clades represent a small fraction and not the most numerous fraction of the Cretaceous mammal clades. Placentals aren't what an alien observer at 70 MYbp would have expected to be the dominant form of large terrestrial life by the time of our present.

> > The evidence for the catastrophe is irrefutable -- dead ocean marine > > sediment layers, pan-planetary iridium layer at the K/T boundary, > > ash-and-fern layers at the boundary, and a mass extinction. > > And I'm not trying to refute it. But I remain skeptical of the power > attributed to it. More to the point, to the extent that it spared > birds, it probably spared some non-avian dinosaurs in some nooks and > crannies.

I think you've got 'spared birds' where you should have 'a few bird species survived'. There was a massive loss of bird diversity.

> Also, if a diverse fauna of neornithines is established before K/T, we > need a mechanism for killing off enantiornithines. A good contender > for their demise is compettion/predation with neornithines. A bad > contender is an all-encompassing instantaneous event--that is, unless > someone is proposing a differential selective mechanism.

People are generally proposing 'dumb luck'; a very few neornithine species made it over the boundary, along with maybe *one* Gondwanan ratite species. (Or maybe more, but not a dozen.)

Every available evidence from the Cretaceous indicates that neornithines were not ecologically dominant at that time. Maybe some small portion of the then-extant neornithine species were more suited to survive, or maybe they just got lucky. It's important to remember that everything to do with a mass extinction event does not have a neat casual reason; dumb luck *matters*.

> > Why you think some small, flying, opportunistic feeders -- do you have > > any idea what ducks will eat? -- surviving makes the mass extinction > > less encompassing I don't understand. Some things survived; they tended > > to be -- among automatic endotherms -- small, opportunistic feeders with > > some means of avoiding dire conditions. (Flight or (probable) > > hibernation plus burrowing.) > > Flying didn't help pterosaurs,

Motor-gliders, rather than continuous flappers, ill equipped to cope with a month of global storms.

> nor enantiornithines; nor would it protect any organism from the > proposed conditions e.g., heat radiation from re-entering ejecta.

Hence the 'dumb luck' part. Sometimes, something would be diving, or in a wet marsh, or behind a big tree and then escape the resulting fire.

It would then have to find food and a mate and food for offspring, and the dire conditions in which to do so would last for a long time; hundreds of generations.

> And why would one exempt na dinosaurs (especially juveniles) from > opportunistic feeding.

Because the dire ecological consequences of the event lasted for, at a minimum, a thousand years. Juvenile non-avian dinosaurs would have to reach sexual maturity in a landscape devoid of sufficient food to do so.

Note that *nothing* terrestrial with an adult body mass over 10 kg made it. That says a great deal about food availability.

> And it is not just ducks, but chickens now (whatever they were in the > Cretaceous).

More or less what they are now -- jungle fowl. And even modern domestic chickens will eat anything, up to and including attempts on the toes of anyone so incautious as to wear sandals near them.

Also note that it's plenty if *one* proto-chicken and *one* proto-goose species make it over the boundary, to explain the present observed diversity.