Re: Selective Extinction

[Pieter.Depuydt@rug.ac.be]

>From what I understand of considering survivors and casualties of 
mass extinctions, there is a pattern distinguishable (at least with 
terrestrial vertebrates); the best chances to survive are with 
generalists of small size (herbivores, carnivores,  preferably 
omnivores); they have large offspring, need relatively little food 
and a small territory, are not tied to a particularly vegetation or 
element of a food chain; consider the PermoTriassic extinction; what 
survived were small carnivores/insectivores/omnivores as 
procolophonians,  the early cynodonts and baurioid therocephalians, 
together with a rather small herbivore (Lystrosaurus) which was more 
adapted to tough vegetation and not as linked to soft waterside 
vegetation as his Permian antecessors. Then the Triassic-Jurassic 
boundary (if this is a mass extinction, which is discussed), 
survivors again were small, rather unspecialized herbivores as basal 
ornithischians and  small prosauropods; small omnivores/herbivores as 
sphenodontids, turtles and tritylodonts; small carnivores as 
sphenosuchians and ceratosaurs. KT event: mammals, lizards and 
snakes, turtles again (allright: why  birds did make it and not their 
small non avian dinosaur cousins is not clear in this scenario).
Plus there seems to be a special category or niche which is quite 
'resistant to extinction': fresh water predators (carnivore, 
piscivore, or carrion feeder) are quite tough: crocodiles and 
their choristodere lookalikes (champsosaurs) went through 
the KT; turtles (most of which are fresh water predators) thrive 
since their origin in Late Triassic times; proterosuchians survived 
the PermoTriassic (if the record of Archosaurus is reliable) and 
temnospondyls got somehow from the Permian through the Triassic and 
Jurassic, with a lone survivor even into the Early Cretaceous. One 
exception: phytosaurs, which were the terror of the Late Triassic 
waterside, and had radiated in several forms of gavial-like 
piscivores and alligator-like carnivorous lurkers, completely went 
extinct at the Triassic Jurassic boundary...

Pieter Depuydt

> Yes, pterosaurs perished (somewhere along the way anyhow).  Maybe they
> weren't as adept at flying as birds.  And as somebody said, "what about the
> mosasaurs and sharks?"  (as in how did my question explain their
> extinctions) I must confess that I thought sharks survived!  You learn
> something new all the time. I suppose a big impact (with intense heat)
> would have  tremendous effects on the oceans- especially if it hit in the
> water.  Maybe the surface water got super hot, devastating air breathing
> aquatics, maybe gigundous waves caused havoc-  yet as I thought I said, my
> question did not pretend to answer the global extinction question.  I know
> dinosaurs were on the wane- I am aware of gradualist ideas on the subject. 
> And it seems there may have been many impacts, perhaps over a long time.  I
> merely wondered if certain sized and heighted creatures were more
> vulnerable to a shock wave than creatures who could lie low, or soar above.
>  In certain isolated scenarios, at least,  it seems they may have been.
> ----------
> > From: Bettyc <Bettyc@flyinggoat.com>
> > To: dinosaur@usc.edu
> > Subject: Re: Selective Extinction
> > Date: Monday, October 27, 1997 10:56 AM
> > 
> > 
> > birds, of course, survived, whereas pterasauroids did not so if you can
> > perhaps explain why?
> > Wehn Mt. St. Helens went off, birds that flew away survived, but still
> > had to deal with the ash that covered everything afterwards to search
> > for food and water.
> > -- 
> >            Betty Cunningham  
> >
> 
>