Starkov's theory and extinction

[KELL00BELL@aol.com]

     Last fall Dr. Starkov proposed that T-rex arose in response to the 
appearance of Alamosaurus in western North America.  This seems probable.  
T-rex evolved great size, super-powerful jaws and robust teeth capable of 
penetrating armor.  These aspects suggest the archpredator coped with large, 
armored prey such as Alamosaurus; otherwise they seem superfluous.  Bladelike 
teeth probably would have always sufficed against unarmored hadrosaurs and 
even ceratopsids.  Ankylosaurs alone were unlikely to have spurred the advent 
of T-rex, or such theropods would have appeared much earlier.  In contrast, 
titanosaurs predated T-rex by only a stage or so, in Cordillera.
     True, Alamosaurus was absent in the better-known T-rex habitats.  It 
did, however, live in inland areas at least as far north as Wyoming, and 
therefore may never have been very far from the Hell Creek, etc. 
environments.  Species are said to evolve in isolation and spread.  
Originally, T-rex could have filled the titanosaur hunter niche, then spread 
to the coastal floodplains, displacing the albertosaurs (which could not 
stand up to the archpredator in battles over territory or in competition for 
food.)  Ornithiscians, of course, also felt the effect.  As Starkov noted, 
ceratopsids had to become larger to survive T-rex.  The replacement of 
Euoplocephalus with Ankylosaurus, which he neglected to mention, is another 
example of T-rex-driven size increase.
     What makes Starkov's theory especially interesting is its potential 
relevance to dinosaur extinction.  If T-rex was well-adapted to hunt 
titanosaurs, the results could have been devastating if or when it gained 
access to the titanosaur-dominated faunas of Gondwana.  The sauropods and 
small ankylosaurs, etc. of southern regions had long confronted only the 
relatively small and weak abelisaurs.  Lacking co-evolutionary preparation to 
withstand T-rex, Gondawana prey could have succumbed very quickly, just as 
avian quarry did when the efficient brown tree snake entered Guam.  This 
theory resembles Bakker's notion of biogeographic chaos, except that the 
principal proposed agency of extinction is predation, not disease.
     A devastating, global radiation of T-rex is not a very far-fetched 
scenario.  The ability of ungulates to enter southern South America by the 
Paleocene, and the migration of marsupials even farther, to Antarctica and 
Australia, attests to a high degree of "interconnectedness" of landmasses 
around K-T time.  T-rex could also have spread far, and fast, with 
devastating results.
     Of course, this scenario cannot fully explain the K-T event.  Soon I'll 
show that a common physical agency of extinction is not necessarily implied 
by the lack of a common biological agency on land and at sea.
     --Tim Donovan