RE: Armadillos at the K/T?

["Jaime A. Headden" <qilongia@yahoo.com>]

John Bois (jbois@umd5.umd.edu) wrote:

<Allow me to suggest that "egg eating" is a poor description of what I'm 
proposing.  "Predation on
offspring" is better.  This may sound like spin control.  It's not!  Predation 
on offspring as a
persistent selective force is a well accepted fact; "egg eating" (for some 
reason, perhaps because
we placentals are somewhat blind to its omnipresence as a selective force in 
extant species) is
perceived as a somewhat exotic practice, and, therefore, unlikely to pose 
threats to any species,
let alone many species.>

  The problem with this is that in all natural ecologies, the prescence of an 
egg-eater or
predator upon eggs or newly hatched young, or what have you, are part of an 
equilibrium,
fluctuating between the extremes of too many prey, to many predators. There is 
no upset in this
equilibrium without the introduction of an alien prescence. We have used the 
bolide hypothesis to
suggest that catalyst to many disrupted ecologies from the Devonian on. There 
is evidence for
this. Humans are another alien introduction (as it were) since we have actively 
sought to inflict
ourselves upon insular ecologies. Note that in savanah Africa and the outback 
of Australia, in
regards to "primitive" or tribal societies of man, there is more or less a 
natural ecology
present. Native Americans (including South Americans) were, in the abscence of 
a "civilization"
rather well-intertwined with the ecology.

  Egg-eating species are naturally in balance with their prey, such as coatis 
(there are animals
like jagarundis and cougars, even peccaries, that will, can, and have [killed] 
coatis for their
predatory ravaging of the young. Never in a natural ecoogy to egg- or 
young-feeders decimate a
population of prey.

<So, I'm not proposing that a single predator evolved and suddenly wiped out 
dinosaurs. I am
saying that there was an increase in potential predators on their offspring.  I 
would include
birds and other mammals.>

  This is not tenable. Whereas the end-Cretacous fauna of North America is 
relatively sparse, the
majority of the forms are either omnivores or herbivores: there are relatively 
few predators. The
mammals present which may have predated upon eggs or young are not of a size, 
sans *Mesodma* and
one or two other forms (as big as a badger, still smaller than most effective 
extant nest-robbers)
or value in an ecology to have mattered --- this may change, but present 
numbers and data do not
suggest that the equilibrium was any less stable then as it was the day the 
dinosaurs died. This
is the best case scenario. Deccan-age India (mid-Maastrichtian to 
pre-end-Cretaceous) have large
scores of large herbivores to the exclusion of predatory animals, including 
mammals or birds.
There is probably a large collection bias based on preservation, so onyl time 
will tell.

<The finding of K/T armadillos--if true--adds value to the hypothesis.>

  On a side note, it is probable that armadillos do not extend to the K/T 
boundary, but the
prescence of basal xenarthrans like the palaeoanodonts make is likely that the 
present and fossil
diversity of edentates (crown group xenarthrans) may have diversified from an 
essentially
palaeanodont stock. There is a rather armadillo-like appearance to these 
critters, so it is likely
that as by the Paleocene and Eocene, which is the present age for the diversity 
of Vermiligua and
Palaeoanodontidae, the diversity does stretch back into the Cretaceous, the 
forms were
palaeoanodont to isectivore-like, and in the latest Cretaceous was the original 
diversity and
acquisition of xenarthran features such as the ankle "twist", hooves, elongate 
tongue-attachment
apparatus (hyoid), tube-like snout and requisite loss of incisors, and the 
novel vertebral
articulations (xenarthroses).

> 


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

__________________________________________________
Do You Yahoo!?
Listen to your Yahoo! Mail messages from any phone.
http://phone.yahoo.com