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Re: Armadillos at the K/T?




John,
Actually I would say that the emergence of xenarthrans probably occurred even earlier than 76 million years ago, but there is no evidence I know of which indicates they ever existed outside of the Americas and Antarctica. Perhaps they were barred from the Old World by competitive exclusion.
But armadillos are generalist feeders, not egg specialists, and there is no reason to assume Cretaceous armadillos (primitive xenarthrans) were not generalists as well. While I can perhaps envisage them driving one or two New World dinosaur species to extinction by egg predation, I still cannot see mammals driving whole families of dinosaurs to extinction by egg predation. Egg predation might be one of many different factors in contributing to normal background rates of extinction, but mass extinctions are a whole different matter. Cretaceous armadillos and other mammals may have been pests to some nesting dinosaurs, but I just don't think they were that much of a threat to dinosaurs in general (especially compared to massive impacts).
-------Ken Kinman
P.S. I have no doubt that the burrowing habits of armadillos is why some of them survived K-T. And being generalist feeders was another plus. On the other hand, their armour was probably of little use in the early Paleocene until other mammals evolved to fill the vacant predator niches.
*******************************************
From: John Bois <jbois@umd5.umd.edu>
Reply-To: jbois@umd5.umd.edu
To: dinosaur@usc.edu
CC: cfsjm@ux1.cts.edu
Subject: Armadillos at the K/T?
Date: Tue, 25 Sep 2001 14:54:55 -0400 (EDT)

"The xenarthran radiation, which corresponds to the emergence of
armadillos, is estimated here to have occurred close to the K/T boundary
(59-76 Myr) and the separation between anteaters and sloths during the
Palaeocene era (51-65 Myr)."  So says Delsuc et al. 2001. The evol. of
armadillos, anteaters and sloths depicted by nuclear and mitochondrial
phylogenies: implications for the status of the enigmatic fossil
_Eurtamandua_.  Proceedings: Biological Sciences (The Royal
Society) Vol. 1267.  Number 1476. Pp. 1605-1615.

Also notes that fossoriality and carapace is the primitive condition.

Sometime ago, I said that small hairy armadillos which take a penalty-free
heavy toll on rhea eggs, were a good model for potential predation on
dinosaur eggs at or around the K/T boundary. HP Kenneth Carpenter
responded that specific adaptations possessed by these creatures
(particularly digging muscles) ruled them out as models.  I argued that
the loose matrix of dinosaur nests made this adaptation unnecessary, that
the relevant point was the ability of small mammals to get into eggs
without crushing them with their jaws (e.g., by knocking them
together).  And that's where
it stopped.  I wonder 1) if this new finding, especially were it to have
fossil support (eventually), would strengthen the notion of large scale
depredations of non-concealed nests; 2) what are the biogeographical
possibilities of a K/T armadillo--wouldn't this animal have the potential
for a semi-global distribution--North and South America--Asia, at
least; and 3) if such depredations occurred, would one expect to find
evidence for it at affected nests?
Thanks.



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