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Ref: Mammal/small dino competition
In Bromham, L., Phillips, and Penny 1999 Growing up with dinosaurs:
molecular dates and the mammalian radiation. _Trends in Evolutionary
Ecology_ 14:113-118, there is a nice overview of the molecules vs.fossils
issue. As noted earlier, the debate is shifting from whether or not
divergence of modern orders was pre-K/T, to whether or not splitting was
accompanied by significant pre-K/T morphological change (see John Alroy's
article in March Systematic Biology). Bromham et al. offer the hypothesis
that many lineages could have evolved in places that don't have a Late
Cretaceous fossil record, eg., Africa. In this view, the diversity seen
in the Paleocene may be the result of the Late Cretaceous drop in sea
level and subsequent immigration into strata which does survive today.
>From my own biased perspective, the molecular evidence is becoming more
compelling as the techniques become more sophisticated. I realize we are
not at the "fact" stage. And yet perhaps we may be more friendly to
tentative hypotheses. One of these is in Bromham et al.: "A Cretaceous
divergence of mammalian orders also implies that many of the
characteristics considered "key innovations" of the mammalian radiation,
such as aspects of brain function, reproduction or metabolism, evolved
long before the extinction of the dinosaurs...If C. mammals, as a whole,
were ecologically diverse as well as phylogenetically diverse (evidenve
from fossil dentition suggests possible mammalian insectivores,
herbivores, granivores, carnivores and scavengers), then it seems
possible that the spectrum of resource requirements could have overlapped
that of the dinosaurs. It is intriguing to note that the projected rise
of the modern mammals coincides with the disappearance of the smaller
dinosaurs, those most likely to have been direct competition with the new
mammals (M.J. Phillips, unpublished)."
How do we get this data?
How can mammals affect dinosaur populations if they are not there, i.e.,
if they were evolving in Africa they could not have affected NA small
Still, we _do_ need an hypothesis for the disappearance of small
dinosaurs. If mammals were indeed diversifying pre-K/T, this hypothesis
would have to be the front runner.
I haven't been able to get Nessov's paper from Bulletin of the Carnegie
Nat. Hist. Mus. which mentions a K/T carnassial. Has anyone seen this?
Do I have Signor/Lipps right in arguing that if a single carnassial exists
at the K/T--i.e., they are extremely rare--this means that animals bearing
them must have existed quite a bit earlier, back into the Cretaceous?