> A friend of mine asked: "Do you believe that the mammals coexisted in
>time with the dinosaurs? And if so, why are they not found together in
>the fossil record?" Answer: Yes, and although mammals are rarely found
>in dinosaur strata, occasionally some of the small mammals are found in
>with the dinosaurs. He reiterated his hydrological model, claiming that
>this would be expected by the flood model.
Mammals and dinosaurs did indeed coexist, but not the current
suite of mammals we see today. By the middle Cretaceous, primitive
mammalian insectivores had evolved(*). By the late Cretaceous, the
Metatheria (marsupials) and Eutheria (placentals) had already
started to diverge. There are even some upper Cretaceous fossils
classified as Primates, although they were not very distinct from
the insectivore stock they evolved from.
[Although it's irrelevent, I'll add some more info]
At this same time, the angiosperms (flowering plants) are
evolving. Also, the insects that now co-exist with angiosperms
were radiating (esp. Lepidoptera (moths and butterflies), Diptera
(true flies) and Hymenoptera (wasps and bees).)
Of course, the K/T extinction followed (if you beleive
the "chicken little" hypothesis, this is due to a large extra-
terrestrial object impacting on earth. All animals over about 25 kg
bit the dust. All the dinosaurs (except birds) croaked -- although
I think a few hung on a while after the K/T, then went extinct.
The big mammalian radiation follows. There was, as a
recent poster pointed out, a review paper in Nature about
this recently. Basically all it said was that the explosion into
all the mammalian Orders happened so quickly that getting accurate
phylogenetic information (at the Order level) is proving difficult.
It also has a short section discussing possible diphyly in bats.
Biologists used to think both Micro- and Mega- Chiroptera were
monophyletic (shared a single common ancestor). Recently, it has
been argued that megabats may have evolved from primates. The
data so far is squishy. The molecular data superficially points
to monophyly; but, in the trees that support monophyly -- rats
get placed in the middle of the tree! Removing the rats is
statistically less favored that diphyly.
The morphological evidence
for diphyly is (to me) rather impressive. Megachiroptera and primates
share the same organization of the optic part of the brain. Also,
(although this is anecdotal at best) I saw (at a seminar) a diphyly
supporter show back to back pictures of a lemur (primate) and a
fruit bat (megachiroptera), their head morphology was astoundingly
similar. At the end of his seminar, he showed a picture of a lemur
leaping from tree to tree and said this lemur was busy evolving into
a bat 8-) One further piece of evidence supporting diphyly is that
microbats echolocate and megabats don't.
Well, that's all the time I have today. Join me soon for
another episode of "How far can Chris digress from the topic at