A friend of mine asked: +quot;Do you believe that the mammals coexisted in time with the d

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> 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. (*) Therians [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 hand?".


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