If it occurred in reasonable abundance it should be noteworthy. There is no reason why a species should spring up and spread in one time period only to disappear or gt sharply reduced in the next. What we should see in the next time period is many varieties of the species rather than fewer to none.
There is no reason any arbitrarily chosen group of organisms should remain at the same level of diversity. We know there are lots of organisms around today that were very diverse in the past, but only have a few survivors today. Rhynchocephalians, a type of reptile similar to lizards, were spread all over the world and very diverse in the Jurassic but, like the dinosaurs, they were mostly wiped out in the K-T extinction event, and now there are only a couple of relict species surviving in New Zealand.
Why would this be a problem? We know that extinction happens, otherwise there would still be dinosaurs everywhere (well, there are of course, but you know what I mean).
But your argument here is particularly odd, since you're complaining about organisms that are abundant, and then vanish, and then reappear as abundant again. There may be cases of that happening, but it's not true of the ones you're talking about. Conifers and ferns never vanished - they've been abundant since their first appearance in the fossil record. It seems odd that you're arguing this is not the case based solely on the fact that RAZD's brief overview of land plant evolution doesn't list every species of plant known from every fossil locality in exacting detail.
quote:Conifers of the Cheirolepidiaceae, on the basis of palynological evidence, extended from the Triassic to the Late Cretaceous or perhaps to the Early Tertiary. They were geographically widespread and especially important in the Jurassic and Early Cretaceous at low palaeolatitudes.
You don't need to go digging in academic journals for this info. You say that, if conifers and ferns appeared in any abundance they would be noteworthy, and indeed if you look at any introductory 'what was life like in the Cretaceous?' article you will indeed find them noted. This is from UCMP Berkeley:
quote:No great extinction or burst of diversity separated the Cretaceous from the Jurassic Period that had preceded it. In some ways, things went on as they had. Dinosaurs both great and small moved through forests of ferns, cycads, and conifers. Ammonites, belemnites, other molluscs, and fish were hunted by great "marine reptiles," and pterosaurs and birds flapped and soared in the air above. Yet the Cretaceous saw the first appearance of many lifeforms that would go on to play key roles in the coming Cenozoic world.
Perhaps the most important of these events, at least for terrestrial life, was the first appearance of the flowering plants, also called the angiosperms or Anthophyta. First appearing in the Lower Cretaceous around 125 million years ago, the flowering plants first radiated in the middle Cretaceous, about 100 million years ago. Early angiosperms did not develop shrub- or tree-like morphologies, but by the close of the Cretaceous, a number of forms had evolved that any modern botanist would recognize. The angiosperms thrived in a variety of environments such as areas with damper climates, habitats favored by cycads and cycadeoids, and riparian zones. High southern latitudes were not invaded by angiosperms until the end of the Cretaceous. Ferns dominated open, dry and/or low-nutrient lands. Typical Jurassic vegetation, including conifers, cycads, and other gymnosperms, continued on into the Lower Cretaceous without significant changes. At the beginning of this period, conifer diversity was fairly low in the higher latitudes of the Northern Hemisphere, but by the middle of the period, species diversification was increasing exponentially. Swamps were dominated by conifers and angiosperm dicots.
See? The spread of angiosperms was the big, important change, and that's why it was the event RAZD's brief summary; which crams hundreds of million of years into a few paragraphs; chose to focus on. But ferns and conifers are happily doing their thing throughout.
Have DNA studies been done to test the subjective assertion that one type of plant evolved from another? How about grasses from angiosperms? Any DNA tests on that supposed relationship?
Of course they have. And they've demonstrated that the closest relatives of grasses are all plants restricted to the southern hemisphere; which makes sense, as the oldest grass fossils are also known from southern continents (though grasses, of course, unlike their relatives, have colonised the whole planet).