Tree Of Life Ebooks Catalog
We've all seen trees of life they begin with an original, pulsating, primordial slime-blob that eventually evolves into everything else as you trace the branches outward (Figure 3.3 is an example). Such trees show who came from whom, and when that occurred. They are common in textbooks and museum displays, and deeply influence our ideas about evolution. But how do we know who gave rise to whom After all, no human witnessed the zillions of speciation events that constitute the tree of life.
Here is a fundamental difference between a cladogram and the more familiar tree of life that we discussed above. The cladogram does not incorporate time, nor does it tell you who the ancestors were. Instead, it can indicate the sequence of the evolutionary events and, more importantly, specify the characteristics that the ancestor possessed. So, in the case of the cladogram in Figure 3.9, we aren't told who was the ancestor of bears, gorillas, and humans, but we infer that the earliest mammal was fur-bearing (among the other characters that diagnose Mammalia). In Box 3.1 cladograms are used to reconstruct the evolution of wristwatches,
One may naturally ask, how does this hole in the hip socket help us identify a dinosaur when out in the field, say on a Gobi expedition The answer is not very often. We can identify certain bones as dinosaurs by default. We might not have the diagnostic hipbones of a fossil but we can still recognize a frill as belonging to Protoceratops, and we know that Protocer-atops is a dinosaur. If we found a more complete skeleton, we might note the ornithischian design of the hip, and ultimately note the giveaway hole in the hip socket. More often, we don't have all the relevant parts of the skeleton. But the fact that an anatomical feature may not always be identified at the outcrop does not make it any less important. These characters, sometimes subtle and difficult to find, are the beacons for the pattern of evolution. They allow us to say a diverse assemblage of creatures arose from a common ancestor in the past, and that this event in the history of life was unique. They also allow us to...
This particular one is a satire by Matt Groening. The image of evolution as a tree, however, is completely familiar. From the Big Book of Hell Matt Groening. All Rights Reserved. Reprinted by permission of Pantheon Books, a division of Random House, Inc., NY. Figure 3.3. A tree of life. This particular one is a satire by Matt Groening. The image of evolution as a tree, however, is completely familiar. From the Big Book of Hell Matt Groening. All Rights Reserved. Reprinted by permission of Pantheon Books, a division of Random House, Inc., NY.
The Tree of Life Web Project The Tree of Life Web Project is a meticulously designed view of life-forms based on their phylogenetic (evolutionary) connections. It is hosted by the University of Arizona College of Agriculture and Life Sciences and the University of Arizona Library. http tolweb.org tree phylogeny.html
It is now clear how a cladogram is tested. The addition of characters can cause the rejection of a cladogram by demonstrating that it is not the most parsimonious character distribution. In contrast, a tree of life presents more difficulties. Aside from requiring the miniscule probability that ancestors and their direct descendants will be preserved, a tree of life is untestable. How does one identify the actual ancestor and its direct descendant Given the absurdity of a claim that these have been found, a tree of life is really more of a story or scenario, than a testable scientific hypothesis. For this reason, here we content ourselves with ciadograms, and do not confuse them with trees of life. As will become evident, much can be learned from ciadograms that will contribute to our desire to know what occurred in ages long past.
Whatever its specific causes, the mass extinction event at the end of the Cretaceous made a gaping craterlike wound in the earth's biota. As I've noted, however, there were survivors. Birds may be the only dinosaurs to last out the Mesozoic but they indeed had company. As our stupendous samples of skulls at Ukhaa Tolgod showed, the Mesozoic world was writhing with lizards and mammals and other vermin that made it through the Cretaceous extinction event. The forests, fields, and deserts of the Mesozoic were teeming with these less conspicuous creatures. Yet the Mesozoic is famous as the age of the dinosaurs. How odd this seems from a purely egocentric perspective. The Mesozoic was also the age of origin of our own branch of the tree of life, the mammals. One wonders whether, if dinosaurs were not so big and so grotesque, what we call the age of mammals currently equated with the Cenozoic beginning only 65 million years ago would be extended back to the early Mesozoic, when the first...
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