How are transitional fossils placed into a certain time period? Is it by looking at the body structures of other animals from different time periods? Carbon dating? using the Geologic column?
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About fossils
- Thread starter Truth in Faith
- Start date
If humans are supposed to be a spin off from apes, and both human and apes exist still.
Is there an ancient species and it's spin off both existing today?
Is there an ancient species and it's spin off both existing today?
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Well, humans Arent a dirrect spin off any any ape alive today. They both come from the same basic branch in the evo tree.
Besides, there are quite a few people here that are spin offs of their parents. Why arent their parents dead?
Besides, there are quite a few people here that are spin offs of their parents. Why arent their parents dead?
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lucaspa
Legend
Each species has characteristics that are unique to it. For instance, H. erectus has prominent brow ridges (and "prominent" can be quantified by measuring height and width) and a backward sweeping forhead. Again quantified by meauring the angle from a vertical line running just in front of the brow ridge and meauring the angle of the top of the cranium with that line.
Humans have much smaller brow ridges and a forehead that is much closer to vertical. Now, if you take all human skulls and measure these you will get a bell-shaped curve for the values of both, centered around the mean. You also get a bell-shaped curve for all H. erectus for these, with a different mean. It turns out the the bell shaped curves really don't overlap.
Now, you find, say, the Broken Hill fossil and you measure the size of the brow ridge and the placement of the forehead. It turns out that these numbers fall between the means obtained for sapiens and erectus. Right between the curves.
Now you have a link. Clear enough or do you have more questions?
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lucaspa
Legend
First, many transistional series come from the same sediments and, as you go up the sediment from bottom to top, you can see the divergence through the fossils of the individuals. This is especially true for invertebrates. The following series are continuous within undisturbed strata at the same place:
1. McNamara KJ, Heterochrony and the evolution of echinoids. In CRC Paul and AB Smith (eds) Echinoderm Phylogeny and Evolutionary Biology, pp149-163, Clarendon Press, Oxford, 1988 pg 140 of Futuyma.
2. Kellogg DE and Hays JD Microevolutionary patterns in Late Cenozoic Radiolara. Paleobiology 1: 150-160, 1975.
2. PR Sheldon, Parallel gradualistic evolution of Ordovician trilobites. Nature 330: 561-563, 1987. Rigourous biometric study of the pygidial ribs of 3458 specimens of 8 generic lineages in 7 stratgraphic layers covering about 3 million years. Gradual evolution where at any given time the population was intermediate between the samples before it and after it.
There is one example of this in the hominid lineage, and that is the Omo I and II beds. A. afrarensis at the botttom, in between afarensis and H. habilis in the middle, then H. hablis, then in-between H. habilis and erectus, and then erectus at the top.
For other transitions, especially for larger animals, often the transitionals are found in several sites. Unless all this happened less than 50,000 years ago, carbon dating is not done.
Instead, what is looked at first are the other fossils in the area to get a rough idea of the dating, since species aren't found all through all sediments. That gives a rough idea of the time. That is then refined by looking for volcanic tufts above and below the sedimentary layer and then dating them by several radiometric dating methods -- K/Ar, Sr/Rb, U/Pb, etc. -- to get dates that bracket the sedimentary rock. Then the layer you are interested in lies between those dates.
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lucaspa
Legend
Web, you answered this in post #13 and I answered in post #19. Why are you asking the exact same question again?
Here is the answer:
In the hominid lineage? No. That species was driven to extinction by its descendents or went extinct due to change in the environment. (well, the daughter species are a change in the environment, aren't they?)
In <B>any</B> lineage? Yes. Absolutely. In fact, hundreds or thousands. I know of only a few.
7. MLJ Stiassny and A Meyer, Cichlids of the rift lakes. Scientific American 280: 64-69, Feb. 1999. These fish have all evolved from a common ancestor in the last 12,000 years. Hundreds of species. The original fish species is still in the lakes.
9. Double dose of DNA. Science 285: 195, 2 July 1999. A rat species, visach rat, has 51 chromosomes instead of the 26 of other rat species. All chromosomes are doubled except the sex chromosome. The original rat species rattus rattus, is still around.
6. B Wuethrich, Speciation: Mexican pairs show geography's role. Science 285: 1190, Aug. 20, 1999. Discusses allopatric speciation. Debate with ecological speciation on which is most prevalent.
11. P. S. Soltis, G. M. Plunkett, S. J. Novak, D. E. Soltis, Am. J. Bot. 82,1329 (1995).
12. N Barton Ecology: the rapid origin of reproductive isolation Science 290:462-463, Oct. 20, 2000. target=_blank>www.sciencemag.org/cgi/content/full/290/5491/462 Natural selection of reproductive isolation observed in two cases. Full papers are: AP Hendry, JK Wenburg, P Bentzen, EC Volk, TP Quinn, Rapid evolution of reproductive isolation in the wild: evidence from introduced salmon. Science 290: 516-519, Oct. 20, 2000. and M Higgie, S Chenoweth, MWBlows, Natural selection and the reinforcement of mate recognition. Science290: 519-521, Oct. 20, 2000
1. ME Heliberg, DP Balch, K Roy, Climate-driven range expansion and morphological evolution in a marine gastropod. Science 292: 1707-1710, June1, 2001. Documents mrorphological change due to disruptive selection over time. Northerna and southern populations of A spirata off California from Pleistocene to present.
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lucaspa
Legend
Darwinism always proposed that apes and humans had a common ancestor. And that has always been mangled by creationists that humans descended from modern apes.
Since man is an ape -- ape being the name of a family in the taxonomic scheme -- it has always been presumed that the common ancestor also belonged to that family. And was thus an ape.
John, I've posted several times the minute fossil evidence linking humans back through other species.
The latest fossils -- Toumai and others -- are so close to the common ancestor point that there is considerable argument as to which side of the pathway they are on. All the discoverers, of course, want them to be on the hominin side, but the mere fact of the argument shows how close to the common ancestor they are.
Take your head out of the sand, John. The fossils do exist.
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It's generally by a combination of as many different independent forms of dating as they can use. The more methods you use, the more accurate your result is likely to be because a single result could be anomalous and without the results from other methods, you'd be less likely to notice. When five methods give the same basic result, you're more likely to find it reliable.
Radiometric dating of nearby rocks is one good way of getting an absolute (rather than comparative) date, but sometimes there aren't any nearby rocks that can be dated that way because radiometric dating almost never works on sedimentary rock so you have to rely on some nearby layer of volcanic rock, and there isn't always one available. That's when you have to start using comparative methods and try to match layers of sediment and fossil with equivalent layers at some distance away where there's also a volcanic layer. Another comparative method is to look for common fossils whose date is known and compare their position in the rock with the position of your fossils.
One method that relies on radioactive decay but isn't the same as radiometric dating is fission track dating, where tracks caused by uranium isotope decay are counted
http://emuseum.mnsu.edu/archaeology/dating/dat_fission.html
Another method used involves determining the magnetism of iron-bearing rocks, since the alignment of the magnetism is affected by the direction of the magnetic field at the time the rock was formed.
If you read Don Johandon's book about Lucy, you'll see that they used several of these methods to get a handle on the date. He must really love seeing all that hard work blown off by creationists in their attempts to discredit dating techniques.
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