Gonna need some sources here. The great preservation we see throughout the Cambrian are just pockets. Due to thing like mudslides. Walk ten feet to the right and there is nothing. I want to know what work you are referring to
James W. Valentine, On the Origin of Phyla (University of Chicago Press, 2004) discusses the quality of the Cambrian record. I don’t have the book with me, but I can get you the references to the studies he mentions when I get home, if you’re interested.
Welcome to PS where we discuss the latest results of scientific inquiry. A book from 2004 would be considered out of date given the recent findings of 2019. Please stay on topic by discussing the implications of the latest findings and analysis.
Not so much as you might think. But Krauze may be misremembering what Valentine said. Perhaps he will clarify his statement or mention approximately where in the book Valentine says it. (I have a copy.)
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It depends on the subject. Sometimes old papers are still extremely relevant, particularly in palaeontology. Unless some later findings have superceded them, the best paper to cite in support of a particular fact could be decades old.
For example, the seminal paper on Zebrafish developmental stages was published in 1995, and is still commonly cited today.
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New Cambrian results from Chengjiang.
I’ll go visit the Chengjiang in a few months, not going near this new Lagerstätte though.
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If I understand cladistics correctly, all fossils are going to be stem groups. No fossil species is considered an ancestor.
As far as I am aware, Cambrian deposits have the same range of quality as all other time periods. There are coarse grained Cambrian deposits that would not have preserved small and fragile organisms. I am sure there are examples of fine grained marine deposits in most other geologic periods.
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I have it.
You apparently understand it incorrectly. A crown group includes the most recent common ancestor of all extant species in a group and all its descendants, extant or extinct. Anything outside the crown group is part of the (paraphyletic) stem group. Some fossils are crown group fossils, some stem group fossils.
Me too, except that preservation of the type found in the Burgess Shale and Chengjiang is quite rare and may be more common in the Cambrian than in many other periods. See for example Butterfield N.J. Secular distribution of Burgess-Shale-type preservation. Lethaia 1995; 28:1-13. It’s not the fineness of the grains, at least not alone, that is responsible for this exceptional preservation. However, there are many examples of Lagerstätten from other periods, such as the Mazon Creek, Solnhofen, Green River, etc.
Sure, but all fossils are still in stem groups of at least 1 crown group. It just depends how wide the crown is. Tiktaalik is in the stem group of tetrapods, but also member of crown-group bony fishes, for example.
Almost true if we extend the concept of “crown group” to species. And some fossils are presumably within crown species. But I get your point. Most fossils are in the stem group of some clade or other, even if that clade is only one species.
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I always welcome good criticism.
What I was ultimately getting at is no fossil species is assumed to be the direct descendant or direct ancestor of any other fossil or living species.
These kinds of discussions of terminology are extremely helpful for those of us who lack training in such topics. Very interesting and much appreciated.
Welcome, @Krauze. I hope we will learn more about you through an introduction thread (a bit of a tradition on Peaceful Science.)
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Valentine on the quality of the fossil record (p. 159):
“One might expect that both the stratigraphic and the fossil records would deteriorate monotonically with the increasing age of rocks, but this is not correct. For example, Sadler (1981) has shown that the completeness of stratigraphic sections is independent of their ages as such; some systems may be more complete than others, but that is not a matter of their ages as such; some systems may be more complete than others, but that is not a matter of their age but rather of their depositional and erosional histories during accumulation. Surviving sections from the Cambrian are not necessarily less complete than surviving sections from, say the Cretaceous, environment for environment. There tend to be fewer Cambrian sections available for study than those of some later systems, because older rocks tend to be covered by younger rocks, and to be sure many Cambrian sections may have been destroyed by erosion. But the sections that we have should not be of less than average completeness, and we have enough of them that we should have a good record preserved at least between the more pervasive gaps. Furthermore, it happens that the Cambrian was a time of generally rising sea levels (fig. 5.2), so the sections that have should be more complete than average. Also, the geography of deposition and the tectonic settings of Cambrian deposits, coupled with the subsequent geometry of their uplift and exposure via erosion, imply that we have a better record of the Cambrian than of some much later systems.”
If I am reading this correctly, Krauze is saying that the Cambrian deposits could have more surviving sections than other time periods because they were buried by later deposits and protected from erosion. Preservation of fossils doesn’t seem to a problem as long as the deposits are protected from geologic processes that would destroy them. The problem with Cambrian deposits is gaining access to them since they are buried under more rock.
I read it as meaning Cambrian deposits are rare because they are covered by so much younger rock so they are hard to locate. But I’m also confused by some of it because the older the rock, if exposed, the longer the erosion history. Which means the older the rocks the less complete they will be due to erosions forces.
I’m not sure who has proposed their age alone makes them less complete. It’s their depositional/erosion histories