Paleoecological studies requiring taxonomic information beyond presence/absence data (i.e. relative abundance) must demonstrate that the sampling regime employed to collect such data adequately fits the faunas under investigation. A study of dense shell beds of the Middle Eocene Gosport Sand of Alabama indicates that, for localities with high abundance and diversity and little internal structure, diversity‐abundance data derived from standard‐sized samples vary significantly and cannot be used to develop consistent species‐level distributional patterns. Based on this result and the additional observation that different species show different patterns of occurrence, we propose an operational approach for determining what sample size will yield reliable distributional data for different proportions of the fauna. In the Gospon, samples of 3–5***1 yield reliable data on the approximately 25% of the species that are most common and abundant; samples of 35–40 I would be necessary to yield similarly reliable data on the next 15‐10% the remainder of species are too rare ever to be realistically examined quantitatively in bulk samples. □Sampling, paleoecology, taphonomy, Mollusks, Gosport Sand, Eocene.
A transect of three holes drilled across the Blake Nose, western North Atlantic Ocean, retrieved cores of black shale facies related to the Albian Oceanic Anoxic Events (OAE) lb and ld. Sedimentary organic matter (SOM) recovered from Ocean Drilling Program Hole 1049A from the eastern end of the transect showed that before black shale facies deposition organic matter preservation was a Type III-IV SOM. Petrography reveals that this SOM is composed mostly of degraded algal debris, amorphous SOM and a minor component of Type III-IV terrestrial SOM, mostly detroinertinite. When black shale facies deposition commenced, the geochemical character of the SOM changed from a relatively oxygen-rich Type III-IV to relatively hydrogen-rich Type II. Petrography, biomarker and organic carbon isotopic data indicate marine and terrestrial SOM sources that do not appear to change during the transition from light-grey calcareous ooze to the black shale facies. Black shale subfacies layers alternate from laminated to homogeneous. Some of the laminated and the poorly laminated to homogeneous layers are organic carbon and hydrogen rich as well, suggesting that at least two SOM depositional processes are influencing the black shale facies. The laminated beds reflect deposition in a low sedimentation rate (6m Ma -l) environment with SOM derived mostly from gravity settling from the overlying water into sometimes dysoxic bottom water. The source of this high hydrogen content SOM is problematic because before black shale deposition, the marine SOM supplied to the site is geochemically a Type III-IV. A clue to the source of the H-rich SOM may be the interlayering of relatively homogeneous ooze layers that have a widely variable SOM content and quality. These relatively thick, sometimes subtly graded, sediment layers are thought to be deposited from a Type II SOM-enriched sediment suspension generated by turbidites or direct turbidite deposition.
Much phylogenetic information has been derived from the analysis of sequence similarity in genes and proteins. These data are generally considered to be more reliable than an examination of the phylogenetic distribution of similar biologically active molecules. However, molecules can provide significant phylogenetic information when accompanied by a careful analysis of their structure, synthesis, genetics and function. Molecules may be highly structurally and functionally constrained. Thus, similar or even chemically identical molecules may be unrelated, and this may be discernible only by examination of information beyond the simple structure of the molecule. Phylogenetic variation in the synthesis of tyrosine and lysine demonstrates that chemical identity of molecules may be brought about by unrelated synthetic pathways. The widespread distribution of collagen triple helices is shown to result from convergence under structural and functional constraints. This is demonstrated by an examination of the steric constraints upon collagens and the presence of several independent families of collagen genes. Lysyl oxidase crosslinking occurs in several unrelated proteins, indicating that similarity in the post-translational modification of proteins is not evidence of homology.
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