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**Andrew1978** · 01-06-2010, 02:53 AM

I've been reading James W. Valentine's On the Origin of Phyla (Chicago, 2004). Valentine looks at how and when the various phyla of the animal world evolved. The book is very technical and sometimes makes for slow reading, but in incorporates material from molecular genetics, EvoDevo, embryology, comparative morphology (the study of form), and paleontology.

Valentine spends about 50 pages on the nature of the fossil record. I thought that I would share the section headings from that chapter. It appears that he wrote the headings as an outline and then filled in the rest of the text. The headings give a good reasonably current perspective on the state of knowledge of the fossil record as it relates to early life on Earth.

The Fossil Record

The Stratigraphic Record is Incomplete in a Spotty Way
Sedimentary Rocks Are Accumulated and Preserved Episodically
Sedimentary “Completeness” Varies with the Resolution that is Desired
The Completeness of Sedimentary Sections is Independent of Their Ages

The Marine Fossil Record, while Incomplete, Yields Useful Samples pf a Rather Consistent Fraction of the Fauna
Local Fossils are Largely Durably Skeletonized and Time-Averaged
Many Local Faunas Are Required in order to Estimate Global Diversity at Times of High Environmental Heterogeneity
Jumping Preservational Gaps is Possible by Extrapolation between Rich Fossil Horizons
The known Geologic Ranges of Taxa are Sensitive to Their Fossil Abundances

There Are Ways of Coping With Incomplete Records
Taxonomic Completeness Increases at Higher Levels of the Taxonomic Hierarchy
Taxonomic Completeness Rises as Larger Bins Are Used to Increase Time-Averaging
Paleoecological and Biogeographic Completeness Increase at Higher Levels of the Ecological Hierarchy
Data from Coarser Units may be Tested by Local Fine-Scale Studies

The Neoproterozoic-Cambrian Fossil Record Provides the Only Direct Evidence of Early Metazoan Bodyplans
Satisfactory Definition and Dating of Late Neoproterozoic and Cambrian Rocks Have Been Accomplished only Recently
Criteria for Defining the Neoproterozoic-Cambrian Boundary Have Varied over the Years
The Age of the Late Neoproterozoic-Early Cambrian Sequence Has Been Established Chiefly by Precision Dating of Zircon Crystals
Late Neoproterozoic and Early Cambrian Geographies Were Very Different from Today’s
Knowledge of Late Neoproterozoic and Cambrian Faunas has Greatly Increased in Recent Decades
Late Neoproterozoic Fossils Include Enigmatic Soft-Bodied Forms and Traces
Earliest Cambrian Faunal Traces Indicate Increases in Body Size and in Biological Activities
Numbers of Crown Phyla Appear During the Cambrian Explosion
The Middle Cambrian Contains Spectacular Faunas, but No Crown Phyla Appear for the First Time
Fauna that Appear After the Explosion Are Soft-Bodied with One Exception (Bryozoa)
If All Phyla Were Present by the Close of the Explosion, Their Records Agree Well with Expectations Based on Their Preservabilites
The Lack of Neoproterozoic Fossil Ancestors of Living Phyla is Not Inconsistent with the Quality of the Fossil record

There is a Vast range of Hypotheses That Attempt to Explain the Cambrian Explosion
Perhaps there Was No Cambrian Explosion
The Explosion Was Due to Physical Changes in the Environment
The Explosion Was Due to Biological Changes in the Environment

In Sum, the Cambrian Fossils Imply an Explosion of Bodyplans, but the Underlying Causes Remain Uncertain The "Neoproterozoic" is what used to be referred to as Late Precambrian.

01-06-2010, 02:53 AM	#15
Andrew1978 Join Date Oct 2005 Posts 565 Senior Member	I've been reading James W. Valentine's On the Origin of Phyla (Chicago, 2004). Valentine looks at how and when the various phyla of the animal world evolved. The book is very technical and sometimes makes for slow reading, but in incorporates material from molecular genetics, EvoDevo, embryology, comparative morphology (the study of form), and paleontology. Valentine spends about 50 pages on the nature of the fossil record. I thought that I would share the section headings from that chapter. It appears that he wrote the headings as an outline and then filled in the rest of the text. The headings give a good reasonably current perspective on the state of knowledge of the fossil record as it relates to early life on Earth. The Fossil Record The Stratigraphic Record is Incomplete in a Spotty Way Sedimentary Rocks Are Accumulated and Preserved Episodically Sedimentary “Completeness” Varies with the Resolution that is Desired The Completeness of Sedimentary Sections is Independent of Their Ages The Marine Fossil Record, while Incomplete, Yields Useful Samples pf a Rather Consistent Fraction of the Fauna Local Fossils are Largely Durably Skeletonized and Time-Averaged Many Local Faunas Are Required in order to Estimate Global Diversity at Times of High Environmental Heterogeneity Jumping Preservational Gaps is Possible by Extrapolation between Rich Fossil Horizons The known Geologic Ranges of Taxa are Sensitive to Their Fossil Abundances There Are Ways of Coping With Incomplete Records Taxonomic Completeness Increases at Higher Levels of the Taxonomic Hierarchy Taxonomic Completeness Rises as Larger Bins Are Used to Increase Time-Averaging Paleoecological and Biogeographic Completeness Increase at Higher Levels of the Ecological Hierarchy Data from Coarser Units may be Tested by Local Fine-Scale Studies The Neoproterozoic-Cambrian Fossil Record Provides the Only Direct Evidence of Early Metazoan Bodyplans Satisfactory Definition and Dating of Late Neoproterozoic and Cambrian Rocks Have Been Accomplished only Recently Criteria for Defining the Neoproterozoic-Cambrian Boundary Have Varied over the Years The Age of the Late Neoproterozoic-Early Cambrian Sequence Has Been Established Chiefly by Precision Dating of Zircon Crystals Late Neoproterozoic and Early Cambrian Geographies Were Very Different from Today’s Knowledge of Late Neoproterozoic and Cambrian Faunas has Greatly Increased in Recent Decades Late Neoproterozoic Fossils Include Enigmatic Soft-Bodied Forms and Traces Earliest Cambrian Faunal Traces Indicate Increases in Body Size and in Biological Activities Numbers of Crown Phyla Appear During the Cambrian Explosion The Middle Cambrian Contains Spectacular Faunas, but No Crown Phyla Appear for the First Time Fauna that Appear After the Explosion Are Soft-Bodied with One Exception (Bryozoa) If All Phyla Were Present by the Close of the Explosion, Their Records Agree Well with Expectations Based on Their Preservabilites The Lack of Neoproterozoic Fossil Ancestors of Living Phyla is Not Inconsistent with the Quality of the Fossil record There is a Vast range of Hypotheses That Attempt to Explain the Cambrian Explosion Perhaps there Was No Cambrian Explosion The Explosion Was Due to Physical Changes in the Environment The Explosion Was Due to Biological Changes in the Environment In Sum, the Cambrian Fossils Imply an Explosion of Bodyplans, but the Underlying Causes Remain Uncertain The "Neoproterozoic" is what used to be referred to as Late Precambrian.
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