I'm not going Phil Just helping with the paper. Dan says they usually get published in a book about the proceedings of the meeting, but he also says the book from the 2004 meeting hasnt been published yet. So it looks like it will be a few years.
AMMONOID MASS MORTALITY BEDS IN THE LOWER TRIASSIC THAYNES FORMATION OF WESTERN UTAH, USA
Dan Stephen, Kevin Bylund, Paul Bybee and Wes Ream
Departments of Earth Science and Biology, Utah Valley State College 800 W. University Parkway, Orem, Utah 84058 USA;
The Thaynes Formation was deposited in the SonomaForelandBasin during the Early Triassic (Olenekian). Outcrops of these epicontinental marine rocks can be seen now in the ConfusionRange of Utah. Most of the Thaynes Formation in western Utah consists of yellow-gray fissile shale and gray-brown limestone that reflect deposition in relatively calm conditions equivalent to basin to outer shelf facies. Occasional, short-term regressions produced a few thin layers of inner shelf siltstone, sandstone, and/or limestone. The Thaynes Formation is well known by professionals and amateurs alike for its densely concentrated ammonoid beds. Indeed, the best locality in the ConfusionRange seems to be inexhaustible, despite the sporadic but dedicated efforts of collectors over at least the past several decades. We recognize three distinct Smithian ammonoid assemblages in the Thaynes Formation of western Utah. Each assemblage occurs within thin, isolated beds of about 20-30 cm thickness. We refer to the lowest of these as the Meekoceras Bed, which is dominated by Meekoceras, Arctoceras, and Aspenites. The middle occurrence is the Inyoites Bed, dominated by Inyoites, Lanceolites, and Pseudosageceras. The uppermost of the occurrences is referred to as the Anasibirites Bed, and is dominated by Anasibirites and Wasatchites. The lower and middle occurrences appear to fall within the Romunderi Zone, whereas the upper occurrence appears to fall within the Tardus Zone. These beds can be confidently identified in outcrops within the study area (~100 km2) and even beyond (e.g., in southeastern Utah). There are numerous possible explanations for dense concentrations of ammonoids, including reproductive mass mortality (semelparity), taphonomic biases (e.g., condensed intervals and post-mortem hydrodynamic transportation), and mass mortality generated by environmental catastrophe. There is some evidence that the Lower Triassic ammonoid beds of the Thaynes Formation in western Utah may have resulted from several different causes. However, we believe the primary cause of these ammonoid beds is related to the unusual ocean conditions documented for the Early Triassic by many other workers. Multiple lines of evidence (e.g., sedimentology, paleontology, geochemistry) indicate that anoxia and hypercapnia are likely culprits for large-scale death horizons during the Early Triassic in general. The fact that these ammonoid beds can probably be traced across hundreds of kilometers strongly suggests that they were produced by basin-wide (and possibly global) catastrophic environmental events.
From: Seventh International Symposium Cephalopods – Present and Past, 2007, Sapporo, Japan. Abstracts of Oral Presentations, pg. 33
You can download the whole Abstract Volume from Here, PDF File (17.6 MB)
What's the evidence for hypoxia and hypercapnia other than the large scope? I forget how much I've mentioned Ward's recent book "Out of Thin Air" about oxygen levels driving evolution, but I really found it fascinating, so I'm curious to learn more about how it applies to cephs. Ward suggested hypothetically, for example, that the funnel and jet propulsion arose in cephs not initially as locomotion, but because there was a sudden drop in oxygen, so they needed a way to pump a whole lot more water past their gills for efficient oxygen extraction for an active lifestyle, and that that indirectly was used for locomotion and then the shell chambers developed to add neutral buoyancy. I forget if I mentioned this, but the recent nautilus embryology paper showed that the origin of the funnel was not where one might expect, like the foot of a gastropod or the arms of a ceph, but rather from the collar region. I seem to remember that it migrates around during development in ways that seem consistent with this hypothesis (although far from conclusive) too.