Wow. Stratigraphy and vertebrate biochronology are tricky fields, especially when they are the basis for determination of the timing of major historical events such as mass extinctions. Erroneous correlation can really skew our hypotheses such as the example from the paper below (the Permian-Triassic terrestrial extinction event in South Africa) or in a case more relevent to myself, whether or not the two major Chinle faunal assemblages (Adamanian and Revueltian) are distinct or overlap (see discussion at Paleo Errata). The Karoo case is intriguing to me as I just finally read Peter Ward's book "Gorgon" a few months back, which detailed the discovery of the postulated extinction interval. As with the Petrified Forest case, vertebrate biostratigraphy data are only as good as the stratigraphic framework upon which they are built. And again an idea that was thought to be pretty well established and supported must be reexamined in light of new data or a new reinterpretation of existing data. As exciting as this seems it is sometimes a nightmare for the non-specialist who is just trying to keep up (especially when they are using this material to teach classes). My own specialist fields (aetosaurs, Chinle Formation)have changed so much, I wonder what do we really know for certain? What are the data really telling us? And how premature are we being when we publish ideas? What is still out there for us to find and what ideas will these new finds turn on their heads next? Of course this is why I find science absolutely thrilling....and why it is so important for us to continue to test ideas (and allow others to test our own).
R. A. Gastaldo, J. Neveling, C. K. Clark, S. S. Newbury (2009). The terrestrial Permian-Triassic boundary event bed is a nonevent Geology, 37 (3), 199-202 DOI: 10.1130/G25255A.1
ABSTRACT - A unique isochronous interval in the Karoo Basin, South Africa, previously has been interpreted to postdate vertebrate extinction at the Permian-Triassic boundary in the Bethulie area, Lootsberg Pass, and elsewhere. It is demonstrated that the laminated beds, or laminites, in the Bethulie region are stratigraphically indistinct. The heterolithic interval exposed on the Heldenmoed farm is ~8 m below the Bethel farm section, <1 km away. At Lootsberg Pass, the laminated interval is below the Permian-Triassic boundary as defined by vertebrate biostratigraphy, rather than overlying it. Hence, this interval, critical to models of end-Permian mass extinction, is neither isochronous across the basin nor unique. Rather, the lithofacies represents avulsion channel-fill deposits within aggradational landscapes. South African models for the response of terrestrial ecosystems to the perturbation in the marine realm require critical reevaluation.
What mutation rate do I want for my experiment?
3 hours ago in RRResearch