Odp: [dinosaur] Dating of dinosaur age during history

[dawidmazurek@wp.pl <dawidmazurek@wp.pl>]

It's more complicated than that. It is the level of 'golden spike' at Fortune Head that is assumed to be 541.0+-1.0 Ma. The boundary is defined by the first occurence of _Treptichnus pedum_, which is not an organism by itself, for one, and actually occurs in older levels at type section ( https://doi.org/10.1017/S001675680100509X ). The first occurence of similar ichnofossils at ~538.5-539 Ma in the section discussed by Linnemann et al. is connected with change in lithology. I think it would be reasonable to assume that the first occurence of a certain behaviour at a specific site has more to do with regional onset of conditions favourable for the tracemakers than with the actual, global evolutionary origin of this specific behaviour. In other words, the Precambrian/Cambrian as defined by ichnofossils may be diachronous.

Dnia 22 listopada 2019 16:54 David Marjanovic <david.marjanovic@gmx.at> napisaÅ(a):

At this opportunity I'll mention that even the 2019-5 version is already outdated in at least one respect: the beginning of the Cambrian is given there as 541.0 Â 1.0 Ma ago, but really happened later, between two volcanic-ash beds dated to 538.58 Â 0.19 and 538.99 Â 0.21 Ma ago.

 

Linnemann, U., Ovtcharova, M., Schaltegger, U., GÃrtner, A., Hautmann, M., Geyer, G., Vickers-Rich, P., Rich, T., Plessen, B., Hofmann, M., Zieger, J., Krause, R., Kriesfeld, L. and Smith, J. (2018, printed 2019) New highâresolution age data from the EdiacaranâCambrian boundary indicate rapid, ecologically driven onset of the Cambrian explosion. Terra Nova 31, 49â58. doi: 10.1111/ter.12368