Or Nova Roma, Second Rome, Eastern Rome, Roma Constantinopolitana, Basileuousa, Megalopolis, the City, Miklagarðr, Miklagard, Miklagarth, RĊĞmiyyat al-Kubra, akht-e Rum, Tsargrad, and City of the Caesar. No matter what it has been called through time and by different people — it is essentially the same place.

All of this came to mind when I was constructing a graphic correlation of several middle and upper Cambrian sections of the Western United States using Peter Sadler’s CONOP program (which he kindly provided to me and answered my questions). Why?


  • is the first taxon location in a section(s) the

  • First Appearance Datum (FAD),

  • First Appearance (FA), or

  • First Occurrence (FO)?

  • Is the last taxon location in a section(s) the

  • Last Appearance Datum (LAD),

  • Last Appearance (LA), or

  • Last Occurrence (LO)?

Like the city in Turkey, they’re all about the same (at least all the firsts and all the lasts and sometimes both the first and lasts together). They all refer to a horizon in a stratigraphic section(s) where a taxon makes its presence known. I am sure there are some out there screaming in their head saying there are definitions to each term, but I don’t care. The real problem is:

Did anyone actually believe that the first or last appearance (or occurrence) of a taxon in the fossil record were actually synchronous? We pretended that they were synchronous because resolution of the diachroneity was not possible (aka, yeah they showed up about the same time, plus or minus 500,000 to a million years) [overstatement!].

What we are really talking about is the timing of the evolution and extinction of a taxon. Perhaps we should use the terms:

ETEVT—Estimated Timing of the EVolution of a Taxon and
ETEXT—Estimated Timing of the EXtinction of a Taxon.

At least no one would to assume that we have accurately dated the evolution or extinction of a taxon given the environmental controls, migration, preservations, and sampling problems on the record of these events.

Fred Sundberg
Show Low, Arizona


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The Trilobite Papers 20 are part of the PaleoNet system. Sponsorship of The Palaeontological Association is gratefully acknowledged.

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