Use the syntax {{Period start|period name|rounding (optional)}}

{{Period start|Cretaceous}}

produces:

145


{{Period start|Cretaceous|-1}}

produces:

150


Periods from the International Commission on Stratigraphy's stratigraphical timescale.

Burgess shale age from Butterfield, N. J. (2006)। "Hooking some stem-group "worms": fossil lophotrochozoans in the Burgess Shale"। Bioessays28 (12): 1161–1166। doi:10.1002/bies.20507

Cambrian stages from आकृति:Cite doi

Mayanian dates from Khomentovsky, V.; Nagovitsin, K.; Postnikov, A (2008)। "Mayanian (1100–850 Ma) – Prebaikalian Upper Riphean of Siberia"। Russian Geology and Geophysics49 (1): 1। doi:10.1016/j.rgg.2007.12.001

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