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 doi: 10.1002/bies.20507
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Cambrian stages from doi:10.1016/j.palaeo.2010.05.041
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Mayanian dates from Khomentovsky, V; Nagovitsin, K; Postnikov, A (२००८), "Mayanian (1100–850 Ma) – Prebaikalian Upper Riphean of Siberia", Russian Geology and Geophysics 49 (1): 1, डिओआई:10.1016/j.rgg.2007.12.001 

Templates for retrieving data about geological periods: