penecontemporary

pene- +‎ contemporary

penecontemporary (not comparable)

1. That lived or existed at almost the same time (as another/others); nearly contemporary

   The chalcolithic Corded Ware culture of North-Central and Eastern Europe has been found to display archaeological as well as genetic affinities to the penecontemporary Yamnaya horizon of the Pontic–Caspian Steppe.

penecontemporary (plural penecontemporaries)

1. That which is penecontemporary, living or existing at almost the same time (as another/others)
   • 2013, Trenton W. Holliday, “Population Affinities of the Jebel Sahaba Skeletal Sample: Limb Proportion Evidence”, in International Journal of Osteoarchaeology‎, page 2:

     However, he found that features more prone to show environmental effects (whether phenotypically plastic or otherwise) separated the tropical Jebel Sahaba skeletons from their penecontemporaries at higher latitudes.

Both the noun and adjective senses are typically used to refer to the past, especially periods of time in the distant past for which exact dates of events are unknown.